Location: Agroecosystems Management Research2008 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 hectares (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 ago), 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 Conservation Effects Assessment Project (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 the United States Department of Agriculture's (USDA) conservation programs in tile-drained watersheds.
3. Progress Report
Major activities on this project included: 1. Completed development phase of a multi-location Conservation Effects Assessment Project (CEAP) database that will be housed at the National Soil Tilth Laboratory (NSTL). Several other CEAP watersheds are beginning to contribute data. 2. Continuation of ongoing water quality monitoring (for nutrients and Eschericia coli (E. coli)) and stream gauging in the South Fork watershed despite major flooding during June 2008; fortunately our gauging station equipment has remained intact. Concentrations of E. coli and Enterococcus were measured in streams, stream sediments, subsurface drainage water and field runoff. A comparison of field runoff from manured and non-manured fields suggests wildlife contributes significant amounts of E. coli into surface runoff. A study was completed that measured E. coli survival in stream water at different times of the year. Survival in stream water was not greatly influenced by temperature. 3. We continue to work on an assessment of riparian corridor stream and sediment conditions in the South Fork watershed, in collaboration with National Sedimentation Laboratory scientists and a visiting scholar. Ongoing work includes an assessment of stream meander movement and channelization, bank stability measurements, and a survey of post-settlement sediment accretion along the river valley. 4. We have begun to evaluate phosphorus (P) dynamics in a riparian buffer by developing methods to quantifying inorganic and organic P fractions in soil solution. In addition, work to progress hydrograph separation and load estimation method comparisons under objectives two and three is underway but in early stages. (NP211, Component 1)
1. Linking Climate Patterns and Crop Yields The relative roles of climate and management in determining environmental performance of agricultural systems are being identified. Climate can have a larger effect on crops than management, and is a critical consideration for determining effects of conservation practices. For example, the nitrogen cycle is dominated by crop uptake and yield, and thereby influenced by climate. We investigated multi-decadal climate variations and associated impacts on corn yield. Long-term yield records showed a significant, nearly-biennial, oscillation between high and low corn yielding years that is associated with large-scale oceanic circulations. High yields were associated with years of sunshine early in the growing season and sufficient rainfall later as crops mature. Possible outcomes include predictive models to guide agricultural management for profitability and reduced nutrient losses. Results will be useful to agricultural and climate scientists interested in crop responses to weather patterns, and the potential for seasonal climate predictions to more tangibly assist crop management. (NP211, Component 1)
2. Carbon (C) Cycling in Soils Has Implications for Water Quality The type of grassland plant communities present in a riparian buffer might influence soil biological processes, with implications for carbon cycling and nutrient losses from buffers to streams. We compared the influence of grass communities (species with C3 versus C4 photosynthesis) on the soil biological response to inputs of fresh organic material and nutrients from the grasses. We found that soil organic matter provided stability to the soil ecosystem and allowed it to respond more rapidly to inputs of these fresh materials. This shows in part how organic matter enhances nutrient retention in soils. These results are of interest to the conservation community, both practitioners and scientists, who need to better understand the linkages between soil quality and water quality. (NP211, Component 1)
3. Identification of Plants for Phosphorus Uptake Buffer uptake of phosphorus (P) varies by grass species and phosphorus availability. Harvesting of buffer vegetation offers the opportunity to increase supply of harvested biomass and remove nutrients that accumulate in buffers. We found that reed canarygrass and switchgrass are better choices than smooth brome for P removal through biomass harvest. Switchgrass took up more P from soil solutions initially high in P, but reed canarygrass performed best when low P solutions had added P (simulating P inputs from runoff). Results add weight to other recent evidence that species selection can be critical in determining the effectiveness of conservation practices. This is of interest to agricultural producers, conservation planners, and policy makers seeking to improve buffer design and considering biomass harvest from conservation plantings. (NP211, Component 1)
5. Significant Activities that Support Special Target Populations