Aquatic Sciences Meeting, Albuquerque 2001

PC18 Biogeochemical Cycles

Date: Thursday, February 15, 2001

Location: Southwest Hall

Heikoop, J, M, Los Alamos National Laboratory (LANL), Los Alamos, USA, jheikoop@lanl.gov

Hickmott, D, D, LANL, Los Alamos, USA, dhickmott@lanl.gov

Longmire, P, , LANL, Los Alamos, USA, plongmire@lanl.gov

NITROGEN-15 SIGNALS OF TREATED SEWAGE WASTEWATER UPTAKE AND TRANSFORMATION IN A CATTAIL MARSH

N-15 of cattails and water in a marsh, occupying a perennial stream receiving treated sewage effluent from LANL's sewage treatment plant, was investigated. Nitrate is attenuated in the marsh from concentrations of 13 ppm at the inlet to ~1 ppm at the outlet. Reference cattail leaves from a local unpolluted reservoir had N-15 values averaging 6.9 ‰. In contrast, cattails directly in the flow path of the sewage effluent had values averaging 26.4 ‰. The heaviest N-15 value was 37.6 ‰, among the highest N-15 values found within any aquatic ecosystem. Sewage effluent had N-15 of 32.4 ‰, whereas background waters have values of 0 ‰, probably representing nitrogen inputs from meteoric precipitation. A strong redox gradient exists within sediments of the wetland, ranging from +188 mV in gravel at the head of the marsh to -240 mV in organic deposits at the distal end. N-15 variation in the cattails, therefore, is likely due to variation in N-15 of source waters and to N isotope fractionation associated with denitrification occurring in the wetland.

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Aquatic Sciences Meeting, Albuquerque 2001

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