Symposium - Panel discussion

Symposium

Day 1 Moderated discussion with panel-Led by Chris Barnhart and Andy Roberts

Questions

· Are there thresholds for the negative effects of sediment on mussels?

· Are these thresholds likely to vary seasonally?

· What life stages are of greatest concern?

· Should we expect different species to generally respond similarly to sediment?

· What attributes (such as grain size…) of sediments are most important for biological effects?

· What are the major data gaps?

Transcript

Q1: Are there thresholds for the negative effects of sediment on mussels?

Chris Barnhart: So, we thought we would start with these, and Steve and I are just going to present these to all the speakers, so any of you that would like to respond, please just unmute yourselves and hold forth. The first one is: are there thresholds for the negative effects of sediment on mussels?

Tom Augspurger - FWS: I think there are. I wouldn't think of the threshold as a bright line, and I don't think that they exist for all adverse effects and for all species, but quite clearly there is a match between exposure information and associated hazard. It shows some thresholds at which you get a departure from normal statistically significance in some cases. Now that can be aggregated across the species particular endpoints, particular aspects of sediment exposure, but I think there's quite clearly some thresholds for negative effects of sediment on mussels.

Jim Stoeckel: I agree, I think it's not just the threshold itself that we've been discussing, but the duration that threshold succeeded as well, because you may be able to exceed those thresholds depending on what the effect is that you're talking about in the season of life history of that species. You may be able to exceed thresholds at certain times of year without much of an effect, whereas at other times of year can be very critical not to exceed that threshold. One nice thing is, you know, for some of the work that Shaylah just has done and then we've done, showed very similar patterns and some similar break points, you know, in terms of suspended solids affecting clearance rates and then potential subsequent effects on fertilization. So that's kind of nice instead of those numbers being all over the place, and maybe some common patterns that occur across a wide range of taxa.

Chris Barnhart: Shaylah, do you have any thoughts on this one?

Shaylah Tuttle-Raycraft: I mean, I guess, I agree with what Jim said. It's nice to see that the thresholds that we find experimentally are relatively consistent. When we're looking at TSS specifically with my work and with work that his lab is doing, the gills are important and they're used for both feeding and reproduction, so that might be why we're getting some of that similarity. As far as coming up with threshold, I think, the reality is that the relationship between TSS and mussels is a lot more complex than we've even started to chip away at. The reality is until we can perfectly replicate a river or lake and that has these mussels in it, I don't know where we're really going to get a perfect threshold of “don't go beyond this suspended sediment”, or “only use these types of sediments”, or “make sure that particle size stays within this range”, or “know the proportion to of inorganic to organic stays this level”. There are so many factors involved that I think we have thresholds, where we can say:” yes, there are definite effects happening”. But as far as quantifying those thresholds, I'm not sure that we're quite there yet, and I'm not sure we're going to get there anytime soon.

Q2: Are these thresholds likely to vary seasonally?

Chris Barnhart: I think it's obvious, from what the speakers told us that these thresholds are likely to vary seasonally which was our second question, let me cut to the chase and maybe this is premature to ask, but would it be reasonable to expect less effect, less negative effects, of suspended sediments on mussels in the winter than in the growth season.

Jim Stoeckel: I can narrowly respond to that based on some, or you know, just on the reproductive effects, and I think so because I am not aware of any taxa that spawn in the winter months. And as we saw, we don’t really seem to be evidence of negative effects of suspended solids on glochidia when they were being brooded by the female, so the long-term brooders that were hold their broods over the wintertime may not be as negatively affected. Metabolism is going to be a lot lower in the winter months not actively growing, so probably going to be relying on their stores of energy that they stored up during the summer in the fall anyway. So yeah, I think that's something to think about.

Chris Barnhart: Steve, you want to take a couple?

Stephen McMurray: Yeah, I was just going to, I guess add into this, and kind of springboard from Jim's answer. But before I start, thank you as well, to all the presenters for taking time to talk to us today and help us out with this and, and thank you to all the attendees that are out there listening virtually. So, one day, maybe we may be able to all see each other in person again. Brian Simmons posted this question and it kind of goes along with the seasonal variation, but would you anticipate any differences during flooding conditions? Brian Simmons asked towards the end of Jim’s presentation, that would you anticipate any differences, I am assuming threshold differences, during flooding conditions?

Jim Stoeckel: So, I think you get some other issues when there's a flood. I mean I don't think the effect on fertilization success would be changed, but there have been some studies that shows that during flood conditions a lot of mussels, not all species but a lot species tend to burrow down into the sediments to help avoid dislodgement. So that might really have negative impact on fertilization, regardless of suspended solids. Just because of you know, if they burrow down beneath the surface they're not as likely to either release sperms or will be able to collect sperm balls, so I think that could have a negative effect on fertilization, you know, that we hadn't really talked about. And then the same thing with you, like Teresa's work, she's talking about sediment stabilities, kind of a similar issue if they do get based remain at the surface and get dislodged may not matter, they're able technically fertilize or move down stream; yes, that's going to have a direct negative impact on fertilization.

Q3. What life stages are of greatest concern?

Stephen McMurray: So, what life stages are of great concern? There we go, so we will go on to Chris’s third question first.

Shaylah Tuttle-Raycraft: I can talk a little bit on my work. I would say the juvenile life stage is something that we need to consider, I think at sometimes, above the adult life stage. And I say that because the formative period of their life is that juvenile stage and that's way their body is growing for the environment that they're in. So, in my case, that they're in a turbid river from, you know, one week old, four weeks old. They're going to grow for that river and if that's just an event, if that's just construction that's poorly mitigated, or something like that, and then suddenly, they're an unclear system will their body doesn't match their environment. And so, for an adult an issue when you take sediments into consideration, but for juveniles that's where they're forming who basically, you know, how they are going to exist in their environment. I think that we need to consider maybe not just treating juveniles, but also considering when they are juveniles, as far as one more planning construction events and things like that.

Chris Barnhart: So, we have a vote for the juvenile stage.

Jim Stoeckel: I think just because I am a contrarian, but I agree with what Shaylah said, and I think are like a lot of times the first reaction is that yeah, the juvenile stage is important because you are not going to replenish the population without sufficient numbers and of juveniles. And juveniles how to adapt to those conditions, it might be worth looking at the literature, conservation literature, for some other organisms, especially looking at, because I think this question has been asked for species that varied according to life history, so for life stage that's most important for a long live organism may be very different from life stage that it's important for a shorter-lived organism. And I think for sea turtles which produce a large number of young, and the young have pretty high mortality rates that they found that the population viability was actually more dependent on adult survivorship because the adults can survive one or two or three bad years. So even if you have high juvenile mortality in some years that those big adults can still come back the next year and produced tons of eggs and baby turtles. But if you have a pretty good year, and you have good juvenile survivorship, but your adult population has crashed due to overharvesting or, you know, any number of factors. That may not make much, it may be harder for that population to recovered just because you might be able to use those large numbers of juveniles in subsequent years.

Chris Barnhart: Teresa will you weigh in on this one?

Teresa Newton: It's a tough one, I mean, while I agree with everything Jim and Shaylah said, they are primarily working on the hazard side--the effect side of the equation Tom talked about. I would agree that juveniles in general are going to be more sensitive, but I guess I'm thinking more on the exposure side. And again, coming from the upper Mississippi, if we've got high flows and high sediment loads, not only could we tumble the adults, but the juveniles might not have a place to settle, and or the adults may not even be able to reproduce. So, I don't think you can look at any one stage in a vacuum. Because if you don't have the adults out there in suitable habitat to provide those juveniles, it doesn't matter if they're the most sensitive stage or not. So that is my two cents.

Tom Augspurger - FWS: It makes me think about a little bit too in terms of what's measurable in chemical toxicity testing. You know, you might want to do something like a three generation reproductive effects assessment to have your exposure match what you perceive to be important population was. But that might not be possible but might be possible is a shorter-term exposure with what you anticipate as a sensitive life stage. A sensitive life stage for that experiment, you know as a surrogate for the taxa as a whole. So, the phrasing of that question, you know, might be better to be teased out in terms of what's the most important life stage from a standpoint of species persistence. As opposed to what's the most sensitive life stage that you can demonstrate an empirical relationship between the stressor and the response, which is what you might need if you're going to go with, you know, like some threshold guideline type approaches as opposed to more theoretical. So that you can tease that question out into a couple of more specific questions. There is uncertainty in a lot of chemical risk assessment, but we get past that all the time, with some simplifications for what it takes to be able to add numbers that can be continually refined with additional experimentation.

Ning Wang: This is Ning. I'm sorry I didn't really follow carefully but maybe somebody already discussed before. We know the young juveniles they have not really divided their gills and the other organ very well, and that's how we will find out how the young juvenile mussels more sensitive to chemicals than the older, so what the sediment particle and to deal with different kind of particles in the water from. I think the same thing, and the younger one may not have that full capacity to deal like the adults or sub-adults. So, I think it makes sense to also designed some studies and to see how the young mussels response compared to the older.

Chris Barnhart: From a regulatory standpoint here, but I guess what we're mainly interested in and Jeff and Baolin, please chime in, we’re mainly concerned about designing relevant experiments to establish standards for control of erosion sediment associated with construction. And I think that, this is mainly going to be short-term exposures. So acute effects are perhaps more of interest than chronic effects. And again, Jeff and Baolin please step in and if you have any comments about this. I agree with Jim that the adults are what generate the juveniles, so we don’t want conditions that are going to kill adults. But the juveniles are more sensitive than the adults in most contexts, so it seemed like a good place to start when you're looking for a threshold. Well, what is next?

Tom Augspurger - FWS: For acute effects here, I guess, it would be worth thinking about how long an adult can use its protective shell to protect all of it soft parts then live on the internal stores, strategies that other life stages and energy reserves, you know might have, might not have those protective mechanisms.

