Aquatic Sciences Meeting, Albuquerque 2001

CS39 Trace Metal Limitation of Biogeochemistry

Date: Tuesday, February 13, 2001, Time: 2:15:00 PM

Location: Dona Ana

Senn, D, B, Parsons Laboratory, Department of Civil and Environmental Engineering, MIT, Cambridge, MA, USA, dbsenn@mit.edu

Hemond, H, F, Parsons Laboratory, Department of Civil and Environmental Engineering, MIT, Cambridge, MA, USA, hfhemond@mit.edu

COUPLED N, FE, AND AS CYLING IN AN URBAN,EUTROPHIC LAKE

Nitrate controls Fe and As cycling in the hypolimnion of urban, eutrophic Upper Mystic Lake (MA). High nitrate and ammonium inputs, coupled with authigenic nitrate production (nitrification), result in several months per year of anoxic yet nitrate-rich conditions in the hypolimnion. As expected, the onset of anoxia triggers Fe and As remobilization from the sediments. However, despite anoxia, remobilized Fe and As accumulate primarily in their oxidized forms (Fe(III)-oxides and As(V)) in the water column. Mass balance estimates indicate that nitrate is responsible for oxidizing the majority of iron, which must initially be remobilized by reductive dissolution as Fe(II). Anaerobic microcosm experiments confirm the feasibility of biologically mediated Fe(II) oxidation by nitrate. Particulate Fe(III)-oxides scavenge the remobilized As; thus, anaerobic Fe(III)-oxide production allows for a continued As sink (via settling) during anoxic periods. Over three years of study, interannual, seasonal, and spatial correlations existed between nitrate depletion and the appearance of As(III) and Fe(II) in the water column. Thus, nitrate assumes the role typically reserved for oxygen in the cycling of Fe and As in this N-polluted urban lake.

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Aquatic Sciences Meeting, Albuquerque 2001

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