Effects of atrazine and linuron on photosynthesis and growth of the macrophytes, Potamogeton perfoliatus L. and Myriophyllum spicatum L. in an estuarine environment

Abstract

Phytotoxicities of the herbicides, atrazine and linuron, were evaluated for two species of submersed vascular plants ( Potamogeton perfoliatus, L. Myriophyllum spicatum, L.) which, until the late 1960s, had been abundant in Chesapeake Bay. Plants were grown in 50-liter laboratory microcosms, containing filtered estuarine water and sediments for a period of 5 weeks and then treated with atrazine or linuron at initial concentrations of 0, 5, 50, 100, 500 and 1000 gmg/liter. Plant responses were measured primarily in terms of apparent O 2 production, P 3, and above-ground biomass for 4 weeks post treatment. In general, at ≥ 50 gmg/liter there was a significant depression in P a for both species and herbicides. However, M. spicatum appeared to be less sensitive, with a significant enhancement in P a of this species at 5 gmg/liter, and linuron was slightly more effective than atrazine at reducing P a for both species. Treatment effects on biomass generally paralleled those for P a . In spite of relatively constant atrazine concentrations (84–89 % remaining at termination), both species exhibited evidence of photosynthetic recovery 2–3 weeks after treatment at concentrations ≤ 100 gmg/liter. Using an exponential dose-response model, I 50 (concentration for 50 % photosynthetic inhibition), ranged from 45–117 gmg/liter for all experiments. In general, in situ concentrations of atrazine and linuron in Chesapeake Bay and its tributaries appear to be sufficient to result in small reductions in P a (2–10%, estimated from dose-response model) during a typical growing season. While such effects may be important for the survival of otherwise stressed plant populations, they suggest that these herbicides, per se, were not the cause of the general decline in abundance of these plants.