Submitted to: International Soil and Water Conservation Conference
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2011
Publication Date: 7/18/2011
Citation: Steiner, J.L., Franklin, D.H., Moriasi, D.N., Duke, S.E., Starks, P.J. 2011. Water quality in the Fort Cobb watershed, USA: spatial and temporal patters of sediment concentration in streams [abstract]. International Soil and Water Conservation Conference, July 17-20, 2011, Washington, D.C. Available on: www.swcs.org/en/conferences/2011_annual_conference/.
Interpretive Summary: Abstract Only.
Technical Abstract: Agricultural watersheds often exhibit impaired water quality due to sediment, nutrients, and associated contaminants. It is difficult to extend field-scale knowledge about agricultural impacts on water quality to watershed-scale because of many complex interactions within the landscape. This research related climate, geographic, physiographic, and management effects to spatial and temporal patterns of sediment within the Fort Cobb Reservoir watershed in southwestern Oklahoma. Water samples were collected bi-weekly from 2005-2009 at 15 sites and analyzed for suspended sediment. Climate was characterized using stream flow, temperature, and distributed precipitation data. Topographic, soil, geologic, and land use data were computed for each contributing area. Spatial autocorrelation was evaluated and regression trees developed for dry and wet phases and presence or absence of spatial autocorrelation. Relationships of sediment to climate and watershed characteristics were stronger when spatial autocorrelation was significant than when it was not, and the wet phase produced stronger correlations than the dry phase. Precipitation-related variables were the most frequently significant. Percent crop land and irrigation in the contributing area were not significantly related to sediment patterns. Negative correlation of total dissolved solids with sediment during the wet phase may indicate the influence of soil and geologic properties on water chemistry as more water flowed through the profile. Significant management-responsive variables were stream channel stability and soil organic carbon (SOC) in surface layer. In the wet phase, degraded stream channels were positively related to sediment when spatial autocorrelation was not present; indicating that increased conservation focus along the channel and riparian areas could be beneficial. Positive correlation of SOC to sediment could be an artifact of the negative relationship between sand content and SOC. To understand agricultural management and conservation effects on water quality at a watershed scale, it is critical to consider prevailing climate conditions and the basic geophysical characteristics of the watershed.