Chris Barnhart: Yes.

Tom Augspurger - FWS: So, if it's defined as an acute exposure, those are things to keep in mind in terms of what would make something sensitive or not.

Chris Barnhart: Hi Patty.

Patty Gillis: Hi Chris. And Teresa pointed out earlier, we're talking mostly in type in terms of the sedimentation today as opposed to what contaminants may be associated with those particles of sediment. So, in terms of designing the experiments, even though they're going to have the different life stages as well as different responses to the increased sedimentation, how do you balance that with the different life stages that have different sensitivity to contaminants that might be coming off those particles. So, kind of two things that might be affecting the animals at once, even though it sounds like you're probably designing experiments purely based on sedimentation as opposed to those that may have associated contaminants. Is that correct?

Q4: Should we expect different species to generally respond similarly to sediment?

Chris Barnhart: As I understand you. Well, we've already seen some evidence that there are species differences.

Tom Augspurger - FWS: You'd have to talk about how big of a difference. There's an appreciable difference though, just because, you know, the numbers are different in terms of like an effect concentration resulting a 20% reduction in what, reproduction, for example. How big of a difference is meaningful and chemical toxicology. Most mussels tend to be within a factor of five of each other oftentimes within a factor of two which might sound like a lot. But we set national water quality criteria which are numeric guidelines despite all that uncertainty when we know that the sensitivity of other taxa from insects to fish to amphibian and reptile vary by orders of magnitude, so how big of a difference is meaningful for standard setting, versus can use statistically show the difference between two species you got. It would surprise me if the difference is never orders of magnitude kind of differences.

Chris Barnhart: Since we have the toxicologists here, I might ask too. Do you think that one or two or how many surrogate species would be appropriate to try to capture the range of response that you might expect, among mussel taxa? You think we can get by working with Fatmucket, or should we try to test several tribes? Should be focused on endangered species since those are the ones that most concern?

Tom Augspurger - FWS: It is hard to test. So, I would be comfortable with surrogates. And I would lean toward mining the existing literature to find out, you know, how big the differences are that have been observed already by tribes to see if that's meaningful rather than an a priori decision.

Teresa Newton: Yes, and I would caution too, that I've seen people use surrogates based on taxonomy. So, species that are in the same genus.. And I've seen people use surrogates for species that they think live in the same habitat, so I think we have to be careful in how we define surrogates. That's something that I've run into recently and trying to find surrogates is challenging. If you were looking at it from a habitat perspective versus a taxonomy perspective you could get two different answers. I would agree with Tom that we’ll often have to develop surrogates for T&E species, but we should define our range of expectations and go from there, and not come up with a magical number.

Jim Stoeckel: I agree with Teresa. It seems like you know that concept of guilds, or maybe not guilds but another concept, like is being proposed for thermal fields of mussels try to put mussels in the thermal sensitive and thermal tolerant guilds might be applied to sediment effects, and you know, we find that even just with thermal tolerance of, like Teresa said, you might get two species that aren't all that closely related, but very similar responses to each other in which, so you know, we're kind of working on that same problem with thermal tolerance and endangered species right now in my lab and using response rather than taxonomy or habitat preferences to try to identify good surrogates and then. So, I think that would be the way to go for sedimentation.

Chris Barnhart: We've got a couple of questions, well a question and an answer in the chat box. Mark Fisher asked regarding TSS thresholds and then consideration of turbid versus clearwater plasticity should the focus be on a specific concentration or on a changeover ambient? And Jeff says “Good question. The EPA guidance has suggested a sediment imbalances and more appropriate way to describe sediment effects, and that is a significant change from normal sediment loading to aquatic systems”. So, sediment imbalance. Brian comments “Shaylah indicated clearance rates increase with velocity, my question was to her regarding whether clearance rates would be different during flooding conditions, given the examples that Jim mentioned?”

Shaylah Tuttle-Raycraft: I guess, for me, I would assume that it would depend on a whole other bunch of factors as far as what they were doing during that flood event. If they're burrowed quite deeply, they're probably not focused on feeding necessarily. So, you would have a difference in clearance rates just based on that in the habitat. But as far as velocity if you only looked at velocity kind of in that, you know, tunnel vision just looking at how velocity affects feeding then yeah it does, but I would expect that environmentally and ecologically that answers a lot more complicated.

Chris Barnhart: Jacobson comments. If folks can open your chat boxes and see these exchanges too. But Rob says a geomorphic perspective is probably easier to identify a biological threshold then to define sediment balance and what is out of balance.

Tom Augspurger - FWS: I think that's a good point and I think the frequency of high events is also we're thinking about. A couple of speakers mentioned, you know, some bottlenecks and mussel life history where males and females need to be in certain proximity, glochidia and need to encounter a host fish that can be affected by flows. Glochidia needs to fall off into suitable habitat that can be affected by flows, wet years dry years, so there may be aspects of mussel life history that means it's not going to be perfect every year under what normal environmental conditions are. I don't think that means that you want to walk away from a biological response with those conditions, because what if those conditions that are adverse became the norm from anthropogenic input as opposed to, you know, those conditions just occurred infrequently enough to let the species persist, I think the biological responses are worth characterizing and then maybe look at the frequency with which does occur in nature, if you have a biological response that's exceeded every single year under natural conditions, then we've probably done something wrong there. But if you have a biological response that's periodically exceeded by natural conditions, but through anthropogenic inputs becomes exceeded nine years out of ten, then maybe that's something that's manageable.

Chris Barnhart: I'll go back to my list.

Baolin Deng: Chris. May I have a question here? For the sediment that there are so many, like you know, inorganic components, organic components. So, as someone being not a mussel biologist, I am wondering how those mussel would be able to sort of separate, to identify what kind of particles you have, some would be rejected, some would be uptaken, what kind of mechanisms are there to separate different type of particles there.

Chris Barnhart: Anybody else want to handle that one?

Shaylah Tuttle-Raycraft: Sure, so as far as mussels do selectively feed, this is another area in Joe's lab that definitely has been under investigation. It's a little bit unknown as far as unionids are concerned. But they can separate toxic algae from non-toxic algae, we know that. They can select for algal particles as opposed to inorganic particles and we know that as well. As far as the actual mechanisms, I know the organs involved and I know the cilia are involved and particles are rejected, with mucus strings and things like that, but how they can exactly discern which particle is beneficial and which one is not, I'm not sure that mechanism.

Chris Barnhart: Sure, that is mainly for marine bivalves not for fresh water.

Jim Stoeckel: I'd agree with everything, and I think Shaylah, the only thing that seems fairly solid is most of that occurs at the palps, but we don't really, that's where the sorting occurs, and that selectivity can, does seem to break down under certain conditions, so if they get totally swamped with, you know, they may have the same amount of food, but the amount of inorganic particles starts to increase then at a low, let me get the word right, at a high organic and organic ratio, they may be able to select pretty well, but then, is that ratio starts to become dominated by inorganics that selectivity starts to really break down quite a bit. But how they do it, like Shaylah said, I'm not sure how they detect those differences.

Q5: What attributes (such as grain size…) of sediments are most important for biological effects?

Stephen McMurray: Was one of the ones on your list that interests me, I think, is what attributes of sediments are most important for biological effects?

Teresa Newton: I think that depends on the life stage, the river system and probably the time of year. I know that's not the answer you wanted, but in some systems that might be suspended, other systems that might be bedload. If we're assuming that suspended sediments are not an issue in the winter, maybe other sediment constituents are, depending on what part of the country you're in. Unfortunately, I think that is going to be very fluid, like most other things.

Chris Barnhart: I was intrigued, Shaylah, that your fine silt was nutritious and delicious, clearance rates went up, and did growth go up too?

Shaylah Tuttle-Raycraft: We didn't look at growth, those were only done on adults, so they're all short term.

Chris Barnhart: But the nutritional content was higher.

Shaylah Tuttle-Raycraft: That was a weird, it was a weird investigation, and it was weird finding, kind of just rolled with what we could. We found some food scientists and tried to figure out how to quantify nutrition in sediment.

Chris Barnhart: You may have described this, but what was the source of your different types of sediment.

Shaylah Tuttle-Raycraft: And so, I’m not sure if I understand the question, but we took bed sediment and used brass sieves

Chris Barnhart: The same source you fractionated it?

Shaylah Tuttle-Raycraft: Absolutely yeah.

Chris Barnhart: So, you did what the mussels could be doing what their labial palps

Shaylah Tuttle-Raycraft: Yeah, we sorted it all by size just using sieves and then from that we put it through a whole bunch of different analyses to try to figure out why that particle selection was bed (3:00:11) on the most, like why that suspension didn't decrease their clearance rates (3:00:12). There was another student in the lab around the same time as I was, and he was looking at mussels’ filter feeding, and how they sort their particle so specifically looking at select feeding on algal particles and how that was affected by flow. And he found that the most selected for alpha particles did fall within that fine silt fraction as well. So, there's just something about the algae in that that they like.

Jim Stoeckel: Shaylah, am I right silt is defined by particle size not by composition like not of what it is just basically defined by the size, so it could be anything from fine particles to, you know, small pieces of clay, I mean it could be organic or inorganic. Because…

Shaylah Tuttle-Raycraft: We did it yeah. It was fine silt sized. Everything fell into that fine fraction.

Jim Stoeckel: Yes. It could also be that, even if the core is inorganic those particles would be colonized by bacteria and so they may be a lot of what you're picking up is could be. I do not know, but some of that organic crashing could be the bacteria associated with those particles, like a sugar coating.

Shaylah Tuttle-Raycraft: Absolutely. Basically, what we found is that the highest organic content was in the clay-sized particles, but that's likely where that bacteria is going to come into play yeah, we had a lot more algae in the fine silts.

