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. 

Outcomes Report

The two six-week Shear Turbulence Resuspension Mesocosm (STURM) experiments proposed were successfully conducted with six undergraduate students and Dr. Jeff Cornwell in summer 2018 and summer 2019 at the Patuxent Environmental and Aquatic Research Laboratory (PEARL), Morgan State University. This research led to publications in respected journals, national and international research presentations by undergraduate students and Dr. Porter, and is advancing the knowledge on the effects of biodeposits in oyster ecology. Too often, biodeposits are ignored in studies, however, this Sea Grant work has clearly demonstrated that biodeposits must be considered when evaluating the use of oysters as a Best Management Practice in the Chesapeake Bay.

Dr. Porter’s STURM publication in the Journal of Experimental Marine Biology and Ecology (2018) led to one invited talk at Virginia Commonwealth University and four invited talks in Germany and in South Korea and collaboration agreements between the University of Baltimore and Inha University, Korea, and Jacobs University, Germany, respectively. In addition, the STURM work led to two provisional US patent-, one US patent- and one International patent- applications. 

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 had not been taken into account when the use of oysters in mitigation of eutrophication in CB was examined. Models did not include the effects of biodeposit resuspension on the ecosystem, nutrient dynamics and light, and experimental data were not available. We used two 6-week long experiments in shear-turbulence-resuspension-mesocosm (STURM, R) systems versus non-resuspension (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 sediment denitrification), the ecosystem function, light and the nitrogen budget. This study helped evaluate ecosystem services benefits of oysters important for oyster restoration and healthy ecosystems and will 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 which was again found here. The Maryland Sea Grant supported STURM facility designed by Porter and Sanford and located at the Patuxent Environmental and Aquatic Research Laboratory (PEARL) was 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. The STURM experiments conducted here are truly interdisciplinary and include interactions of biology, chemistry and physics. Often, as in this study, indirect effects are uncovered that cannot be detected with traditional approaches or can’t be deciphered from field studies due to high variability. In Porter et al. (2020), biodeposits had no negative effects on the phytoplankton and zooplankton communities, and biodeposit resuspension in this experiment significantly positively affected ecosystem function by oysters, contrary to what we had expected. Oyster biodeposit addition and resuspension efficiently transferred phytoplankton carbon to zooplankton carbon, thus supporting the food web in the estuary (Porter et al. 2020). In another experiment, concentrations of nitrite plus nitrate were significantly higher in the water column of the resuspension tanks with biodeposit resuspension, suggesting a high level of resuspension-mediated nitrification. Seabed and bottom boundary-layer biogeochemical processes affected the nutrient and oxygen dynamics in this project. The STURM system allowed new directions to include tidal and sediment and biodeposit resuspension to be included in whole ecosystem studies, something not previously possible. Moreover, our study found that biodeposits are important to be considered when studying the effect of oysters and water flow on benthic-pelagic coupling processes and must be included in models. 

Dr. Porter mentored six female Sea Grant supported undergraduate students for their 10-week summer research on this grant, one of them a minority student originally from Nigeria. During their 10-week internships, the students and Dr. Porter worked daily one-on-one at PEARL. The undergraduate students were very enthusiastic and positive about their summer internships in their written PEARL internship evaluations. All students presented their work as posters or oral presentations at numerous conferences such as Coastal and Estuarine Research Federation (CERF), Atlantic Estuarine Research Society (AERS), the Chesapeake Watershed Forum, as well as the undergraduate research conference Inspired Discoveries at the University of Baltimore and at PEARL, Morgan State University. In addition, a female and a male undergraduate student (Sarah Davis, Eric Robins) participated as co-authors on a publication of the Sea Grant work for Marine Ecology Progress Series in 2020 (MEPS 640: 79-105) and additional undergraduate students and a graduate student are participating as co-authors on publications.

