HYDROGEOCHEMISTRY OF SULFUR ISOTOPES IN THE KALIX RIVER CATCHMENT, NORTHERN SWEDEN

The S-34-to-S-32 ratio in dissolved SO4 has been studied in the Kalix River, Northern Sweden, and its catchment. Weekly sampling over 17 mon ths revealed temporal variations from + 5.3 parts per thousand up to 7.4 parts per thousand in the delta(34)S values in the river. Snow an d rain samples showed lower delta(34)S values (average + 5.6 parts per thousand and + 5.0 parts per thousand, respectively). The atmosphere is the major source for S in surface waters in the catchment, and the heavier delta(34)S values in the river are a result of SO4 reduction w ithin the catchment. Most of the temporal variations in the delta(34)S value in the river are caused by a mixing of water from the mountain areas (relatively light delta(34)S) and the woodland. The delta(34)S v alue is relatively heavy in the woodland tributaries because of bacter ial SO4 reduction in peatland areas influenced by groundwater. The hig hest delta(34)S values were measured during the spring flood, in June and in November. These heavy delta(34)S values are related to differen t types of water with diverse origins. The heavy delta(34)S values coi nciding with the early spring flood originate from peatland areas in t he woodland. Relatively heavy delta(34)S values (up to + 14.4 parts pe r thousand) were registered in mire water. Smaller variations of the d elta(34)S value during summer and early autumn most likely were caused by the input of ground-mire water during heavy rains. A correlation b etween increased TOC concentrations and increased delta(34)S values wa s observed. The heavy delta(34)S values in June and November probably originate from SO4 reduction in bottom water and sediments in lakes wi thin the catchment. Bottom water, enriched in S-34-SO4, was transporte d in the river during the spring and autumn overturn. (C) 1997 Elsevie r Science Ltd.