Location: Agroecosystems Management Research2009 Annual Report
1a. Objectives (from AD-416)
This project describes Watershed Assessment Studies (WAS) to be conducted in two Iowa watersheds that are benchmark watersheds of ARS’s Conservation Effects Assessment Project (CEAP). This project consists of three objectives that are to: 1) Develop and implement a data system to organize, document, manipulate, and compile water, soil, management, and socio-economic data for assessment of conservation practices at field, farm, and watershed scales for the South Fork of the Iowa River and Walnut Creek, Story County watersheds. 2) Measure and quantify water quality, water quantity, and soil quality effects of conservation practices at the field, farm, and watershed scale for the South Fork of the Iowa River and Walnut Creek (Story County) watersheds. Two sub-objectives are: a) Quantify extent and placement of conservation practices in the South Fork watershed and impacts of those practices on water and soil quality. b) Relate contaminant sources to transport paths and processes for pathogens, antibiotics and nutrients using hydrologic and land use data with isotope- and DNA-based methods. 3)Assess and evaluate watershed and river basin responses to current and improved management practices for water quality by comparing observed to model-predicted results for the South Fork of the Iowa River and Walnut Creek (Story County) watersheds.
1b. Approach (from AD-416)
The work will take place in the Iowa River’s South Fork watershed (78,000 ha), and in Walnut Creek watershed, Story County (5,200 ha). Both watersheds are within the area of most recent glaciation in Iowa (about 10,000 years B.P.), known as the Des Moines lobe. Walnut Creek has a water quality database dating to 1991, and a history of watershed modeling and nutrient-management research. The South Fork watershed also has challenges associated with intensive livestock production. Its water quality database dates back to 2001, and information on conservation practices have been gathered and targeting methods explored. This research will leverage these assets towards attaining CEAP goals through database development, watershed assessments and modeling studies. Watershed assessment studies for the South Fork will include combined geographic analyses of soil survey, topographic, crop cover, and conservation-practices inventory data to improve our ability to assess the targeting of conservation practices towards sensitive lands. Combined hydrologic and water quality data will be used to evaluate effects of practices on runoff water quality and better understand how different pathways of water movement impact water quality as measured at the watershed scale. Source tracking methods for fecal-contaminant indicator bacteria will be developed and tested. Finally watershed models will be evaluated to improve our ability to predict the impact of changes in conservation systems that are reasonable future scenarios. Thereby, the project will develop information that can increase the effectiveness of USDA’s conservation programs in tile-drained watersheds.
3. Progress Report
Major activities on this project included: 1. A multi-location Conservation Effects Assessment Project (CEAP) database, known as STEWARDS (Sustaining The Earth’s Watersheds – Agricultural Research Data System) has been implemented and is housed at the National Soil Tilth Laboratory (NSTL). Data from ten CEAP watersheds, including eight outside Iowa, are published on the on-line database, and data from three additional watersheds are being processed for inclusion. This is substantial progress that is ahead of schedule. 2. Continuation of ongoing stream gauging and water quality monitoring. Water quality parameters being tracked include nutrients and Eschericia coli (E. coli)) in the South Fork Iowa River watershed, nutrients in Walnut Creek (Story Co. Iowa), and for nutrients and sediment at Walnut and Squaw Creeks (Jasper Co. Iowa). The work in Jasper County is new and will provide a watershed-scale context to research on prairie reconstruction that is being conducted under Objective 2. The focus of this research continues to be in the South Fork Iowa River, where concentrations of nutrients and E. coli and Enterococcus were measured in streams, stream sediments, subsurface drainage water and field runoff. 3. An assessment of riparian corridor conditions in the South Fork watershed was progressed in collaboration with National Sedimentation Laboratory scientists and a Chinese visiting scholar. This work quantified stream meandering and channelization, and post-settlement sediment accretion within the river valley. 4. Hydrograph separations of multiple contaminants during a single event were used to identify major pathways contributing nutrients, bacteria, and sediment, providing an integrated water quality assessment from a single runoff event that occurred in 2006. In addition, research to evaluate phosphorus (P) contributions to streams from riparian pastures, and compare methods of estimating contaminant loads in streams was progressed.
