Consider a virgin terrain with highly variable lithology just exposed to the geological agents of weathering. Here, local lithology controls the development of runnel (Dodge-Wan and Nagarajan, 2016) and its progression into a stream and then a river. The weathering pattern guided by local climate, the intensity of weathering, aspect and gradient that drives rainwater to pass towards downhill, are some of the factors that influence the development of the drainage network in a river basin. Thus, highly variable lithology results in the formation of small streams, and that is how we observe considerable geochemical and provenance heterogeneity in Taiwanese rivers (Deng et al., 2019). The presence of a large number of small streams in an area may represent local lithological heterogeneity. For the same reason, in geochemical surveys, it is very much essential to collect sediment samples from low-order streams apart from the river where these streams deliver their water and sediment. If these streams have a distinct isotopic signature of a conservative trace element in its water column, then it might be possible to estimate the contribution of freshwater from each stream into the river. Such a technique might be useful where stream gauges are not available.
References
Dodge-Wan, D., Nagarajan, R., 2016. Runnel development on granitic boulders on the foothills of Mount Kinabalu (Pinosuk Gravel Formation, Sabah, N Borneo). J. Mt. Sci. 13, 46–58. https://doi.org/10.1007/s11629-014-3169-z
Deng, K., Yang, S., Bi, L., Chang, Y.-P., Su, N., Frings, P., Xie, X., 2019. Small dynamic mountainous rivers in Taiwan exhibit large sedimentary geochemical and provenance heterogeneity over multi-spatial scales. Earth and Planetary Science Letters 505, 96–109. https://doi.org/10.1016/j.epsl.2018.10.012
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