Contrasting Impacts of a Native and Alien Macrophyte on Dissolved Oxygen in a Large River

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.