Location: Agroecosystems Management Research2012 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:
Final report for Project 3625-13000-009-00D which has been replaced by Project 3625-13000-010-00D. For additional information, see the new project report. Objective 1. ARS watershed data from Conservation Effects Assessment Project (CEAP) watershed were compiled into a database that is publicly available via the internet. This provides ARS customers/public better opportunities to review the scale of ARS CEAP research & specific monitoring results. A review of watershed research across ARS-CEAP watersheds was published to provide succinct information about watershed scale conservation assessments & factors that contribute to uncertainty in those assessments. Objective 2A. An inventory of conservation practices in the South Fork of the Iowa River provided an illustration of the importance of addressing transport pathways, because most conservation practices controlled surface runoff, but few practices address tile drainage, which contributed the most substantial hydrologic pathway, delivering nearly all nitrate & a substantial portion of P & E. coli. Historical sedimentation of the South Fork impacted flood severity & sediment loads in this watershed. Riparian zone management including rotational grazing & stabilized cattle crossings can promote stable banks to mitigate some impacts of erosion under flood conditions. Changes in shallow groundwater quality during establishment of prairie vegetation showed landscape patterns of nitrate & phosphorus differed, with clear implications & challenges for managing agricultural landscapes for improved water quality. Objective 2B. Analysis of an individual rainfall runoff event quantified the contribution of runoff, tile drainage, & in-stream processes to transport of nutrients, sediment, & E. coli. The importance of streambanks as a source of sediment was shown. Degradation of sulfamethazine in soil & stream sediment was described mathematically as a bi-phasic process, with initially fast then slowing as bioavailability is decreased. Bioreactors for nitrate removal were able to remove herbicides & antibiotics. The dynamics of E. coli populations in streams was assessed. Objective 3. The quality of tile drainage water can be improved with several practices including bioreactors, drainage water management (DWM), cover crops & wetlands. The efficacy of these practices were documented in several experiments and/or simulated in modeling studies. The potential reduction of nitrate loads to the Mississippi River by DWM & cover crops were estimated using simulation models. Results show these practices have the potential to achieve substantial reductions of nitrate loads at reasonable costs. The effects of long-term climatic trends & cycles on agricultural production & watershed hydrology were shown. Cyclic oceanic oscillations explained significant variations in crop production in Iowa. Long term climatic trends revealed that trend of increasing discharge & baseflow since the 1970s were linked to increasing precipitation & humidity, suggesting that climate change may have influenced the trend of increasing hypoxic zones in the Gulf of Mexico.
1. Improved method for validating watershed models. Watershed models are widely used to estimate the effects of farming practices on hydrologic processes and losses of nutrients and sediments in streams. Watershed simulation models make calculations of hydrologic processes that generate stream flow on a daily basis, but these models are usually validated using measured data averaged by month. This is because there are validation targets established in the literature for monthly validation, and because statistical issues involved with comparing observed and simulated data over many years of record become simplified with monthly data. Validation at the daily time interval should better indicate how well the simulation model represents the actual hydrologic responses of a watershed. ARS scientists in Ames, Iowa, used a statistical technique called autoregression to develop daily watershed data. These daily data provide the basis for evaluation of watershed model accuracy. This approach is improved because the daily data capture short-term stream responses to precipitation, which are a key to estimating nutrient and sediment loss. The approach will need broader testing, but could be used to develop watershed-specific modeling goals and a potential framework for comparison of modeling results across watersheds. This research is of greatest interest to the watershed modeling community and those who are hoping that watershed models can become a more consistently useful tool for watershed management.