Dawson J J, Bakewell C, Billett M F
Department of Plant & Soil Science, University of Aberdeen, UK.
Sci Total Environ. 2001 Jan 29;265(1-3):153-67. doi: 10.1016/s0048-9697(00)00656-2.
Data on small-scale spatial variations in instantaneous fluxes and concentrations of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and free carbon dioxide (CO2) are presented for a small acidic headwater stream in NE Scotland. Chloride is used as a conservative element to estimate additional, diffuse inputs of water into the main stem of the stream, other than those from tributaries. Downstream changes in instantaneous carbon fluxes were calculated and then used to estimate losses and gains of carbon within the stream system. Dissolved organic carbon concentrations in the stream ranged from 1.19-6.06 mg l(-1) at its source to a maximum of 10.0-25.3 mg l(-1) as the stream passed through deep peats; DOC concentrations then declined in the lower part of the catchment. DIC concentrations were initially low, increased to 1.5-3.0 mg l(-1) and then decreased to 0.1-1.65 mg l(-1) at the lowest site. Free CO2 concentrations increased from 0.35 mg l(-1) at the stream source to 3.30 mg l(-1) as the stream passed through the peat dominated area. Continually high inputs of CO2-rich water (> 6.0 mg l(-1)) from tributaries maintained these high concentrations in the main stem, until approximately 1.74 km downstream, when there was a rapid decline in concentration. Significant changes in DOC, DIC and CO2 fluxes occur over a distance of 2.7 km downstream from the stream source to the catchment outlet. Between 5.64-41.5 mg C s(-1) as DOC and 2.52-16.2 mg C s(-1) as DIC are removed from the water column. Between 6.81 and 19.0 mg C s(-1) as CO2 is lost along the stream length as progressive equilibration with the atmosphere occurs. We estimate that 11.6-17.6% of the total DOC flux is removed from streamwater by in-stream processes. Dissolved inorganic carbon (HCO3- and free CO2) losses are in excess of nine times its measured flux at the outlet of the catchment. These results suggest that in-stream processing of DOC and DIC and outgassing of CO2 are important controls on the spatial variability of carbon fluxes within headwater streams in upland catchments dominated by organic-rich soils.
本文给出了苏格兰东北部一条酸性小源头溪流中溶解有机碳（DOC）、溶解无机碳（DIC）和游离二氧化碳（CO₂）的瞬时通量及浓度的小尺度空间变化数据。氯化物被用作保守元素，以估算除支流外进入溪流干流的额外、分散的水输入量。计算了瞬时碳通量的下游变化，然后用于估算溪流系统内碳的损失和增益。溪流中溶解有机碳浓度在源头处为1.19 - 6.06 mg l⁻¹，当溪流流经深层泥炭地时，最高可达10.0 - 25.3 mg l⁻¹；DOC浓度随后在集水区下游部分下降。DIC浓度最初较低，增加到1.5 - 3.0 mg l⁻¹，然后在最低处降至0.1 - 1.65 mg l⁻¹。游离CO₂浓度从溪流源头的0.35 mg l⁻¹增加到溪流流经泥炭主导区域时的3.30 mg l⁻¹。来自支流的富含CO₂的水（> 6.0 mg l⁻¹）持续高输入维持了干流中的高浓度，直到下游约1.74 km处，浓度迅速下降。从溪流源头到集水区出口的下游2.7 km距离内，DOC、DIC和CO₂通量发生了显著变化。水柱中去除的DOC为5.64 - 41.5 mg C s⁻¹，DIC为2.52 - 16.2 mg C s⁻¹。随着与大气的逐步平衡，沿溪流长度损失的CO₂为6.81 - 19.0 mg C s⁻¹。我们估计，溪流过程从溪水中去除了总DOC通量的11.6 - 17.6%。溶解无机碳（HCO₃⁻和游离CO₂）的损失超过了其在集水区出口处测量通量的九倍。这些结果表明，DOC和DIC的溪流处理以及CO₂的脱气是对以富含有机质土壤为主的高地集水区源头溪流中碳通量空间变异性的重要控制因素。
