Role of a Resilient Submersed Plant Bed in Mitigating the Effects of Increasing River-borne Particulate Inputs to Chesapeake Bay: Nutrient Cycling
Principal Investigator:W. Michael Kemp
Institution:Horn Point Laboratory, University of Maryland Center for Environmental Science
Co-Principal investigator:Jeffrey C. Cornwell, Horn Point Laboratory, University of Maryland Center for Environmental Science
Strategic focus area:Resilient ecosystem processes and responses
The overall objective is to understand the extent to which increasing inputs of particulate nitrogen (PN) and especially particulate phosphorus (PP) are bioavailable such that they will stimulate algal growth and degraded water quality. We will measure how water column processes cause release of bioavailable dissolved P from PP as it is transported seaward. We will also measure sediment release of dissolved P from PP sinking to mid-Bay sediments to asses if it is sufficiently large and early to stimulate P-limited algal growth. We will study related processes in the Bay's largest submersed plant (SAV) bed (~50 km2), which has been a highly resilient system and is located just below the dam. We will test the hypothesis that this bed traps large fractions of the total river-borne PP and PN loads and retains these nutrients during the growing season (Apr-Oct) when they might otherwise degrade water quality outside the bed. These data will help to improve model simualtion of key processes and to assess alternative management actions to minimize ecological impacts of planned reservoir modification.
We will conduct field surveys during 3 seasons (spring, summer, fall) with a stratified sampling schedule. Year 1 studies will involve mostly descriptive measures of key properties, while Year 2 studies will focus more on experimental process measurements. Sampling sites will include stations near the dam, above the SAV bed, in bed (near edge and center), along adjacent channel west of bed and down-bay from bed. Most sampling will focus on relatively shallow areas (<5 m). We will characterize suspended materials entering the Bay below the dam (e.g., strength of P attachment to particles, lability of PN, % organic). We will conduct P desorption experiments along salinity gradient from tidal fresh to oligohaline regions and sediment-water solute fluxes from intact cores. Inside SAV bed, we will sample over diel cycle to test effects of variations in pH on dissolved P concentrations in overlying waters.
Recent analyses suggest trends of increasing particulate P and N loading from Susquehanna River to upper Bay. These trends, which appear related to sediment infilling of Conowingo reservoir, represent a large impediment to achieving TMDL allocations needed for improved Bay water quality. To assess ecological consequences of increased PP and PN, we must understand how bioavailability changes in time and space and especially within the Bay's largest SAV bed, potentially capable of huge nutrient retention during the spring/summer.