Abstract

Fluxes of nutrients transported by groundwater contribute to eutrophication in Indian River Bay, Delaware. Fresh and saline groundwater discharge rates and porewater salinity depend on system hydrology, mechanisms of groundwaterbaywater exchange, and geologic heterogeneity. The interactions between these factors produce complex flowpaths and mixing that may affect nutrient bioavailability by causing biogeochemical transformations prior to discharge.

The hydrology, stratigraphy, subsurface salinity and Nspecies distributions, and submarine groundwater discharge (SGD) rates and patterns were characterized at Holts Landing State Park. A buried paleochannel and near-bottom confining beds, expected to control both flow and mixing in the subsurface, were located with offshore chirp seismic profiling and coring. Electrical resistivity surveys and vertical porewater salinity profiles to depths of up to 17m indicate that a zone of freshened groundwater extends hundreds of meters offshore. Onshore and offshore multi-level wells were sampled to obtain a 3D distribution of N species in the subsurface. SGD measurements from Lee-type seepage meters were collected to better understand discharge salinity, rates, and spatial and temporal SGD patterns. Measurements indicate that SGD is primarily saline, and that the lowest salinity groundwater discharges near the shoreline in the area away from the paleochannel feature and along the submerged paleochannel/interfluve boundary. Hydraulic head and permeability measurements in onshore and offshore wells provide information on site hydrology and temporal change. Data were incorporated into a groundwater flow model of the Indian River Bay watershed, which provides a larger-scale estimate of groundwater flowpaths and SGD fluxes and patterns along the entire bay shoreline.

Citation

Michael, H.A., C. Fernandez, C.J. Russoniello, A.S. Andres, K.D. Kroeger, D.E. Krantz, J.F. Banaszak, A. Musetto, K. Myers, L.F. Konikow and J.F. Bratton. (2011): Geologic and hydrologic control of porewater chemistry and submarine groundwater discharge into Indian River Bay, Delaware. Goldschmidt 2011 conference, Prague, Czech Republic, August 14-19. p. 1462.