ZOSTERA-MARINA L GROWTH-RESPONSE TO ATRAZINE IN ROOT-RHIZOME AND WHOLE-PLANT EXPOSURE EXPERIMENTS

Atrazine ro-4-[ethylamino]-6-[isopropylamino-]-s-triazine?? ), a triaz ine herbicide, is one of the most widely used herbicides in the Chesap eake Bay watershed. Increased use of atrazine in the 1970s coincided w ith a decline in the abundance of Zostera marina L. (eelgrass). Ground -water surveys have found atrazine in concentrations that may affect e elgrass growth and survival. The effects of atrazine in groundwater di scharges on the growth of eelgrass through root-rhizome exposure were examined in laboratory systems. A long term, dynamic, groundwater simu lation study was conducted with atrazine concentrations ranging from 0 .0 to 2.5 mg.1(-1). No significant effects on chlorophyll content, gro wth or survival were detected. A static root-rhizome exposure experime nt was conducted using split chamber exposure systems to verify these results, atrazine concentrations were increased by an order of magnitu de. Neither mortality nor significant effects on plant growth were det ected (maximum atrazine concentration 7.6 mg.1(-1)). A static, whole p lant exposure experiment was conducted, and mortality was observed at atrazine concentrations of 1.9 mg.1(-1) and above. This work suggests that eelgrass is not susceptible to atrazine through root-rhizome upta ke, and that atrazine exposure via groundwater seepage did not cause t he declines in eelgrass abundance and distribution.