A method to evaluate pollutant loads from tile drains

The quantification of pollutant loads from agricultural non-point source po llution is difficult because: (1) there is no direct means of continuously recording pollutant concentration; (2) and available human resources and fu nds always limit sampling. For those reasons, sampling strategy and polluta nt concentration interpolation methods are essential to estimate pollutant loads. In this study, a method was tested to evaluate pollutant loads using daily flow volume and daily mass load regression for nitrate-nitrogen, ort hophosphate-phosphorous and atrazine. The method worked well for nitrate-ni trogen, but generally did not work well for either orthophosphate-phosphoro us or atrazine. Nitrate-nitrogen load was calculated for several tile-monit oring stations based on this method. Results were compared with volume inte rpolation methods; the difference between the two methods is not significan t at the 95% level of confidence. This method can provide a reliable estima te of nitrate-nitrogen loads where limited samples are available. This meth od was not successful with orthophosphate-phosphorous or atrazine.