Transport of biodeposits and benthic footprint around an oyster farm, Damariscotta Estuary, Maine

The benthic impact of aquaculture waste depends on the area and extent of waste accumulation on the sediment surface below and around the farm. In this study we investigated the effect of flow on biodeposit transport and initial deposition by calculating a rough aquaculture footprint around an oyster aquaculture farm in the Damariscotta River, ME. We also compared a site under the farm to a downstream away site calculated to be within the footprint of the farm. We found similar sediment biogeochemical fluxes, geochemical properties and macrofaunal communities at the site under the farm and the away site, as well as low organic enrichment at both sites, indicating that biodeposition in this environment likely does not have a major influence on the benthos. To predict accumulation of biodeposits, we measured sediment erodibility under a range of shear stresses and found slightly higher erosion rates at the farm than at the away site. A microalgal mat was observed at the sediment surface in many sediment cores. Partial failure of the microalgal mat was observed at high shear velocity, suggesting that the mat may fail and surface sediment erode at shear velocities comparable to or greater than those calculated fromin situ flow measurements. However, this study took place during neap tide, and it is likely that peak bottom velocities during spring tides are high enough to periodically clear under-farm sediment of recent deposits.

Automated summary

The benthic impact of aquaculture waste is influenced by the accumulation and flow of waste around and below the farm. A study on an oyster aquaculture farm in the Damariscotta River found that despite slightly higher sediment erodibility at the farm compared to a downstream site, similar biogeochemical fluxes, geochemical properties, and macrofaunal communities indicated minimal impact on benthos. The study also observed microalgal mat presence and partial failure under high shear velocity, but suggested that peak bottom velocities during spring tides may periodically clear under-farm sediment of recent deposits.