Suitability of Submarine Groundwater Discharge in Monterey Bay as a Nutrient Source to Phytoplankton

Abstract:

Monterey Bay, California is the location of recurring harmful algal blooms. These massive growths of phytoplankton occur in the Northeastern portion of the bay, known as the “incubator”, and have been shown to harm the entire food chain with neurotoxins. A significant source of nutrients is needed by algal blooms, and could be from submarine groundwater discharge (SGD). SGD is the ubiquitous movement of groundwater from the land into the sea and is a mixture of freshwater and seawater which has entered the coastal aquifer. Previous studies have shown that SGD at one site in the incubator contains nutrients for phytoplankton similar to the Redfield ratio, which induces phytoplankton growth in the bay. This study aims to determine whether SGD in other locations throughout the incubator are also similar to Redfield ratios, thereby making SGD a viable source of nutrients to phytoplankton throughout the bay. In the northernmost beaches of the incubator, nitrate was depleted relative to silicate. However, transformations in the groundwater in the coastal aquifer pushed the Redfield ratios closer to the ideal. In the southward beaches, the ratios shifted and both silicate and phosphate were depleted compared to nitrate. These findings illustrate the impact of SGD on the health of both a foundation and potential killer in the Monterey Bay food chain.