Nutrient Spiraling Experiments as Evidence of Stream Structure-Function Relationships

Gavin Downs, Purdue University

Abstract

Geographical and stream network context shape how streams and rivers form, which in turn affects ecological functions. When the landscape becomes managed by human activity such as urbanization and agricultural development, streams are negatively impacted through excessive erosion and elevated nutrient loading. Environmental managers attempt to mend these symptoms by reconfiguring stream channels to mimic the geomorphic structure of natural waterways. However, the relationship between structure and function has not been clearly identified. Using a meta-analysis approach, I analyzed studies from a mosaic of stream conditions that related stream structure to biological functions using nutrient addition experiments. I found that nitrate uptake velocity was negatively correlated with NO3:SRP ratios suggesting that uptake increased under P-rich conditions. Nitrate uptake also was optimized at intermediate transient storage metric exchange rate values. Phosphorus uptake velocity was optimized in intermediate sized streams. Engineered channels in restored streams mimicked net stream storage, but this was mainly storage in deep surface pools. This resulted in no significant difference in nitrate uptake compared to degraded streams. However, phosphate uptake was significantly increased back to natural stream condition levels. A case study of a restoration project confirmed these results. Further research should focus on methods that differentiate smaller scale structures in streams to further structure-function relationships.

Degree

M.S.A.B.E.

Advisors

McMillan, Purdue University.

Subject Area

Agricultural engineering

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