Intrastream variability in solute transport: Hydrologic and geomorphic controls on solute retention
Intrastream variability in solute transport: Hydrologic and geomorphic controls on solute retention
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溶质输送的河内变化：水文和地貌对溶质滞留的控制
DOI：
10.1029/2012jf002455
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
R. Schumer
中科院分区：
文献类型：
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作者：
S. Patil;T. Covino;A. Packman;B. McGlynn;J. Drummond;R. Payn;R. Schumer
水文波动和地貌的非均质性预计会在河流中的溶质运移中产生很大的变异性。然而，由于大多数河流的溶质注入数据有限，这种可变性还没有得到充分的探索。在这里，我们分析了沿着斯特林格溪的81条示踪剂注入穿透曲线(BTC)，这是蒙大拿州5.5km2的一个 分水岭。在一条2600 m的河道中，对27个河段进行了三种基流条件下的BTC测量。上游(第一个1400 m)的BTC具有后退的尾部，坡度较浅，表明溶质保留率较高。相反，下游河段(1 400~2 600 m)的BTC具有较陡峭的后退尾部，表明相对于上游河段，溶质保留率较低。BTC尾矿沿河道的差异与河道形态和基岩地质的变化相吻合。具体地说，河道坡度从上游的5~6%增加到下游的9%，河道弯曲度从上游的最大1.32下降到下游的1.02，下伏基岩由砂岩(上游)变为花岗片麻岩(下游)。重要的是，只有在两个最低的基流条件下，才能明显地观察到BTC尾部的流内差异。BTC尾坡的空间变异性在低流量时对局部流量的变化最敏感，在高流量时对河道弯曲度的变化最敏感。BTC尾坡在上游随局部流量和流速的变化而变化，而在下游不随流量和流速变化。这些结果表明，河道形态和溶质滞留之间的局部相互作用随着水文条件的不同而不同，并且在较高的水流流量下，溶质滞留变得更加均匀。
Hydrologic fluctuations and geomorphic heterogeneity are expected to produce substantial variability in solute transport within rivers. However, this variability has not been sufficiently explored due to the limited availability of solute injection data in most rivers. Here, we analyzed 81 tracer injection breakthrough curves (BTCs) along Stringer Creek, a 5.5 km2 watershed in Montana. BTC measurements were obtained for three baseflow conditions at 27 reaches along a 2600 m stream channel. BTCs in upstream reaches (first 1400 m) had receding tails with shallow slopes, indicating high solute retention. Conversely, BTCs in downstream reaches (1400 to 2600 m) had receding tails with steeper slopes, indicating low solute retention relative to upstream reaches. Difference in BTC tails along the stream channel coincided with changes in channel morphology and bedrock geology. Specifically, channel slope increases from 5–6% (upstream) to 9% (downstream), channel sinuosity decreases from a maximum of 1.32 (upstream) to 1.02 (downstream), and the underlying bedrock changes from sandstone (upstream) to granite‐gneiss (downstream). Importantly, intrastream differences in BTC tails were distinctly observable only during the two lowest baseflow conditions. Spatial variability of BTC tail‐slopes was most sensitive to changes in local discharge at low flow, and to changes in channel sinuosity at high flow. BTC tail‐slopes varied temporally with local discharge and velocity at upstream reaches, but not at downstream reaches. These results suggest that local interactions between channel morphology and solute retention vary with hydrologic conditions, and that solute retention becomes more homogeneous at higher stream discharge.