In Possession Sound, a salt wedge estuary in the Whidbey Basin in Northwest Washington State, interactions between the saltwater of Puget Sound and the freshwater of the Snohomish River create a dynamic environment. Students from the Ocean Research College Academy deployed two Sea-Bird Conductivity-Temperature-Depth (CTD) probes within the estuary to monitor water chemistry in this complex system. A grant from the National Science Foundation supported eleven students to analyze water chemistry data from summer 2018 to increase their understanding of biogeochemical processes in the estuary and communicate their knowledge to the general public. Data from the month of May were analyzed to investigate the river’s influence on the temperature and salinity. Lower levels of salinity correlated with peaks in freshwater input as indicated by river discharge data. Salinity also correlated with tide height. To further investigate the spatial influence of the Snohomish River on Possession Sound, this study endeavored to manufacture a Fast Oceanographic Automated Measurement (FOAM) sampler in collaboration with Gravity Consulting. This device uptakes surface water and pumps it over an EXO 2 Sonde to measure surface water chemistry while traveling on a research vessel, associating data with GPS points, to track the freshwater plume. Salinity was used to examine the relationship between the spatial extent of the plume, river discharge, and tidal patterns, and temperature and pH was analyzed to explore the influence of the river. Lower salinity levels were used as indicators of higher freshwater influence. During periods of high river discharge, average salinity values will be lower and the freshwater influence will cover a larger area. During high tides, higher average salinity values are expected and there will be smaller areas of freshwater influence. It is hypothesized that areas of higher river influence will be warmer and more acidic than areas of increased saltwater influence.

Students of the Ocean Research College Academy (ORCA), an early college program through Everett Community College, have monitored bacteria data near Everett, Washington where the Snohomish River meets the Possession Sound since 2004. Used as an indicator of fecal contamination, Escherichia coli (E. coli) are found in the intestinal tract of humans and other homeothermic animals. This study investigates the spatial and temporal trends of E. coli levels at three sites within the Possession Sound between 2014-2019 in order to better elucidate the ecosystem’s health and potentially negative anthropogenic influences. Variation in coliform levels were analyzed with regard to physical and chemical factors such as tidal stage, depth, the Snohomish River discharge, salinity, temperature, dissolved oxygen, pH, and point sources  including combined sewer outflows and storm drains. Water samples were collected with a Niskin bottle while a YSI 650 CTD or a YSI EXO Sonde was utilized to measure salinity, temperature, dissolved oxygen, and pH for each of the samples. ORCA students followed the Coliscan® Easygel® Protocol for inoculation, incubation and quantification. Data were reported as colonies of E. coli per 100 mL of water. Preliminary results show that E. coli levels have a seasonal correlation with river discharge, increasing in the fall, winter, and spring months when river discharge spikes. Coliform levels are higher at the halocline than at the surface or near-deep. Further sampling at additional upriver sites will demonstrate more sources of E. coli data. The results of this study will provide a foundation for understanding the fluctuations in the spatial and temporal trends of E. coli levels within the Possession Sound in order to better assess threats to the ecosystem health.

Eelgrass (Zostera marina) is an ecologically important species of marine angiosperm that inhabits sublittoral sediments in the northern hemisphere. Eelgrass beds provide critical food and habitat for many species of fish, invertebrates, and birds. Its root system has the capacity to interact with both the water column and sediment, making it uniquely poised to influence metal cycles within the ecosystem, including those affected by anthropogenic activity. Eelgrass, sediment, and water samples were collected from three sites in Possession Sound, a part of Puget Sound that borders the City of Everett and contains the Snohomish River Estuary. Samples were processed in the University of Washington Isotope Geochemistry Lab before being analyzed for trace metal concentrations using an ICP-MS. In addition, two-meter long sediment cores were taken from three sites in the Possession Sound and the bottom 5cm were analyzed, allowing the researcher to quantify the anthropogenic influence on metal concentrations within sediment. It was hypothesized that the roots, shoots and blades of the eelgrass would exhibit differing concentrations of heavy metals, and that sediment collected within eelgrass beds would contain higher concentrations of metals than sediment collected outside eelgrass beds. Additionally, samples from sites closer to human activity would contain higher concentrations of metals and a greater proportion of metals from anthropogenic sources. Preliminary results of the ongoing study show that concentrations of arsenic, copper, and zinc were higher in eelgrass blades than roots, and eelgrass tissue had higher metal concentrations than the surrounding sediment. These results suggest that eelgrass uptakes metals from its environment, accumulating as well as translocating them in its tissues. Additionally, study locations nearer to the mouth of the Snohomish River and human activity had higher concentrations of heavy metals overall in both sediment and eelgrass.