Ocean acidification is a global crisis that is mainly caused by too much carbon dioxide in the atmosphere being absorbed by bodies of water, altering the water chemistry. Ocean acidification has large visual consequences, such as the bleaching of coral reefs, but less obvious, small scale influences are also found in the Salish Sea. A major indication of global warming’s effects on local water systems is pH, or the measure of how acidic or basic a solution is. Previous global studies have shown that pH has been decreasing (becoming more acidic) over the years, while the overall temperatures have been rising. The goal of this study is to observe how changes in lowernig pH are related to temperature changes in the watercolumn of Possession Sound, a salt wedge estuary, near Everett, Washington. We utilized pH and temperature vertical profiles collected from a YSI EXO Sonde, a deployment device that utilizes sensors and precise calibrations to monitor water quality, over six years to assess the degree of ocean acidification locally. Trends were analyzed according to depth and season. Preliminary studies of this particular site have shown minor changes compared to the extreme trends recorded in other ocean environments. Given the potential for negative impacts on the estuary, it is worth expanding the study by investigating a longer time frame. Local estuary data regarding depth and season will allow people to better understand how these variables change in our environment and gain a greater understanding of climate change’s influences on ocean acidification locally.

Possession Sound, located in Everett, Washington, includes the second largest source of freshwater in Puget Sound from the Snohomish River. This salt-wedge estuary serves as a home to a wide selection of phytoplankton, which provide energy to a variety of organisms farther up the food chain. Water chemistry often determines where phytoplankton accumulate prior to their recycling as nutrients. Ocean Research College Academy students utilize water chemistry data (temperature, salinity, dissolved oxygen, pH, turbidity and chlorophyll concentration) from two sensors deployed in Possession Sound: One in the river and one two miles away at Mukilteo. While plankton samples are collected in the Sound, rarely are plankton collected in the river and compared to chlorophyll concentrations. This study will look at abundance and diversity of phytoplankton collected in the river at various tide stages and compare these to Mukilteo samples. I hypothesize that flood tide samples will be similar, while ebb tide phytoplankton and chlorophyll levels will decrease. The preliminary data revealed that chlorophyll and temperature levels did not vary significantly between the two sites despite the widely differing salinity levels. The next steps of the study are to determine the plankton density of phytoplankton species across the two most recent years of data. Results will enable us to explore further into plankton presence in relation to chemical variance in water systems.