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The sensitivity of water chemistry to climate in a forested,nitrogen-saturated catchment recovering from acidification
Institution:1. Department of Geography, The University of Western Ontario, 1151 Richmond St. North, London, Ontario N6A 5C2, Canada;2. U.S. Geological Survey, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523-1499, USA;3. Department of Watershed Sciences, Utah State University, 5210 Old Main Hill, Logan, UT 84322, USA;4. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523-1499, USA;5. Climate Change Institute, University of Maine, Orono, ME, USA;6. Centre for Teaching and Learning, The University of Western Ontario, 1151 Richmond St North, London, Ontario N6A 3K7, Canada;7. Department of Environmental Science and Policy, University of California, Davis, One Shields Ave, Davis, CA 95616-5270, USA;8. Biology Centre of the Czech Academy of Sciences, Institute of Hydrobiology, ?eské Budějovice 370 05, Czech Republic;9. Department of Ecology, University of Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria;10. WasserCluster Lunz - Inter-University Center for Aquatic Ecosystem Research, Dr. Carl Kupelwieser Promenade 5, A-3293 Lunz am See, Austria;11. Center for Lakes and Reservoirs and Department of Environmental Science and Management, Portland State University, Portland, OR 97203, USA;12. Global Water Center and Biology Department, University of Nevada, 1664 N. Virginia St, Reno, NV 89557, USA;13. U.S. Geological Survey, Columbia Environmental Research Center, 4200 East New Haven Road, Columbia, MO 65201, USA;14. Department of Forest and Wildlife Ecology, University of Wisconsin, Madison, WI, USA;15. Paleoecological Environmental Assessment and Research Lab (PEARL), Department of Biology, Queen''s University, 116 Barrie St., Kingston, Ontario K7L 3N6, Canada;p. Institute of Earth Sciences, University of Applied Sciences and Arts of Southern Switzerland, Canobbio CH-6952, Switzerland;q. US Geological Survey/INSTAAR, 4001 Discovery Drive, Boulder, CO 80303, USA;r. Department of Fish, Wildlife, and Conservation Biology, Colorado State University, 1474 Campus Delivery, Fort Collins, CO, USA;s. Bren School of Environmental Science and Management, University of California, Santa Barbara, CA, USA;1. Department of Ecosystem Biology, Faculty of Science and SoWa, University of South Bohemia in ?eské Budějovice, Czech Republic;2. IFER - Institute of Forest Ecosystem Research, Jílové u Prahy, Czech Republic;3. Global Change Research Institute of the Czech Academy of Sciences, Bělidla 986/4a, Brno, Czech Republic;4. Biology Centre of the Czech Academy of Sciences, Institute of Hydrobiology, ?eské Budějovice, Czech Republic;1. IFER – Institute of Forest Ecosystem Research, Cs. armády 655, 254 01 Jílové u Prahy, Czech Republic;2. Institute of Botany of The Czech Academy of Sciences, Zámek 1, 252 43 Pr?honice, Czech Republic;3. Biology Centre CAS, Institute of Hydrobiology, Na Sádkách 7, 370 05 ?eské Budějovice, Czech Republic;4. Global Change Research Institute CAS, Bělidla 986/4a, 603 00 Brno, Czech Republic;5. Swedish University of Agricultural Sciences, Faculty of Forest Sciences, Department of Forest Resource Management, SE-901 83 Umeå, Sweden;6. Charles University, Faculty of Science, Department of Physical geography and Geoecology, Albertov 6, 128 43 Prague, Czech Republic;1. Biology Centre of the Czech Academy of Sciences, v.v.i., Institute of Hydrobiology, Na Sádkách 7, ?eské Budějovice 37005, Czech Republic;2. Faculty of Science, University of South Bohemia, Brani?ovská 31, ?eské Budějovice 37005, Czech Republic;3. Faculty of Economy, University of South Bohemia, Studentská 13, ?eské Budějovice 37005, Czech Republic
Abstract:Fluxes of major ions and nutrients were measured in the N-saturated mountain forest catchment-lake system of ?ertovo Lake (Czech Republic) from 1998 to 2014. The lake has been rapidly recovering from atmospheric acidification due to a 90% decrease in sulphate (SO42?) deposition since the late 1980s and nitrate (NO3?) contribution to the pool of strong acid anion and leaching of dissolved organic carbon (DOC) have increased. Present concentrations of base cations, phosphorus (P), total organic N (TON), and ionic (Ali) and organically bound (Alo) aluminium in tributaries are thus predominantly governed by NO3? and DOC leaching. Despite a continuing recovery lasting 25 years, the ?ertovo catchment is still a net source of protons (H+), producing 44 mmol m?2 yr?1 H+ on a catchment-area basis (corresponding to 35 μmol L?1 on a concentration basis). Retention of the deposited inorganic N in the catchment averages 20%, and ammonium consumption (51 mmol m?2 yr?1) and net NO3? production (28 mol m?2 yr?1) are together the dominant terrestrial H+ generating processes. In contrast, the importance of SO42? release from the soils on terrestrial H+ production is continuously decreasing, with an average of 47 mmol m?2 yr?1 during the study. The in-lake biogeochemical processes reduce the incoming acidity by ~40%, neutralizing 23 μmol L?1 H+ (i.e., 225 mmol m?2 yr?1 on a lake-area basis). Denitrification and photochemical and microbial decomposition of DOC are the most important in-lake H+ consuming processes (50 and 39%, respectively), while hydrolysis of Ali (from tributaries and photochemically liberated from Alo) is the dominant in-lake H+ generating process. Because the trends in water chemistry and H+ balance in the catchment-lake system are increasingly related to variability in NO3? and DOC leaching, they have become sensitive to climate-related factors (drought, elevated runoff) and forest damage that significantly modify the leaching of these anions. During the study period, increased exports of NO3? (accompanied by Ali and base cations) from the ?ertovo catchment occurred after a dry and hot summer, after forest damage, and during elevated winter runoff. Increasing DOC export due to decreasing acid deposition was further elevated during years with higher runoff (and especially during events with lateral flow), and was accompanied by P, TON, and Alo leaching. The climate-related processes, which originally “only” confounded chemical trends in waters recovering from acidification, may soon become the dominant variables controlling water composition in N-saturated catchments.
Keywords:Nitrogen  Sulphur  Organic carbon  Aluminium  Base cations  Phosphorus  pH
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