R/P-62

Effects of Oyster Biodeposit Resuspension on Nutrient Release and Ecosystem Dynamics in Chesapeake Bay

Principal Investigator:

Elka Porter

Start/End Year:

2018 - 2020

Institution:

University of Baltimore

Co-Principal Investigator:

Lawrence Sanford, Horn Point Laboratory, University of Maryland Center for Environmental Science

Strategic focus area:

Healthy coastal ecosystems

Description:

While existing research addresses many of the important issues of oysters in Chesapeake Bay (CB), the fate and effects of resuspended oyster biodeposits in aquaculture areas on the nutrient, light, zooplankton and phytoplankton dynamics have not been taken into account when the use of oysters in mitigation of eutrophication in CB is examined. Currently, models do not include the effects of biodeposit resuspension on the ecosystem, nutrient dynamics and light and experimental data are not available. We propose two 6-week long experiments in shear-turbulence-resuspension-mesocosm (STURM, R) systems versus nonresuspension (NR) systems to study the effect of biodeposit resuspension in high flow and low flow areas right next to and under mimicked aquaculture rafts on the nutrient dynamics (including denitrification), the ecosystem function, light and the nitrogen budget. This proposed study will help evaluate ecosystem services benefits of oysters important for oyster restoration and healthy ecosystems and may help the evaluation of the use of oysters as Best Management Practice (BMP) and the siting of oyster aquaculture. In our previous research on coupling between sediment resuspension and ecosystem processes, we have often found nonlinear, unexpected responses of both nutrient dynamics and ecosystem function. The Maryland Sea Grant supported Shear Turbulence Resuspension Mesocosm (STURM) facility designed by Porter and Sanford and located at the Patuxent Environmental and Aquatic Research Laboratory (PEARL) will be used for the experiments and is a one of a kind system that mimics high bottom shear stress due to tides and storms, realistic water column turbulence levels, and realistic benthic-planktonic interactions over extended periods. We will examine the effect of biodeposit resuspension right next to and under mimicked aquaculture rafts on nutrient regeneration and phytoplankton growth, effects on denitrification and the effect of oysters on water clarity, compared to mimicked low flow areas right outside and under aquaculture rafts. Moreover we will measure ecosystem variables such as zooplankton abundance and composition. Our data will be utilized by the CBP Oyster BMP expert panel, the Chesapeake Bay Foundation, Maryland DNR, NOAA, and the Oyster Recovery Partnership. We will provide an experiential learning experience to undergraduate students through internships. 

Impact/Outcome:

Filter-feeding Oysters Clean the Bay's Water, but What About Their Feces?

Summary: A Maryland Sea Grant-supported study of the effects of oyster biodeposits (feces and pseudofeces) in the water column and on the bottom uses a novel technology and provides new data that can improve ecosystem model accuracy, and inform oyster aquaculture siting and Best Management Practices.

Relevance: Oyster aquaculture in the Chesapeake Bay helps to keep the fishery economically viable, allows the wild population to recover, and improves the Bay's water quality. However, scientists and managers know little about oyster biodeposits-oyster feces and pseudofeces-and how they behave both in the water column, where they can be resuspended due to tides, storms, and currents, and on the bottom, where they can potentially turn sediments anoxic and overwhelm macrofauna. Scientists do not know enough about their potential effects on the complex dynamics of light, benthic organisms, and water quality, including dissolved oxygen and nutrients. A better understanding of oyster biodeposits' effects in water and sediment will provide new data to more accurately evaluate the use of oysters as a water quality Best Management Practice as well as inform siting of aquaculture projects.

Response: A Maryland Sea Grant-supported scientist and five Maryland Sea Grant-funded undergraduate students conducted experiments over two summers using the Shear Turbulence Resuspension Mesocosm (STURM) facility at the Patuxent Environmental and Aquatic Research Laboratory to examine the effects of biodeposits in the water column and in sediment. In these experiments, they were able to accurately mimic current and bottom shear-which lifts biodeposits from the bottom and resuspends them in the water column-versus conditions where biodeposits settle in sediment, mimicking areas of low current and no resuspension. First they compared the effects of externally introduced biodeposits in both environments without oysters in the tanks, and then compared the same with oysters installed in rafts in the tanks. They analyzed sediment cores and water for multiple indicators including dissolved oxygen, nitrites, nitrates, and ammonia to see the effects of biodeposits.

Results: Analysis of the STURM results is ongoing, but the successful application of the system will allow researchers to include tidal and episodic sediment and biodeposit resuspension in whole ecosystem studies for what is believed to be the first time. This will provide new data on oyster biodeposits for resource managers and system models. Researchers in Germany and Korea are collaborating with the principal investigator to use the STURM system. The principal investigator has applied for U.S. and international patents for the STURM paddle design and is expanding her research this year to study the way that currents and erosion export biodeposits from aquaculture sites.

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