INFERRING HYDROLOGICAL PROCESSES IN A TEMPERATE BASIN USING ISOTOPIC AND GEOCHEMICAL HYDROGRAPH SEPARATION: A RE-EVALUATION
✍ Scribed by J. M. BUTTLE; D. L. PETERS
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 278 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0885-6087
No coin nor oath required. For personal study only.
✦ Synopsis
Simultaneous monitoring of conservative and non-conservative tracers in stream¯ow oers a valuable means of obtaining information on the age and ¯ow paths of water reaching the basin outlet. Previous studies of storm¯ow generation in a small forested basin on the Canadian Shield used isotopic (IHS) and geochemical hydrograph separations (GHS) to infer that some event water during snowmelt reaches the stream via subsurface pathways, and that surface water runo is generated by direct precipitation on to saturated areas (DPSA) in the stream valley. These hypotheses were tested for rainfall inputs using simultaneous IHS ( 18 O) and GHS (dissolved silica) of basin storm¯ow, supplemented by hydrochemical and hydrometric data from through¯ow troughs installed on basin slopes. Comparison of pre-event and subsurface water hydrographs did not provide conclusive evidence for subsurface movement of event water to the stream, owing to the appreciable uncertainty associated with the hydrograph separations. However, IHSs of runo at the soil±bedrock interface on basin slopes indicated that event water comprised 25±50% of total runo from areas with deep soil cover, and that these contributions supplied event water ¯ux from the basin in excess of that attributable to DPSA. The surface water component of storm¯ow estimated from the GHS was also largely the result of DPSA. GHS assumes that dissolved silica is rapidly and uniformly taken up by water in®ltrating the soil and that water moving via surface pathways retains the low dissolved silica level of rainfall; however, neither assumption was supported by the hillslope results. Instead, results suggest that the observed depression of silica levels in basin storm¯ow previously attributed to dilution by DPSA was partly a function of transport of dilute event water to the channel via preferential pathways. Implications of these results for the general use of simultaneous IHS and GHS to infer hydrological processes are discussed.