Impact of stacked conservation practices on phosphorus and sediment export at the catchment scale

Best management practices (BMPs) are effective in reducing nutrient and sediment export, but further understanding of the benefits of the stacked BMPs is needed. This catchment-scale study was established to evaluate the impact of hydrology and BMPs on phosphorus (P) and sediment losses. Two adjacent catchments, one with a lower level of BMP adoption (Low-BMP #11) and one with a higher level (High-BMP #12), were compared for total P (TP) and total suspended solids (TSS) export. The BMPs include nutrient management plans, reduced tillage, grassed waterways, terraces, and perennial vegetation. The TP event-flow-weighted (EFW) concentration was significantly higher at Low-BMP #11 (0.293 mg L^-1) than at High-BMP #12 (0.069 mg L^-1). There was no significant difference in TP base-flow-weighted (BFW) concentrations between Low-BMP #11 (0.035 mg L^-1) and High-BMP #12 (0.037 mg L^-1). The TSS-EFW (148.0 vs. 18.6 mg L^-1) and TSS-BFW (13.3 vs. 6.9 mg L^-1) concentrations were also higher at Low-BMP #11 than at High-BMP #12. High-BMP #12 had lower TP (0.36 vs. 0.59 kg ha^-1 yr^-1) and TSS (253 vs. 1,961 kg ha^-1 yr^-1) loading than Low-BMP #11. The lower TP export at High-BMP #12 was likely attributed to the effectiveness of stacked erosion control BMPs and nutrient management plans. Overall, lower P and sediment loading was observed when a greater areal extent of stacked practices was implemented at the catchment level. This finding provides vital information to encourage wider BMP adoption at the watershed scale.