Jim Stoeckel: Yeah, I think that's an important thing to bring up because I always like, I make the same mistake in my presentations. I have a defined inorganic particles as sand, silt, and clay, that's not necessarily true, because a lot of times that's defined is just size not what the composition is.

Shaylah Tuttle-Raycraft: Yeah, absolutely.

Chris Barnhart: I remember the fine sieves being 5 to 38 microns, is that right?

Shaylah Tuttle-Raycraft: Yeah, that's what we used.

Chris Barnhart: And what was the next smaller?

Shaylah Tuttle-Raycraft: We did zero to five. So, clay sizes typically defined as zero to four, but we didn't get a sieve that small. I went from zero to five, it was the closest we could get to clay sizes.

Chris Barnhart: I think filtration efficiency drops off fast after two microns, so a lot of that may just be passing the sieve, not being filtered.

Chris Barnhart: I've got a question for Teresa. Do you think that it might eventually be possible to build mussel habitat? Or do you think you're at that point now in the Mississippi, where you could design structures that would create solutions that you need.

Teresa Newton: We are trying to do that. In the upper Mississippi, managers, for example, frequently build islands to reduce wind fetch and typically those islands have also been designed to support ducks and fish. We are slowly convincing them to also be inclusive of mussels in their design features. Some managers have the vision that different biotic groups are exclusionary and need to understand that we may be able to add habitat features that are conducive to birds, fish, and mussels. For mussels, let’s tweak the design a bit to improve sediment stability and then monitor mussel assemblages. So, we are getting to the point, where the managers and the engineers are willing to try things that might support mussels if it doesn't wreak havoc on the other parts of the system. For example, if they were to rotate an island, let's say 10 degrees one way or another, or armor it with a different type of substrate that might improve habitat for mussel. So, we're starting to try things like that. The issue we have is that most of the funds are obligated for construction, with considerably less for monitoring, so it's a hodgepodge of when some of these activities can be monitored to see if they've been effective. But I've certainly, in my 30-year career, seen a different change in vision in terms of what we can do, and the managers are certainly open to other suggestions if they can be accommodated without derailing other parts of the system.

Chris Barnhart: That's fascinating.

Jim Stoeckel: Teresa, I have a question for you to along these lines, so with sediment stability, so now I'm out in the stream looking for mussels, a lot of times, you know, find these patches have a consolidated sediments, then, you know, can stick my finger in them, but it's, you know, it's kind of sticking stuck together, but then when I started digging mussels out, you know, it's really fine sediment and you can destroy that patch pretty quickly, just goes into solution and washes downstream really well. Had you guys worked with what types of particles consolidate better than others? So, it's not just, you know, I think it's not just a matter of particle settling out at the deposition zones, but whether they can consolidate.

Teresa Newton: Yes. That's the essence of the shields diagram is that you not only have to know the boundary Reynolds number, but something about the type of sediment. And that depending on the sediment type, that will dictate substrates stability. And I can't remember exactly, it's kind of a U-shaped diagram. So, I don't know exactly where those conditions are. Sometimes the management actions on the upper Mississippi River get criticized for being non-ecological, like when they put bulldozers in the river and destroy habitat. But I have to say that there's been a few actions that they're doing that probably promote mussel habitat. So, in one of our pool-wide surveys, we noticed all kinds of mussels in a backwater lake, and that sort of went against what we had thought as we don't typically see a much diversity in our backwater lakes. This wasn't a case where it was just a bunch of juveniles, we had multiple year classes, we had multiple species, we had adults and juveniles mixed in. And so, I called a hydraulic engineer and asked what's going on in this backwater? And he was like, oh yeah, the core cut a channel in there that diverts 10% of the river water because they were worried about low dissolved oxygen. Now that backwater is receiving flow, it's receiving food, it's more oxygenated, it's removing waste. And lo and behold, another pool right up the river a bit, same thing another backwater with lots of mussels. Samer response, the COE placed a water diversion cut in there, too. So, some of these actions may actually be helping mussels. If you get systems that are not terribly healthy for mussels because they don't have enough flow, or they freeze, a lot of these actions that move flow rates around, can benefit mussels. And I think they're starting to see that in the upper Mississippi at least. So, it wasn't designed that way but it's working out well for mussels so that's always a bit of good news.

Chris Barnhart: Do you think those habitats will be for the long run, are they going to be ephemeral?

Teresa Newton: We're looking at that. The interesting fact is that there's a variety of year classes and a variety of species in some of them. So, they're at least persisting for more than a year, some of them maybe for five. But like I said, we haven't been able to go back in, and repeat these pool-wide surveys; we're hopeful that we're going to get funding next year to repeat our first one and it'll be like 14 years later, so that'll be the first time we'll be able to actually test that, but I'm optimistic because, like I said, we're seeing multiple species and multiple age classes.

Chris Barnhart: Teresa, you mentioned a mark recapture study and I didn't catch all of it, but it reminded me that I wanted to ask you about these flushes of juveniles that you sometimes find in places that are not for the long run, places where the stability isn't long term, do you think that those juveniles after they've recruited and grown for a year, or maybe more that they might eventually end up in a different deposition environment they get moved out of the nursery and find their way into the real mussel bed, or do you think they're just doomed?

Teresa Newton: We sampled in this one side channel and we just found the mother lode of babies, I don't know, densities must have been 100 or so per square meter, but you could kind of tell they were mostly the same species and the same year class, so we suspected that they had been washed in because we'd recently had a high water event, and they've got washed into the side channel and settled, and then we went back like a couple years later, and we didn't see that pulse at that site. So, either they died, or they got washed downstream. But we're starting to see episodes of good year classes like for a given species. I showed results from our recent surveys, and in pool 13, the pool-wide population estimate was about 600 million mussels, and a substantial fraction of that was age zero Utterbackia imbecillis. Conditions must have just been perfect for the recruitment of that species. So that's telling me that those conditions when we sampled had a good year class, and then talking to others up and down the river, I think, Heidi was on here, they're seeing similar things in a few other pools, so those things are hard to tease apart, but that dominance we hadn't been seen until the 2019 surveys. What's the fate of those mussels? Are they going to remain? Who knows? U. imbecillis is a short-lived species, so it’s fate may be quite different than if it was a long-term species. So, I’m not sure I answered your question, but I do not think we often know the fate of displaced mussels, but I suspect they do get washed into areas where the habitat is not suitable. How long they persist there is unknown. I hpe to be able to address this question in future years.

Chris Barnhart: We're still waiting to see recruitment in places where we've established populations of adults, and you can't help wandering or hoping that the babies are being produced, they're just not ending up where the adults are, that they're settling somewhere else, maybe downstream, maybe upstream, depending on what the host fish do. But I've never thought of mussel beds as necessarily being self-sustaining, seems like there must be a lot of movement between these areas, either by host fish or by bed movement.

Teresa Newton: Yes, we are curious about this too. In our PIT—tag study, we hypothesized differences between the core and the periphery of mussel beds were related to suitable habitat as inferred by substrate stability. We suspect that in some of our upstream populations, there may be source and sink population dynamics going on, where you've got some sources that are delivering mussels to the core (high-quality areas), and then, when conditions deteriorate, populations in the periphery (low-quality areas) may be important over a short period to sustain them until conditions improve in core areas. So that's an area of research I think that we’re woefully shy on understanding how that affects things.

Stephen McMurray: Yeah, not to jump in on your conversation here, but we have one more question for Teresa from Andy Roberts in the chat. You stated mussels occur, where there's low shear stress during high water events, then what about the other side of the spectrum? High energy depositional areas of what point does deposition become an issue for mussel habitat? Do diverse mussel beds have no deposition of sediments?

Teresa Newton: Yes, we do not deal with the other side of the coin very often in the upper Mississippi, as we tend to have a lot of flow. But in some of the backwater areas, we’re seeing deposition of silty sediments, leading to low dissolved oxygen and high concentrations of toxic, chemicals like an unionized ammonia; these conditions are likely to have an effect on mussels. But our hydrophysical models typically don't predict many mussels in these depositional areas, and if we do see some, they tend to be a different species assemblage, so it's not that we discount them, but they are small fraction of what we typicall observe in the upper Mississippi. But, to be honest, we haven't spent as much time or effort in those depositional areas other than to identify that if you don't have enough flow in these areas where you have the depositional sediments, then you're going to have problems with food being delivered, low oxygen and high ammonia so it's kind of that balance of the deposition and the high flows.

Q6: What are the major data gaps?

Stephen McMurray: Okay well, I have 4:40, and to get to a point where we can wrap things up a bit maybe. If each of our speakers wouldn't mind spending just a couple minutes kind of telling us what you think the major data gaps are for the effect of sediment on mussels. So, we will go in an order of speakers, Teresa, do you want to kind of lead us off? what you think that major data gap?

Teresa Newton: I think we need to better understand how different species and different life stages respond to different sediment forms. The threshold concept that Jim was referring to. If you think about it like a bell-shaped curve, what are those bounds of that bell-shaped curve that allow a given species or life stage to exist within that threshold. We certainly cannot do it on every species and every system, but if we sort of take the approach that they've done with thermal guilds, then perhaps we could come up with some threshold values for sensitive vs. tolerant species or however we wish to categorize mussels and the life history stage. I think having that would be a good place to start. It does get complicated because do you have a threshold for survival, one for growth? But I think we should start developing those as they could be useful in species status assessments. There's so much interest right now in rivers and flow regimes. For example, the TNC has a large initiative on sustainable river flows and they are dealing with massive uncertainties in how mussels are going to respond to variable flow (and consequent sediment) regimes if they change how they operate their dams. So, I think the more we can quantify what those thresholds are for different species, life stages, thermal guilds, endpoints, etc. That's ultimately going to get us where we need to go. It's going to be a long haul, but I think it has the potential to get us there.

