Commencement Bay 4/10/26

Welcome to Commencement Bay!

Audrey and James lowering the CTD with a view of the Port of Tacoma.

Heading out on the Welander

Credit: (Mcshane 2023)

Aerial view of the Puyallup River sediment plume.

Commencement Bay is a deep-sea harbor that is located between Point Defiance and Browns Point, at the southern end of the Main Basin of Puget Sound. Commencement Bay is 2 miles wide (3.2 km) and 560 ft deep (170 m) at the entrance. With its original formation resulting from glacial ice sheet intrusion, the bay has undergone changes due to urbanization and industrialization since the 1800s (U.S. Army Corps of Engineers 1981). The eastern part of Commencement Bay was once broad tideflats that were formed by the Puyallup River delta, but they were dredged and filled between 1920 and the 1960s. This dredging and filling has resulted in the channelization of the Puyallup River, and around 5 square miles of wetlands were eliminated in the process (U.S. Army Corps of Engineers 1981). The primary source of fresh water in Commencement Bay is the Puyallup River. The tideflats contain 8 waterways: Thea Foss, Middle, Sitcum, Blair, St. Paul, Wheeler-Osgood, Milwaukee and Hylebos.

With this area being dredged and filled for industrial use, many toxins are transported by the rivers that feed Commencement Bay fresh water and accumulate in the estuarine system. The EPA placed Commencement Bay on the Superfund National Priorities List in 1983 due to widespread contamination of the water, sediments, and upland areas. These contaminants include PHAs, PCBs, and fecal sterols, which can be found in higher concentration in the bay where the fine sediment accumulates due to stratification of the water (Takesue RK et al., 2017). The sewage outfall location was changed from the Puyallup River to Commencement Bay in 1987 (Washington State Department of Ecology, 1995).

The purpose of the Commencement Bay survey was to characterize the physical, chemical, and biological conditions of the estuary and assess the factors influencing ecosystem health. This survey also supports the long-term monitoring effort to assess the effectiveness of restoration work in this historically contaminated ecosystem.

Sampling Stations - First Commencement Bay Survey

Inner Latitudinal Transects in Commencement Bay

Figure 1: Sampling stations. Data taken 10 April, 2026.

Table 1: Station identification and information. Credit: James Simpson

Meteorological Conditions During Sampling Period

Partly cloudy conditions in the morning with calm waters, there was an increase in wind and cloud coverage by the afternoon sampling. Conditions were ideal for sampling.

April 9, 2026 (Day Prior to Sampling)

April 10, 2026 (Day of Sampling)

Figure 2: Weather Conditions for April 9th -10th, 2026

Meteorological Data

Figure 3: Atmospheric pressure on day of sampling

NOAA Tides & Currents

Atmospheric pressure was steadily decreasing during the time of sampling (April 10th, 12:00 PM- 2:49 PM)

Tidal Patterns During Sampling Period

Figure 4: Tidal patterns for 10th April, 2026 (Sourced from NOAA).

Credit: NOAA Tides and Currents

Tacoma, WA - Station ID: 9446484

Water levels, meteorological data and tidal prediction data are collected from sensors located in the Sitcum Waterway in Commencement Bay, Tacoma, Washington.

NOAA Tidal Patterns

CTD Contoured Water Property Sections

Commencement Bay 4/10/26 (1st Survey)

Inner Latitudinal Transect (Stations: 5, 6, 7, 8)

Temperature (℃)

Salinity (PSU)

Density (kg/m³)

Temperature, salinity and density are compared here because of their strong influence on one another within this estuarine system. There is a distinct surface layer across the transect with higher temperature, and lower salinity and density; this is likely due to the freshwater input of the Puyallup River. Sampling was conducted during an ebb tide; water levels had begun decreasing from the morning high tide. This likely enhanced the level of stratification we see in the transect as surface waters are transported seaward.

Dissolved Oxygen (mL/L)

Fluorescence (mg/m³)

Transmissivity (%)

In the graph, fluorescence was concentrated in the upper 5 m of the water column and declined rapidly below 5-10 m, indicating that phytoplankton biomass was greatest in the surface waters where light was available for photosynthesis. The transmissivity graph shows that transmissivity was lowest near the surface and increased with depth. Lower transmissivity observed near the surface is likely due to greater concentration of suspended particles and phytoplankton; this is likely due to the freshwater input of the Puyallup River plume. Overall, the water quality was relatively consistent across the transect. Additionally, the dissolved oxygen graph is relatively consistent, and the surface oxygen levels corresponds with the region of highest fluorescence, suggesting that photosynthetic activity by phytoplankton contributed to oxygen production in the water column.

