Date Awarded

2024

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Advisor

Mark J. Brush

Committee Member

Christopher J. Hein

Committee Member

Bongkeun Song

Abstract

Salt marshes provide a wide range of ecosystem services, including sediment capture, nutrient transformation, and water quality improvement. Several processes facilitate nutrient removal by marshes, including: 1) storage in plants and algae, 2) storage in and transformation by resident animals, 3) storage in sediments, and 4) microbial denitrification. Sediment removal occurs primarily through sedimentation and bivalve filtration followed by burial. However, salt marshes are increasingly being lost to sea level rise and coastal development, diminishing these services at a time when coastal systems are subject to anthropogenically elevated loads of nitrogen, phosphorus, and sediment (NPS). To address NPS inputs, the Chesapeake Bay Program (CBP) has identified best management practices (BMPs) to reduce non-point source coastal pollution. One BMP is a nature-based coastal adaptation called a living shoreline, which has become a replacement habitat for natural marshes. These constructed habitats leverage ecological processes to provide functions similar to natural marshes. This shoreline restoration provides watershed-scale benefits across natural and human communities, improving ecosystem services provided by the shoreline. However, limited tools are available to compute NPS removals by living shorelines, and those that exist are based on data from natural marshes. This project filled that gap by building a site-specific model for computing annual NPS removals by living shorelines calibrated to data collected from these created habitats. This simulation model was developed by combining existing models of Spartina alterniflora, benthic microalgae, sediment biogeochemistry, and Crassostrea virginica. Models were replicated and parameterized for Spartina patens and Geukensia demissa using literature. The model is forced using local climatic, tidal, and water quality data and upland loading of NPS from the CBP. Field observations demonstrated that living shorelines are important mediators of nutrient cycling and NPS removal. The model closely reproduced seasonal patterns in the data and predicted annual removals of 70 g N m-2, 5.26 g P m-2, and 7,820 g TSS m-2 (total suspended solids). Spartina biomass was the largest sink for N and P, while burial was the largest sink for TSS. Highest areal removal rates for N and P were in the high marsh, while areal rates of TSS removal were highest on the sill due to high bivalve densities. Model results indicated that living shorelines removed approximately one third of daily tidal N and P inputs and >100% of tidal TSS inputs. Living shorelines are an effective tool for reaching Total Maximum Daily Loads (TMDL) at local scales, with an average of 14-34 acres (median 4-8) needed to achieve mandated NPS removals in individual CBP Land-River Segments. Finally, predicted removals were greater than values used in CBP BMP documentation, suggesting living shorelines are undervalued as a NPS removal strategy. This research created a widely applicable and directly accessible model for local stakeholders to assess NPS removals by living shorelines. The increased understanding of living shoreline function and the model developed here can inform regulatory decisions and support living shoreline restoration based on the ability of this BMP to assist in reaching TMDL goals.

DOI

https://dx.doi.org/10.25773/v5-wqk5-3q02

Rights

© The Author

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