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Tracing subsurface water flowpaths by means of dissolved Ba/Sr, Ca/Sr and 87Sr/86Sr ratios
| Content Provider | Semantic Scholar |
|---|---|
| Author | Land, Maud |
| Copyright Year | 1998 |
| Abstract | When studying field weathering processes and catchment mass balances it is of critical importance to know which sources of surface water are the most important. However, despite numerous studies, the origin of stream water is still a matter of controversy. Different runoff mechanisms include Horton overland flow, saturation overland flow, and subsurface flow. The subsurface flow may be dominated either by displacement of old water, or by rapid throughflow emphasizing macropore flow. Stream water during snowmelt or a storm event is often considered a mixture of new water (precipitation) and old water. The old water, or pre-event water, is usually regarded as groundwater. However, recent studies have shown that soil water may also constitute a significant part of the old water component. Both isotopic and chemical tracers have been used in various mixing models in order to trace different water masses. The most frequently used isotopic tracers have been H and O isotopes which provide good information about the new and old water content in a stream, but less information about the subsurface flow paths. The chemical tracers most often employed have been concentrations of various elements. However, in many situations the elemental concentrations in stream water are diluted by precipitation or horton overland flow, which obscures the tracer signals from the subsurface flowpaths. One way to overcome this is to use element ratios as tracers since very dilute components will influence element ratios in a mixture insignificantly compared to components with high cincentrations. Both dissolved and particulate element ratios have been used as tracers in other studies (e.g. N~grel et al., 1993; Ingri and Widerlund, 1994; Ingri et al., 1997; Land and I)hlander, 1997). In this study we show how Ba/Sr and Ca/Sr ratios can be used to resolve the subsurface flow into three different components: soil water, shallow groundwater, and deep groundwater. In an attempt to validate the results Sr isotopes were also employed as a tracer. The idea behind the use of Ba/Sr and Ca/ Sr ratios as tracers is that these elements occur in different minerals with different weathering susceptibility. Usually, Sr substitutes Ca or K, whereas Ba usually substitutes K, and the K-minerals in granitoids are generally more resistant to weathering than the Ca-minerals. As weathering intensity and solution chemistry change along a flow path, the relative importance of different minerals in the weathering process should change. If this is the case, the dissolved element ratios should also change. This study was performed in a relatively small (9.4 km 2) catchi!aent drained by a first order stream. The peak discharge during snowmelt in early May is about 750 1 s -1, while the base-flow discharge during summer is 20-30 1 s -1. The catchment is mainly covered by podzolized till (more than 90 % of the area), classified as typic haplocryod. Bedrock outcrops and mires add up to less than 7 % of the area, and there are no lakes in the catchment. The till, supporting mainly pine and spruce forest, is unsorted and consists mainly of granitic material. It is underlain by a 1.8 Ga granite. The chemical composition of soil water, shallow groundwater and stream water was measured for a period of more than one year, including two snowmelt seasons. In addition a few chemical analysis of precipitatation, throughfall, and deep groundwater were performed. The soil water was sampled by tension lysimeters from four depths: 5 cm (E-horizon), 15 cm (Bsl-horizon), 40 cm (Bs2horizon), and 100 cm (C-horizon). Shallow groundwater and deep groundwater were sampled in recharge areas at the depths of 2.3-5.2 and 20-25, respectively. The Sr isotopic composition was measured in selected soil water, groundwater and stream water samples. |
| Starting Page | 850 |
| Ending Page | 851 |
| Page Count | 2 |
| File Format | PDF HTM / HTML |
| DOI | 10.1180/minmag.1998.62a.2.114 |
| Alternate Webpage(s) | http://www.minersoc.org/pages/Archive-MM/Volume_62A/62a-2-850.pdf |
| Alternate Webpage(s) | https://doi.org/10.1180/minmag.1998.62a.2.114 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
