Past Research

Metabolic controls on carbon emissions and export in running waters

We quantified the role of aquatic ecosystem metabolism in modifying stream network carbon fluxes in the boreal Krycklan Catchment. We also used data and model simulations to identify the principal sources of carbon dioxide emissions from streams and rivers. With J Karlsson, R Sponseller, J Klaminder, M Rosvall (Umeå University), H Laudon (Swedish University of Agricultural Sciences), et al.

Hotchkiss, E.R., R.O. Hall, R.A. Sponseller, D. Butman, J. Klaminder, H. Laudon, M. Rosvall, & J. Karlsson. 2015. Sources of and processes controlling CO2 emissions change with the size of streams and rivers. Nature Geoscience 8: 696-699.

Hotchkiss, E.R., R.M. Burrows, J. Klaminder, H. Laudon, R.A. Sponseller, & J. Karlsson. Distinct role of whole-stream metabolism on carbon fluxes in a boreal river network. In Preparation.

Nutrient limitation in boreal streams

We explored interactions between nutrient and carbon availability, metabolism, and microbial assemblages in boreal streams with varying water chemistry and landscape characteristics. With R Burrows (Griffith University), M Jonsson, R Sponseller (Umeå University), H Laudon, B McKie (Swedish University of Agricultural Sciences).

Burrows, R.M., E.R. Hotchkiss, M. Blackburn, & R.A. Sponseller. Stream nitrate uptake dynamics in a nitrogen-limited region. In Preparation.

Tracing carbon sources in boreal stream food webs

Large subsidies of terrestrial organic matter support heterotrophic carbon (C) and nutrient demands in boreal streams, but the degree to which in-stream photosynthesis contributes to food web dynamics is not well known. We used stable isotopes to measure the contributions of terrestrial and aquatic C to invertebrate consumers. We also linked diet sources with ecosystem C pools and fluxes, including rates of whole-stream metabolism. 

Hotchkiss, E.R., E. Landström, J. Karlsson, & R.A. Sponseller. High autochthonous support of macro-invertebrates in heterotrophic boreal streams.
 In Preparation.

Fate of newly fixed carbon in a mountain stream (NSF DDIG)

Despite the longstanding appreciation that algal C can fuel stream food webs, we know little about how primary production contributes to C cycling in running waters (e.g., the capacity of primary producers to influence C dynamics; the time scales over which newly fixed C turns over in different stream C pools). Using a whole-stream 13CDIC (dissolved inorganic C) pulse-chase experiment, we applied a novel combination of an ecosystem-level tracer addition and modeling to trace 13CDIC assimilation by algae, short-term release as CO2 and dissolved organic C, and longer-term fate of newly fixed C. While biology governed short-term fluxes of algal C, hydrology likely controlled longer-term fates.

Nutrient and carbon cycling in rivers

We measured nitrogen, phosphorus, and carbon uptake and spiraling in rivers of the western and midwestern United States. My project employed a two-compartment Bayesian model and experimental microbial dissolved organic C (DOC) consumption assays to identify a positive priming effect in increasing microbial consumption of more refractory C. Biologically available DOC likely stimulates (i.e., primes) the consumption of more stable DOC by heterotrophic microbes in rivers.

Microbial assemblage structure and freshwater carbon cycling

We used microbial assemblage data and measurements of microbial carbon consumption from different freshwater ecosystems to test how microbes may respond to changes in carbon and nutrient sources.

Gregory, S.A., N.C. Berg-Mattson, A.L. Saville, R.O. Hall, & E.R. Hotchkiss. Microbial assemblage structure and carbon source control dissolved organic carbon consumption. 

Consequences of multiple species invasions in a productive spring stream

Four non-native fish species (convict cichlid, green swordtail, guppy, tadpole madtom) and one non-native snail species (red-rim melania) have established populations in Kelly Warm Springs, Grand Teton National Park, Wyoming. We used historical samples to compare densities and biomass of native invertebrate species before and after the red-rim melania invasion. To quantify how multiple species invasions may influence stream food webs, we also measured fish and invertebrate population densities and biomass as well as fish stomach contents along a natural temperature gradient. 

