Comparing King County CTD Data with Phytoplankton Biomass and Abundance in Puget Sound’s Main Basin to Determine Leading Causes of Harmful Algal Blooms

Abstract

This study investigates the relationship between phytoplankton growth and different environmental factors, hypothesizing that an increase in the stratification of Puget Sound’s Main Basin will result in an increase in phytoplankton biomass and the possibility of harmful algal blooms (HABs). CTD data was collected from 7 stations in the Main Basin by King County’s Department of Natural Resources & Parks for phytoplankton biomass (g C L-1), NO2 and NO3 concentration (mg N L-1), Chl-a (g L-1), salinity (PSS), and water temperature (C) in 2018 and 2019. There were earlier peaks in biomass in 2018 in May averaging at 700 g C L-1 compared to the later 2019 peaks in June averaging at 1000 g C L-1. Biomass and nutrient concentration were concluded to have a statistically significant correlation when plotted against one another and a linear regression was conducted. Salinity depth profiles indicated earlier water column stratification in 2018 and surface temperature was approx. 1.5 C greater in June of 2019 for 2 stations. A FlowCAM was used to identify phytoplankton taxa to determine the abundance of potentially toxic species. Multiple potentially toxic phytoplankton taxa were found at the 3 stations of focus including Akashiwo sanguinea, Pseudo-nitzschia sp, Chaetoceros, Thalassiosira, and Heterosigma akashiwo. These species accounted for the majority of the total phytoplankton abundance in 2019, indicating that later occurring blooms have greater potential to result in an HAB.