| Summary: | Possession Sound, an estuary located in Everett, WA, is influenced by the interaction of seawater from Puget Sound and freshwater from the Snohomish River. Students at the Ocean Research College Academy (ORCA) study eelgrass (Zostera marina) in the estuary, specifically near Mukilteo, Whidbey Island, and the Snohomish River. In previous studies, Z. marina exhibited a high uptake capacity for metals concentrated in sediment; however, low pH levels can desorb heavy metals from sediment, causing bioaccumulation in phytoplankton and limiting primary production. While Z. marina photosynthesizes, it is hypothesized to possess the ability to biodegrade heavy metals in sediment via oxygen exchange, stimulating microbes to degrade contaminants. Thus, lower heavy metal concentrations were expected in Z. marina relative to phytoplankton. It was additionally proposed that with increasing proximity to the river, heavy metal concentrations would increase in both organisms, and that concentrations in Z. marina would be lower in low-pH environments. Heavy metals were extracted from sediment, root, shoot, and blade, and analyzed in an Inductively Coupled Mass Spectrometer (ICP-MS) by Everett Environmental Lab. At Mukilteo and Whidbey, copper and zinc concentrations in Z. marina consistently exceeded detection limits, with the highest zinc concentration of 45.7 J mg/kg in the blade at Whidbey, and the highest copper concentration of 10.8 mg/kg in the root at Mukilteo. Cadmium was highest in blade and shoot samples at both sites, but undetected in phytoplankton. However, arsenic was highly concentrated in phytoplankton (30.7 mg/kg at Mukilteo, relative to detection limit of 8.478 mg/kg), as was zinc, with a mean concentration of 4700 mg/kg. Additional data, including chlorophyll concentrations and pH, are being collected to ascertain the necessity of certain metals for specific parts of Z. marina, and to analyze concentrations in the context of acidity and primary production.
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