AN INVESTIGATION OF SEDIMENT RESUSPENSION’S ROLE IN THE PROLIFERATION OF HARMFUL ALGAL BLOOMS

Suspended sediments are a primary factor in the degradation of water quality, habitat, and aquatic life, causing negative impacts on local ecosystems and economies. When bottom sediments are advected from a bed, other materials such as pollutants, nutrients, and organic matter are re-released into the water column. Among the organic materials accumulated on beds are cysts from various dinoflagellate.

The Lafayette River, a microtidal estuary connected to the Chesapeake Bay, is no stranger to water quality issues. After years of efforts including the addition of bioswales, bioretention grids, living shorelines, the estuary was finally deemed “restored” in 2018, as a result of oyster reef restoration and construction. However, not all major water quality problems had been solved with these efforts. Harmful algal blooms still persist, as they have, nearly every summer.

Previous research conducted in the Lafayette observed elevated turbidity linked to bloom formation. Additional studies have suggested that the resuspension sediments may be a factor in the initiation or intensification of algal blooms due to advection of previously burred nutrients back into the water column.

In an effort to investigate sediment resuspension’s possible effects on algal blooms, this study was designed to identify and quantify sediment resuspension and it’s causing forces. Current velocity, wave height, and suspended sediment concentration were measured using acoustic and optical sensors, in conjunction with CTD measurements, benthic sediment samples, and water samples. Meteorological data including hourly wind speed and direction as well as precipitation totals were also assimilated. Chlorophyll-a measurements in conjunction with microscopy were used to monitor and confirm the occurrence and species of the algal blooms. The Chlorophyll-a and nutrient data were examined for correlation to resuspension events.

Three monospecific blooms of harmful algae occurred, in succession, over the summer of 2018. Results show resuspension events followed by elevated Chlorophyll-a, appearing to fuel and support algal growth. The intensity of these blooms appear to increase due to bottom sediment resuspension which may either contain nutrients that supported the already present algae, algal cysts that increased bloom density or both.