Predicting dissolved organic carbon concentrations in Swedish boreal streams from map information

Abstract: When sampling watercourses for environmental assessment it is not feasible to sample all the headwaters or at least not a large fraction of them. This because of the great number of headwaters and their variability in both flow and water chemistry. So if map data could help to predict the water chemistry found on specific headwaters this would be a great asset for environmental assessment of streams. This study addresses the possibility of predicting the dissolved organic carbon (DOC)concentrations of headwaters during low flow conditions in boreal catchment networks from map information (land-use, soil and vegetation data). DOC was chosen as the test variable to model in this study because of its importance for aquatic ecosystems and strong couplings to other chemistry data (implicit in this is that if DOC is predicted well other chemistry could also be predicted well). Statistical models relating water chemistry to map information were derived from DOC measurements on different catchments in the boreal zone of Sweden using multivariate techniques. The sizes of the studied catchments ranged between 0.01-346 km2. Up to 62% of the spatial variation in DOC-concentrations could be explained by the information on any single map and a combination of soil and land-use map variables explained up to 90% of the variation in DOC. As other studies have found, the coverage of peat showed a positive correlation with DOC. The scale of the map material used in modelling did not seam to matter, with the 1:100 000 land-use map working as well as the 1:20 000 scale map, if not better. Little success was however found in making predictive models of DOC, but the likelihood of a model being close to acceptable was greater for transfers in time (predicting concentrations during a different year on the sites used for calibration) than in space (predicting concentrations on a nearby catchment.) Relationships between map information and DOC from downstream sites could not model data upstream on the same catchment. The difficulty in predicting low flow DOC from map variables is a complication when trying to develop tools for the environmental assessment of headwaters.