Temporal Variability in Water Quality and Phytoplankton Biomass in a Low-Inflow Estuary (Baffin Bay, TX)

Low-inflow estuaries are subject to inconsistent seasonal and interannual variability in precipitation and watershed influences on hydrology, complicating understanding and prediction of water quality and phytoplankton dynamics. We quantified variability in environmental conditions and phytoplankton biomass over an 8-year period in a eutrophying lagoonal estuary (Baffin Bay, Texas) that experiences prolonged low inflow conditions punctuated by episodic high inflow events, resulting in a large interannual salinity range (20-62 in this study). Using a 90th percentile threshold of chlorophyll a concentration to classify blooms, we observed a higher frequency of blooms at high salinity conditions (20% of high salinity observations were blooms) compared to intermediate (5%) and low (6%) salinity. The conditions and composition of blooms varied at different salinities, with blooms at high salinities dominated by the ecologically damaging brown tide Aureoumbra lagunensis, whereas lower salinity blooms were dominated by a variety of phytoplankton groups. The distinct bloom communities that developed under different salinities suggest that complex drivers of community dynamics are at play in Baffin Bay and provide insight into what we can anticipate during future periods of prolonged drought, as well as following sporadic heavy rainfall events, both of which are expected to increase in frequency with climate change.

Automated summary

This study quantified the variability in environmental conditions and phytoplankton biomass over an 8-year period in a low-inflow estuary, and found that bloom frequency was higher at high salinity conditions. Different salinity levels also resulted in different bloom compositions and conditions. This provides insight into understanding and predicting water quality and phytoplankton dynamics under future climate change.