In situ determination of dissolved organic carbon in freshwaters using a reagentless UV sensor

Reliable, high temporal and spatial resolution data are essential for enhancing our understanding of aquatic dissolved organic carbon (DOC) biogeochemical cycling. This paper describes a novel UV spectrophotometric sensor for the real time, in situ, high resolution (every 30 s) mapping of DOC in freshwaters. The sensor incorporates high resolution, multi-wavelength spectral acquisition (256 channel photodiode array) and a hybrid linear analysis (HLA) curve fitting algorithm. The portable and reagentless in situ UV sensor has a good linear range (0.5-15 mg C L(-1)) and precision (mean RSD 8.5%, n = 7 standards each measured 5 times) and quantitative recoveries were obtained for spiked river water (93.8 +/- 6.2%, n = 35). The DOC field data were in good agreement with results from a laboratory high temperature combustion method (t test (p = 0.05) gave P = 0.20 (n = 14), 0.89 (n = 21) and 0.92 (n = 15) for three separate freshwater deployments). These data suggested that solar radiation, coupled with microbial uptake and release, together with the physico-chemical parameters of hydrological flow, temperature and pH were significant drivers of DOC cycling in this ecosystem. Real time data processing provided an immediate data stream for mapping diurnal and/or seasonal DOC cycling. This capability will enhance our understanding of DOC sources, delivery mechanisms and internal cycling and support sustainable catchment management.