Climate Impacts Research Centre (CIRC)

Tracing the origin of dissolved organic matter in stream water

The aim of this study is to trace the origin of dissolved organic matter (DOM) in streams in order to better understand how different components of the terrestrial landscape affects the export of DOM. We will use a novel approach were stable sulfur isotope ratios in DOM is used a chemical tracer for different terrestrial DOM sources. Terrestrial DOM is expected to be affected by a changing climate with consequences for the receiving aquatic ecosystems. This project will investigate a number of different environments to trace the origin of DOM in streams.

For instance, we will test if we can separate between stream water DOM originating from the riparian zone from more upland areas. We assume that bacterial sulphate reduction is assumed to separate the two areas. Other possibilities were the method can be used is areas were we have separation in terrestrial end-members related their deposition history or due to different inputs such as bedrock and deposition. The latter will be tested in the Abisko region were we have large differences in the isotopic value of the bedrock and the deposition. Combining this isotopic approach with molecular level spectroscopic techniques will add qualitative information on the characteristics of different DOM sources. This combined approach will enable us to better understand how different environmental conditions affect DOM functionality and export. This VR-financed project is done in cooperation with Prof. Per Persson (Umeå University), Prof. Carl-Magnus Mörth (Stockholm University) and Prof. Hjalmar Laudon (SLU, Umeå).

Below is a figure from ES&T (Giesler et al., 2009, ES&T 43:447-452) where the approach was used for the first time in freshwater streams. Note the drastic drop in d34S-DOS in the wetland-dominated stream. The drop coincided with the disappearance of soil frost on the mire. We believe that this is linked to release of DOC from the soil depths were bacterial sulphate reduction is dominating.