| Summary: | When considering fluctuations in temperature, salinity and dissolved oxygen, tides and currents are two influential factors that affect an estuary system. The pycnocline created by these factors has a significant influence on plankton growth and primary productivity in an estuarine system. Monthly research cruises since the fall of 2007 to the Snohomish River delta with the Ocean Research College Academy (ORCA), an early college program through Everett Community College located at the Everett waterfront, monitor the local marine system and provide a historical data set for use in analysis. The delta hosts significant plankton growth along a sudden drop off of the shelf into the deeper waters of Possession Sound. Changes in the cline were first analyzed by isolating tidal and river flow variables as well as seasonal changes. Factoring in the change in water height between measured tide stages, the current speed can be determined and variability in temperature, salinity and dissolved oxygen can be viewed independent of the tidal influence. The changes between different cycles of spring and neap tides as well as variations in river outflow are points of interest due to the hypothesized signature these events exhibit on the cline. The research sites of Mukilteo, Buoy, and the Snohomish River were used to analyze the impact of distance from the river, tides and currents, and river flow on salinity, temperature, and dissolved oxygen. It was hypothesized that spatial differences and river flow would have a greater impact than tides on the pycnocline depth.
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