Vertical mixing in estuaries is largely produced by the interaction of river outflow, tides, floor and shoreline shape, weather, water chemistry, and other abiotic factors. Because currents transport sediments, nutrients, plankton, pollutants and microplastics, and chemical conditions such as salinity and temperature as they drive mixing or stratification, they are a defining feature of any estuarine ecosystem. Their patterns and mechanisms must be understood in order to support the health of these systems. The purpose of my project is to discover patterns in vertical current velocities in the Possession Sound estuary off of Everett, WA—a small subregion of the Salish Sea—at different depths and distances from the seasonally fluctuating Snohomish River and the channel from which saltwater tides enter the estuary. I collected vertical velocity data down the water column using a boat-mounted acoustic doppler current profiler at different locations along the southeastern shoreline between the river mouth and Mount Baker Terminal in Everett, from late summer, 2022, into winter, 2023. I compared my data to USGS river discharge data, NOAA tidal predictions, and the rough bathymetric character of the location. My preliminary analysis suggests a correlation between increasing upwards vertical velocity and increasing depth at all locations, without regard to tidal stage or river discharge, although it may not be statistically significant. This implies depth has the greatest effect on vertical current velocity, possibly due to a related factor such as chemistry or bathymetry, an observation that can be used to design future studies in this region.

The Everett Marina is a heavily developed area that has significantly altered water flow from the Snohomish River compared to its natural state. Anthropogenic alteration of this environment led to buildups of sediment, which has required dredging at increasingly shorter intervals leading up to the present. In order to explain sediment accumulation in the marina, this study examines the movement of currents and the abundance of sediment using an Acoustic Doppler Current Profiler (ADCP); data were recorded from June 2020 to August 2021 and compared to recent data I recorded from February and March of 2023. I hypothesized that current direction would be variable and speed would be sluggish due to the shallow depth. In addition, I hypothesized that seasonal changes such as snowmelt in spring and rain in winter would impact the velocity of the currents. Because sediment movement is largely impacted by currents, I hypothesized that sediment abundance would reflect seasonal changes in water flow. Analysis of water current data between June 2020 and August 2021 demonstrates a significant correlation between the velocity of North/South currents and the magnitude of tide stages, but river discharge levels appear to have less of an effect on current speed in the marina. The susceptibility of this area to tides more than river discharge suggests that it is easier for sediments to accumulate in one area as opposed to being swept away. Future analysis will compare this past data to the present and investigate potential correlations with sediment abundance.

Local bathymetry in estuaries strongly affects water current direction and speed. Water current and speed, or the water flow, determine the circulation of nutrients and oxygen within the estuary. To assess the relationship between water currents and slopes in an estuary, I utilized a boat-based acoustic doppler current profiler (RD Instruments Workhorse 600 kHz ADCP) to measure water speed and direction with depth. Based on preliminary analysis, water direction is consistent at surface level but becomes inconsistent beyond that. Speed is mostly between 0 cm/s and 50 cm/s, but becomes more varied beyond 30 meters. However, that may be due to inaccuracies in measurement, as data collection becomes less consistent beyond that depth based on our current ADCP configuration. The average direction of data at each depth doesn’t change significantly with depth. In summary, speed is mostly consistent with depth near a slope, whereas the direction is not. So, the bathymetry may have a greater effect on water direction than speed. For future work, investigating these patterns with higher resolution datasets will shed more light on any potential patterns.

The interaction between incoming salt water from the ocean, which is driven by tides, and exiting freshwater from rivers drives circulation through estuarine environments. As a result of the interaction between the incoming water and the exiting water, nutrients and sediment are moved around the estuary. This study focuses on the interaction between tides and the Snohomish River as it enters the Possession Sound estuary, located in Everett, Washington. To acquire data, I deployed a boat-mounted acoustic Doppler current profiler (ADCP), which uses sound to measure water current direction and velocity. I collected these data at varying tide stages at three different sites between the Snohomish River’s southern output to nearby Mount Baker Terminal, located 3.6 miles southwest of the river output. I have collected 8 samples over the course of 7 months at both ebb and flood tide stages. Each transect survey lasted 3-6 minutes and collected data from the first 20 meters of the water column. To get accurate analysis of current velocity and direction I split the data into categories based on depth. Preliminary analysis shows a southward current at many sites during all tide stages and depths. This raises questions about the scope of the river influence and the potential for southward currents regardless of tidal stage. However, further analysis of current velocity and river discharge are needed. Due to the complexity of the currents in the area, understanding how the river and the tides are interacting can provide a greater understanding of how these currents are impacting the dispersal of sediment and nutrients throughout the estuary.

Possession Sound, WA, serves as an important foraging area for a group of seasonally resident gray whales Eschrichtius Robustus. This group of predominantly Eastern North Pacific Gray Whales that visit Possession Sound (Sounders) arrive as early as January and continue migrating towards other feeding grounds near May. If the frequency of sounds within the hearing range of these gray whales (50 to 5000 Hz) exceeds comfortable levels, they may have difficulty foraging. To monitor these relationships, we looked at the frequency and amplitude of sound near Mt. Baker Terminal (MBT) in Possession Sound, WA, from January 2021 to May 2021 with a specific focus on sounds from 50 to 5000 Hz. To gather this data, we used a SoundTrap 300 HF hydrophone, which is currently mounted to a dock at MBT. From January 2021 to February 2021, the hydrophone recorded continuously at a 96-kilohertz sampling rate. From March 2021 to May 2021, the hydrophone was set to record the first fifteen minutes of every hour at the same sampling rate. Preliminary research shows that Possession Sound has a consistent prevalence of ambient and intermittent noise within the established frequency range and peak amplitudes as high as 164 dB. This level of noise may have the potential to negatively affect gray whale behavior and foraging success. Future research should be conducted to see how current and future vessel slow-down trials will impact the frequencies and amplitude of local noise. Future research should also include comparing the MBT sound profile to other sites in the Salish Sea to better understand if the amplitude increase is unique to the area or a cause for wider concern.

Botryllus schlosseri is a non-indigenous species of colonial tunicate commonly found in many marinas of the Puget Sound. Colonies of Botryllus can grow asexually through the process of blastogenesis (also called ‘budding’) which involves the formation of buds which mature into new zooids on a weekly cycle. Apoptosis and oxidative stress are involved in the final stage of blastogenesis, a time when the system resorbs the zooids and the newly matured buds take over. Although nickel has been found to be genotoxic and can induce many aspects of the cellular stress response in animals, little research has characterized these effects on marine invertebrates. In this study, we performed acute exposures of nickel chloride at sublethal concentrations in B. schlosseri collected from the field to identify changes to blastogenic timing, DNA damage, apoptosis, and the oxidative stress response. These data will establish the in vivo tolerance and stress responses of B. schlosseri to nickel exposure. Furthermore, these data will inform future studies which seek to use nickel as an immortalization agent in cell culture with the goal of generating the first continuous cell line for any marine invertebrate species.