SAV recovery and estuarine nutrient cycling

Although nutrient load reductions have been a primary management strategy for Chesapeake Bay restoration, internal ecological processes, such as seasonal nutrient retention in submersed aquatic vegetation (SAV) beds, may also play an important, complementary role. For example, if SAV increasingly retain nitrogen and phosphorus as they recover, they could potentially limit regional phytoplankton production, thereby decreasing the magnitude of seasonal bottom-water hypoxia. However, we lack sufficient details about the factors controlling the magnitude of an important mechanism of SAV-mediated nutrient sequestration–particulate nutrient trapping–to make inferences about its importance relative to total loads to the system.

In this project, we aim to address this knowledge gap by 1) quantifying seasonal N and P retention rates in Chesapeake Bay SAV beds through both particle trapping and plant assimilation, 2) deriving relationships between nutrient retention, plant species characteristics, and SAV patch size and configuration, and 3) comparing SAV-mediated nutrient retention in the upper Chesapeake Bay to total seasonal loads to the system. To accomplish these objectives, we will measure seasonal sediment deposition and plant assimilation rates in and near SAV beds comprised of a range of sizes, configurations, and species compositions before plants emerge in the spring and during the SAV biomass peak in the summer. Spatial and temporal differences in rates will indicate SAV bed effects on these processes. We will then use relationships between bed characteristics and retention rates, together with publicly available SAV spatial data, to estimate N and P retention in all upper Bay SAV beds and compare this quantity to growing season N and P loads to make inferences about the relative importance of SAV as a seasonal nutrient sink.

Currently, the simulation models used to set Chesapeake Bay nutrient and sediment load reduction goals only coarsely parameterize SAV- enhanced sediment trapping and were calibrated with data that precede recent SAV resurgences. This work will benefit the management community by informing refinement of the models, which may not accurately account for SAV effects on sediment and nutrient transport. More broadly, we anticipate that our results will enhance our understanding of fundamental ecological processes controlling estuarine recovery.

I am collaborating with Dr. Cindy Palinkas from University of Maryland Center for Environmental Science Horn Point Laboratory on this ongoing project with funding from Maryland Sea Grant.