COI Funded Project: The Influence of Tidal Pumping on Denitrification in Waquoit Bay Sediments
Project Funded: 2004
Key Words: Hydrology, Sedimentary Geochemistry, Estuarine Sciences, Water Resources Environmental Impacts, Nearshore Processes
We propose to investigate the influence of tidal pumping on nitrogen cycling in near shore sediments of Waquoit Bay, MA. (Tidal pumping is the advective flow of water across the sediment-water interface in response to tidal changes in sea level.) We hypothesize that tidal pumping enhances mixing between fresh and salty groundwater within the sandy sediments of the groundwater discharge zone at the head of Waquoit Bay, and that this mixing in turn enhances the overall rate of denitrification in these sediments. Pore water data collected by Joint Program student Emilie Slaby document the impact of tidal pumping on salinity and nutrient (nitrate and ammonia) distributions within the top few tens of cm of the sediment at the head of the bay. We propose to add d15N(nitrate) analyses (to document denitrification) and dissolved organic carbon concentration analyses (to assess the importance of carbon supply as a limit to denitrification) to Slaby's 2004 sampling and analytical program. Our sampling will continue to include both flow measurements, using seepage meters and estimates based on head differential over the top meter of the sediments, and pore water sampling within the top half meter of the sediment, using manual syringe sippers. The insight we gain into tidally-driven mixing and its effect on denitrification within the fresh water - saltwater transition zone of the shallow Waquoit Bay sediments will help us understand the controls on the denitrification rate over the more extensive deeper portions of the subsurface freshwater-saltwater interface.