NERC Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.
STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX11 0QX, UK.
Sci Total Environ. 2017 Jan 1;575:496-512. doi: 10.1016/j.scitotenv.2016.08.201. Epub 2016 Oct 19.
River water-quality studies rarely measure dissolved inorganic carbon (DIC) routinely, and there is a gap in our knowledge of the contributions of DIC to aquatic carbon fluxes and cycling processes. Here, we present the THINCARB model (THermodynamic modelling of INorganic CARBon), which uses widely-measured determinands (pH, alkalinity and temperature) to calculate DIC concentrations, speciation (bicarbonate, HCO; carbonate, CO; and dissolved carbon dioxide, HCO) and excess partial pressures of carbon dioxide (EpCO) in freshwaters. If calcium concentration measurements are available, THINCARB also calculates calcite saturation. THINCARB was applied to the 39-year Harmonised Monitoring Scheme (HMS) dataset, encompassing all the major British rivers discharging to the coastal zone. Model outputs were combined with the HMS dissolved organic carbon (DOC) datasets, and with spatial land use, geology, digital elevation and hydrological datasets. We provide a first national-scale evaluation of: the spatial and temporal variability in DIC concentrations and fluxes in British rivers; the contributions of DIC and DOC to total dissolved carbon (TDC); and the contributions to DIC from HCO and CO from weathering sources and HCO from microbial respiration. DIC accounted for >50% of TDC concentrations in 87% of the HMS samples. In the seven largest British rivers, DIC accounted for an average of 80% of the TDC flux (ranging from 57% in the upland River Tay, to 91% in the lowland River Thames). DIC fluxes exceeded DOC fluxes, even under high-flow conditions, including in the Rivers Tay and Tweed, draining upland peaty catchments. Given that particulate organic carbon fluxes from UK rivers are consistently lower than DOC fluxes, DIC fluxes are therefore also the major source of total carbon fluxes to the coastal zone. These results demonstrate the importance of accounting for DIC concentrations and fluxes for quantifying carbon transfers from land, via rivers, to the coastal zone.
河流水质研究很少常规测量溶解无机碳（DIC），我们对 DIC 对水生碳通量和循环过程的贡献知之甚少。在这里，我们介绍了 THINCARB 模型（THermodynamic modelling of INorganic CARBon），该模型使用广泛测量的决定因素（pH 值、碱度和温度）来计算淡水的 DIC 浓度、形态（碳酸氢盐，HCO；碳酸盐，CO；和溶解二氧化碳，HCO）和过量二氧化碳分压（EpCO）。如果有钙离子浓度测量值，THINCARB 还会计算方解石饱和度。THINCARB 应用于 39 年的协调监测计划（HMS）数据集，涵盖了所有向沿海地区排放的英国主要河流。模型输出与 HMS 溶解有机碳（DOC）数据集以及空间土地利用、地质、数字高程和水文数据集相结合。我们首次对英国河流中 DIC 浓度和通量的时空变化、DIC 和 DOC 对总溶解碳（TDC）的贡献以及风化源和微生物呼吸产生的 HCO 和 CO 对 DIC 的贡献进行了全国范围内的评估。在 HMS 的 87%的样本中，DIC 占 TDC 浓度的 50%以上。在英国的七大河流中，DIC 平均占 TDC 通量的 80%（从高地河流泰河的 57%到低地河流泰晤士河的 91%）。即使在高流量条件下，DIC 通量也超过了 DOC 通量，包括在排水高地泥炭流域的泰河和特威德河。鉴于英国河流的颗粒有机碳通量始终低于 DOC 通量，因此 DIC 通量也是向沿海地区输送总碳通量的主要来源。这些结果表明，为了量化从陆地通过河流向沿海地区输送的碳转移，考虑 DIC 浓度和通量非常重要。
