Scaling of Nutrient Transport in Surface Runoff: From Plot to Watershed.
Douglas Smith1, Elizabeth Warnemuende1, Chi-hua Huang1, and Dennis C. Flanagan2. (1) USDA-ARS, 275 S Russell St, West Lafayette, IN 47907-2077, (2) USDA-ARS National Soil Erosion Research Lab, 275 S Russell St, West Lafayette, IN 47907
Best management practices (BMP’s) are implemented on a field by field basis, and most research data collection on their effectiveness are performed at the plot or field scales. There is little evidence on how plot or field based data can be scaled-up to assess the overall watershed scale impact. This study was conducted to evaluate the scaling relationships for nutrient transport in surface runoff to watershed scales in northeast Indiana. Rainfall simulations occurred on plots adjacent to monitored fields, that are nested within a series of watersheds ranging from 300 to 19,000 ha. Nitrogen and phosphorus concentrations are continuously monitored in ditches and streams. Responses of nutrient concentrations and nutrient loads during storm events were compared at several different scales. At the plot scale, following fertilization, mass losses of NO3-N ranged from 0.47 to 1.75 kg ha-1, while at the field scale mass losses from single storms ranged from 0.1 to 7.5 kg ha-1. There were three orders of magnitude difference between soluble P concentrations before and after fertilization at the plot scale. At the field scale, soluble P concentrations ranged from about 0.0001 to 0.01 kg ha-1, and were more representative of the loads observed at the plot scale prior to fertilization. Rainfall intensities and duration were held constant for plot studies, whereas field scale data are collected from natural runoff event with no control over intensity or duration. Nitrate-N loads for greater from no-tilled plots than tilled plots, however the opposite trend was observed at the field scale. These data will be used to assist in developing relationships between what is observed at the plot, field and watershed scale.