Land-use effects on water quality of a first-order stream in the Ozark Highlands, mid-southern United States

Urban and agricultural land uses can alter the natural hydrologic conditions of streams and rivers and often degrade water quality. In the Ozark Highlands of the mid-southern United States, the climate, topography, soil properties, karst limestone geology, agricultural practices and rapid urbanization make water quality of particular concern due to the increased potential for water quality degradation by contaminant leaching to groundwater and runoff to surface waters. The objective of this study was to evaluate the effects of season (i.e. dry/cool and wet/warm) and riparian land use (i.e. urban, grazed pasture, ungrazed pasture, wetland, cultivated agriculture and grassland) on surface water quality in a first-order stream within a diverse agricultural watershed in the Ozark Highlands. Water samples were collected twice a month within each land use during base-flow conditions from October 2006 through October 2007. Samples were also collected periodically during storm-flow conditions from October 2006 through December 2007. The greatest in-stream pH was adjacent to the grazed pasture. In-stream NO₃-N concentrations were greatest adjacent to the cultivated agriculture and grassland during the dry/cool season (i.e. October 2006 to March 2007) and averaged 2.67mgL^-1. In-stream soluble reactive P (SRP) concentrations were greatest adjacent to the grassland during the wet/warm season (i.e. April 2007 to October 2007) and averaged 0.81mgL^-1. Concentrations of SRP, K, Mg and Zn were greater during storm- than base-flow conditions and in-stream As concentrations frequently exceeded 0.01mgL^-1. Discharge and in-stream NH₄-N concentrations were unaffected by land use or season and averaged 0.003m³s^-1 and 0.10mgL^-1, respectively, across all land uses and seasons. Results of this study clearly demonstrate the significant effect of adjacent land use on in-stream water quality of a first-order stream in a diverse agricultural watershed and highlight the importance of managing upstream land use in order to regulate downstream water quality.