Researcher ORCID Identifier

0000-0002-8530-9984

Graduation Year

2023

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts

Department

Biology

Second Department

Politics and International Relations

Reader 1

Sarah Gilman

Reader 2

Nancy Neiman

Reader 3

Jeremy Testa

Rights Information

© 2022 Desa K Bolger

Abstract

As aquaculture increases in the United States (Ray et al. 2021), ecosystems may improve from oysters’ ability to reduce eutrophication (Newell 1988) and the economy could benefit from the promotion of additional harvests and nitrogen-crediting systems. Although many studies have examined Crassostrea virginica (the Eastern oyster) and its relationship to the nitrogen cycle in natural settings, few have studied nitrogen cycling and associated ecosystem effects of on-bottom aquaculture. I hypothesized that Eastern oysters in on-bottom cages in high-energy farms have limited effects on nitrogen cycling due to high flow rates dispersing biodeposits. To test this hypothesis, I measured porewater concentrations and surface sediment samples (nitrogen, phosphorus, and carbon) to estimate fluxes and quantify the impacts of oyster aquaculture on sediment biogeochemistry near Solomons Island (Patuxent River) and the Potomac River, both in the Chesapeake Bay system.

Though I detected no sizable difference between the percent carbon and percent nitrogen levels in the surface sediment in either site, porewater data at CBL showed sulfide and ammonium levels were consistently higher in the farms. These elevated levels of estimated ammonium and nitrite fluxes suggested an amplification of remineralization and nitrogen cycling associated with biodeposits concentrated in the farm. At the Potomac site, extremely high porewater concentrations were found at the control location (station 1), which made it challenging to discern farm-associated effects. However, at both the Patuxent and Potomac sites, there was evidence of higher concentrations of particulate carbon and nitrogen beneath cages relative to areas outside of the cages.

This study suggests that high-flow oyster aquaculture farms can concentrate biodeposits in protected areas (e.g., under cages), but that surface sediments are not organic matter enriched, likely because wind and wave energy actively resuspend and mix sediments. These findings support our hypothesis that high energy conditions would limit a farm’s effect on nitrogen cycling. However, the enrichment of organic matter under cages at both sites and porewater nutrient accumulation at CBL did not support our hypothesis and suggest that sediment enrichment with biodeposits does accumulate in more stable environments (porewaters). Future studies, including larger sample sizes and tracking the impacts of cages versus bags, should also be investigated, as these tests may continue to show support for implementing oyster aquaculture in nitrogen-crediting systems.

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