Pesticides used for crop protection and increasing agricultural production are frequently detected in water bodies. The National Center for Water Quality Research has been monitoring pesticide concentrations in 10 rivers in the Lake Erie and Ohio River basins continuously since 1983. Since then we have measured 20 pesticides that are widely used in agriculture in nearly 20,000 samples. The main objectives of the program are to accurately quantify spatial and seasonal pesticide trends from watersheds of varying land uses and to assess the long-term effects of changing agricultural management practices on the prevalence of pesticides. A stratified sampling technique was adopted where more intensive sampling was conducted during the growing season from mid-March to early October. Samples were collected 3 times per day during high flow periods, 7 days a week using automated samplers. All pesticides we measured were mostly below detection limits during the non-growing season, which ranged from mid-October to mid-March. During the non-growing season, samples were collected bi-weekly. Intense sampling during growing season enabled us to get detailed concentration and loading trends during storm events. During the first few seasonal runoffs, chemographs rise rapidly, peak during peak discharge and decline thereafter not exhibiting any substantial tailing. Peak atrazine, simazine, and acetochlor concentrations were variable over time and showed no distinct decreasing trends. Our concentration data is paired with the discharge data from USGS gaging stations located in close proximity to our sampling stations, to calculate time-weighted mean concentration (TWMC), flow-weighted mean concentrations (FWMC) and loads. Long-term herbicide concentration trends and loads from selected watersheds will be discussed in this paper. Atrazine had the highest concentration of all the measured pesticides, ranging from 0.01 – 121.46 µg/L followed by metolachlor ranging from 0.01 – 98.76 µg/L. FWMC is often higher than TWMC for atrazine. Scale effect is prominent with higher peak concentrations in smaller watersheds for a shorter period of time but higher loads in larger watersheds. Long-term monitoring of pesticides in natural waters is important because concentration and load vary annually and the trends depend on many factors such as pesticide application rates and amounts, growing season length, precipitation intensity and discharge.

Long-term trends in pesticide concentrations and loads in Lake Erie tributaries

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.