Walnut Creek and Squaw Creek Watersheds, Iowa: National Institute of Food and Agriculture-Conservation Effects Assessment Project

Authors: OSMOND, DEANNA - North Carolina State University; GASSMAN, PHILIP - Iowa State University; SCHILLING, KEITH - Iowa Department Of Natural Resources; KLING, CATHERINE - Iowa State University; HELMERS, MATTHEW - Iowa State University; ISENHART, TOM - Iowa State University; SIMPKINS, WILLIAM - Iowa State University; Moorman, Thomas; Tomer, Mark; RABOTYAGOV, SERGEY - University Of Washington; JHA, MANOJ - North Carolina Agricultural And Technical State University; HOAG, DANA - Colorad0 State University; MEALS, DON - Icenine Environmental Consulting; ARABI, MAZDAK - Colorad0 State University

Submitted to: Soil and Water Conservation Society
Publication Type: Book / Chapter
Publication Acceptance Date: 2/15/2012
Publication Date: 6/30/2012
Citation: Osmond, D., Gassman, P.W., Schilling, K., Kling, C.L., Helmers, M.J., Isenhart, T., Simpkins, W., Moorman, T.B., Tomer, M.D., Rabotyagov, S., Jha, M., Hoag, D., Meals, D., Arabi, M. 2012. Walnut Creek and Squaw Creek Watersheds, Iowa: National Institute of Food and Agriculture-Conservation Effects Assessment Project. In: Osmond, D.L., Meals, D.W., Hoag, D.L.K., Arabi, M., editors. How to Build Better Agricultural Conservation Programs to Protect Water Quality. Ankeny, IA: Soil and Water Conservation Society. p. 201-220.

Interpretive Summary:

Technical Abstract: The Walnut Creek Watershed NIFA-CEAP Watershed project was designed to assess water quality benefits and economic costs from the adoption of a prairie ecosystem (conservation practice implementation) at a watershed scale. This chapter describes and summarizes the paired watershed (Walnut Creek and Squaw) findings from a long-term study, initially funded by the U.S. Environmental Protection Agency Section 319 National Nonpoint Source Monitoring Program, and continued through NIFA-CEAP. The treatment watershed pair, Walnut Creek, was planted to native prairie, which by 2005 represented 23.5 percent of the land use in the watershed. Walnut and Squaw creeks are affected by many agricultural nonpoint source water pollutants, including sediment, nutrients, pesticides, and animal waste. Nitrate and pesticide parameters were sampled biweekly or monthly at 10 sites across the two watersheds in March through September, while four sites were sampled once each in August, October, December, and February. Turbidity and suspended solids were monitored daily with the automatic samplers and data was compiled for storm event statistical evaluation. An important result of subwatershed monitoring showed that row crop conversion to prairie resulted in a 30% decrease in NO3-N concentration while CRP conversion to row crop resulted in a 1200% increase in NO3-N concentration. There appears to be a much longer lag time between reducing pollutants than adding pollutants in this system. Suspended sediment concentrations were similar in Walnut Creek and Squaw Creek. Project researchers believe that the lack of change in sediment load following treatment could be due to the highly seasonal pattern of sediment export, the fact that stream power was not reduced by the treatments, failure to address streambank erosion, and long-term sediment storage in floodplains and stream channels. In the Squaw Creek watershed, the conservation practices team used SWAT to assess the effects of placement of warm season grasses by changing the location of the grass within the watershed. Modeled results indicated that Conservation Reserve Program conversion to row crops increased nitrate, while planting grass in Highly Erodible Lands or in the upper part of the watershed reduced nitrate. The calibrated SWAT model was used for the Squaw Creek watershed to conduct optimization analyses as a function of conservation practice water quality effectiveness and costs. The application of genetic algorithm modeling approach, which interfaced environmental output estimated with SWAT and cost data, showed different adoption patterns for Squaw Creek depending on the conservation practices implemented. For instance, land retirement reduced N the most (70%) but had the greatest cost. Mulch till and reduced till had the lowest impact on N reduction and also the lowest cost. Taken together, the water quality and modeling results indicated that nitrate can be reduced by a change in cropping systems but that the cost will be significant.