Central Nebraska Basins Study Unit

Effects of Nutrient Enrichment on Stream Ecosystems

The goal of a new NAWQA study for Cycle II is to determine how biological communities and processes respond to varying levels of nutrient enrichment among agricultural streams from contrasting environmental settings. The Central Nebraska Basins study area was one of five NAWQA study units selected to represent different environmental settings influenced by agricultural activities, with three additional study units beginning field work in fiscal year 2005. The study has four objectives:

• Determine how biological communities are related to nutrient conditions in streams.
• Evaluate the relations between nutrients, algae, and stream metabolism, or the processes whereby carbon dioxide and nutrients are consumed by algae-producing oxygen, and algal decomposition consumes oxygen and recycles nutrients.
• Determine how algae, stream metabolism, and nutrient dynamics are interrelated within short lengths of a few representative streams.
• Determine the extent to which relations between biological communities and nutrient conditions can be generalized to larger regions by using analyses of geographic factors.

For the Nebraska component of the study, a list of potential study sites was compiled and their respective drainage areas were characterized using geographic data. Following field reconnaissance sampling, an integrated nutrient index was constructed. Study sites were selected early in 2003 to characterize the range of the nutrients within a single nutrient region. The selected sites represented as narrow a range of stream size, type, and hydrologic setting as is practical for that region.

Data for assessments of water quality, algae, invertebrates, and physical habitat were collected at 28 Nebraska streams during summer 2003. At each sampling site, water-quality, invertebrate and algal community structure and physical habitat parameters were assessed. At a subset of 20 sites measurements of specific conductance, pH, water temperature, and dissolved oxygen were collected at 5- to 15-minute intervals for a 48-hour period to allow the calculation of stream metabolism.

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