Possession Sound is a dynamic salt wedge estuary system near Everett, Washington that is fed by the Snohomish River. In salt wedge estuaries, a mix of salt and fresh water creates a salinity gradient between the two sources, with the denser, saltier water making up the lower sections of the vertical gradient, and the freshwater residing above it. Turbulence from river flow and tidal currents decreases the concentration of suspended sediment in the water column, measured as turbidity. As stratification increases, turbulence increases too, which then causes lower turbidity. This study explores influences on turbidity at the Everett Marina during the year 2020. In the Everett Marina, North flow corresponds with flood tides, and South flow during ebb tides. During these tidal exchanges, the prediction is that when the tide is slack, the horizontal velocities of the water would show an east/west flow. This east/west flow would create vertical mixing because of upwelling and higher turbidity in the water. Two-dimensional horizontal river flow velocities from 0.9 to 4.9 meters from the riverbed at half-meter and meter increments were measured using a grant-supported deployment of an Aquadopp ADCP (Acoustic Doppler Current Profiler). Turbidity was collected using a CTD deployed 1.7 meters from the surface. The volume, velocity, and sediment deposition of river water were compiled from the United States Geological Survey (USGS), and tide heights were published by the National Oceanic and Atmospheric Administration (NOAA). Preliminary results indicate an inverse relationship between tidal height and turbidity and with an emphasis on further Spatio-temporal relationships, more conclusions may be found. The Everett Marina hosts dredging of the estuary in order to maintain safe river flow to the Possession sound itself. Without this river flow, needed nutrients may not reach the saltwater, disrupting the ecosystem, and increasing flooding.

In this study, I aimed to determine whether the genetic signature of Nitrate Reductase (NR) from phytoplankton in the environment is correlated with the in-situ nitrate concentration. To accomplish this, I first generated a phylogeny of phytoplankton NR amino acids sequences to determine if the sequences separate into monophyletic groups that match their taxonomic identification. Secondly, I placed RNA transcripts for NR derived from samples collected off the coast of Hawaii onto the tree to determine which clades expressed NR. Finally, I constructed heat maps to show the abundance of RNA transcripts for each phytoplankton clade by latitude and nitrate concentration to establish trends in phytoplankton phyla distribution. Results indicated that all phytoplankton, no matter phyla or cell size, were more abundant in higher nitrate concentrations. If instead RNA transcript abundance was normalized by chlorophyll concentrations, there was little separation in distribution based on plankton size, and different trends based on phyla emerged. Alveolata, Archaeplastida, and Stramenopiles were found in similar low to moderate nitrate concentrations (0.0023µM-0.8052µM). In contrast, Cryptista did not display a consistent trend across the phylum, as all clades displayed different abundance patterns. Haptophyta, both large and small, made up a significantly higher proportion of phytoplankton found in low nitrate environments (0.0009µM). These results indicate that there is separation of phytoplankton phyla by nitrate concentration, supporting the hypothesis that these phyla have evolved to utilize different ecological niches, however further research is needed with higher taxonomic resolution to fully quantify the factors controlling the distribution of different phytoplankton clades.

Local processes in marine ecosystems, including coastal estuaries, modify ocean acidification caused by rising atmospheric CO2. Because ocean acidification poses a threat to shell-forming organisms, it is critical to understand how these processes affect acidification in specific regions. In the Snohomish River estuary, freshwater from river discharge deposits directly into Possession Sound, impacting the salinity and temperature of the area. River discharge in estuaries has been found to be slightly acidic, as well as a source of nutrients that fuel blooms of phytoplankton. Large phytoplankton blooms can lower the pH at depth because of the process of respiration, which releases CO2 and decreases dissolved oxygen levels. My research examines changes in pH with temperature, salinity, chlorophyll, and dissolved oxygen at different depths in Possession Sound, Washington, using data collected from January 2017 through January 2021 with a YSI EXO2 Sonde. I hypothesized that near-surface depths and sites located closer to the river would have lower temperatures and salinities correlating with lower pH. Additionally, lower dissolved oxygen at greater depths would correlate with greater amounts of chlorophyll and a decrease in pH at depth. Depths near the halocline were predicted to have alkaline pH values due to photosynthetic organisms. I analyzed data using Microsoft Excel and R Studio. Results found that with chlorophyll less than ~1.25 RFU, pH was greater than 8.0, while with lower dissolved oxygen, pH was less than 7.75. Temperatures less than 10°C corresponded with more pH values between 7.0 and 7.5, while salinity had no apparent trend. In most seasons, pH appeared to decrease slightly at greater depths. The exception to this was winter, when more acidic pH values were observed at near-surface depths. Overall these results indicate that local processes in the Snohomish River estuary are affecting changes in pH.

The ocean is extremely important in the biogeochemical cycling of carbon, nitrogen and other elements. Half of all photosynthesis occurs within the ocean, mostly from marine algae, phytoplankton. Additionally, half of all nitrogen, a key nutrient for both terrestrial and marine plants, is lost through the conversion to N2 from microbial processes called denitrification. Another product of denitrification is N2O, a greenhouse gas 310 times more potent than CO2 that also has the potential to damage the ozone layer. Denitrification occurs in anoxic environments, such as special areas called Oxygen Deficient Zones (ODZs), which in certain areas start at about 100 meters deep in the water column. Prochlorococcus, a marine phytoplankton, is the most abundant photosynthesizer on the planet and the low-light ecotype of Prochlorococcus can inhabit the edge of the euphotic zone and continue to photosynthesize. It has been found in an unlikely environment: The top of ODZ in the Eastern Tropical North Pacific (ENTP) located off the Western coast of Mexico. This is interesting because photosynthesizers traditionally don’t reside in low oxygen content areas. The Prochlorococcus found in the ODZ has been observed with a Hybrid Cluster Protein (HCP), which in other organisms, such as E. coli, is responsible for the reduction of NO to N2O for intracellular purposes. There are three identified classes of the hybrid cluster protein represented in multiple bacteria. We explored which of these classes were present in Prochlorococus' HCP. We started by investigating the metagenome generated from a 2012 ENTP ODZ cruise for genes containing the HCP, using various Python programs, we were able to obtain full length sequences, 8 of which were a match to previously identified Prochlorococcus. These sequences were then aligned against organisms with known HCP classes to compare different amino acids at key differentiating positions. From the alignment we were able to find that ENTP ODZ Prochlorococcus have a class 1 HCP.