Riparian buffer effectiveness as a function of buffer design and input loads

Authors: FEI, JIANG - Pennsylvania State University; PREISENDANZ, HEATHER - Pennsylvania State University; Veith, Tameria - Tamie; RAJ, CIBIN - Pennsylvania State University; DROHAN, PATRICK - Pennsylvania State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2020
Publication Date: 10/11/2020
Citation: Fei, J., Preisendanz, H., Veith, T.L., Raj, C., Drohan, P. 2020. Riparian buffer effectiveness as a function of buffer design and input loads. Journal of Environmental Quality. 49(6):1599-1611. https://doi.org/10.1002/jeq2.20149.
DOI: https://doi.org/10.1002/jeq2.20149

Interpretive Summary: Landowners have expressed frustration in the lack of options provided for design and management of stream-side buffer zones that will be cost-shared or reimbursed. Based on stakeholder feedback, this study compares nutrient and sediment losses from six different designs of buffers. A buffer design that allows harvesting in a portion of the buffer was found to control nutrient and sediment losses almost as well as the same design without harvesting. This suggests that adding the option for partial harvesting of buffers may encourage adoption by more landowners without sacrificing water quality. Also, this study demonstrated that it is important to consider both percent pollutant reduction and total pollutant load reduction when evaluating buffer performance. Considering both reduction types gives a better understanding of how buffers will respond to both low and high flow events and both low and high pollutant loss conditions.

Technical Abstract: Although many agricultural watersheds rely heavily on riparian buffer adoption to meet water quality goals, design and management constraints in current policies create adoption barriers. Based on focus group feedback, we developed a flexible buffer design paradigm that varies buffer width, vegetation, and harvesting. Sixteen years of daily-scale nutrient and sediment loads simulated with the Soil and Water Assessment Tool (SWAT) were coupled to the 3-zone Riparian Ecosystem Management Model to compare the effectiveness of traditional, policy-based buffer designs to designs that are more flexible and integrate features important to local farmers. Buffer designs included: (i) 10 m grass; (ii) 15 m grass; (iii) 15 m deciduous trees; (iv) 30 m grass and trees; (v) 30 m grass and trees with trees harvested every 3 years; and (vi) 30 m grass and trees with grass harvested every year. Allowing harvesting in one zone of the buffer vegetation (either trees or grasses) minimally impacted water quality (< 5% change). Additionally, buffers with lower removal efficiencies generally removed higher masses than buffers with higher removal efficiencies when the buffers received higher input loads. Thus, by using a lens of mass reduction instead of focusing only on percent reduction, watershed-wide buffer implementation may be better targeted to total nitrogen, phosphorus, and sediment reduced. These findings have important implications for informing flexible buffer design policies and enhanced placement of buffers in watersheds impaired by nutrient and sediment.