title: From greening to browning: Catchment vegetation development and reduced S-deposition promote organic carbon load on decadal time scales in Nordic lakes.
abstract: Increased concentrations of dissolved organic carbon (DOC), often labelled "browning", is a current trend in northern, particularly boreal, freshwaters. The browning has been attributed to the recent reduction in sulphate (S) deposition during the last 2 to 3 decades. Over the last century, climate and land use change have also caused an increasing trend in vegetation cover ("greening"), and this terrestrially fixed carbon represents another potential source for export of organic carbon to lakes and rivers. The impact of this greening on the observed browning of lakes and rivers on decadal time scales remains poorly investigated, however. Here, we explore time-series both on water chemistry and catchment vegetation cover (using NDVI as proxy) from 70 Norwegian lakes and catchments over a 30-year period. We show that the increase in terrestrial vegetation as well as temperature and runoff significantly adds to the reduced SO4-deposition as a driver of freshwater DOC concentration. Over extended periods (centuries), climate mediated changes in vegetation cover may cause major browning of northern surface waters, with severe impact on ecosystem productivity and functioning.
authors.affiliation: Department of Natural History, NTNU University Museum, Norwegian University of Science and Technology, N-7491 Trondheim, Norway.|Norwegian Institute for Nature Research, P.O. Box 5685 Sluppen, NO-7485 Trondheim, Norway.
authors.forename: Anders G
authors.initials: AG
authors.lastname: Finstad
authors.affiliation: University of Oslo, Department of Biosciences, P.O. Box 1066, Blindern, 0316 Oslo, Norway.
authors.forename: Tom
authors.initials: T
authors.lastname: Andersen
authors.affiliation: University of Oslo, Department of Biosciences, P.O. Box 1066, Blindern, 0316 Oslo, Norway.
authors.forename: Søren
authors.initials: S
authors.lastname: Larsen
authors.affiliation: University of Oslo, Department of Biosciences, P.O. Box 1066, Blindern, 0316 Oslo, Norway.
authors.forename: Koji
authors.initials: K
authors.lastname: Tominaga
authors.affiliation: Norwegian Institute for Nature Research, P.O. Box 5685 Sluppen, NO-7485 Trondheim, Norway.
authors.forename: Stefan
authors.initials: S
authors.lastname: Blumentrath
authors.affiliation: Norwegian Institute for Water Research, Gaustadalléen 21, NO-0349 Oslo, Norway.
authors.forename: Heleen A
authors.initials: HA
authors.lastname: de Wit
authors.affiliation: Norwegian Institute for Nature Research, P.O. Box 5685 Sluppen, NO-7485 Trondheim, Norway.
authors.forename: Hans
authors.initials: H
authors.lastname: Tømmervik
authors.affiliation: University of Oslo, Department of Biosciences, P.O. Box 1066, Blindern, 0316 Oslo, Norway.
authors.forename: Dag Olav
authors.initials: DO
authors.lastname: Hessen