Epsilon Archive for Student Projects

Abstract

Organic carbon as an important water quality factor was investigated in 13 riparian zones (RZs) and 14 stream sites in the 67 km2 boreal Krycklan catchment in Northern Sweden during 2008 to 2009. For comparisons of up- and downslope locations, also three sites with different distances to the stream were analysed. The RZs are characterized by various hydro-morphological soils while stream sites differed in land use type. The study aimed at clarifying connections between riparian and stream water focussing on spatial variability of the bioavailability of total organic carbon (TOC) in RZs and streams. Objectives were to test whether the hydrochemical signal of stream TOC character is created in the RZ or in upslope locations, and analyse the spatial and temporal variability of TOC in soil and stream water as well as at up- and downstream locations all over the catchment area. Investigations were based on TOC concentration and exports as well as the biologically-relevant indices absorbance ratio A254/A365 and specific ultraviolet absorbance (SUVA254) index. In direct comparison, riparian soils and (first-order) streams agreed better in biological indices than TOC exports with the latter varying more than related A254/A365 and SUVA254. The ranges of organic carbon concentrations were quite similar in streams and riparian soils. The biological indices were mainly consistent. High A254/A365 and low SUVA254 values both indicated good bacterial growth and bioavailability of TOC. Volume-weighted bio-logical indices matched well comparing RZs and streams -independently of soil type classification or related land use type-, indicating exports of similar carbon character with almost the same aromaticity and expected bioavailability from both locations. This again emphasizes the hypothesis of RZs as playing a key role in determining the chemical status of streams. At the whole-catchment-scale, up- and downstream locations showed similar decreasing TOC export tendencies in downstream direction with higher temporal and spatial variability in RZs and the same carbon bioavailability by volume-weighted A254/A365. The volume-weighted SUVA, however, did not give such a clear picture. In conclusion, biological indices were useful in characterizing and assessing bioavailability of organic carbon between different locations; but research questions remained.