Articles | Volume 13, issue 19
Biogeosciences, 13, 5567–5585, 2016
Biogeosciences, 13, 5567–5585, 2016

Research article 07 Oct 2016

Research article | 07 Oct 2016

Trends in soil solution dissolved organic carbon (DOC) concentrations across European forests

Marta Camino-Serrano1, Elisabeth Graf Pannatier2, Sara Vicca1, Sebastiaan Luyssaert3,a, Mathieu Jonard4, Philippe Ciais3, Bertrand Guenet3, Bert Gielen1, Josep Peñuelas5,6, Jordi Sardans5,6, Peter Waldner2, Sophia Etzold2, Guia Cecchini7, Nicholas Clarke8, Zoran Galić9, Laure Gandois10, Karin Hansen11, Jim Johnson12, Uwe Klinck13, Zora Lachmanová14, Antti-Jussi Lindroos15, Henning Meesenburg13, Tiina M. Nieminen15, Tanja G. M. Sanders16, Kasia Sawicka17, Walter Seidling16, Anne Thimonier2, Elena Vanguelova18, Arne Verstraeten19, Lars Vesterdal20, and Ivan A. Janssens1 Marta Camino-Serrano et al.
  • 1Research Group of Plant and Vegetation Ecology, Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium
  • 2WSL, Swiss Federal Institute for Forest, Snow and Landscape Research, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland
  • 3Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
  • 4UCL-ELI, Université catholique de Louvain, Earth and Life Institute, Croix du Sud 2, 1348 Louvain-la-Neuve, Belgium
  • 5CREAF, Cerdanyola del Vallès, 08193, Catalonia, Spain
  • 6CSIC, Global Ecology Unit CREAF-CSIC-UAB, Cerdanyola del Vallès, 08193, Catalonia, Spain
  • 7Department of Earth Sciences, University of Florence, Via La Pira 4, 50121 Florence, Italy
  • 8Division of Environment and Natural Resources, Norwegian Institute of Bioeconomy Research, 1431, Ås, Norway
  • 9University of Novi Sad-Institute of Lowland Forestry and Environment, 21000 Novi Sad, Serbia
  • 10EcoLab, Université de Toulouse, CNRS, INPT, UPS, Avenue de l'Agrobiopole – BP 32607, 31326 Castanet Tolosan, France
  • 11IVL Swedish Environmental Research Institute, Natural Resources & Environmental Effects, 100 31, Stockholm, Sweden
  • 12UCD School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, D04 V1W8, Ireland
  • 13Northwest German Forest Research Institute, Grätzelstr. 2, 37079 Göttingen, Germany
  • 14FGMRI, Forestry and Game Management Research Institute, Strnady 136, 252 02 Jíloviště, Czech Republic
  • 15Natural Resources Institute Finland (Luke), P.O. Box 18, 01301 Vantaa, Finland
  • 16Thünen Institute of Forest Ecosystems, Alfred-Möller-Straße 1, 16225 Eberswalde, Germany
  • 17Soil Geography and Landscape Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, the Netherlands
  • 18Centre for Ecosystem, Society and Biosecurity, Forest Research, Alice Holt Lodge, Wrecclesham, Farnham, Surrey GU10 4LH, UK
  • 19Research Institute for Nature and Forest (INBO), Kliniekstraat 25, 1070 Brussels, Belgium
  • 20University of Copenhagen, Department of Geosciences and Natural Resource Management, Rolighedsvej 23, 1958 Frederiksberg C, Denmark
  • anow at: Free University of Amsterdam, Department of Ecological Science, Boelelaan 1085, 1081HV, the Netherlands

Abstract. Dissolved organic carbon (DOC) in surface waters is connected to DOC in soil solution through hydrological pathways. Therefore, it is expected that long-term dynamics of DOC in surface waters reflect DOC trends in soil solution. However, a multitude of site studies have failed so far to establish consistent trends in soil solution DOC, whereas increasing concentrations in European surface waters over the past decades appear to be the norm, possibly as a result of recovery from acidification. The objectives of this study were therefore to understand the long-term trends of soil solution DOC from a large number of European forests (ICP Forests Level II plots) and determine their main physico-chemical and biological controls. We applied trend analysis at two levels: (1) to the entire European dataset and (2) to the individual time series and related trends with plot characteristics, i.e., soil and vegetation properties, soil solution chemistry and atmospheric deposition loads. Analyses of the entire dataset showed an overall increasing trend in DOC concentrations in the organic layers, but, at individual plots and depths, there was no clear overall trend in soil solution DOC. The rate change in soil solution DOC ranged between −16.8 and +23 % yr−1 (median  = +0.4 % yr−1) across Europe. The non-significant trends (40 %) outnumbered the increasing (35 %) and decreasing trends (25 %) across the 97 ICP Forests Level II sites. By means of multivariate statistics, we found increasing trends in DOC concentrations with increasing mean nitrate (NO3) deposition and increasing trends in DOC concentrations with decreasing mean sulfate (SO42−) deposition, with the magnitude of these relationships depending on plot deposition history. While the attribution of increasing trends in DOC to the reduction of SO42− deposition could be confirmed in low to medium N deposition areas, in agreement with observations in surface waters, this was not the case in high N deposition areas. In conclusion, long-term trends of soil solution DOC reflected the interactions between controls acting at local (soil and vegetation properties) and regional (atmospheric deposition of SO42− and inorganic N) scales.

Short summary
We investigated the long-term trends of dissolved organic carbon (DOC) in soil solution and the drivers of changes in over 100 forest monitoring plots across Europe. An overall increasing trend was detected in the organic layers, but no overall trend was found in the mineral horizons. There are strong interactions between controls acting at local and regional scales. Our findings are relevant for researchers focusing on the link between terrestrial and aquatic ecosystems and for C-cycle models.
Final-revised paper