Environ. Sci. Technol. 2009, 43, 447–452
Spatial and Seasonal Variations in Stream Water δ34S-Dissolved Organic Matter in Northern Sweden R E I N E R G I E S L E R , * ,† ¨ RKVALD,‡ LOUISE BJO HJALMAR LAUDON,§ AND ¨ RTH‡ CARL-MAGNUS MO Climate Impacts Research Centre, Department of Ecology and Environmental Science, Umeå University, Box 62, 981 07 Abisko, Sweden, Department of Geology and Geochemistry, Stockholm University, 106 91 Stockholm, Sweden, and Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden
Received June 28, 2008. Revised manuscript received October 31, 2008. Accepted November 03, 2008.
The discharge of terrestrial dissolved organic matter (DOM) by streams is an important cross-system linkage that strongly influences downstream aquatic ecosystems. Isotopic tracers are important tools that can help to unravel the source of DOM from different terrestrial compartments in the landscape. Here we demonstrate the spatial and seasonal variation of δ34S of DOM in 10 boreal streams to test if the tracer could provide new insights into the origin of DOM. We found large spatial and seasonal variations in stream water δ34S-DOM values ranging from -5.2‰ to +9.6‰ with an average of +4.0 ( 0.6 (N ) 62; average and 95% confidence interval). Large seasonal variations were found in stream water δ34S-DOM values: for example, a shift of more than 10‰ during the spring snowmelt in a wetland-dominated stream. Spatial differences were also observed during the winter base flow with higher δ34SDOM values in the fourth-order Krycklan stream at the outlet of the 68 km2 catchment compared to the small (50% of total S before analyses. We found that 10 dm3 of stream water was sufficient to obtain the necessary amount of organic S. The second obstacle was solved by the second cross-flow filtration step. The SO42fraction is dominant in the stream water and accounts for approximately 80% of the total S in the Krycklan catchment streams (N ) 384); however, the 1-kDa filter is permeable to SO42- ions and will, thus, dilute the SO42- in the retentate and concentrate the amount of organic S. Losses of DOM due to the second filtration step are unavoidable but were minor (
