Stream-watershed relationships in the Missouri Ozark Plateau province
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Land use was the most influential watershed characteristic determining stream chemical concentrations of 23 streams that drained watersheds with different land uses, geologic bedrock, and soil associations in the Missouri Ozark Plateau Province. Streams were investigated from June 1979 through September 1980 and compared to determine relationships among watersheds, stream water chemistry, and algal biomass. Three streams were monitored for each of the following single land use, non-point watersheds--urban, pasture, and forest, the dominant land uses in the Ozarks, to determine how land use affects stream chemical concentrations. Streams draining non-point source, multiple land use watersheds were compared to determine how several land use practices on specific watersheds influence the chemical and algal composition of streams. Streams draining watersheds with urban land use had the highest chemical concentrations, and streams draining forest watersheds the lowest. Streams draining pasture watersheds were intermediate, more closely resembling forest streams in overall salinity, and urban streams in nitrogen and phosphorus. The variables: NO3-N, SO4^=, TP, NA+, Ca++, Cl^-, TN, NO2-N, and KSP were most influenced by land use and distinctly characterized land use by differences in concentration. Significant positive correlations were determined between urban and pasture areas on multiple land use watersheds and concentrations of plant nutrients and salinity in the stream. Human populations and animal units were features of urban and pasture areas that influenced stream chemical concentrations. Stream variable concentrations increase along a continuum in response to increased urban or pasture areas. In contrast, significant negative correlations were found between the forest area on a watershed and concentrations of most measured variables. Algal biomass in these streams was governed by plant nutrients, streamflow, and morphological characteristics of the stream. Benthic algal biomass was governed by various combinations of TP, NO3-N, NH3-N, current velocity, stream length, and stream gradient depending upon season. Planktonic biomass was governed by TP and NH3-N. Significant correlations between benthic algal biomass upstream from a sampling point and average downstream export of planktonic chlorophyll a indicate that planktonic algae are derived from benthic populations on the streambed. Given appropriate conditions, non-point sources and point-sources can have the same effect on stream algal biomass. The influence from non-point sources on watersheds to stream water chemistry and algal biomass can be reduced in complexity and the effects quantified. Prediction of stream chemical concentrations and algal biomass from watershed land use can be used to assess changes in streams that may occur as the result of watershed alterations.
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