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Steven PowersAdvisor: Dr. Emily Stanley Contact Information: Research Interests. Ecosystem Effects of Dam Removal: the Role of Nutrients and Sediment Retention of nutrient and sediment pulses in aquatic ecosystems Traditional studies of nutrient and sediment retention quantify processes during steady-state conditions, when ambient concentrations are low. Consequently, there is a limited understanding of the uptake and fate of materials pulses despite the fact that a large proportion of annual loads may be delivered to streams in pulses including, but not limited to, floods. For example, we have observed large pulses (>5-fold ambient concentrations) of soluble phosphorus associated with minor rain events that did not measurably alter discharge in Big Spring Creek, a Wisconsin stream in an agriculturally-dominated watershed. In light of these insights, we examined nutrient and sediment pulses with event sampling and experimental releases. Sediment plumes were found to substantially bias measurements of nutrient uptake, and in low gradient systems, propagated over relatively short distances before settling. However, nutrient pulses traveled far. With nutrient retention metrics, we quantified the ability of streams to mitigate pulses and found that although measurable net retention of phosphorus occurred consistently across streams subjected to pulses, the ability of lotic systems to remove phosphorus during pulse events is limited.
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