Factors impacting the variability of effectiveness of agricultural best management practices (BMPs) in Minnesota

Abstract. In the development of nutrient reduction strategies for agricultural watersheds in the TMDL process, effectiveness values are frequently used from the Agricultural BMP Handbook for Minnesota. However, BMP effectiveness is highly variable due to differences in hydrologic pathways, biogeochemical cycles, landscape position and management. In the updated manual the objective was to describe the primary causes and relative amounts of variability for managers so more realistic TMDLs goals are set. A database of BMP effectiveness studies was used to compare variability of effectiveness values by BMP type, landscape position and target nutrient, nitrogen, phosphorus and sediment, with; n = 17-100. The coefficient of variation (c.v.) was used to compare between studies. There were no significant differences in variability by landscape position or flow path. However there was a significant difference in the c.v of dissolved vs. particulate pollutant efficiency. Dissolved phosphorus had the highest variability with a c.v. of 1.98 for 31 studies while sediment and particulate phosphorus had c.v. values