MIXING GEOMORPHOLOGY AND ECOLOGY: RELATIONSHIPS BETWEEN FISH POPULATIONS AND STREAM BED PERMEABILITY

Increased sediment loads have contributed to a decline in population of gravel-spawning fishes throughout agricultural areas of eastern United States. Interest in the causes and effects of this decline is linking biologists with geomorphologists to create the hybrid field of biogeomorphology. The link between spawning success rates and gravel permeability has been experimentally studied since the 1960's. Gravels with high permeability have been shown to have higher egg and fry survival rates for many gravel-spawning fishes. Active monitoring of gravel permeability is only recently being explored. The permeameter is an in situ tool that can be used to accurately measure streambed gravel permeability. We used this instrument to test the permeability of spawning gravels on Smith Creek (Rockingham County, Virginia), a stream heavily impacted by sediment from poor agricultural practices (ie overgrazing, denuded riparian vegetation) over the last one-hundred years. A major watershed improvement project is just beginning on Smith Creek including riparian revegetation and cattle fencing. Changes in gravel permeability in Smith Creek after restoration efforts will provide useful information on the link between the biological health (populations of gravel spawning fishes) and geomorphological conditions of Smith Creek. This project provides a benchmark for monitoring the ties between changes in gravel-spawning fish populations and gravel permeability. The occurrence of a recent (June 26, 2006) 100-year magnitude flood on Smith Creek provides a unique opportunity to begin benchmark permeability measurements using the permeameter at a time when the gravels will likely be cleanest.