Nutrient concentration gradients and biological response in central Nebraska streams

ABSTRACT: Nutrients and excessive algal productivity are leading causes of water-quality degradation in streams and rivers draining agricultural regions. Federal guidance for establishing regional nutrient criteria are being developed for use in stream eutrophication monitoring and management programs. The development of nutrient criteria will be aided by a national study the U.S. Geological Survey is conducting to document how biological communities and stream metabolism respond to a gradient of nutrient conditions among streams draining agricultural areas or land uses. The primary objectives of this study are to determine relations between nutrients and biological community structure, relations between nutrients and stream metabolism, and how these relations vary within and between different environmental settings across the United States. Sixty candidate stream reaches in central Nebraska were selected using digital map data for streams, basinlandscape features, and estimated nutrient inputs derived from county-level fertilizer sales, atmospheric deposition, and livestock data. A field reconnaissance of the streams was conducted during summer 2002 to define an expected range of nitrate and orthophosphate concentrations during low-flow conditions. Although agricultural production in the region is uniformly intensive, nitrate concentrations during the stream reconnaissance ranged from (0.1 to 6.2 mg/L as nitrogen and orthophosphate concentrations ranged from, 02 to 6.3 mg/L as orthophosphate. During summer 2003, water chemistry, stream and riparian habitat, algal and macroinvertebrate communities, and stream metabolism will be sampled at 28 streams in central Nebraska, as well as in other agricultural regions of the United States.