CO2 dynamics along Danish lowland streams: water–air gradients, piston velocities and evasion rates
CO2 dynamics along Danish lowland streams: water–air gradients, piston velocities and evasion rates
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DOI：
10.1007/s10533-011-9696-6
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发表时间：
2012-11
期刊：
影响因子：
4
通讯作者：
K. Sand‐Jensen;P. Staehr
中科院分区：
文献类型：
--
作者：
K. Sand‐Jensen;P. Staehr
在丹麦西兰的农业景观中，我们测量了沿着两条20 km长的溪流的8个站的流通室中CO2浓度，并确定了水-气界面的逃逸率和活塞速度。这两条溪流的CO2过饱和度为9-18倍，1 - 3月的日平均值为240和340 μM，6 - 8月的日平均值为130和180 μM。其他6条河流的年CO2中位数为212 μM，4口地下水威尔斯井的年CO2中位数为460 μM，而7个湖泊为弱过饱和（29 μM）。流表面上方的空气浓度接近平均大气条件下，除了在平静的夏夜。活塞速度从0.4到21.6 cm h− 1与水流速度密切相关，从而可以计算整个水流的逃逸率。CO2逃逸率在中游最高（170- 1，200 mmol m− 2 day −1），富CO2土壤水进入快速水流，而在缓慢流动的下游，速率低十倍（25-100 mmol m− 2 day −1）。CO2逃逸主要来源于土壤水CO2的输入。沿沿着两条低地河流的CO2逃逸的变化覆盖了以前报道的亚北极和温带河流的大部分范围。在两个河流集水区的预算中，通过水文循环从土壤中损失的碳是大量的（3.2-5.7 mmol m− 2天−1），主要是通过矿物溶解（69-76%）和有机碳输出（15-23%）形成HCO 3 −消耗的CO2相对于溶解的CO2输出（7-9%）。
We measured CO2concentration and determined evasion rate and piston velocity across the water–air interface in flow-through chambers at eight stations along two 20 km long streams in agricultural landscapes in Zealand, Denmark. Both streams were 9–18-fold supersaturated in CO2with daily means of 240 and 340 μM in January–March and 130 and 180 μM in June–August. Annual CO2medians were 212 μM in six other streams and 460 μM in four groundwater wells, while seven lakes were weakly supersaturated (29 μM). Air concentrations immediately above stream surfaces were close to mean atmospheric conditions except during calm summer nights. Piston velocity from 0.4 to 21.6 cm h−1was closely related to current velocity permitting calculation of evasion rates for entire streams. CO2evasion rates were highest in midstream reaches (170–1,200 mmol m−2day−1) where CO2-rich soil water entered fast stream flow, while rates were tenfold lower (25–100 mmol m−2day−1) in slow-flowing lower reaches. CO2evasion mainly derived from the input of CO2in soil water. The variability of CO2evasion along the two lowland streams covered much of the range in sub-Arctic and temperate streams reported previously. In budgets for the two stream catchments, loss of carbon from soils via the hydrological cycle was substantial (3.2–5.7 mmol m−2day−1) and dominated by CO2consumed to form HCO3−by mineral dissolution (69–76%) and export of organic carbon (15–23%) relative to dissolved CO2export (7–9%).