Stephen McMurray: Thank you. Tom?

Tom Augspurger - FWS: I think that, for me, the biggest area, I think that would be the most helpful to advance it in terms of a gap would be depending on the audience for the threshold is to have some discussion about the level of information that would be needed, which isn't a right or wrong issue, it's a matter of risk tolerance and what the norms are for that area. There's everything, you know, for a chemical like ammonia from national water quality criteria which embrace the uncertainty of sensitivity of a wide range of organisms to state standards to site-specific water quality standards to permit limits increasing specificity. And the narrower the circle is drawn, maybe the smaller the group of people was who are involved in decision making. And you can discuss what type of information it is that they want. For example, would they want to see repeated testing to narrow competence intervals of the final recommendation, or would they like to see a bunch of species testing to show increase relevance? To me, those aren't right or wrong answers, but they're answering both questions by a group of people if you're not deriving, you know, a threshold for freshwater mussel biodiversity worldwide, or for North America, or for the US, but you're doing it for construction projects in Missouri. The stakeholders just got a lot smaller in terms of framing the risk question. Maybe it's a time of year issue or that is a particular species issue, maybe it is efficacy of certain BMPs. I would spend more time, I think, trying to make the question as narrow as possible and finding out for the existing regulatory and non-regulatory environment, what is it that typically serves as good decision support. And I guess one other thing that I'll mention is, we spend a lot of time talking about all the complexities of exposure, very few of those, my experience is measured in reality. We have turbidity in TSS in North Carolina, and that's a, unless it's a special study we do not routinely know shear stress, you do not routinely know bedload, you do not routinely know settable solids and dissolved solids. All that can be measured, but it's not routinely measured. So, I guess part of that discussion with the smaller group of people if the goal was numeric thresholds to serve that group would be operational questions as well. How are we going to make it work if our thresholds, you know, are more elaborate than what our exposure measures are for compliance monitoring? Then they might not serve as well, so there's a couple of ways to get at the issue of unknown complexity, one is to list all the questions, another one is to start crossing questions off the list because they don't seem as relevant to the decision makers as some others.

Stephen McMurray: Thanks Tom. Shaylah?

Shaylah Tuttle-Raycraft: So, I obviously agree with Teresa and Tom said, and I think I'll build a little bit off what Tom was saying, and I think one of the biggest gaps we have is that we're not measuring these responses in real life. So, we're replicating them in lab settings which is great, but you're just missing so many factors. So, I think that that needs to be included in anything when we're trying to suss out a threshold is that we really need to see how they're reacting in life. It's great for me to say TSS affects feeding, and you increase TSS above eight and feeding goes down, but the reality is we don't know that's happening in real life. We don't know that in a real system with flow and temperature and you know the appropriate inorganic, organic content of that system that response is going to be identical, we just don't know that. And the other thing that I think we need to focus on in on a little bit more is species recovery or organism recovery. So, if they have a period that's going to decrease feeding or reproduction, can they recover from that how quickly, can they recover from that exposure, these we just don't know.

Stephen McMurray: Good, Thank you. And Jim? You had time to make notes.

Jim Stoeckel: Lot of the good ideas are taken. But I think to me, I would break it down into sediments, settled sediments, and suspended sediments with the settled sediments. I think the work that Teresa has done has really pointed out the importance of stability, and I think that's a huge thing. So, I think a lot more research now has to be done into what helps sediments consolidate, how do we, what can we do physically in terms of the engineers to, you know, like you were discussing before, to help create or manage for stable zones. And then what are the characteristics of those sediments that help them become more stable, is it size, is if some sort of sticky bacterial coating that helps, that once they're settled, it helps them to kind of stick together rather than just easily becoming resuspended. There's a lot of different physical things that can be looked at, that I don't know very much about, I think, would be great for future research. And then for suspended solids, I think there's still a lot of black boxes in the life history, so we sort of always say, well, mussel spawn and then glochidia are developed, but we don't really know what the cues are for mussel spawner. so that it's easy for broadcast spawners because they have to coordinate their spawnings so that the eggs and sperm are in the water at the same time. But for sperm casters, they don't really need to do that, they can spawn in an extended period of time that gives them some advantages. Because if you have a high turbidity, then you can maybe delay spawning until that goes way, but we don't know if they do, and what are the cues that causes the males to spawn, and then what affects the sperm balls that are traveling downstream. And you know, the sediments really interfere with their travel, do they break them up? There's just not much known about that whole fertilization phase, and I think that's an important phase, as we talked about before just the whole sorting issue, which plays a huge part both in effects on feeding and growth and on reproduction, you know, we sort of know about how they decide of feeding, but we don't know how plastic the palps in the gills are, and what the physiological mechanisms are that allow them more or less efficient sorting. And then, I think the question has come up. My final thing has come up in this in Shayah’s talk in particular, what is this great question of which turbidity is so bad or suspended solids are not good, how do we get good mussel populations and some of these big turbid river systems, and that's super important question and I think by studying species and subpopulations that are very successful instead of concentrating on threatening endangered species. And looking at some of these successful taxa that do well in these highly turbid systems and then, you know, compare the physiology and behavior to those taxa that are better or subpopulations that are in the clear water systems. I think that would really help us to start tease out, the adaptations for surviving in turbid environment, or how to sediment in an environment and what promotes those adaptations, and you can they be induce or you just fix based on genetics that’s a long-winded answer because I had time to think about it so, and I hope that might help.

Chris Barnhart: That is such a great summary well, it's ten till. I've been tasked with trying to summarize this but Jim you did a good job at summarizing it. I think we can all agree that mussels are unique in the number of different ways that they are potentially impacted by sediments. You've got fertilization to start things off where the sperm balls are drifting downstream, and they have to be presumably captured by the same mechanism that the females are feeding with and have to compete for places on the gills with whatever else is suspended in the water. Then there's a larval stage and we didn't talk about brooding, but I would, well Jim, you did a little bit, but brooding has got to be a sensitive stage. We've done experiments where we expose brooding females to hypoxia and levels of hypoxia that will kill the brooding embryos have no impact on survival of the adult females so. And they're far more sensitive than the juveniles are. They're almost bulletproof when it comes to low oxygen, so all these different life stages all affected in different ways. Then the juveniles are in the sediment and you can't be much more intimately exposed to sediment toxicity than a juvenile mussel living in pool water for months or years at a time before they get access to the water column. We've learned that hydrology can yield to 75-85% predictability for where mussels are going to be found, I think that's incredible. And it suggests that maybe there's some hope that we could structure habitats or recognize areas in the habitat that are vulnerable to disruption to flow and sedimentation. And what about tomorrow? Well, tomorrow the speakers are going to discuss sediment processes and rivers, and we'll try to place these in the context of transportation projects which I am afraid, maybe we didn't give enough attention to here but it's good to cast the net broadly for starters. We want to place these ideas in the context of construction and minimizing impacts on protected species.

Day 2 Moderated discussion with panel-Led by Baolin Deng, Kathleen Trauth and Henry Brown

Questions:

· How are decisions currently made regarding the conduct of construction/maintenance activities with the potential for the loss/disturbance of soils?

· Are different types of sediments handled differently? What sediment properties/characteristics are important?

· Is there adequate information to manage different sediments/characteristics?

· What engineering and/or management tools are used to mitigate soil loss/increases for different types of aquatic system sediment?

· What are best management practices for protecting freshwater mussels from influence of sedimentation episode?

· How important are the flow conditions related to episodic sediment events?

· What are the most important monitoring/management methodologies and parameters to protect freshwater mussels?

Transcript

Baolin Deng: I am checking the chat box here. Looks like we still have one or two questions for Bree. And one is from Mark Fisher. Earlier Chris Goodson mentioned that the Georgia DOT has recently received guidance from the US Fish and Wildlife, saying that sedimentation impacts can occur to aquatic species up to one kilometer. Seems a good piece of information, what do you think, Bree?

Bree McMurray-Missouri DOT: I'm gonna say show me the data. But if they're talking about mussel impacts, and if they're talking about chemical impacts, yeah, maybe so. But if we're talking about sedimentation, as far as particulate matter, show me the data. We were talking about, we don't have a lot of threshold data, so I'd like to say, you know, to justify something that far downstream, I’m not saying it's not accurate, I just don't know in what context. But I would say we're just discussing these crucials in state of Missouri, we air on the side of caution a lot, and if we can't measure an impact, but you also like there's no way to measure that impact, we air on the side of, well, we can't say there's no effect, so we'll always include our BMPs will do the right time of year, small impacts, especially in temporarily, and we will try to justify that, you know, we can't say we're not having any impact, but we're pretty sure we're not going to have an adverse impact, and here's why and that's the way we are as consults. So you know, setting up our, like I said, we do not go out, kind of like Ryan said, we do not go out and measure how much sediment is escaping from the project. You know, downstream oftentimes that is information that comes from the general public, and it's usually a turbidity situation like hey, we can see your plume of soil in the stream, but again potentially more data that needs to be taken in the field, use a bridge construction project as an experiment to coordinate and get out there and collect some data. I know generally we're not in the business of the research part of it, but obviously through this symposium might be going that way, so you know, some more gaps that need to be explored.

Baolin Deng: Yeah, it looks like Ryan also has a question for you. Could you just ask here?

Ryan Foley: I saw Fabian, and he has his hand up.

Fabian Bombardelli: I just wanted to point out what Bree was mentioning. I think that the response depends on each situation, so you need to be conservative. In engineering, we have some rules of thumb that we use, and the rule of thumb says that, basically, each perturbation that you observe in a flow is affecting downstream in a distance of about 40 to 60 times the width of the channel or the water depths, whatever is larger. So if you have to deal with a big river, it could be even longer than the width or depth. So it depends on the magnitude of the change that you introduce, it depends how deep your water depth is. It depends on many, many things that pertain to each specific case. But in general, I mean the advice that Bree was mentioning that in each case we need to be conservative and cautious, as these rules are crude. That is the way to go.

