Temporal Responses of the Macrophyte, Potamogeton perfoliatus L., and Its Associated Autotrophic Community to Atrazine Exposure in Estuarine Microcosms

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Abstract
Effects of the herbicide, atrazine, on the submersed vascular plant,Potamogeton perfoliatus, were monitored for 4 wk in 700 l microcosms containing water, sediments and plants from upper Chesapeake Bay. Two atrazine treatments (plus controls) were employed in duplicate systems, with water column concentrations averaging about 0.13 and 1.20 μg per 1, respectively. Atrazine concentrations at low dose were in the range of the highest values reported in Chesapeake Bay, and significant decreases in apparent O2 production (Pa) ofP. perfoliatus were observed immediately following treatment. However, significant recovery of Pa was evident at low dose within 2 wk, even though atrazine levels remained relatively constant. At the higher atrazine treatment, phytotoxic effects were even more pronounced, with no recovery occurring during the study period. Integrated community production and consumption of O2 followed patterns similar to those forP. perfoliatus alone, with some minor increases in relative contributions of other autotrophic groups (phytoplankton, epiphytes, benthic microalgae). While areal densities of plant shoots for the experimental populations were unaffected by the lower treatment, total biomass decreased significantly, lagging 2–4 wk after the initial decrease in Pa. Morphology of individual shoots was markedly influenced by atrazine, with significant increases in mean shoot length and decreases in weight per unit length. Furthermore, chlorophylla content of leaves increased 5-fold with atrazine treatment. These effects are similar to previously reported shade adaptations of this and other submersed plants.