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CONTRASTING IMPACTS OF A NATIVE AND ALIEN MACROPHYTE ON DISSOLVED OXYGEN IN A LARGE RIVER



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Ecological Applications 12 5 2002 pp 1496 1509 q 2002 by the Ecological Society of America CONTRASTING IMPACTS OF A NATIVE AND ALIEN MACROPHYTE ON DISSOLVED OXYGEN IN A LARGE RIVER NINA F CARACO1 JONATHAN J COLE AND Institute of Ecosystem Studies Box AB Millbrook New York 12545 USA Abstract In aquatic systems low dissolved oxygen DO has been identified as a serious water quality problem Here we use empirical data and modeling to explore the hypothesis that the introduction of an alien aquatic macrophyte Trapa natans may have had dramatic impacts on the frequency and extent of low DO events in the Hudson River Continuous measurements with moored instruments demonstrated that in large macrophyte beds dominated by a native species Vallisneria americana DO never declined below 5 mg L during the summer growing season In contrast during this same time period extremely low DO was common in large beds dominated by Trapa natans with DO values below 2 5 mg L occurring up to 40 of the time This difference in DO can be modeled based on species differences in the balance of respiration and in water photosynthesis The low DO values in Trapa beds suggest that these beds may be poor habitats for sensitive fish and invertebrates and that redox sensitive chemical reactions may be altered within Trapa beds Key words aquatic plants Hudson River hypoxia introduced species oxygen dynamics Trapa natans Vallisneria americana INTRODUCTION The vegetated areas in aquatic systems can be important to ecosystem function in lakes rivers and estuaries Wetzel 1983 Kemp et al 1984 Macrophyte beds generally have high primary production Sondergaard and Sand Jensen 1979 Wetzel 1983 and can thus be important sources of organic matter supporting higher trophic levels and influencing the net metabolism of aquatic systems France 1995 Duarte and Cebrian 1996 Further beds can trap sediment be sites of intense nutrient cycling and provide important habitat for fish and invertebrates Carpenter 1980 Graneli and



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