title: Global effects of agriculture on fluvial dissolved organic matter.
abstract: Agricultural land covers approximately 40% of Earth's land surface and affects hydromorphological, biogeochemical and ecological characteristics of fluvial networks. In the northern temperate region, agriculture also strongly affects the amount and molecular composition of dissolved organic matter (DOM), which constitutes the main vector of carbon transport from soils to fluvial networks and to the sea, and is involved in a large variety of biogeochemical processes. Here, we provide first evidence about the wider occurrence of agricultural impacts on the concentration and composition of fluvial DOM across climate zones of the northern and southern hemispheres. Both extensive and intensive farming altered fluvial DOM towards a more microbial and less plant-derived composition. Moreover, intensive farming significantly increased dissolved organic nitrogen (DON) concentrations. The DOM composition change and DON concentration increase differed among climate zones and could be related to the intensity of current and historical nitrogen fertilizer use. As a result of agriculture intensification, increased DON concentrations and a more microbial-like DOM composition likely will enhance the reactivity of catchment DOM emissions, thereby fuelling the biogeochemical processing in fluvial networks, and resulting in higher ecosystem productivity and CO2 outgassing.
authors.affiliation: Department of Bioscience, Aarhus University, Denmark.
authors.forename: Daniel
authors.initials: D
authors.lastname: Graeber
authors.affiliation: Department of Geosciences, Federal University of São João del-Rei, Brazil.
authors.forename: Iola G
authors.initials: IG
authors.lastname: Boëchat
authors.affiliation: Faculty of Natural Resources, Environmental Science Nucleus, Catholic University of Temuco, Chile.
authors.forename: Francisco
authors.initials: F
authors.lastname: Encina-Montoya
authors.affiliation: Faculty of Natural Resources, Environmental Science Nucleus, Catholic University of Temuco, Chile.
authors.forename: Carlos
authors.initials: C
authors.lastname: Esse
authors.affiliation: Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Gelbrecht
authors.affiliation: Department of Theoretical and Applied Ecology, CURE - Faculty of Sciences, Universidad de la República, Uruguay.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Goyenola
authors.affiliation: Department of Geosciences, Federal University of São João del-Rei, Brazil.
authors.forename: Björn
authors.initials: B
authors.lastname: Gücker
authors.affiliation: Department of Ecosystem Research, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
authors.forename: Marlen
authors.initials: M
authors.lastname: Heinz
authors.affiliation: Department of Bioscience, Aarhus University, Denmark.
authors.forename: Brian
authors.initials: B
authors.lastname: Kronvang
authors.affiliation: Department of Bioscience, Aarhus University, Denmark.|Department of Theoretical and Applied Ecology, CURE - Faculty of Sciences, Universidad de la República, Uruguay.
authors.forename: Mariana
authors.initials: M
authors.lastname: Meerhoff
authors.affiliation: Instituto de Ciencias Marinas y Limnologicas, Facultad de Ciencias, Universidad Austral de Chile, Edificio Emilio Pugin, Campus Isla Teja, Valdivia, Chile.
authors.forename: Jorge
authors.initials: J
authors.lastname: Nimptsch
authors.affiliation: Department of Ecosystem Research, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
authors.forename: Martin T
authors.initials: MT
authors.lastname: Pusch
authors.affiliation: Department of Natural Sciences, Federal University of São João del-Rei, Brazil.
authors.forename: Ricky C S
authors.initials: RC
authors.lastname: Silva
authors.affiliation: Department of Plant Biology and Ecology, Faculty of Science and Technology, University of the Basque Country, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: von Schiller
authors.affiliation: Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Zwirnmann