LOW STREAM-FLOW MEASUREMENT AND STREAM CO2 EMISSION CALCULATIONS, KONZA PRAIRIE LTER SITE, NORTHEASTERN KANSAS, USA

Accurate measurements of low stream flow are important for characterizing a wide spectrum of stream-discharge related parameters, such as watershed water balance, nutrient export, and CO₂ flux. Stream-flow measurement in remote areas or at research sites requires equipment that is portable, has minimal power requirements, and is not disruptive to the stream. For use in such settings, we constructed a pitot tube for low-velocity streamflow (PLVS), calibrating it in the laboratory against known water velocities. Calibration is required because the PLVS does not perform ideally, possibly because of friction between water and the glass of the pitot tube. We used the PLVS to measure stream velocities at the Konza Prairie Long-Term Ecological Research Site and Biological Station, an unplowed, tallgrass prairie in northeastern Kansas. In an upland watershed, we successfully measured stream velocities at two sites along a single stream in early August and mid November, 2008; velocities ranged from 0.012 to 0.64 m sec^-1. We also measured stream depths, cross-section lengths, and water pH and specific conductance, and collected filtered water samples for further laboratory analysis. Using the velocities, water depth and cross-section length, we calculated stream discharge. Using the change in water chemistry and discharge between the two sites, we determined the net carbon emissions from the stream to be about 3.2 (early August) to 1.3 (mid November) Mg C km^-2 yr^-1 (million grams of carbon per square kilometer per year). We propose that the PLVS is an easily manufactured, accurate and convenient tool for measuring low stream velocities.