Interest in biorenewable energy is increasing due to concerns associated with continued reliance on fossil fuels. As the primary producer of crops used as feedstocks for ethanol production and other biorenewable energy sources, the Midwest in general, and Iowa in particular, is likely to incur a high percentage of the benefits and costs of the biorenewable energy initiative. Of significant potential concern is the impact of feedstock selection, management, and harvest on nutrient and sediment losses to receiving water bodies and the resulting impact on the integrity of aquatic resources. In the short term, increases in corn acreage, or large-scale conversion of Conservation Reserve Program lands to feedstock production, have the potential for significant negative impacts on water resources. In the longer term, conversion to perennial-plant based feedstocks for cellulosic feedstocks has great potential to positively impact aquatic integrity and water quality. However, in order to make a credible assessment of impacts of such change, significant knowledge gaps regarding the function of such landscape features need to be addressed. Managed riparian buffers, composed of woody and nonwoody vegetation, are being used to reduce inputs of nutrients, sediments, and chemicals to streams that commonly result from intensive agriculture. In central Iowa, previous studies conducted by the Iowa State University Agroecology Issue Team demonstrated that buffer attributes (e.g., physical structure, root uptake) reduce nutrient and sediment loading to streams. However, responses of most ecosystem components, including populations and communities of aquatic organisms, remain poorly studied. The emerging biorenewables initiative is likely to generate even greater agricultural production, particularly on lands susceptible to high runoff and soil erosion. Therefore, it is critical that we identify functional qualities (e.g., spatial distribution, length and width, vegetation composition and age) of effective riparian buffers and apply this knowledge to design and manage systems that protect aquatic ecosystems in an economically-viable manner. Animal and plant populations and communities respond to and reflect all physical, chemical, and biological attributes of their environment, including conditions affecting human health. Additionally, biological communities are sensitive to episodic events (e.g., pulses of contaminant inputs during high surface-water runoff) and rare contaminants that are undetected by periodic measurement of selected physical and chemical ecosystem attributes. Because organisms are now acknowledged to be definitive indicators of water quality, they are increasingly being used for regulatory assessments (e.g., USEPA) and are likewise essential tools for assessing riparian buffer effectiveness. In this study, invertebrate and fish community characteristics (i.e., species composition, abundance, growth) will be evaluated in three central Iowa streams with and without managed riparian buffers of different age, size, and structure (N = 40 total stream reaches). Instream habitat features (e.g., streambed substrate particle sizes, coarse particulate matter abundance, temperature, turbidity) will also be measured in riffles, pools, and runs where fish and invertebrates are sampled. Results of this study will produce quantitative measures of buffer effectiveness that will help guide future riparian management strategies in agroecosystems. In addition, this study will provide a platform for expanding the scope and scale of our investigations. Planned studies to increase mechanistic understanding of riparian buffer effects in agroecosystems include analyses of buffer effects on stream metabolism (e.g., dissolved oxygen, primary production), and nutrient- and energy-flow pathways through aquatic food webs. The proposed research will also provide a platform for investigating emerging issues across Iowa. Issues include conservation of systems influenced by production of biorenewable feedstocks (i.e., cereal grains, cellulosic materials in riparian buffers), lake and reservoir restoration activities, and biological assessment of recently reclassified headwater stream systems.