Events

Mike Limm
NCED Postdoctoral Associate
St. Anthony Falls Laboratory

ABSTRACT

Disturbance by flooding can dramatically disrupt population and community structure in stream ecosystems. If strongly interacting species are affected, energy and nutrient dynamics may be altered. In a Northern California stream we quantify the impact of the limnephilid caddisfly Dicosmoecus gilvipes on periphyton structure and ecosystem processes, quantify how Dicosmoecus vulnerability to disturbance can vary with ontogeny, and investigate how their case design influences fluid flow resistance.

Dicosmoecus larvae reduced periphyton accrual, gross primary productivity, and ammonium uptake, and their impact persisted 46 days after the larvae were removed. Critical fluid flow threshold (sufficient to dislodge larvae from substrates) increased with larval size, as did larval flow velocity preference. The lateral extensions Dicosmoecus build on their case provided stability against overturning in fast flow and may improve their ability to forage efficiently in turbulent flow conditions. Our results suggest any change in flood timing, frequency, and/or magnitude due to river regulation or climate conditions may impact Dicosmoecus populations and alter ecosystem processes in Northern California streams.

Nicholas Olson
M.S. Candidate
Department of Civil Engineering,
UMN Advisors: John Gulliver and John Nieber

ABSTRACT A field experiment was conducted to determine the effectiveness of remediation techniques to alleviate soil compaction and increase infiltration. Deep tillage and compost addition are two techniques commonly used in agricultural practices to reduce the level of soil compaction. These techniques were implemented on three sites in the metropolitan area. Each site was divided into three plots: tilled, tilled with compost addition, and a control plot for comparison. To determine the effectiveness of each remediation technique, before and after measurements of saturated hydraulic conductivity (Ksat), soil bulk density, and soil strength were used to assess the level of compaction. Deep tillage was effective at reducing the soil strength. Soil strength was approximately half that of the control plot in the first six inches of soil. However, tilling did not significantly improve the bulk density of the soil. At two of the sites, tilling was ineffective at improving the infiltration capacity of the soil. Tilling may have damaged natural pathways in the soils, thus reducing the permeability. Tilling was effective at remediating the soil at one site, which may not have had as extensive a network of natural pathways as the previous two sites. The geometric mean of Ksat was 2.1 to 2.3 times that of the control plot. Compost addition was the most effective soil remediation technique. Similar reductions in soil strength were found in the tilled plot. Soil bulk densities on the compost plots were 18-37% lower than the control plots. The infiltration capacity of the soil was improved. The geometric mean of Ksat on the compost plots was 2.7 to 5.7 times that of the control plots. The results of these findings will be useful in revising stormwater Best Management Practices to include guidelines on soil compaction prevention and remediation of compacted sites.