UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS
Location: Water Quality and Ecology Research
Title: The stream channel incision syndrome and water quality
Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 2009
Publication Date: January 10, 2010
Citation: Shields Jr, F.D., Lizotte Jr, R.E., Knight, S.S., Cooper, C.M., Wilcox, D.L. 2010. The stream channel incision syndrome and water quality. Ecological Engineering 36(1):78-90. DOI:10.1016/j.ecoleng.2009.09.014.
Interpretive Summary: Current federal legislation mandates regulation of stream water quality to meet concentration targets referred to as “total maximum daily loads,” and remedial strategies for nonattaining streams draining agricultural and mixed-cover watersheds usually focus on management on nonpoint source pollution. However, many processes responsible for degradation of stream biological resources are tightly linked to channel erosion and only indirectly to land use. Water quality measurements were collected from five years from a severely eroded stream and a nearby stable stream in northern Mississippi. Prior research had documented superior fish populations and habitat in the stable stream. Findings showed that water quality was inferior in the eroding stream, and that water quality degradation was related to the flashy hydrology typical of the straightened, enlarged channel. Although the stable stream received runoff from an urbanizing watershed, it was apparently protected by forested floodplains and wetlands. These findings will assist land use managers in developing realistic goals and effective management plans for stream water quality.
Watershed development often triggers channel incision, which accounts for 60-90% of sediments leaving many disturbed watersheds. Impacts of such incision on water quality processes and the implication of such impairment on stream biota are relevant to issues associated with establishing total maximum daily loads. Discharge, basic physical parameters, solids, nutrients (nitrogen and phosphorus), chlorophyll and bacteria were monitored for five years at two sites along a stream in a mixed cover watershed characterized by rapid incision of the entire channel network. Concurrent data were collected from two sites on a nearby stream draining a watershed of similar size and cultivation intensity, but without widespread incision. The second stream was impacted by watershed urbanization, but a buffer zone of floodplain wetlands was located between the study reach and development. Data sets describing physical aquatic habitat and fish fauna of each stream were available from other studies. Results showed that the incised stream was characterized by much flashier hydrology and had levels of turbidity and solids that were two to three times higher than the nonincised, urbanizing stream. Total phosphorus, total Kjeldahl N and chlorophyll a concentrations were significantly higher in the incised stream, while nitrate was significantly greater in the nonincised, urbanizing stream (p < 0.02). Physical aquatic habitat and fish populations in the nonincised urbanizing stream were superior, as it supported almost twice as many species and yielded more than four times as much biomass per unit of effort. These results suggest that degradation of physical habitat and perturbation of stream hydrology by channel incision contribute to a syndrome of ecological degradation. Ecological engineering of stream corridors must focus at least as much energy on mediating hydrologic perturbations as pollutant loadings.