HR: 17:15h
AN: H24A-06    [Abstracts]
TI: Submarine groundwater discharge to Salt Pond (MA) estimated from continuous 222Rn measurements
AU: * Crusius, J
EM: jcrusius@usgs.gov
AF: USGS, 384 Woods Hole Road, Woods Hole, MA 02543
AU: Koopmans, D
AF: USGS, 384 Woods Hole Road, Woods Hole, MA 02543
AU: Ryckman, L
AF: U. Pennsylvania, Inst. Environmental Studies, Philadephia, PA 19104
AU: Charette, M
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road MS#25, Woods Hole, MA 02543
AU: Halloran, K
AF: Bucknell U., Dept. Biology, Lewisburg, PA 17837
AU: Kroeger, K
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road MS#25, Woods Hole, MA 02543
AU: Henderson, P
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road MS#25, Woods Hole, MA 02543
AU: Bratton, J
AF: USGS, 384 Woods Hole Road, Woods Hole, MA 02543
AU: Colman, J
AF: USGS, 10 Bearfoot Road, Northboro, MA 01532
AU: Masterson, J
AF: USGS, 10 Bearfoot Road, Northboro, MA 01532
AB: Submarine groundwater discharge (SGD) is the dominant means of freshwater delivery to many coastal embayments on the glaciated coast of Cape Cod (MA). This discharge is the focus of considerable research, in part because the common practice of domestic wastewater treatment via septic systems has led to elevated levels of nutrients in groundwater. However, SGD is frequently diffuse, rendering it difficult to quantify. SGD was therefore estimated by a variety of means in Salt Pond, a weakly stratified estuary 8.2 ha in area with a maximum depth of 9 m that is located at the northern (inland) end of Nauset Marsh (MA). One approach relied on continuous measurements of radon, which offers an excellent means of quantifying SGD delivery to coastal waters because radon is: 1) strongly enriched in groundwater relative to surface water; 2) non-reactive; 3) continuously supplied by long-lived parent isotopes; and 4) provides an integrated signal from a wide area. Continuous measurements of radon, salinity, temperature and water depth were carried out for four days in June, 2004 in a narrow channel that connects Salt Pond to the adjacent Nauset Marsh. The radon-based SGD estimate was derived using a mass balance approach based on radon outflow from the pond, corrected for inputs from the adjacent Nauset Marsh and losses due to gas exchange and decay. In addition, the radon content of groundwater was determined from piezometer samples. This approach yielded a pond-integrated upper limit of discharge of roughly 5 cm/d, a figure that is very similar to a multi-year average flow estimate from a previously-developed hydrologic model. SGD estimates using seepage meters deployed in shallow waters were more than a factor of two higher than the radon and model estimates, which may indicate that discharge occurred only in the shallow regions of the pond and not through the deeper, fine-grained sediments. Further research is needed in order to determine the reasons for the differing estimates.
DE: 1832 Groundwater transport
DE: 1871 Surface water quality
DE: 1050 Marine geochemistry (4835, 4850)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting