Assessing the impact of EQIP-funded agricultural conservation practices on water quality in Colorado: the Republican, South Platte, Arkansas, and Rio Grande watersheds
Date
2021
Authors
Trotter, Brianna, author
Arabi, Mazdak, advisor
Bhaskar, Aditi, committee member
Paustian, Keith, committee member
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Abstract
Water quality degradation is one of the world's most pressing environmental concerns. The implementation of Colorado Regulation 85 (5 CCR 1002-85) in 2012 has led to increased awareness of the potential water quality impacts of agricultural and other nonpoint sources of pollution. The use of agricultural conservation practices is widely accepted as a means of reducing nonpoint source pollution from agricultural runoff. The Natural Resources Conservation Service (NRCS) implemented the Environmental Quality Incentives Program (EQIP) under the 1996 Farm Bill to assist producers with applying sustainable on-farm conservation practices. However, there has been limited research to quantify the progress on water quality protection resulting from the application of EQIP-funded practices in Colorado. Water quality models have become increasingly relevant in determining watershed-level characteristics related to environmental concerns. The Soil and Water Assessment Tool (SWAT) model has been a prevailing water quality model in many studies researching the effects of agricultural nutrient runoff. SWAT simulates surface, subsurface, and shallow groundwater hydrologic processes and simulates specific farming practices and their corresponding effects, including erosion, runoff, and edge-of-field losses. In this analysis, SWAT simulation quantified the effects of specific EQIP-funded agricultural conservation practices on field runoff in the Republican, South Platte, Arkansas, and iii Rio Grande watersheds of Colorado. Practices included in this analysis were varying levels of tillage, irrigation systems, and establishment of a conservation buffer. Edge-of-field discharges of Total Nitrogen (TN) and Total Phosphorus (TP) were modeled before and after EQIP conservation practices were implemented. The modeling included EQIP conservation practices applied between 2008 and 2018 and incorporated existing Colorado State University (CSU) edge-of-field water quality data, providing a means of calibrating the model to realistic and attainable results. Results showed the most significant county-level average annual percent reductions in TN came from counties with high adoption of EQIP-funded irrigation practices, such as sprinkler or drip irrigation. On average, these counties yielded a 7.1% reduction in TN per county, which equates to 6.8 tons of TN reduced across all four watersheds. The combined reductions in TN from all EQIP-funded practices averaged 8.2% per county, which totaled approximately 19.5 tons reduced across all four watersheds over the full ten-year period of analysis. The greatest reductions in TP were observed in counties with high adoption rates of irrigation system upgrades, which yielded an average 33.5% reduction in TP per county. The implementation of all EQIP-funded practices produced a 27.7% average reduction in TP per county across all counties considered. This was equivalent to a TP reduction of 263.3 tons across all four watersheds throughout the full ten-year period of analysis. The findings indicate the modeled EQIP conservation practices are significantly reducing nutrient losses from irrigated agricultural lands.
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Subject
edge-of-field runoff
total nitrogen
water quality
EQIP
agricultural conservation
total phosphorus