Pesticide flow and concentration variation through the McPherson Valley Wetlands.

Abstract

Pesticides pose a serious threat to wetlands due to their effects on the water, soil, plant life, and the animals that inhabit these areas. The rate that these pesticides degrade or move through the wetland plays an important role in the affect pesticides have in contaminating the wetland and its flora and fauna. After being applied to the area corn fields, the amount of pesticide residue that will contaminate the wetland depends highly on the soil types and the amounts of precipitation that follows the application. The pesticide monitored during this study was atrazine. Atrazine is the primary herbicide used in Kansas, it is used to control weedy plant species where corn and milo are the primary row crops. The study was completed at the McPherson Valley Wetlands located four miles west of the city of McPherson in Central Kansas. The wetland covers approximately 595 hectares, depending on the season, and receives runoff from 3200 hectares that lie directly north of the wetland. Sample sites ranged from where the runoff enters the wetland to a canal where water drains out. The pH of the water was recorded for each sample along with alkalinity, temperature, and dissolved oxygen. High performance liquid chromatography (HPLC) was the procedure used to determine atrazine residue concentrations in the samples. The objective of this study was to determine if the pesticide concentrations change from site to site as the runoff water flows through the wetland. The changes in the water chemistry along with animal and plant life will be used to help analyze the problem of herbicide contamination. The McPherson Valley Wetlands acts as a reservoir for runoff that contains large quantities of agricultural herbicides. The hypothesis to be tested was that the wetland rids itself of these contaminants by using the process of dilution due to the runoff activity following the initial application. The extent that the McPherson Valley Wetlands rids itself of the residues was determined from the study. A Two-Way Analysis of Variance was used to analyze differences in the water samples among sampling locations in the wetlands and among sampling dates. Linear regression was used to determine the rate of degradation of pesticide residue in the wetland. Very small amounts of herbicide residues were found in the wetland. Concentrations were highest in the samples taken directly following the first runoff event after the application of the herbicide. Samples taken in August, which also were taken following a runoff event, also contained high concentrations of herbicide in comparison to samples taken in other months. The highest concentrations found were 0.33 ug/L and a mean for all the samples was 0.106 ug/L with a standard deviation of 0.088 ug/L. The physicochemical properties of the wetland showed minor affects caused by the herbicide residues.