Aquatic Sciences Meeting, Albuquerque 2001

SS05 Groundwater at Aquatic Margins (Environmental Connections)

Date: Wednesday, February 14, 2001, Time: 2:00:00 PM

Location: Cimarron

Nowicki, B, , University of Rhode Island Graduate School of Oceanography, Narragansett, USA, bnowicki@gso.uri.edu

Gold, A, , URI Natural Resources Science, Kingston, USA, agold@uriacc.uri.edu

Mckenna, J, , Williams College Mystic Maritime Program, Mystic, USA, jmckenna@mystic.org

Addy, K, , URI, Kingston, USA, kaddy@uriacc.uri.edu

Requintina, E, , URI/GSO, Narragansett, USA, requintina@gso.uri.edu

Davis, J, , URI/GSO, Narragansett, USA, jdavis@gso.uri.edu

PRELIMINARY STUDIES OF GROUNDWATER AT ESTUARINE MARGINS: NUTRIENTS AND DISSOLVED GASES

Nitrate is the most common groundwater pollutant in the U.S. and is a major cause of eutrophication in coastal waters. We are testing the hypothesis that coastal margins contain unique physical and biogeochemical features that stimulate denitrification and the removal of nitrate from groundwater. Groundwater at 3 sites at the coastal interface in Rhode Island and Massachusetts is being sampled seasonally for dissolved gases, nutrients, and carbon to determine dominant biogeochemical transformation pathways. Drive point piezometers are used to characterize hydrologic flowpaths, and consevative tracers (Ar, SF6) are used to evaluate the fate of 15N enriched groundwater. Without NO3 removal, groundwater NO3 concentrations (9-190 um/l) and N/P ratios (44-170) are considerably higher than those in adjoining estuaries (1-10 um/l NO3; N/P=7-8). Dissolved N2/Ar ratios in groundwater are higher than equilibrium values in 92% of 170 wells sampled, suggesting that N2 production via denitrification is important. Results from in-situ 15N tracer experiments show high rates of denitrification (36-80 ug N/kg/d) in high and low marsh groundwater and lower rates (<0.5 ug N/kg/d) in upland fringing the saltmarsh.

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Aquatic Sciences Meeting, Albuquerque 2001

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