Macrophyte Influences on Sediment Resuspension and Export in a Shallow Impoundment

ABSTRACT

Sediment resuspension dynamics and discharge of sediment downstream in Marsh Lake (Minnesota) were examined during 1991 and 1992 under a variety of wind conditions. Based on a theoretical wave model, nearly the entire sediment surface area (81–100%) can be disturbed by wave activity at wind velocities as low as 15 km/h blowing from any direction. As an apparent result of dense submersed macrophyte beds that in 1991 covered nearly the entire lake, measured sediment resuspension was much less frequent than expected from wave theory in 1991 than in 1992. Critical thresholds of wind velocity required to resuspend sediment were much higher in 1991 (~ 20 km/h) than in 1992 (~ 12 km/h), resulting in a lower frequency of resuspension events in 1991 (5%) than in 1992 (32%). Discharge of resuspended sediment to downstream Lac Qui Parle Reservoir was much less in 1991 when submersed macrophytes were abundant than in 1992 when macrophytes were absent. These results suggest that the development and maintenance of stands of submersed aquatic macrophytes may be an effective management tool for limiting wind-driven sediment resuspension and sediment discharge in shallow impoundments and lakes.

Key Words:

• resuspension
• sediment
• seston
• shallow reservoirs
• waves
• wind