Diel ecosystem respiration in streams

Most aquatic ecosystem metabolism calculations assume respiration is constant over 24-hours or that diel respiration can be estimated using changes in water temperature. These assumptions limit our knowledge of diel mechanisms governing freshwater ecosystem metabolism and C cycling, as biologically available organic C may also vary over 24-hours. We used diel δ18O2 and O2 data, coupled with a Bayesian process model, to estimate diel ecosystem metabolism in three Wyoming streams. We found that daytime respiration exceeded nighttime respiration and temperature-adjusted calculations of respiration did not account for the magnitude of diel respiration modeled with δ18O2.

Controls on nitrate uptake in a semi-arid stream 

We quantified the role of hydrology, geomorphology, and biology in governing water chemistry and nitrate uptake along three different reaches of Red Canyon Creek, Wyoming.

Hubbard, K.A., L.K. Lautz, M.J. Mitchell, B. Mayer, & E.R. Hotchkiss. 2010. Evaluating nitrate uptake in a Rocky Mountain stream using labelled 15N and ambient nitrate chemistry. Hydrological Processes 24: 3322-3336.

CO2 production by invasive snail calcification

We measured rates of biomass and CO2 production during growth and calcification by the invasive freshwater snail, Melanoides tuberculata, in Kelly Warm Springs, Wyoming. We also compared Melanoides CO2 and secondary production with ecosystem metabolism and fluxes of CO2 from the stream to the atmosphere. While snail biomass and calcification rates were high, CO2 produced from calcification was small compared to net ecosystem CO2 production. High rates of primary production appears to buffer the impacts of high-density invasive snails on native invertebrates and stream C cycling.

Hotchkiss, E.R., & R.O. Hall. 2010. Linking calcification by exotic snails to stream inorganic carbon cycling. Oecologia 163: 235-245.

Denitrification in a tropical stream 

The loss of fish species may alter stream nitrogen (N) budgets. Land use changes and increased sedimentation also alter benthic substrate and N availability, and both are important factors in denitrification. We quantified denitrification in Rio Las Marías, Venezuela and compared denitrification to other rates of ecosystem N loss and cycling.

Solomon, C.T., E.R. Hotchkiss, J.M. Moslemi, A.J. Ulseth, E.H. Stanley, R.O. Hall, & A.S. Flecker. 2009. Sediment size and nutrients regulate denitrification in a tropical stream. Journal of the North American Benthological Society 28: 480-490.

Land use and stream nitrogen cycling

ERH was a graduate assistant for the last season of LINX2 research on nitrogen (N) transport and uptake in streams using 15N tracer additions in urban, agricultural, and reference streams in and around Grand Teton National Park, Wyoming.

Lotic Intersite Nutrient eXperiments (LINX)

Sea turtle population dynamics

ERH collected data on reproductive females, nesting activities, and hatch success of hawksbill, leatherback, and green sea turtles on Buck Island Reef National Monument. ERH also helped with exotic mammal removal and monitoring, in-water juvenile hawksbill mark and recapture, and the creation of a plant ID database for Buck Island, St. Croix, U.S. Virgin Islands.

Productivity of restored and managed wetlands

ERH assisted with a project studying the density, diversity and productivity of aquatic plants and macroinvertebrates in a restored wetland, and their impact on waterfowl feeding behavior in Two Rivers National Wildlife Refuge, Illinois. 

Two Rivers National Wildlife Refuge

Conjunctivitis and house finch behavior

ERH's undergraduate research project quantified changes in house finch feeding behavior and aggression when infected with Microplasma gallisepticum.

Hotchkiss, E.R., A.K. Davis, J.J. Cherry, & S. Altizer. 2005. Mycoplasmal conjunctivitis and the behavior of wild house finches (Carpodacus mexicanus) at bird feeders. Bird Behavior 17: 1-8.

Nutrient limitation in a tropical stream (OTS REU

ERH studied the role of limiting nutrients on chironomid larvae growth rates in the laboratory at La Selva Biological Station, Costa Rica. ERH also helped with a project measuring nutrient limitation of in-stream microbial respiration.

Nitrogen cycling in streams and reservoirs

ERH's independent project compared potential rates of nitrification and denitrification in streams surrounded by different land-use types (forested, urban, and agricultural). ERH also assisted with field and laboratory work for several projects studying the nitrogen dynamics in Michigan streams and a reservoir in Illinois.

Tank Research Group

Genetic diversity of spatially isolated switchgrass

ERH quantified the genetic diversity of spatially isolated switchgrass populations from the eastern United States.

Plant Systems Biology