Commencement Bay 4/17/26 (2nd Survey)

Latitudinal Transect (Stations: 5, 6, 7, 8)

Temperature (℃)

Salinity (PSU)

Density (kg/m³)

The second survey appears to be more mixed than the first survey in salinity, density, and temperature. This is likely due to the tidal conditions for the day. During the second survey, sampling began shortly after the morning low tide and continued into a period during which the tide continued to rise. As the tide rises, marine water is transported into Commencement Bay. Tidal currents can increase vertical mixing, which is apparent in the comparison between the first and second survey of stations 5-8 in Commencement Bay.

Dissolved Oxygen (mL/L)

Fluorescence (mg/m3 )

Transmissivity (%)

Credit: Contour graphs created for 2nd Commencement Bay Survey by James Simpson and Cristian Carreno

The second survey seems to show a more uniform distribution of fluorescence throughout the water column, suggesting a more dispersed phytoplankton population rather than a concentrated surface bloom. Transmissivity was relatively consistent in both surveys, indicating similar consistent water clarity down through the water column. Dissolved oxygen remained highest near the surface in both surveys but was more uniform in the second survey.

Team A re-coiling the line before departure.

James and Audrey lowing the CTD and Niskin bottle into the water.

Commencement Bay (First Survery)

Comparison of CTD Data with Discrete Water Sample Data

Figure 5: Correlation between CTD fluorescence measurement and chlorophyll measurement in discrete samples. Credit: James Simpson

Figure 6: Correlation between CTD dissolved oxygen measurements and measurement in discrete samples. Credit: James Simpson

Discrete samples were taken from 1 m below the surface of the water and near the bottom of the sampling area for each station. The samples were analyzed by the estuaries team in the lab to verify results collected by the CTD.

Left - There is very little correlation between the discrete and CTD chlorophyll reading, as shown by the R2 value (0.3163). The unit equivalence of mg/m3 is µg/L. This was our first attempt at compiling this data; therefore, the correlation factor appears to be low as we learned how to run these samples.

Right - There is very little correlation between the discrete and CTD dissolved oxygen reading, as shown by the R2 value of 0.3635.

Secchi Disk

Figure 7: Inital Secchi reading; depth given in meters. Credit: James Simpson

The Secchi depth is a measure of water clarity, with greater depths indicating clearer water and lower concentration of suspended particles. The Secchi depth reading ranges from 0.5 m to 2.5 m. Station 5 and 8 had the highest reading at 2.5 m, indicating the clearest water conditions, while Station 7 had the shallowest Secchi depth at approximately 0.5 m, indicating the lowest water clarity. Station 6 had a reading of 1.1 m, in the middle. The reduced clarity observed at Station 7 can indicate higher concentration of suspended sediments, organic matter, or phytoplankton compared to the other stations.

Phytoplankton

Table 2: Nets phytoplankton abundance table. Credit: James Simpson

Figure 8: Surface phytoplankton abundance graph. Credit: James Simpson

Please note that color scheme for the phytoplankton bar graph is not standardized between sections of the webpage.

The phytoplankton abundance table indicates there was a large presence of phytoplankton during the time of sampling with blooms occurring at station 5 and station 8. Actinoptychus senarius and Chaetoceros debilis were common among all four stations.

Credit: EOS - Phytoplankton Encyclopedia Project. 2023. Eoasubcca.

Chaetoceros debilis

Credit: EOS - Phytoplankton Encyclopedia Project. 2023. Eoasubcca.

Actinoptychus senarius

Nutrient Data

Figure 9: Si(OH)₄ concentrations

Figure 10: NO₃ concentrations

Table 3: Nutrient levels for both surface and deep water measurements in Commencement Bay.

Nutrient concentration varied spatially throughout Commencement Bay, with the highest concentration observed at the surface at station 6 (Near Sewage Outfall). Higher concentrations of total nutrients were observed at the surface than at depth across all stations, indicating that freshwater input contributes significantly to nutrient loading in this area.

Figure 10: NO₃ and Si(OH)₄ concentrations

Figure 11: Comparison between NO₃ and Si(OH)₄

There is a moderate correlation between the concentration of NO₃ and SI(OH)₄. The largest presence of SI(OH)₄ was observed at station 6.