Dr. Porter uses results from her STURM research in lectures and laboratories she teaches at the University of Baltimore. Classes in which she intersperses her research approaches and findings are ENVS 175 Introduction to Ecology (taught to non majors) and ENVS 285 Environmental Chemistry, a class taken by Environmental Sustainability majors. For ENVS 285 Environmental Chemistry, Dr. Porter created a laboratory exercise using different concentrations of total suspended solids from a mock storm that the students had to analyze TSS, PIM and POM of, measure turbidities and write a scientific abstract on. A lecture on benthic-pelagic coupling and water quality was created for ENVS 285 Environmental Chemistry. A lecture on Chesapeake Bay water quality was created for ENVS 175 Introduction to Ecology.

Moreover, Sara Blickenstaff used this 2018 summer research for her ENVS 490 capstone project for graduation. Regina Minniss and various students have taken the summer research at PEARL as an ENVS 289 independent study course. Sabrina Tolbert combined her summer 2019 research with Biol 494, an internship course offered by Frostburg State University.  

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.

 

Assessing Oyster Feces’ Effects on Water and Sediment

Recap: In first-of-their-kind experiments, Sea Grant-supported researchers examined how oyster feces and pseudofeces—known as biodeposits—affect the biogeochemistry and sediment beneath aquaculture sites both in the water column and on the seabed.

Relevance: Maryland has prioritized oyster aquaculture as a way to improve the Chesapeake Bay’s water quality, provide aneconomic option for watermen, and enhance the depleted population of wild Eastern oysters (Crassostrea virginica). As of December 2020, there were 486 active shellfish leases in Maryland’s portion of the Chesapeake Bay and Coastal Bays, comprising 7,539 acres. While oysters’ filter-feeding ability to clean water is well understood, researchers know little about the effects of what are collectively called biodeposits—oyster feces and pseudo feces (particles of grit and other matter that oysters ingest, which are expelled without going through the digestive tract). Better understanding of these biodeposits’ effects in the water column and in bottom 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: Maryland Sea Grant-supported researchers used the Shear Turbulence Resuspension Mesocosm (STURM) facility at the Patuxent Environmental and Aquatic Research Laboratory (PEARL) to study the effects of biodeposits in the water column and in sediment. This specialized facility allowed whole-ecosystem experiments that mimicked factors such as current and bottom shear, which re-suspend biodeposits in the water column, as well as conditions of no current and no resuspension. Among their results, researchers found that in resuspension, biodeposits lowered oxygen and notably increased nitrates and nitrites in the water column. Light was similar during mixing-off and resuspension experiments, and biodeposits did not impact the amounts of benthic algae in either situation. Flux results from sediment cores showed that sediment oxygen uptake is significantly higher in non-resuspension situations with added biodeposits. Biodeposits had no negative effects on zooplankton or phytoplankton communities. In fact, biodeposit resuspension efficiently transferred phytoplankton carbon to zooplankton carbon, supporting the estuarine food web. The research is continuing in 2021 to examine how the movement, or export, of oyster biodeposits from aquaculture sites affects the surrounding environment. This study also verified that further research is needed on biodeposit resuspension and especially its effects on the nitrogen cycle.

Results: This data—which are the first to quantify and illuminate how oyster biodeposits affect the water column and seafloor sediment—clearly indicate that oyster managers must consider biodeposit resuspension when siting oyster farms and managing oyster populations. Researchers at the University of Maryland Center for Environmental Science (UMCES), who are also supported by Sea Grant funding, are using this data to help test and validate a model that predicts the fate and nitrogen removal associated with different types of oyster aquaculture. The principal investigator shared her results with the Oyster Recovery Partnership, NOAA, the Chesapeake Bay Program’s Oyster Best Management Panel expert group, and the Maryland Department of Natural Resources.

The Blue Crab: Callinectes Sapidus

An essential resource for researchers, students, and managers.  Get your copy today!

pile of cooked crabs

5825 University Research Court, Suite 1350 | College Park, MD 20740 | Phone: (301) 405-7500 | Fax: (301) 314-5780 | Contact Us

  • Twitter
  • Facebook
  • YouTube
  • Flickr
  • RSS