Using the Soil and Water Assessment Tool to Estimate Achievable Water Quality Targets through Implementation of Beneficial Management Practices in an Agricultural Watershed

Abstract

Runoff from crop production in agricultural watersheds can cause widespread soil loss and degradation of surface water quality. Beneficial management practices (BMPs) for soil conservation are often implemented as remedial measures because BMPs can reduce soil erosion and improve water quality. However, the efficacy of BMPs may be unknown because it can be affected by many factors, such as farming practices, land-use, soil type, topography, and climatic conditions. As such, it is difficult to estimate the impacts of BMPs on water quality through field experiments alone. In this research, the Soil and Water Assessment Tool was used to estimate achievable performance targets of water quality indicators (sediment and soluble P loadings) after implementation of combinations of selected BMPs in the Black Brook Watershed in northwestern New Brunswick, Canada. Four commonly used BMPs (flow diversion terraces [FDTs], fertilizer reductions, tillage methods, and crop rotations), were considered individually and in different combinations. At the watershed level, the best achievable sediment loading was 1.9 t ha(-1) yr(-1) (89% reduction compared with default scenario), with a BMP combination of crop rotation, FDT, and no-till. The best achievable soluble P loading was 0.5 kg ha(-1) yr(-1) (62% reduction), with a BMP combination of crop rotation and FDT and fertilizer reduction. Targets estimated through nonpoint source water quality modeling can be used to evaluate BMP implementation initiatives and provide milestones for the rehabilitation of streams and rivers in agricultural regions.

Ammonia Stripping of Biologically Treated Liquid Manure

“…Yang et al (2012) propose APS for suspended sediments and soluble P based on comparison of modeled loads before and after BMP implementation. Using the Soil and Water Assessment Tool (SWAT), sediment and soluble P loads were modeled for a New Brunswick (potato-dominated) watershed following implementation of four commonly used BMPs (fl ow diversion terraces, fertilizer reductions, tillage methods, and crop rotations), singly and in combination.…”

“…In the case of the approach developed by Rousseau et al (2012), watershed maps are generated that show APS values for a specifi c pesticide and the likelihood of exceeding its IPS for a given river segment and scenario (current or choice of BMPs). Yang et al (2012) produced charts that show the mean, maximum, and minimum load reductions predicted to occur in response to BMP application. In both cases, however, it should be noted that fi nal decisions about implementing BMPs will most likely be based on social and economic, as well as environmental, considerations; the former two conditions (farm and/or rural social and economic conditions) were not considered under NAESI.…”

Determining sources of fine-grained sediment for a reach of the Lower Little Bow River, Alberta, using a colour-based sediment fingerprinting approach

“…Clearly, upstream and IRF channel were the most certain sediment sources during the 4 yr study period. Different than traditional pear-shaped headwater watersheds with no external tributary channel input (e.g., Yang et al 2012;Barthod et al 2015), the study catchment is located on a reach of LLBR with an upstream inlet and a downstream outlet. Therefore, sediments from upstream and tributary subwatershed in the current study should not be ignored when estimating the sources of the downstream sediment samples.…”

Development of Environmental Thresholds for Streams in Agricultural Watersheds

“…Unlike many pesticides that have toxicological IPS, suspended sediments and P are not inherently toxic but cause ecosystem changes through indirect effects such as water opacity, smothering or scouring (sediments), or eutrophication (P). Yang et al (2012) propose APS for suspended sediments and soluble P based on comparison of modeled loads before and after BMP implementation. Using the Soil and Water Assessment Tool (SWAT), sediment and soluble P loads were modeled for a New Brunswick (potato‐dominated) watershed following implementation of four commonly used BMPs (flow diversion terraces, fertilizer reductions, tillage methods, and crop rotations), singly and in combination.…”

“…The modeling approaches applied by both Rousseau et al (2012) and Yang et al (2012) lend themselves to use by farmers or decision makers to assist with BMP selection. In the case of the approach developed by Rousseau et al (2012), watershed maps are generated that show APS values for a specific pesticide and the likelihood of exceeding its IPS for a given river segment and scenario (current or choice of BMPs).…”