| Popis: |
Determination of the 87Sr/86Sr ratio in rain-water, stream-water, soils and rocks in two Scottish catchments has provided useful information on mineral weathering. Over a period of 26 months, the 87Sr/86Sr ratio in rain-water had mean values of 0.7095 and 0.7098 (n = 12) whereas stream-water had mean values of 0.7080 (n = 16, in catchment in Devonian andesites with strontium isotope ratios of 0.7117–0.7232 in the rocks and soils) and 0.7184 (n = 16, in catchment of Cambrian metamorphic rocks with strontium isotope ratios of 0.7360–0.8218 in the rocks and soils), respectively. The mineralogy consists predominantly of varying proportions of quartz, plagioclase feldspar and K-feldspar with some mica and chlorite. The fact that the 87Sr/86Sr ratios in the stream in the andesitic catchment are lower than for the rain-water probably indicates preferential weathering of plagioclase feldspar releasing 86Sr, rather than K-feldspar and mica which contain greater amounts of 87Sr. The 87Sr/86Sr ratio acts as a tracer for the origin of the solutes in the stream-water. Long-term monitoring of the strontium isotope ratio in stream-water could be a potential means of detecting relative changes in soil weathering rates due to environmental change. |
