K.E. Lee, D.G. Huggins, E.M. Thurman 1
This research assessed the effects of the hydrophyte community structure in wetland mesocosms on the degradation of two commonly used herbicides, atrazine and alachlor. The research was conducted for 383 days at the University of Kansas Nelson Environmental Study Area near Lawrence, Kansas. Wetland treatments, consisting of three mesocosms each, included openwater mesocosms with no or limited macrophyte communities, mesocosms with a predominate submergent hydrophyte community (Potamogeton spp. and Najas quadalupensis), and mesocosms dominated by an emergent hydrophyte community (Typha latifolia and T. augustifolia). Atrazine and alachlor were added to wetland mesocosms to obtain approximate concentrations of 25 g/L each. Atrazine mass loss was more rapid in the emergent mesocosms than in the open or submergent mesocosms. The dissipation halflife of atrazine mass in the emergent mesocosms was 5870 days compared to 85115 days for the open and submergent mesocosms. Alachlor dissipated more rapidly than atrazine under all treatments. More than 50% of the alachlor concentration and mass were lost within 21 days under all treatments (dissipation halflife of alachlor mass ~ 10 to 20 days). Deethylatrazine (DEA) was a metabolite of atrazine detected in all mesocosms. The mean DEAtoatrazine ratio (DAR) under all treatments increased during the two growing seasons and stabilized during the winter when biological communities and processes are relatively inactive. The DAR was significantly different among the treatments (emergent > submergent > open) for the first 126 days. These results indicate that (1) hydrophytes were not as important as other factors in alachlor degradation, and (2) wetland hydrophyte community structure (i.e. open, submergent, or emergent) was the primary ecological determinant of atrazine degradation rate.