Binbin Wang, U. of Missouri: I also want to add the flow is another factor that actually Fabian’s presentation showed the very strong flow sedimentation interactions, so that's it's hard to tell it's not like a one-size-fits-all type of situation probably.

Fabian Bombardelli: You can probably say that when you have heavier materials like coarse sands and even gravel, you will expect that anything happening with them will take shorter distances, because they tend to settle faster. But for silts and clays, it is probably kilometers.

Bree McMurray-Missouri DOT: Right. That's something that we may be don't queue into as much. We don't do a lot of mussel surveys in our prairie streams. Our federally listed species are going to be more of our cobble gravel streams, so that's the kind of sediment that's being mobilized, because that is going to fall out pretty quickly, and what we're looking at avoiding is depositing sediments are creating an island right on top of the mussel bed. A lot of our impacts for, you know, are we putting enough in suspension for a long enough period of time that we're going to impact the feeding of this endangered species in this bed downstream, 300 feet downstream, a half mile downstream. We just to be quite honest, we don't measure that, we don't know. We make assumptions that we think we're doing the right thing, and that's the part that's missing now is getting together with those that go out, and they measure this kind of stuff. We're not in the research business, we're in construction business. But we absolutely want to do the right thing, so telling you how we do things. However, harsh or large impact that may sound, or look, we need feedback to improve how we're doing things, or to look at those. We may find out that you have to go a kilometer downstream with all your surveys to make sure that you're not impacting beds at that distance but currently we don't have guidance or evidence and our streams in our physiographic region to support that amount of work. But we're not opposed to.

Baolin Deng: Thank you. Ryan, would you like to ask a question before we go to the panel discussion?

Ryan Foley: Yeah one last one. Bree, so we don't have any mussel critical habitat in Minnesota. The Fish and Wildlife Service just came out with their five-year work plan and it looks like they are going to look at some critical habitat destinations for a couple of species we have up here, Spectaclecase and Snuffbox. And there's been some consultation about, you know, that St. Croix river has both of these species and seems like a good spot as any forest critical habitat. And I was asking, how is that going to affect our transportation project? And I was like I don't know man, like I just got here and I've never worked with transportation in critical habitat, so I guess that my question to you is, I know you guys have done in Missouri have got the Neosho Mucket and Rabbitsfoot critical habitat down your way. So does MoDOT, how does your work across those streams differ than streams that are not designated critical habitat, if any?

Bree McMurray-Missouri DOT: We sent Andy Roberts out in the coldest streams on the coldest day that we can find, and happened to tell us if the habitat is suitable at the bridge. And I mean quite literally that's what happens is we go straight to all these. Those of you may not deal with critical habitat, and we've done some consultations is like there's generally biological physiological factors that you have to have in order for it to be categorized as critical habitat. And that may not be like the entire reach, so we go to that spot in the reach for that bridge is. When I say we, I absolutely mean Andy and Steve, they are co-works. And they first and foremost, you know, are finding any mussels, is there any bed habitat. And if we've got bedrock in that particular area, well, that absolutely doesn't meet the critical habitat guidelines, so we're on a not likely to adversely affect critical habitat at that point. We are under, so for those of you also that don't do a lot of consultation for federal projects, Federal Highways will not approve a project that will adversely modify critical habitat. So if you get to that point, you haven't got project anyway. So I would say my advice would be get real buddy buddy with your Fish and Wildlife Service partners, and if when you have a project that's going to come up on critical habitat, walk with them every step of the way. I think we kind of cut our teeth on critical habitat with another aquatic species with Nangua darter and that one's kind of a builder because they're critical habitat goes 50 feet outside the banks. So what the farmers are doing in the field may not have, you know, they don't count, but if we're going to bring in and lay down rock, it's later going to be put in as stabilization, we have to include some of that for put up a habitat impact. So after doing that mussel critical habitat is like a cake, not a problem. But I would just say yeah work really closely the first time, first few times it comes up very closely with your federal partners, because it'll be the first time that they're doing it too. So as long as you all are on the same page from the get-go, you should be fine.

Ryan Foley: We all stumble over all of our feet together.

Bree McMurray-Missouri DOT: That's right.

Q1: How are decisions currently made regarding the conduct of construction/maintenance activities with the potential for the loss/disturbance of soils?

Baolin Deng: Thank you. We'll have this moderated discussion for the next 45 minutes or so. First, we have a set of questions that the organizing committee has thought about, and we would like to get some input from the panelists. Then after that, the floor would be open to all, so we will have this open discussion. Either you could send your comments through the chat box, or just unmute you to talk. As the first question, I would like to ask the panelists, that may be more relevant to Bree and Ryan, how our decisions are currently made regarding the conduct of construction, maintenance activities with the potential for the loss and the disturbance of soils?

Bree McMurray-Missouri DOT: Oh, let Ryan talk for a while, since you gave the erosion presentation.

Baolin Deng: Good, that's good.

Ryan Foley: Let's see, how our decisions currently made regarding the conduct of construction maintenance activities. I guess, unless I misinterpret the question, it's basically just making sure that we have a smaller footprint as possible, limit that soil exposure time. And just keep on going with our BMPs. And the BMPs, if it's a steeper slope might use some blankets versus rolled control products. Yeah, I don't know I may answer on the right track with this question?

Brian Williams: With any construction project, you're always going to be constrained with your NPDs permit regarding land disturbance. And so we always look at those projects, looking at post construction or a temporary BMPs. And outfalls, intermediates to meet the requirements that in NPDs permit, and so that's going to lead into protection of any species that may be in streams or, water quality in itself. So whether it be a maintenance project, whether it be a construction project, consideration of those outfalls in any as “don't want to discharge this, may contain sediments”. Ryan said it best in his presentation, the intent is to limit the amount of sedimentation and erosion. You'll never stop it completely, and so doing what you can do as an organization or as a group to limit the amount of sedimentation that occurs by best management practices, the more the better. And that's kind of Missouri's approach that we've taken since we've been under consent decree with EPA and Department of Justice back in 2015 through 2018. And so the approach that we've taken from the construction standpoint is get the BMPs out early and make sure you're maintaining what's out there. So I hope that helps kind of answer that question, if you got any other questions, I'd be happy to help answer.

Baolin Deng: Thank you.

Q2: Are different types of sediments handled differently? What sediment properties/characteristics are important?

Kathleen Trauth: Yeah and I wonder if I, could you know follow that up is, you're saying you're, you know, it's with the NPDs permit, so do you, and those BMPs, do you, I don't know, tailor them to, the location or what you've got, so if you've got discharges, are you looking at the site and what might be what you're disturbing and so are you differentiating between the different types of sentiments and how you manage them?

Brian Williams: Typically, in Missouri we look at semi-standardized BMPs, so we obviously are preferred go to permanent control is a silt fence. Go to ditch check would be a rockets check. If we have special conditions, circumstances where we might want to look at silt curtains those types of things, we've definitely look at site specific needs, and make those adjustments through the design process. We develop our own urgent site control plans through our design process. So it's not left just to construction to determine what to put out there. They have the flexibility to adjust the plan as to deal conditions necessitate. Maintenance is a little bit different animal, if we've got, we do really small projects with maintenance, so we limit the amount of large projects over an acre. And if we're doing things like that, where we were going to be a concern of discharging to an outfall, they'll definitely call in, either myself or other construction staff around the area that might be able to help them, lead them in the right direction with what appropriate BMPs might be out there.

Kathleen Trauth: Let me follow up on that if I could. So free thinking about kind of the standard BMPs that you go to, do you have, you know, when you're managing the runoff and you're trying to contain in a particular storm, what is your kind of experience with sort of detention basins, do you use those? Because I'm thinking now we've talked about if we have gravel streams and we can, you know, those might settle out more quickly, but if you have the clay particles, what kind of, what is your strategy for dealing with them.

Brian Williams: So historically we've not really used in recent years, now I've been with MoDOT 28 years, so when I use the term recent, that's within the probably the last 10 years. We haven't done a lot of big projects, we've been basically taking care of the system type projects. But we're not buying right away so those sediment basins, in particular, to be constructed in accordance with our permit really required a lot of area, so we didn't really build a lot of sediment basins. And in recent years, now our standards do require and then our guidance does require that any place we have an outfall, we are installing a sediment trap, which is a bigger more robust style looking ditch check that as an impoundment functioning similar to a sediment basin. And then, those are it all outfalls prior to any discharge to surface waters. So, every project should have the standardized silt fence, ditch checks, and sediment traps. And that way we're limiting the amount of unimpounded discharges before we reach any outfalls where we could affect any type of species in surface water.

Bree McMurray-Missouri DOT: I would add a little bit to that too. When you're talking about specifically this question in relation to like mussel streams and run off into a stream situation, and Ryan had a really good point to make, disturb as little vegetation as you can. That's also one of our kind of standard practices is minimizing your footprint. We have a lot of specifications for, you know, when you need to revegetate immediately like there is temporary vegetation, so in my presentation, I said, some of these access roads, your hall roads, they won't be vegetated for the entire point of the project, but there are other ways to keep those sediments in place. We might have large rock and then smaller rock dealing in the places, and then you put your aggregate on top, so that you can use that kind of locks its keys into place. And then you have particular catchers kind of through the rock, that's kind of your rock filter and then we have our erosion control on the bottom of those access points. When we do have temporary crossing, it's built the same way, we're putting clean Quarry run rock in the system. Limited number of fines and that's through a lot of our standard specifications to it's like 5% or 10% something like that, under a certain size. And then, all of your elements are done then from that rock pads, so the improvements that we've been trying to make over time too, Kathleen, are the width of the top of that how high is it can it be over top of that losing the sediment that's on the aggregate that's on top. Do you have adequate flow through the structure so that you're not going over the top of the structure except for extreme high events. So we are trying to control our elements that are constructed in the water and we're trying to control is, Brian was saying a lot of the stuff, from soil even leaving the ground and entering the water, and it's all, as Brian said a game on minimizing, you can't stop it completely but we're trying to control minimize the best we can.

