The Capacity of Oyster Aquaculture to Improve Water Quality in Rhode Island Coastal Lagoon Systems.

In Rhode Island, coastal lagoons are a focal area for expansion of shellfish aquaculture, while many have water quality issues because of anthropogenic inputs. In response to these issues, several studies have proposed oyster aquaculture (Crassostrea virginica, the Eastern Oyster) as a way to restore or improve water quality in coastal systems because of their effects on primary production and nutrient cycling in the water column and benthic environment via filter-feeding. We assessed the effects of oyster aquaculture on water quality in three coastal lagoons in Rhode Island: Ninigret, Winnapaug, and Potter ponds. We compared water quality parameters in areas currently used for oyster aquaculture to those in similar areas not previously used for aquaculture. We measured water pH, temperature, salinity, dissolved oxygen (DO), ammonium, nitrate, chlorophyll a, and total suspended solids (TSS) between May and October in 2016, at all oyster and control sites.  To examine the relationship between the water column and the saturated soils, we also analyzed soil pore water sulfide levels.  Oyster aquaculture sites had lower chlorophyll a and higher DO concentrations for the warmest months, when oyster filtration is at peak activity (June - August). Other water quality parameters were similar for control and aquaculture sites. Oyster sites also showed greater evidence of soil pore water sulfides compared to control sites, with the majority of sulfides present within the upper 10 cm of soil for both sites. Our results suggest that oyster aquaculture has a positive impact on water quality, but may increase sulfide levels in the soil.