| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4436158 | Applied Geochemistry | 2011 | 9 Pages |
The Nandong Underground River System (NURS) is located in a typical karst area dominated by agriculture in SE Yunnan Province, China. Groundwater plays an important role in the social and economical development in the area. The effects of human activities (agriculture and sewage effluents) on the Sr isotope geochemistry were investigated in the NURS. Seventy-two representative groundwater samples, which were collected from different aquifers (calcite and dolomite), under varying land-use types, both in summer and winter, showed significant spatial differences and slight seasonal variations in Sr concentrations and 87Sr/86Sr ratios. Agricultural fertilizers and sewage effluents significantly modified the natural 87Sr/86Sr ratios signature of groundwater that was otherwise dominated by water–rock interaction. Three major sources of Sr could be distinguished by 87Sr/86Sr ratios and Sr concentrations in karst groundwater. Two sources of Sr are the Triassic calcite and dolomite aquifers, where waters have low Sr concentrations (0.1–0.2 mg/L) and low 87Sr/86Sr ratios (0.7075–0.7080 and 0.7080–0.7100, respectively); the third source is anthropogenic Sr from agricultural fertilizers and sewage effluents with waters affected having radiogenic 87Sr/86Sr ratios (0.7080–0.8352 for agricultural fertilizers and 0.7080–0.7200 for sewage effluents, respectively), with higher Sr concentrations (0.24–0.51 mg/L). Due to the overlapping 87Sr/86Sr ratios, it is difficult to distinguish the sources of Sr in groundwater samples contaminated by agricultural fertilizers or sewage effluents based only on their 87Sr/86Sr ratios. However, 87Sr/86Sr ratios do provide key information for natural and anthropogenic sources in karst groundwater.
Research highlights► Spatio-temporal variations of Sr concentrations and Sr isotopic composition of groundwater were investigated in a karst underground river system. ► Agricultural fertilizers and sewage effluents significantly modified the natural Sr isotopic signature of karst groundwater. ► Sr in the carbonate aquifers was relatively non-radiogenic, with low Sr concentrations, while anthropogenic Sr correlated with agricultural fertilizers and sewage effluents was relatively radiogenic, with higher Sr concentrations. ► 87Sr/86Sr ratios can provide key information for natural and anthropogenic sources in karst groundwater.
