Epsilon Archive for Student Projects

Abstract

Carbon lateral exports from terrestrial soils to the water conduit have been recently recognized as important components of global C budgets. These fluxes play also a major role in several processes within freshwaters that are important for biodiversity and human health. Swedish boreal forest is of special interest since part of the large amount of C stored within soils is exported as DOC. The export occurs mainly to small headwaters streams that vary greatly in spatial scales. This study attempts to estimate the distribution of TOC for all Swedish headwater streams by using a model that predicts TOC long-term concentrations in headwater streams smaller than 3Km2 and that is based on wetland percentage, altitude and precipitation levels. For the purpose all Swedish catchments draining to these streams were identified and exports from the remaining larger streams were divided by a factor of 50%. The results showed that export fluxes in northeast regions had the highest mean values where wetland and forests were predominant. The southeast characterized by the predominance of agricultural soils had the lowest fluxes.
Fluxes of TOC for major 43 river mouth basins were found to vary from 2.1 to 7.6 g C m-2 yr-1. Losses of C within these basins of C had a mean value of 35% and were found to
be mostly related with WRT as C losses increased with longer WRT. Basin with high agricultural fractions gained C which may be related to the inputs of nutrients in
freshwaters. C losses in middle basins suggested that the model is capable of estimating mean TOC concentrations but less accurate predictions were found in low and high TOC
concentrations. Comparisons with literature revealed good agreement for TOC export estimates and losses, although in different magnitudes. Nonetheless, most studies focused
on export estimates based on C transformations within freshwaters which may not correspondent to the amount of C that leaves the soils. Further studies may focus on C
exports from agriculture soils and improving the models accuracy to predict low and high TOC concentrations.