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PHOTOSYNTHETIC RESPONSES OF VALLISNERIA AMERICANA FOLLOWING EXPOSURE TO ATRAZINE AT THREE NUTRIENT REGIMES
Citation:
Dantin, D D., R. Boustany, M A. Lewis, Moss, AND J M. Macauley. PHOTOSYNTHETIC RESPONSES OF VALLISNERIA AMERICANA FOLLOWING EXPOSURE TO ATRAZINE AT THREE NUTRIENT REGIMES. Presented at Society of Wetland Scientists, New Orleans, LA, June 8-13, 2003.
Description:
The effects of anthropogenic contaminants on Gulf of Mexico plant communities are poorly understood despite the threatened condition of a number of seagrass communities and wetland habitats. In this study, we focused particular attention on the concern that elevated nutrient
loading affects the ability of submerged aquatic vegetation (SAV) to tolerate environmentally relevant levels of herbicide contamination, specifically atrazine. Vallisneria americana acclimated for 6 months to three nutrient regimes, were exposed to 0, 11 and 100 ppb atrazine
and the effects were monitored using pulse amplitude modulated (PAM) fluorometry (PAM) at 0, 24, 48, and 96 h. The low (1/3 ambient), high (3x ambient), and ambient nutrient regimes were based on calculated ambient loadings rates for the St. Johns River, FL, at NH4 = 9.57 mg/l/d,
NO3 = 18.09 mg/l/d, and PO4 = 7.5 mg/l/d. Using rapid light curve techniques (RLC), the PAM observations showed significant reductions in electron transport rate (ETR), which is an indication of Photosystem II efficiency, from 24-96 h post exposure to atrazine. Depression of the ETR was magnified by higher nutrient concentrations. The toxicological response observed at 11 ppb atrazine (also the proposed water quality criterion) was greatest when combined with high nutrient loading. A long-term mesocosm study is needed to link measurements of PAM to
physical impairment under exposure to low doses of environmental stressors. These observations of nutrient contaminant interactions provide new information regarding the impacts of low concentrations of water-borne contaminants on aquatic macrophytes. In addition, the use of PAM fluorometry continues as a promising assessment tool for near-coastal environmental evaluations, as related to critical wetland and near-coastal vegetated habitats.