Kathleen Trauth: Okay, great I think that kind of answered a couple of the about the sentiment, and then if we have enough information are there, I don't know, is there more information, because I know we had talked a little bit about like the size and the angularity, the makeup is likely to impact the pH, are there any other characteristics that might be kind of impacting or create an impact?

Baolin Deng: Kate, actually l would like to follow up specifically to see whether Fabian would be able to answer. For example, we have this runoff from a farmland, most likely you would have a higher concentration of organic materials, the soil sediments may be more mature and then you just construction process probably those less weathered sentiment will be disturbed in terms of the transport processes, are there differences expected?

Fabian Bombardelli: Yes, if you have a, let's say, more organic content, you will expect it to add to the sediment cohesiveness if the sizes are fine enough. And if they are, this cohesive dynamics is different; I mean in the sediment transport field we divide precisely between non-cohesive and cohesive sediments. In the former category, we have some, let's say, better prediction tools than for cohesive, i.e., less uncertain tools to predict for non-cohesive sediment. So the bottom line is that with the organic part and the cohesion forces, particles in some cases would produce flocs. In addition, compared to larger materials, in cohesive sediments the fall velocity varies significantly. So the dynamics is completely different and if you have, for example, fines within the area of non-cohesive sediment, they are treated differently than sands, gravels and boulders. Like Brian was mentioning, if you have fines, fines are very difficult materials to handle at the site, but you could produce some retention ponds. Because if you don't reduce the velocity significantly, fine sediments will keep going with the current. So you really need to reduce the velocity such that sediments will have the opportunity to go to the bottom. And again, there is very, very fine material which is called wash load. I mean they are so, so tiny that they almost never interact with the bed so they may be within the river for kilometers and kilometers and kilometers, but that's very, very, very fine material.

Q3: Is there adequate information to manage different sediments/characteristics?

Kathleen Trauth: Thank you. So I don't know, do we think we have the adequate information or what, I don’t know, are there other information that we just don't have about the sediment, or because we've talked about the minerals, the organics, natural, I don't know, are there is there any kind of anything about the characteristics that we may be missing?

Ryan Foley: I would say, before we even get to that, we just need to have a better way of quantifying the sediments that escape our sites and impacts and how much of it enters our rivers and then we can get into what the impacts our mineral versus organic versus micro or nano plastics that sort of thing.

Kathleen Trauth: And more basic then.

Fabian Bombardelli: Coming from the sediment transport field, plastics are a different thing for us, so I respect your justification, Ryan; your arguments seem fine. There's nothing wrong there, but I mean if you address the classical sediment motion and transport field (in books and papers), those do not address plastics, so there you have a relatively new field for plastics. I mean, I don't see any problem in considering part of the big picture sediment transport and plastics in a potentially unified way in the future. But, for plastics, it seems to me that there are even less pieces of information available. I have not seen, for instance, fully agreeable and general ways for calculating settling velocity for plastics, which is one of the basic parameters for natural systems. There are some papers out there, but not with the same extension as in natural sediments. For plastics, I have not seen anything like that, I have not seen reliable and agreeable transport formulas for plastics either. I have seen some attempts, but nothing we could all agree on, that we can…

Ryan Foley: Yeah, just trying to throw a wild card out there.

Fabian Bombardelli: Again I'm not criticizing the presentation; that is why, when you were presenting, I didn't say anything because it's completely okay. It makes a lot of sense to include a kind of manmade elements into part of the bigger picture of sediment transport. It is OK, but what I'm saying is that, if you open any book on my shelf on sediment transport, they don't include plastics, and there is no equivalent set of tools like you have for the natural sediments.

Ryan Foley: Yep, I was just trying to muddy the water.

Bree McMurray-Missouri DOT: Oh it's getting worse, I will say in it, something that I didn't mention during my presentation, but another one of the tools that we have used on occasion not all projects is a turbidity barrier. It's, my understanding of it is that you only use it for temporary applications. It's kind of like a floating net, maybe? Tt's got to be anchored properly, has to be deployed properly, but it can be put in a system when you are installing your temporary access, your temporary causeway, your walk pads. And then it's meant to be, you know, of course collected and removed properly, so that you're collecting things that you're going to throw into the water column, you're going to stop the velocity and you're going to let it settle. Then you collect that, move it to an upside up location and, then again when you're removing the temporary rock structure, also you're going to stir up bottom sediments so you deploy the turbidity curtain again. And it would be like between you and a very sensitive resource. So it's not something that would be left in place, it's only usable in certain conditions where the velocities not going to just take it with it and go downstream, but it is another tool that we've kind of looked at an extremely sensitive situations say were very close to a known list of species mussel bed, and we're not physically going to be laying rock on top of it, but we are going to be within maybe100, 150 feet of the head of this bed, what can we do to just without even knowing, how far is it going to go, or what's chemical composition of what's being stirred up without even knowing those things we're putting kind of a barrier in place to block, move safely and get all those variables out of the water column. And again, we're kind of making an assumption that it's better than doing nothing. I don't know that really any studies have been done for how, what I will say, how good that is a blocking all sentiments or half the sentiments or whatever. But it's just another tool that we've used without even really having the data. And that's probably more of a construction industry. Try at, you know, based on visual, you can see when you have a sediment plume, when you're walking around in the stream and you kick up water, you're kicking up sediments. On a very large scale when you're dumping tons and tons of rock into the stream, you're stirring up sediments, and people can see that the folks that are downstream swimming in the water they see this plume of sediment come downstream, and they know it's from your construction jobs. So it's kind of more of a maybe a visual or physical reason for employing those measures. But turns out maybe it's pretty good idea in some respects. They said we don't know if we're doing the right thing, but we hope that we are. We're trying different things to try to decrease the release of sediments from our sites.

Kathleen Trauth: Thank you.

Ryan Foley: So when we have, Bree, when you have Andy and Steve go out there and did quadratic for you, we have to do a sedimentation plan for all those plumes that they stir up?

Bree McMurray-Missouri DOT: Yeah, they're the experts, so I'm leaving it up to them, they have like section six per minute, so I'm just going to assume that they are allowed.

Q4: What engineering and/or management tools are used to mitigate soil loss/increases for different types of aquatic system sediment?

Henry Brown: So I think we're ready for the next question here on the list, and that is what engineering and or manage we've kind of touched on this a little bit already, but what engineering and management tools are used to mitigate soil loss or increases for different types of aquatic system sediment?

Fabian Bombardelli: You mean soil loss from the slopes and measures to prevent erosion; is that where the question points to?

Henry Brown: Yeah, just to mitigate…

Fabian Bombardelli: Yes, this is an interesting topic and some solutions were already put forward by the Incas in Peru in the 1400s-1500s. The Incas constructed some terraces. They built terraces so they would reduce the slope, and would contain with just vegetation the possible erosion (in addition to an underground system). You cannot prevent some erosion from occurring in first place therein because it's a natural place, but you could limit the transport of sediment. So what the Incas did was to first of all put grass on the slope. So if it rains it doesn't have too much opportunity to massively scour the sediment. These techniques were used widely, and you can plant vegetation, where these vegetation pieces retard the scour from the slopes, and you have similar techniques that you use in practice today with, let's say, some structures, but those are very costly.

Bree McMurray-Missouri DOT: If I can share my screen for a minute?

Bree McMurray-Missouri DOT: A bigger picture of a smaller one that I had. This going here. Give me thumbs up when you can see the picture there. Okay, so this was a really awesome project that we just did and compared to some of the other pictures I showed, that's a lot of open dirt, but this was designed. This is, I don't know if you can see my mouse as it's moving or not, but from the back of the picture coming forward into the foreground there, this area is benched or terraced like Fabian was saying. So instead of working it down a slope and trying to put rocker or, erosion socks or something like that across a slope they benched it to work coming down toward the stream. They had this off to the left here, so you got the main road that's kind of up down in the picture and then off to the left you got this area where there's it looks like extra causeway well that's where they needed to build the pier for the new bridge. And that the water back behind, there is a scour that needs to be filled in. So this was all going to be filled with rock anyway. And so they built these terraces all around it and that might be kind of like an instream detention basin, because you have all of this larger rock on the bottom, and then you have your aggregate on top in order for the trucks to travel and drive on. So we kind of try to manage the stuff coming off the dry land. With a lot of rock, and a lot of berms, and a lot of terracing. And then what's coming through, I'll stop sharing my screen, but what's coming through the causeway, we're trying not to constrict flow, so that we don't create scouring event or we're not pushing water to one side or the other of the stream, so that we're going to lay down all this rock on top of the substrate and when it's done we're going to peel it right back up. And we're going to try not to dig down into the stream. And in a lot of ways that's you know, more, and again, it depends case by case, for your project area if you don't have any habitat for mussels in that particular area where you're laying down rock, well that's where you should lay the rock down. You know, you're not laying it on top of a gravel bar, you're not excavating the gravel bar to make the causeway, you're bringing clean rock and you're taking out clean rock, the expectation is you're going to remove everything that you put in. And after the project is done, we, this is on this project, it was really kind of awesome we went back and had the contractor put more rock down. So before it was, we had the contract to put more rock down to continue to protect any erosion events. And then, when it was done, Fish and Wildlife went back out and check the habitat that was there that they had done pebble counts on prior to putting down our big rock. And when it was removed went back out to check the habitat and a lot of it was still there, not undisturbed, of course, but a lot of it was still there. So we're starting to do more of that. We're looking at how much of the usable habitat did you actually disturb and factoring that in before and after, was it a good plan, or do you need to change the plan, the next time.

