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Research article - Peer-reviewed, 2016

Boreal forest riparian zones regulate stream sulfate and dissolved organic carbon

Ledesma, Jose; Futter, Martyn; Laudon, Hjalmar; Evans, Christopher; Köhler, Stephan

Abstract

In boreal forest catchments, solute transfer to streams is controlled by hydrological and biogeochemical processes occurring in the riparian zone (RZ). However, RZs are spatially heterogeneous and information about solute chemistry is typically limited. This is problematic when making inferences about stream chemistry. Hypothetically, the strength of links between riparian and stream chemistry is time-scale dependent. Using a ten-year (2003-2012) dataset from a northern Swedish catchment, we evaluated the suitability of RZ data to infer stream dynamics at different time scales. We focus on the role of the RZ versus upslope soils in controlling sulfate (SO42-) and dissolved organic carbon (DOC). A priori, declines in acid deposition and redox-mediated SO42- pulses control sulfur (S) fluxes and pool dynamics, which in turn affect dissolved organic carbon (DOC). We found that the catchment is currently a net source of S, presumably due to release of the S pool accumulated during the acidification period. In both, RZ and stream, SO42- concentrations are declining over time, whereas DOC is increasing. No temporal trends in SO42- and DOC were observed in upslope mineral soils. SO42- explained the variation of DOC in stream and RZ, but not in upslope mineral soil. Moreover, as SO42- decreased with time, temporal variability of DOC increased. These observations indicate that: (1) SO42- is still an important driver of DOC trends in boreal catchments and (2) RZ processes control stream SO42- and subsequently DOC independently of upslope soils. These phenomena are likely occurring in many regions recovering from acidification. Because water flows through a heterogeneous mosaic of RZs before entering the stream, upscaling information from limited RZ data to the catchment level is problematic at short-time scales. However, for long-term trends and annual dynamics, the same data can provide reasonable representations of riparian processes and support meaningful inferences about stream chemistry. (C) 2016 The Authors. Published by Elsevier B.V.

Keywords

Heterogeneity; Acidification; Upscaling; Catchment science; Biogeochemistry; DOC

Published in

Science of the Total Environment
2016, volume: 560-561, pages: 110-122
Publisher: ELSEVIER SCIENCE BV

Authors' information

Ledesma, Jose
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Centre for Ecology and Hydrology (CEH)
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment

Associated SLU-program

SLU Future Forests

Sustainable Development Goals

SDG6 Clean water

UKÄ Subject classification

Oceanography, Hydrology, Water Resources
Climate Research
Geosciences, Multidisciplinary
Other Earth and Related Environmental Sciences
Environmental Sciences

Publication Identifiers

DOI: https://doi.org/10.1016/j.scitotenv.2016.03.230

URI (permanent link to this page)

https://res.slu.se/id/publ/77027