Phytoplankton production depends on a number of factors including nutrient availability, water chemistry variables, and light penetration. Previous studies have shown light penetration to be important for submerged aquatic vegetation, the primary producers that support the marine food web and the ecosystem. Possession Sound is a productive sub-basin of the Salish Sea with complex influences on local water chemistry and primary productivity. Given the significance of primary production in a salt water estuary, this study looks at the seasonal relationships between water chemistry and light penetration, measured by photosynthetically active radiation (PAR) in the Possession Sound estuary across three sites. I collected Seabird CTD and YSI EXO profile data as well as PAR sensor results, in Possession Sound from July 2022 through March 2023. Accompanied with historical data collected by past Ocean Research College Academy researchers, I analyzed site dependent relationships as well as the seasonal relationships. Preliminary analyses showed PAR decreasing with higher salinity and turbidity, but increasing with temperature. Limited connection was observed with dissolved oxygen. Studying the relationships among light penetration and water chemistry allows us to better understand the complex relationships among the key factors determining seasonal primary production.

 Primary production is critical to study due to the central role it plays in marine ecosystems. It fluctuates due to solar radiation and nutrients, among other factors, which are all highly dependent on season. Nutrient levels vary due to many factors such anthropogenic input, upwelling, and river discharge levels. The latter of two which are highly dependent on season. Excess amounts of nutrients can lead to harmful algal blooms and hypoxia, which can be detrimental to surrounding ecosystems and industries. However, nutrients are also essential to primary production and, therefore, the whole ecosystem. I analyzed chlorophyll quantity, an indicator of primary productivity, in relation to nitrate and phosphate levels seasonally across three sites in Possession Sound, WA, USA, from 2016-2022. River discharge from the Snohomish River, along with Possession Sound’s proximity to metropolitan centers, contributes to high amounts of anthropogenic nutrient influence. I participated in field collection for this data, in addition to completing data compilation and analysis independently. My early analysis indicates that chlorophyll quantities are higher in the spring and summer compared to winter and fall across all sites. Levels of both nitrates and phosphates are highest in the winter and fall. This suggests an inverse relationship between chlorophyll and nutrients. However, there is a time-lag between when chlorophyll begins to increase and then nitrates begin to decrease and vice versa. Studies of this type can provide insight into how nutrients, especially those that are anthropogenically sourced, affect primary production. This is essential for understanding seasonal shifts in ecosystems, such as Possession Sound, and how human-influence is affecting our environment.

Unique relationships between photosynthetic active radiation (“PAR”), turbidity, chlorophyll, and dissolved oxygen (DO) can impact primary productivity levels and directly relate to the health of an estuary. Previous studies show that microbial processes depend on PAR and dissolved oxygen. To some extent, this can govern the rate of near-surface mixing, affecting turbidity and the amount of chlorophyll produced. My preliminary results using data from Possession Sound, a salt wedge estuary, show similar patterns. By examining the previous Ocean Research College Academy’s (ORCA) profile data from 2015-2022, I observed that an increase in chlorophyll corresponded with an increase in turbidity. Further, if there is an increase in chlorophyll, there is an increase in dissolved oxygen. From the fall of 2022 to spring of 2023, I collected additional profiles, including PAR data, from three sample locations in Possession Sound. My results show that when PAR is high, chlorophyll levels and turbidity are also high. However, PAR values are inversely proportional to dissolved oxygen concentrations. This means there are correlations among chlorophyll, turbidity, DO, and PAR values with depth. However, PAR can be affected by many factors, so it is difficult to say that any one of these parameters directly relate to PAR values with depth. Future research can examine different parameters affecting PAR with depth, as availability of sunlight and nutrient levels can also affect PAR data.

In estuaries and marine environments, eelgrass (Zostera spp.) is considered a keystone species as many marine species depend on the beds for food and shelter. Eelgrass beds also trap sediment, stabilize substrate, reduce wave energy and reduce coastal erosion. The degradation of eelgrass beds can instigate a decline in those species that rely on the eelgrass beds. Eelgrass is traditionally mapped using aerial photographs or diving surveys, which can be time-consuming and ineffective. Another strategy is to use boat-mounted Acoustic Doppler Current Profiler (ADCP), to create transects of eelgrass beds through backscatter data. The purpose of this study is to assess the application of an ADCP to map local eelgrass beds in Possession Sound and determine its advantages over single-beam sonar. I used a boat-mounted RD Instruments Workhorse 600kHz ADCP during transects of a Possession Sound eelgrass bed. Raw data was filtered using Excel to isolate backscatter data for analysis and visualization. These results were compared to the results from a single-beam sonar system. It is expected that the height of the eelgrass and extent of the beds will be seen through the visualizations, even in winter and early spring surveys. A multibeam sonar like an ADCP will be more efficient in mapping a greater area of eelgrass beds as well as providing greater clarity in visualizations than a similar single-beam sonar through the ADCP’s emittance of multiple sound impulses at once.

River otters (Lontara canadensis) are high trophic level opportunistic feeders. Their diet, examined through scat, provides key information about local ecosystems. Previous studies have observed a diet dominated by fish, including studies in California (90%), Utah (96.5%), and North Dakota (83%); however, my preliminary results on otter diet at the mouth of the Snohomish River highlight a greater variation in observed prey. The meeting of the Snohomish River and Possession Sound creates a salt wedge estuary with extensive tide flats, providing access to diverse freshwater and saltwater prey species. From 2012-2015, river otter scat samples were collected, dissected, and identified by students at the Ocean Research College Academy (ORCA). Averages over the three years showed that fish were the dominant prey type in fall, winter, and summer; however, crustaceans dominated the river otter diet in the spring. In this study, I dissected scat samples from fall 2022 through spring 2023 from 2 sample locations in Everett Marina. In the more recent data, fall 2022 has followed the pattern of these historical studies, but the winter samples have indicated a shift of fish and crustaceans. In fall 2022, 5/25 samples showed 50% or fewer fish bones, while winter 2023 showed 11/13 samples with less than 50% fish bones. Given that otters are described as opportunistic feeders, this shift in winter diet, relative to previous years, may suggest a significant environmental shift. Future research must examine physical environmental features such as changes in river discharge and/or water temperature. Identifying specific fish species in samples may also reveal prey availability throughout the seasons.