1. Hydrologic changes in the Midwest result more from shifts in climate than land use. Hydrologic shifts towards greater discharge have been observed in the Midwest but it is not certain whether this trend results from changes in agricultural land use or changes in climate. When evaluating simultaneous shifts in how energy (evaporative demand) and water (precipitation) was partitioned during a long-term, small-watershed experiment, effects of land use (watershed treatment) and climate trend (time) became readily distinguished. Applying the technique to four larger watersheds across the Midwest, increasing discharge was shown more attributable to climate change than land-use change. Changes in land use, in particular increased soybean acreage, did show a shift towards increasing discharge that could be attributed to decreased crop water use. But, since 1975 and after this change in cropping occurred, changing climate in the form of increased precipitation and decreased evaporative demand has been the dominant influence on watershed hydrology. The trend impacts issues such as Gulf of Mexico hypoxia, which expands as both nutrient losses and discharge increase. Results are of interest to all groups interested in conservation effectiveness in the Midwest (i.e., conservation groups, policy developers, environmental and commodity groups), because increased discharge from agricultural watersheds, due to climate change, inherently increases the challenges of retaining agricultural nutrients within soils.
2. Impacts of historical sediment accretion and channel straightening on the South Fork Iowa River. Soil erosion that followed agricultural land clearing produced sediment that accumulated in river valleys and continues to influence rivers and be a source of streambank sediment loads today. We asked whether historical sediment has contributed to sediment loads in an Iowa watershed with low relief and limited settlement history (160 years). We found recent sediment along the South Fork Iowa River averaged 2.6 ft thick out to a distance of 260 ft from the channel, and equated to 69.8 tons per acre of soil that was eroded from uplands across this 158,000 acre watershed. The volume of this sediment has reduced the capacity of the floodplain to store floodwater by an estimated 4123 acre-ft, after discounting for the sediment’s volume of pore space. In addition, channel straightening of the South Fork and its tributaries has reduced channel length by up to 15%, hastening routing of water to the Iowa River. River restoration projects need to be conducted recognizing that bank erosion and exacerbated flooding may result from historical legacies within our river valleys. This is of particular interest to water resource managers and aquatic ecologists who are developing and implementing river restoration and watershed management plans.
3. Major pathways followed by multiple pollutants in an agricultural watershed segregated. Water quality studies are typically conducted on single contaminants, but developing comprehensive water quality strategies in watersheds usually requires an understanding of the sources and dynamics of multiple contaminants. We analyzed four contaminants (i.e, nitrate, phosphorus, E. coli, and sediment) at three locations during a single runoff event in a tile-drained watershed. The finding that nitrate loads were dominantly carried via tile drainage was expected, and that sediment was dominated by channel and bank sources was expected but not necessarily to the extent observed (78%). The most unexpected result was that about half the phosphorus and a third of the E. coli loads were attributed to surface intakes that drain surface depressions and road ditches in this glacial landscape. Conservation strategies in this watershed are currently focused on erosion control and nutrient management; but these results suggest that buffering of tile intakes and streambank stabilization are now just as important. This study is of interest to conservation and environmental professionals and policy makers, as well as agricultural stakeholders, who seek to develop improved strategies to comprehensively address agricultural water quality issues.
4. Predicting sulfamethazine behavior in soil. Antibiotics administered to swine enter the environment when swine manure is land applied and have been detected in surface and groundwater. Leaching to subsurface drainage tiles is affected by sorption to the soil and a method of predicting this binding from soil organic matter and pH was developed. Potential leaching is greatest in soil with higher pH and low organic matter. The degradation of sulfamethazine in water and soil is characterized by a biphasic pattern with rapid degradation followed by a slower phase. Degradation becomes limited by decreased bioavailability with increased time in the soil. This research contributes to the knowledge of how these contaminants behave in the environment and may allow the development of manure management practices that decrease the risk to water quality. The research is of interest to scientists, environmental groups and farm producer organizations.
5. Practices altering the distribution of cattle in riparian pastures may reduce nonpoint source pollution of surface water. Understanding how grazing management can impact water quality is important in a number of Midwest watersheds. Research in southern and central Iowa has shown that restricting access of cattle to pasture streams by using either stabilized crossings or rotational grazing reduces the risk of phosphorus losses by altering where and when grazing takes place. While grazing management will affect the risk of phosphorus and sediment losses from direct fecal deposition or in precipitation runoff, stream bank erosion is more dependent on stream hydrology and precipitation events than grazing management. These results are of interest to the conservation community, both practitioners and scientists, who need to understand the linkages between pasture management and stream water quality.Malone, R.W., Ma, L. 2008. N uptake effects on N loss in tile drainage as estimated by RZWQM. In: Ma, L., Bruulsema, T., Ahuja, L., editors. New Advances in Understanding and Quantification of Plant N Uptake. Boca Raton, FL. CRC Press. p. 259-275.