Assessment of riparian buffers’ effectiveness in controlling nutrient and sediment loads as a function of buffer design, site characteristics and upland loadings

Abstract. Riparian buffers are a widely adopted agricultural best management practice due to their ability to reduce sediment and nutrient loads to streams. Current efforts in the Commonwealth of Pennsylvania to incentivize widespread adoption of riparian buffers have fallen short as the state struggles to be in compliance with Chesapeake Bay restoration goals. Constrained buffer design in current policies has been identified as one of the barriers to adoption, and therefore this research explores the water quality tradeoffs that may result from a more flexible buffer design paradigm. The Spring Creek watershed in central Pennsylvania was selected as the case study watershed to test the effectiveness of four different buffer designs (variations in vegetation and width) and two alternative buffer management scenarios that involved harvesting of either grass or trees from the buffer. Three crop rotations were simulated in the Soil & Water Assessment Tool (SWAT), with nutrient and sediment loads coupled to the Riparian Ecosystem Management Model (REMM) to better understand how input loads affect the effectiveness of a specific buffer design and how the effectiveness of a buffer design changes as a function of input load. Simulations were run at a daily scale for 16 years, allowing annual-scale performance as well as event-specific performance to be investigated. The results revealed that knowing annual removal efficiency of a buffer is insufficient and that adoption recommendations should be made based on loads treated by the buffer, as higher nutrient and sediment masses may be reduced by buffers with lower removal efficiencies.