title: Urban point sources of nutrients were the leading cause for the historical spread of hypoxia across European lakes.
abstract: Enhanced phosphorus (P) export from land into streams and lakes is a primary factor driving the expansion of deep-water hypoxia in lakes during the Anthropocene. However, the interplay of regional scale environmental stressors and the lack of long-term instrumental data often impede analyses attempting to associate changes in land cover with downstream aquatic responses. Herein, we performed a synthesis of data that link paleolimnological reconstructions of lake bottom-water oxygenation to changes in land cover/use and climate over the past 300 years to evaluate whether the spread of hypoxia in European lakes was primarily associated with enhanced P exports from growing urbanization, intensified agriculture, or climatic change. We showed that hypoxia started spreading in European lakes around CE 1850 and was greatly accelerated after CE 1900. Socioeconomic changes in Europe beginning in CE 1850 resulted in widespread urbanization, as well as a larger and more intensively cultivated surface area. However, our analysis of temporal trends demonstrated that the onset and intensification of lacustrine hypoxia were more strongly related to the growth of urban areas than to changes in agricultural areas and the application of fertilizers. These results suggest that anthropogenically triggered hypoxia in European lakes was primarily caused by enhanced P discharges from urban point sources. To date, there have been no signs of sustained recovery of bottom-water oxygenation in lakes following the enactment of European water legislation in the 1970s to 1980s, and the subsequent decrease in domestic P consumption.
authors: Centre-Eau Terre Environnement, Institut National de la Recherche Scientifique, Quebec, QC, Canada G1K 9A9; jjenny@bgc-jena.mpg.de.|Centre de Recherche en Géochimie et Géodynamique (GEOTOP) Research Center, Montreal, QC, Canada H3C 3P8.|Max Planck Institute for Biogeochemistry, 07745 Jena, Germany.
authors: Jean-Philippe
authors: http://orcid.org/0000-0002-2740-174X
authors: JP
authors: Jenny
authors: Geological Survey of Canada, Bedford Institute of Oceanography, Dartmouth, NS, Canada B2Y 4A2.
authors: Alexandre
authors: A
authors: Normandeau
authors: Centre-Eau Terre Environnement, Institut National de la Recherche Scientifique, Quebec, QC, Canada G1K 9A9.|Centre de Recherche en Géochimie et Géodynamique (GEOTOP) Research Center, Montreal, QC, Canada H3C 3P8.
authors: Pierre
authors: http://orcid.org/0000-0001-5465-1966
authors: P
authors: Francus
authors: Department of Biology, McGill University, Montreal, QC, Canada H3A 1B1.|Departement des Sciences Biologiques, Université de Montréal, Montreal, QC, Canada H2V 2S9.
authors: Zofia Ecaterina
authors: http://orcid.org/0000-0002-4137-5058
authors: ZE
authors: Taranu
authors: Department of Biology, McGill University, Montreal, QC, Canada H3A 1B1.|Groupe de Recherche Interuniversitaire en Limnology, McGill University, Montreal, QC, Canada H3A 1B1.
authors: Irene
authors: I
authors: Gregory-Eaves
authors: Centre-Eau Terre Environnement, Institut National de la Recherche Scientifique, Quebec, QC, Canada G1K 9A9.|Centre de Recherche en Géochimie et Géodynamique (GEOTOP) Research Center, Montreal, QC, Canada H3C 3P8.
authors: François
authors: http://orcid.org/0000-0002-0546-7780
authors: F
authors: Lapointe
authors: Department of Earth Sciences, University of Ottawa, Ottawa, ON, Canada K1N6N5.
authors: Josue
authors: J
authors: Jautzy
authors: Geological Survey of Finland, 02151 Espoo, Finland.
authors: Antti E K
authors: AEK
authors: Ojala
authors: Institut National de la Recherche Agronomique UMR 42 Centre Alpin de Recherche sur les Réseaux Trophiques des Écosystèmes Limniques (CARRTEL), Université de Savoie, 74203 Thonon-les-bains Cedex, France.
authors: Jean-Marcel
authors: JM
authors: Dorioz
authors: Department of Geological Sciences, Indiana University, Bloomington, IN 47405.
authors: Arndt
authors: A
authors: Schimmelmann
authors: Arbeitsgruppe Geomorphologie und Polarforschung (GEOPOLAR), Institute of Geography, University of Bremen, D-28359 Bremen, Germany.
authors: Bernd
authors: B
authors: Zolitschka
keywords: Anthropocene; lake hypoxia; land cover/uses; meta-analysis; varves