Sediment Data

The Commencement Bay (First Survey) stations were located near the mouths of freshwater and wastewater inputs, which contributed to the elevated levels of fine sediment observed in the sediment samples from stations 5 and 8. Station 5 and station 8 sediment samples were both dominated by silt, followed by clay. Both samples show a moderate amount of total organic carbon present.

Discussion of Observations

Samples taken from Commencement Bay on April 10th, 2026, provided the team with data that helped create a picture of how freshwater influence, tides, and human interaction change the composition of the water column and the nutrient availability in this complex estuarine system.

The inner latitudinal transect (stations 5, 6, 7, and 8) from the first Commencement Bay survey shows salinity, density, and temperature following a similar trend. The tide during the first survey was an ebb tide, with ocean water receding from the morning high tide. With freshwater entering near these stations and their proximity to the Puyallup River, a stratified surface layer was expected, with fresher, warmer water overlying the colder, saltier water. In contrast, during the second Commencement Bay survey, sampling began at low tide and continued as the tide rose. It was observed through the water property contour sections that the deeper water column was better mixed than in the first survey, as strong tidal currents affect vertical mixing.

Elevated dissolved oxygen concentration in the upper 5m corresponds with areas of high fluorescence in the first Commencement Bay survey. Fluorescence is a proxy for phytoplankton abundance; this relationship suggests that phytoplankton photosynthesis contributed to the observed increase in dissolved oxygen levels. The highest concentration is at station 5 (Head of the Hylebos) and spans to lower concentrations at station 7 (Mouth of the Puyallup River). Freshwater from the Puyallup River likely introduced nutrients that supported the elevated fluorescence observed. During the ebb tide, freshwater moves from the Puyallup River to the Main Basin via the northern part of Commencement Bay around Browns Point. Transmissivity is relatively uniform throughout the water column here. As the deeper water column recedes with the tide, there does not appear to be much turbulence during sampling. During the Second Commencement Bay Survey, a better-mixed lower water column was observed across the previously mentioned parameters, with increased transmissivity in the lower water column.

The phytoplankton abundance table from the First Commencement Bay Survey indicated a large presence of phytoplankton across the stations, which is reinforced by the fluorescence shown on the contour graphs. These stations were sampled when freshwater input exceeded the inward flow of seawater into the bay. Typically, we would expect to see higher nutrient concentrations at greater depths in the water column, but this was not the case during our survey. Across all stations, the upper water column had higher concentrations of all analyzed nutrients, with station 6 having the highest total concentration. Our results may indicate that a large volume of nutrients is being brought in by the rivers and the sewage outfall (station 6). There is potential for the sewage outfall to directly contribute to Si(OH)₄ levels. Maguire and Fulweiler (2017) found that effluent wastewater can be a source of silicate because the treatment process likely does not remove it before deposition. This nutrient is vital for the persistence of phytoplankton as they (diatoms) utilize dissolved silicate to build their shells. In comparing nutrient levels between the first and second Commencement Bay surveys, it was observed that nutrient levels remained consistent across all stations, but station 6 had a significantly higher Si(OH)₄ concentration in the first survey.

Overall, the physical and biological patterns that were observed in Commencement Bay appear to be strongly influenced by both natural and anthropogenic processes. Previous studies have shown that Commencement Bay receives large volumes of fine sediment from the Puyallup River (Takesue et al. 2017), and that circulation patterns driven by tides and stratification of the water column influence how these materials are distributed. Previous studies have characterized the Hylebos and Blair Waterways as areas of higher contamination, and there were extensive cleanup efforts to improve water quality and ecosystem health. The level of contamination from the industrial waterways was measured in the sediment sampled collected, and levels of contamination were also found in salmon far from the suspected source; as well as fish with live lesions and crustaceans with gill and antennal gland disorder in areas with higher levels of contamination (Long ER. 1982).

The data collected during the first Commencement Bay survey suggests that tidal conditions influenced the level of stratification that was observed during sampling. Fresh water from the Puyallup River into Commencement Bay delivered nutrients that supported phytoplankton growth in the upper 5m of the water column, as indicated by elevated fluorescence concentrations. Photosynthesis of the phytoplankton increased the dissolved oxygen concentration. During the second survey, stronger tidal mixing reduced stratification and more evenly distributed dissolved oxygen and fluorescence. This constant tidal exchange that Commencement Bay experiences contributes to the resilience and complexity of this estuarine system.

Data Repository

Phytoplankton Nets

Phytoplankton Surface

Sediments

Page developed by Emily Kreidler and Sonam Sherpa

Page updated

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