Identification of geographic runoff sources in a data sparse region: hydrological processes and the limitations of tracer‐based approaches

Abstract

Abstract:There exists a growing need to improve our understanding of catchment processes on larger scales. This need is especially enhanced in rapidly developing countries such as China where the turnover of traditionally used land to urbanized and industrialized areas influences water resources. In this study, we chose a multi-tracer approach in a large, ungauged basin in Inner Mongolia to elucidate the processes that generate stream flow. We applied end member mixing analysis (EMMA) to identify and quantify the major runoff generating sources in a three end member system. Stream water and a set of eight possible end members were sampled throughout three consecutive vegetation periods. Samples were analysed with an inductively coupled plasma-mass spectrometry (ICP-MS) and an ion chromatograph (IC) for a suite of 33 solutes including 24 cations and 7 anions. We determined that seven tracers exhibited conservative behaviour, they were Li, Rb, Sr, Na, Mg, Cl and electrical conductivity (EC). Stable water isotopes (υD and υ 18 O) highlight differences between the end members. Our results indicate strong interannual variability of end member composition and contribution between the 3 years. We were able to identify shallow groundwater aquifers as important runoff generating sources in some years and deeper groundwater aquifers in other years which vary in rainfall and discharge. A shallow sand dune aquifer which covers a significant part of the area plays an important role in storing and contributing water to the river. Our results also suggest that the major runoff generating source in the dryer year has not been identified yet. Our results prompt us to focus future work on understanding interannual changes in end member contribution especially in semi-arid regions.

Contributing sources to baseflow in pre‐alpine headwaters using spatial snapshot sampling

“…design most sampling locations, including sites with high wetland percentage, had high Ca and low DOC concentrations and we concluded that their streamwater originated from runoff sources other than wetlands. The DOC concentrations in this study were in the same range as at other headwaters (James and Roulet, 2006;Likens and Buso, 2006;Tetzlaff and Soulsby, 2008); but one order of magnitude lower compared to Swedish headwaters (Temnerud et al, 2007).Bivariate solute diagrams and multivariate principal component analysis are established methods to distinguish between different spatiotemporal patterns of streamwater composition and characterise specific geographic water sources of different catchments in relation to their multiple variables (Barthold et al, 2010;Christophersen and Hooper, 1992;Fröhlich et al, 2008). In our study the bivariate representation of Ca and DOC was useful to identify three runoff sources: deep groundwater from springs, shallow groundwater and wetlands sampled in the drainage ditch of WS04.…”

“…Bivariate solute diagrams and multivariate principal component analysis are established methods to distinguish between different spatiotemporal patterns of streamwater composition and characterise specific geographic water sources of different catchments in relation to their multiple variables (Barthold et al, 2010;Christophersen and Hooper, 1992;Fröhlich et al, 2008). In our study the bivariate representation of Ca and DOC was useful to identify three runoff sources: deep groundwater from springs, shallow groundwater and wetlands sampled in the drainage ditch of WS04.…”

“…To predict potential changes, it is important to understand water sources and transit times along the various flow paths. Tracer approaches are commonly used to study sources and flow paths of water (Barthold et al, 2010;Christophersen and Hooper, 1992;Hrachowitz et al, 2011;Inamdar et al, 2013;Lu, 2014;Penna et al, 2014a;Rodgers et al, 2005;Soulsby et al, 2007).…”

“…To predict potential changes, it is important to understand water sources and transit times along the various flow paths. Tracer approaches are commonly used to study sources and flow paths of water (Barthold et al, 2010;Christophersen and Hooper, 1992;Hrachowitz et al, 2011;Inamdar et al, 2013;Lu, 2014; Penna et al, 2014a; Rodgers et al, 2005;Soulsby et al, 2007).Of the different environmental tracers, the isotopes 2 H and 18 O have been found to be especially useful to identify sources of streamflow based on differences in the isotopic composition of the sources, e.g., rainfall and groundwater (Hrachowitz et al, 2011b;Tetzlaff and Soulsby, 2008). Hydrochemical tracers such as Ca or DOC, on the other hand, provide information on flow pathways as the concentrations depend on what the water encounters on its way from rain to stream (Inamdar et al, 2013;James and Roulet, 2006;Likens and Buso, 2006).…”

Characterisation of stable isotopes to identify residence times and runoff components in two meso-scale catchments in the Abay/Upper Blue Nile basin, Ethiopia

“…However, stable isotopes have the potential to provide enormous benefit with respect to hydrological process understanding and sustainable planning of water resource management strategies and policies in such data-scarcs areas (Hrachowitz et al, 2011a). This potential has been demonstrated in numerous other regions worldwide (Kendall and Caldwell, 1998;Kendall and Coplen, 2001;Gibson et al, 2005;Barthold et al, 2010;Kirchner et al, 2010).…”