Aquatic Sciences Meeting, Albuquerque 2001

PC10 Ecological Fluxes: Organisms, Atmospheres, Oceans, Lakes, and Rivers

Date: Wednesday, February 14, 2001

Location: Southwest Hall

Tobias, C, R, Ecosystems Center, Mar Bio Lab, Woods Hole, MA 02543, USA, ctobias@mbl.edu

Harvey, J, W, US Geological Survey, Reston, VA, USA,

Anderson, I, C, Va Inst Mar Sci, Gloucester Point, VA, USA,

SEASONAL QUANTIFICATION OF GROUNDWATER DISCHARGE THROUGH FRINGING MARSHES TO ESTUARIES

Groundwater discharge into a fringing estuarine wetland was estimated using three independent methods (Darcy’s Law, salt balance, and Br tracer). Similar seasonal patterns of discharge shown by both Darcy’s Law and the salt balance, differed in the estimated magnitude of discharge by 2-4 fold in Spring and 10-fold in Fall. Darcy estimates of mean discharge ranged between -8.0 and 80 L m-2 day-1. The salt balance predicted discharge of 0.6 to 22 L m-2 day-1. The Br tracer estimate of discharge was nearly equal to the salt balance estimate. Based upon the tracer test, porewater conductivity profiles, and error estimates for the Darcy and salt balance approaches, we concluded that the salt balance provided a more certain estimate of discharge at high flow (Spring). The Darcy method provided a more reliable estimate during low flow (Fall). Groundwater flushing of porewater in the Spring lowered porewater salt and sulfide concentrations by > 2-fold. This flushing of the wetland subsurface may represent an important mechanism by which narrow fringing marshes seasonally relieve salt stress and export solutes to the estuary.

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Aquatic Sciences Meeting, Albuquerque 2001

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