Q5: What are best management practices for protecting freshwater mussels from influence of sedimentation episode?

Baolin Deng: Thank you. Time goes fast, we have a good discussion here. Next question, we have come up with is what are the best and management practices for protecting freshwater mussels from influence of sediment episode? I guess we're talking about not a long-term sedimentation impact, but if you have this -term episode, whether there's a major impact on that.

Ryan Foley: I will offer that it's all about site stabilization. For instance, when we have projects that are within 200 feet or so of waterways, especially during the fish spawning season, we have to stabilize that site on a nightly basis. Just in case, I think what we're getting that is a big storm comes through and has a big washout or something like that. Those, you can't foresee those events, so just making sure you have the site nice and tidy I think that is the best we can do for now.

Bree McMurray-Missouri DOT: I'm going to offer that when we've gotten a lot better at our general practices when we are putting pipes for that flow through a causeway. We're getting better anchoring them, we're getting better at increasing the numbers of them, so that we're not overwhelming them. So those are kind of best practices that have come with experience. Like Ryan said, making sure that you are tight and as tidy as you can be on your project. We don't allow construction equipment to be parked on these temporary work pads when they're not in use. So they're not supposed to just have equipment out there forever and ever. When you have high flow events, it's flowing over and around your tractors and whatever else you have stored out on site. We do a lot of water quality protection measures are also going to protect species that are in aquatic system. So I guess set a couple of times, we've got Standard Specification Manuals and every DOT in the nation has got Standard Specification Manuals and a lot of the Water Quality Protection Measures, and you know, 100 and something state and federal laws are built into those protection measures that we have to follow for every contract.

Baolin Deng: So for some of those construction sites, you could potentially spray some polymers to stabilize the soils, is that a common practice or not?

Bree McMurray-Missouri DOT: I'm going to defer to Brian on that one, did you ever heard of that Brian?

Brian Williams: I'm sorry, could you repeat that, please?

Baolin Deng: At least in the research community sometimes people are thinking that you could spray some kinds of polymers onto those loose soils there, so those will not be sort of washed away more easily, so I don't know, has this has been practiced or not?

Brian Williams: Yeah, that's becoming more of the BMPs folks are using. I'm not really a big fan of it just because it doesn't always function as adequately as other BMPs. You know, most of the time when we're around streams like Bree indicated. We're pushing clean rock no, little to no sentiments as we can keep from the streams. Using those over spray materials, to me, as I like to call them a feel-good measure that they just don't function as well as other BMPs so that we can put out there that ensure that we're catching those sediments when they begin to move so.

Baolin Deng: Thank you.

Ryan Foley: Yeah, from our standpoint, the, you know, use additional, even more foreign substances into the environment, this is not ideal for us.

Q6: How important are the flow conditions related to episodic sediment event?

Henry Brown: Okay, I guess the next question we have here on the list, how I'm getting back to the episodic events, how important are the flow conditions related to episode sediment events?

Bree McMurray-Missouri DOT: I’ll take a stab at that one. You know, like we said some of our streams are extremely flashy, move a lot of gravel just several times throughout the summer. And when mussels are in an area that happens to be stabilized by vegetation, or the stream flow, the system we have a lot of streams that have dams on them. So the releases are timed and, you know, that not every situation is ideal and we try to plan for the normal flow time of the year, but knowing that if you've got a construction access, temporary construction access, and wood pats out there, you're probably going to have a few high flow events during that time period, and we have made some improvements on designing those a little better. They're not just a whole bunch of rock dumped out there, it's actually kind of keyed in where there's, what I am gonna say, specifications for how wide the bottom should be, for how tall the structure is going to be, as for how stable it will be. So there's maintaining the flow through the structure for mussels is always going to be sometimes we disallow a full causeway, because it's going to push water when you have a high flow event. It's going to go around the outside instead of flowing through your structure. Or it's going to pick up your pipes and it's just going to tumble them down because it's too much water to try to hold back and push the pipes, so we do take into account. You know, is it a flashy stream? Does it move a lot of rock? What is your base sentiment type? And then doing some of the hydraulic analyses, if we don't know we can answer those questions, or we have a very sensitive resource nearby, we do those hydraulic analyses that will give us some of those answers, and tell us how big to make a causeway, or how narrow across the top it should be, how many pipes will need to be put in.

Q7: What are the most important monitoring/management methodologies and parameters to protect freshwater mussels?

Baolin Deng: Any other panelists would like to weigh in on that? I know some of these questions are sort of repeated to a certain degree, because we're all talking about this approach is to protect the mussels here. The last question I have it here is what are the most important and monitoring and management methodologies and parameters to protect freshwater mussels there. The monitoring certainly is important, and I am wondering that without monitoring, then we don't know how good our practice would be. I am wondering that whether we have some comments here.

Ryan Foley: Yeah, I think monitoring is an overlooked aspect of it, I think from our perspective, it's sort of post project monitoring is almost are reserved for only federally listed species, rather than state listed and species. So I think if you do a relocation, it's pretty standard to kind of monitor how those relocated individuals were doing. But I don't know. I know Heidi has done is on the call, but I know that she and West Virginia DOT has done monitoring and assessment of recolonization of areas that are salvage from mussels. So there's a lot that monitoring is very important, but I don't think we do enough of it.

Bree McMurray-Missouri DOT: I would tend to agree, and I would, I can't answer this question but I’d love to hear the answers. We do not do a lot of, even just being out on site and watching how the construction is going. We don't do a whole lot of that. We have construction inspectors. If things go catastrophically wrong, they know to call our office. If things, it's not going to work out and they need to change the design or they need to change the wood pads or we lost to wood pad, they're going to call us. So we sometimes we find out just when things don't go as planned, but I absolutely think that there should be some aspects of monitoring when it does go as planned. You know, taking water samples we don't do, we're not in a business of water quality monitoring. If MoDOT, but you know, why can't we partner with somebody who does? I think it would be a lot easier to get a more systematic approach if we had something kind of like the symposium in this research project to start getting to those answers. And you know, knowing how much is moving through the system is a hard question to answer when nobody is looking at how much is moving through the system. So yeah, it's another one of those data gaps, how do we get those answers, how do we know what's, the best thing to monitor to make sure that we're protecting the mussels.

Ryan Foley: Kind of going along with that construction monitor, we've had instances where hey here's the footprint of this bridge replacement project, and we're going to relocate or salvage the mussels from this area. And then the barge just go in, we moved the mussels and the barge come in, and Man, they just want another 20 feet this way or 20 feet that way, and we have told them hey you know we agree to these construction limits, and so the term of the construction creep, where you know hey we've already got this huge swath of area that we can work and what's another 20 feet. So I think you know, we brought up a good point of just what's on paper is not always what's actually occurring on the ground and it's important to keep an eye on the construction footprint itself.

Baolin Deng: Thank you. We have finished all the questions there. I would like to open to questions from the audience. If you have any, please send your questions through the chat box or just to unmute you, so you can ask the panelists directly. There's a question here by Steve. Is monitoring done to confirm that engineering controls are effective, the monitoring is done in compliance with a 16402 NPDES permitting? Okay, that is the response from Brian.

Bree McMurray-Missouri DOT: Yeah I was gonna say for soil leaving the ground that could enter the stream, yes, there is definitely monitoring, very very very heavy monitoring. Is there monitoring that's done in the stream to see how much sediment is put into the column? Not that I know of. You know, like I said when the public drives by, and they're like oh my gosh you know, this is the Meramec river and there's this huge plume of sediment, what's going on, it must be a construction project. You know. Then we might get like a violation or somebody will come in and say hey you have this release of sediment. And turns out, yes, we did, and we knew about it, and it's all authorized and permitted by the core and it's within limits, we think, but we, as far as I know, I know no one in this office actually goes out on our projects and is doing any kind of water quality sampling, turbidity sampling. Brian is absolutely fantastic at what he does, but he's one man in the whole state, we don't have, I saw Ryan has got maybe four or five erosion control specialists. That he gave information for, you know, in our state Brian Williams kind of has, he's got the whole thing in his pocket. We have a lot of inspectors around the state that help, and help self-police. But having a research objective or having a question to answer, I think, would help direct where can we employ this, where can we start finding this out.

Brian Williams: You know, part of Missouri's EPDS permit with Department Natural Resources requires that we evaluate outfalls 50 foot downstream. More just from the sedimentation aspect, make sure our piece are functioning as they're designed and intended not necessarily from the aspect of looking at species, but you know, there is a little bit of monitoring of those of those outfalls looking for sediment deposits. You know, so we can make adjustments to any of our stormwater management plans, or you know, swift plans basically. And that way we're being proactive and doing the right thing, so that is part of the permit requirement is a 50 foot evaluation of any out falls.

Baolin Deng: I have a question, especially for you two who are working in the state government. There are so many agencies that could be involved like DNR, Department of Conservation, Fish and Wildlife Service, how do you coordinate this kind of activities, I mean, who is responsible to what, is there a flow chart that you follow?

Bree McMurray-Missouri DOT: Somebody get an idea? And we put Andy and a scuba suit and we're off running money. We do have good collaboration. And I would say by and large, if things like this are done it kind of comes up project by project. If Andy would like to see something done on a project then we'll make it happen. Or if he would like to see something done on a project then we'll make it happen. But by and large, we don't have like an internal, you know, set of research questions to answer “hey let's go monitor all of our stuff”. It's one aspect that I think we could do better on. And hopefully like I said, having this grant to do, this research is going to open that door a little wider, to make those relationships a little easier. I think if we had a list of what questions would you like to answer and then start passing that list around when we start having those meetings about who wants to be responsible for this part of this question? And MoDOT can you get us on site on an active job? Yeah we can do that. But we can't just say DNR is going to show up, or NBC might show up, or Fish and Wildlife Service might show up to monitoring active project, because the contract won't let him in. So the access part we can handle that. Setting up the design for what needs to be collected, we are maybe not so good at that. And that's what we rely on our partners for.

Baolin Deng: Ryan, any comments on that?

Ryan Foley: Yeah, you're right there's a lot of cooks in the kitchen with these regulations. And you know, luckily for us from the erosion control standpoint. There's site specific and minor differences between the agencies but seems like there's a generally agreed upon set of best management practices that we follow and that solves kind of 90% of our issues with following these provisions that are permits.

Baolin Deng: Yesterday there's another question on what are the major data gaps, I found that is very informative, there is good information there. I know we have been talking about this all this afternoon, but I would really like each of the panelists to briefly summarize what are the major data gaps and weather we could eventually have a way to fill those data gaps. We will start with Bree or Ryan, either way would be fine.

Bree McMurray-Missouri DOT: I will just beat the drums more and say that I, we should probably be monitoring in some aspects what's coming off of our instream temporary projects. I mean we can, as Brian said, with MDEs permits, we're dealing with runoffs. But with what's being stirred up in water column, and how much turbidity is there generated from this project, and how much does flow in volume of water and sediment size effect do, are we really having, you know, is all of our particulate not particulate, but as all of our larger size sediments dropping out in that 300 foot distance that we think they're dropping out at. That might be one way to, one place that we can start on a mussel project. That the thresholds and all that the biology that definitely needs to come into it, too. But then, once we have those thresholds, are we exceeding those thresholds on a construction project. That's a question that we do not see.

Ryan Foley: Can I goes into another quantification and the characterization of the sediments that runoff from the streams from our projects, it's like once it hits that water, this is mystery, you know, who knows where it's going, or what it's doing. We think it's bad, but we don't know how bad it's. You know, we just had the conversation in this panel about how long we have, or how big of an indirect impact area from these sediment plumes may be. So there's a lot we don't know.

Fabian Bombardelli: Yes, I would like to add to this the issue of heterogeneity, because when we have, let's say, big areas of sediment we tend to just get samples in one place or two places or five please at most, but that doesn't mean that we had a nice large-area characterization with those five places. So, very often we rely on a few points when dealing with large areas and certainly need to worry all the time to what extent our sampling is characteristic in the entire area.

Fabian Bombardelli: I think there were two questions, there was somebody who raised hand, and somebody who wanted to make a comment?

Kathleen Trauth: Yeah Heidi has done had her hand up for a while. Heidi, are you still there?

Heidi Dunn: Yeah I'm still here. I just was this kind of the conversation, and we work with the DOT and probably 10 states and the sediment question comes up every time I work on a bridge. How far down as the impact and what impact does it have? Should we move the mussels out of the area of the direct impact? Is the impact on mussels worse if we move them than as if we leave them. How is that impact? What's going to happen? And what I can see from the research out there, like everybody was just saying we don't know. And I think the I-74 bridge was a on the bridge so far possibly doing a downstream sediment, you know, characterization and monitoring the mussel bed over four or five years. And so far, I haven't seen an impact. We set transits at various distances and did measure this built along transits, and then also did a three random start designing on a on the mussel bed, to see what was going on. I think we went about 400 meters downstream to a mussel bed. And then we found about a kilometer downstream, where we had a couple land areas, everybody was silted in and died, whether that was the effect of the bridge, or whether that was natural sedimentation, we have no clue. Because we didn't monitor that far downstream. So I think lots of unanswered questions and I would really encourage anybody that's doing a mussel project or doing any kind of construction, a bridge to start with some sort of monitoring program downstream, because it is a big unknown and until we get some on, it's hard to say, these impacts could be long term. Let's just say most mussels we were talking yesterday about the impacts to juveniles and maybe it's too bad, your class too. But what happens to the adults timing wise, if we are having these impacts during the fall and everybody clams up and use all these energy reserves, and then we’re going into winter and they don't have the energy reserves to survive the winter, we're going to see the mortality in the spring, so those monitoring programs need to go on a couple of years, maybe after the impact happens. Or maybe we need to think about you know, timing earlier in the year, I don't think that you're ever going to avoid spawning or glochidia release, because everybody releases in a different time and everybody's spawning at a different time, so I don't think you'd have a window to do anything except during the winter. And then are we impacting a more of that time, you know. So there's a lot of lot a lot of unanswered questions and until we get out there, and you know, get some monitoring done we're never going to know, so I just wanted to make that comment, so I agree with everybody, we need a lot of monitoring.

Baolin Deng: Thank you so much, Heidi. I almost missed your comment here, I didn't pay attention to the chat box. Any other questions, comments from the audience, from the organizing committee, from the panelists?

Fabian Bombardelli: I think Andrew wanted to make a comment.

Andrew Roberts: Sure if we have time. There are a couple of questions about data gaps and the valley, I guess, important monitoring and management tools for mussels and I think early on, Chris Barnhart asked about post construction monitoring and my wi-fi has been cutting in and out during part of this, I don't know if I'm answering some of these questions. But I just wanted to say that we had, and Bree had talked about a project that we worked on together fairly recently on the Bourbeuse river where MoDOT and Fish and Wildlife Service and Department of conservation all work together and we did a pre-construction survey for freshwater mussels. And the thing about mussels is, I think that we all know by this point, but it's important to remember is that they can't swim away from these impacts. They're like sitting ducks and so and they're always kind of in the same place so they're pretty easy to monitor. So that is an important tool is monitoring. And we did a pre-construction monitoring, and to get an idea of density and what species were there. They ended up being a couple of endangered species there, and some species of conservation concern, and a pretty good diverse mussel beds there, that we were concerned about that actually was downstream of the bridge and under the bridge, and actually extended upstream from the project as well. So we had a mussel bed there and MoDOT did a really good job of assessing the hydrological impacts of a causeway that was planned for this project, and we were, they were able to very accurately determine the, I guess, the scouring effect of that causeway and where that scouring was going to occur downstream. And so we did do a post construction assessment and mussel survey to look at, because we, this was one project where we did decide since the mussel bed was right directly on the footprint of the project, we decided that, you know, mitigation for lost habitat was appropriate, but we weren't exactly sure where those impacts were going to be. So the post project assessment became really important to determine maybe the area of the impact in my area would be mitigated for have lost habitat. So we went in afterwards, and this gets to the, I'm getting to what data gaps or tools we need. You know, we were able to assess the mussels post construction, but one thing we tried to do was look at the substrate and how the substrate changed, and where the scouring occurred. And it was pretty obvious where the severe scouring occurred, where the causeway, just directly downstream the causeway. Because that was scoured out, and the channel had changed, and what once was kind of compacted gravel that we usually find on this mussel bed, this is now kind of a clay bottom and all that material kind of worse downstream. But we tried to use a pebble count, like a Wolman pebble count to determine if we did that before and after a project is to try to determine if the substrate it changed. And I guess that worked out okay. From what we can tell, MoDOT did a really good job of estimating those hydrological impacts and it seemed like we were very close as to how far downstream, the stream bottom had had changed. But it would be nice to have some kind of way to, I guess, assess the stream bottom composition of these mussel beds, and so we can see if that composition has changed or if there's been deposition or scouring. You know downstream of the impacts and or the project, because that was one couple of the questions we had was, you know, where was the stream bed scoured in the sediments carried away, and where did those sediments end up, and did the composition of the substrate where the mussels were living changed downstream. So would be really nice to have some kind of tool to not only measure the composition of the substrate where the mussels are living, so that we can see if that has changed after the project, but also the compactness of that substrate, too. I just don't really know how to measure that compact missing which it seems to be very important for habitat component for these animals.

Baolin Deng: Thank you, Andy. I am in charge in wrapping this symposium up, and we have five minutes before 5 pm. First, I want to thank all the people who have participated in this symposium, all the speakers, organizing committees, to make this symposium a success. I think it is, like the first day we had 140 people at the peak participated. And today around 110. So we have a good number of people who would be able to stick around to the very end. We set our objectives to communicates the science, the state of the art; we want to share the best practice; want to discuss the data gap. I think for each of those objectives I have learned a lot. In this regard, I think we have a successful symposium. One thing that really struck me is that the whole mussel issues, the management issue, is very very multidisciplinary. And there are a lot of things we could look at and also we need to examine this from different point of view. For example, we need to really look at the biological aspect and engineering aspect and also the regulatory aspect in order to manage the endangered species of mussels. In terms of research, we need to look at the field- versus the lab-based research. And we need to look at the modeling versus experimental aspects, to look at organic rich natural sediment versus those less weathered clay particles and minerals, and to look at those round particles versus the angular particles. The sediment particles sometime would have this organic coating, sometimes we call those as natural organic material corona over there, versus those fresh particles. Overall, I think we have a lot of angles, aspects we could look at. To the end probably we need to see whether we could come up with some results that could be implemented for management practice. For example, two things that have sticked with me, that what will be the threshold if there is one. Will that be like eight milligram per liter in terms of this total suspended solid, or if there is this kind of threshold at all. Another thing is the distance of impact, would that be 100 meter or one kilometer? Hopefully with the research and with monitoring, we will have some kind of answers for that in the future. That is the first symposium we are trying to work on, to bring people together to discuss about that. Probably after two years or three years, we will be able to bring people back together. Hopefully by that time it would be face-to-face meeting, will see whether we would make assessment and evaluate how much progress we have made, whether we could have answered some of the questions, filled the data gaps we discussed and identified today.

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