Original ArticleSegment-based assessment of riparian buffers on stream water quality improvement by applying an integrated model

•SWAT and REMM models were integrated to simulate the effectiveness of buffer segments with varied-width and vegetation species along each side of streams.•As the buffer drainage area contributing to each buffer segment varies drastically, the input of sediment, nitrogen, and phosphorus varied too.•From the modelling, the contribution of each segment in reducing sediment, nitrogen and phosphorus varied drastically from segment to segment.•This work could be a useful tool for riparian buffer designation and management.

As Best Management Practices, Riparian buffers are crucial to reduce pollutant loadings from upland area to streams. While fixed-width riparian buffer zones are relatively simple to be designed and implemented, variable-width buffer zones have the benefit to protect biogeochemical and ecological functions of riparian zones. With the variation of width, vegetation type, and topography, the filtering function of the riparian buffers could be varied from segment to segment along a stream. The developed REMM-SWAT interface could be used to assess riparian buffer zones at a segment level. This interface could obtain characteristics of each buffer segment and generate upland water and pollutants input, simulated with SWAT model, for each segment. From the modelling, the contribution of each segment in reducing sediment, nitrogen, and phosphorus varied drastically from one to another. The maximum reduction of runoff, sediment, nitrogen, and phosphorus for unit riparian buffer length was 3.83 mm m-1 yr-1, 202.4 kg m-1 yr-1, 1.01 kg m-1 yr-1, and 132.49 g m-1 yr-1, respectively. The minimum reduction of these pollutants was zero as there was no buffer drainage area for some buffer segments. As riparian buffers have numerous functions, the design of the buffers should comprehensively consider each of its function. This developed software could be applied as an assistant tool with other riparian buffer tools for varied-species and −width riparian buffer zones design.