ARS | Publication request: HOW DO YOU DETERMINE IF A CHANGE IN MANAGEMENT PRACTICES HAS CAUSED AN IMPROVEMENT IN WATER QUALITY?

Submitted to: International Association of Environmental and Analytical Chemistry
Publication Type: Abstract Only
Publication Acceptance Date: September 13, 1999
Publication Date: N/A

Technical Abstract: The US EPA drinking water standard for atrazine is 3 ug/L for a running average of four quarterly samples. Some Missouri reservoirs that are used as public water supplies have exceeded the atrazine standard, so watershed management plans must be developed. These plans will call for changes in field management practices to reduce the average concentration of atrazine in the reservoirs. The atrazine standard is time-weighted, but reservoirs fill according to inflow volume, not time. In Missouri, a disproportionate volume of streamflow occurs during the second quarter of the year, when atrazine concentrations are the highest. The highest second quarter concentrations are observed during moderate to very high runoff events. Also, the amount of streamflow during the first, third, and fourth quarters exerts a great deal of influence on the running average atrazine concentrations. These weather related differences in concentration have nothing to do with implementation of atrazine best management practices. A method is needed to filter out weather effects, and thus determine if management practice changes are affecting herbicide transport. Goodwater Creek in north-central Missouri has been monitored for herbicides since 1992. Approximately 95% of the annual mass transport of atrazine takes place in about a 45 day period during the second quarter. The correlation between atrazine load and total streamflow during this critical loss period is very high (r**2>0.9). No significant changes in atrazine management practices have occurred during this period. The effectiveness of proposed management practices in reducing atrazine losses can be determined by comparing the observed atrazine load to that predicted from the baseline data for similar streamflow conditions.