%ARodríguez‐Cardona, Bianca [Department of Natural Resources and the Environment University of New Hampshire Durham New Hampshire USA, Département des sciences biologiques Université du Québec à Montréal Montréal Québec Canada]%AWymore, Adam [Department of Natural Resources and the Environment University of New Hampshire Durham New Hampshire USA]%AArgerich, Alba [School of Natural Resources University of Missouri Columbia Missouri USA]%ABarnes, Rebecca [Environmental Studies Program Colorado College Colorado Springs Colorado USA]%ABernal, Susana [Centre d’Estudis Avançats de Blanes (CEAB‐CSIC) Blanes Spain]%ABrookshire, E. [Department of Land Resources and Environmental Sciences Montana State University Bozeman Montana USA]%ACoble, Ashley [National Council for Air and Stream Improvement, Inc. Corvallis Oregon USA]%ADodds, Walter [Division of Biology Kansas State University Manhattan Kansas USA]%AFazekas, Hannah [Department of Natural Resources and the Environment University of New Hampshire Durham New Hampshire USA]%AHelton, Ashley [Department of Natural Resources and the Environment, and the Center for Environmental Sciences and Engineering University of Connecticut Storrs Connecticut USA]%AJohnes, Penny [School of Geographical Sciences University of Bristol Bristol UK]%AJohnson, Sherri [USDA Forest Service Pacific Northwest Research Station Corvallis Oregon USA]%AJones, Jeremy [Institute of Arctic Biology &, Department of Biology and Wildlife University of Alaska Fairbanks Fairbanks Alaska USA]%AKaushal, Sujay [Department of Geology University of Maryland College Park Maryland USA]%AKortelainen, Pirkko [Finnish Environment Institute Helsinki Finland]%ALópez‐Lloreda, Carla [Department of Natural Resources and the Environment University of New Hampshire Durham New Hampshire USA, Department of Biological Sciences Virginia Polytechnic Institute and State University Blacksburg Virginia USA]%ASpencer, Robert [Department of Earth, Ocean and Atmospheric Sciences Florida State University Tallahassee Florida USA]%AMcDowell, William [Department of Natural Resources and the Environment University of New Hampshire Durham New Hampshire USA]%BJournal Name: Global Change Biology; Journal Volume: 28; Journal Issue: 1; Related Information: CHORUS Timestamp: 2023-08-27 08:47:35 %D2021%IWiley-Blackwell %JJournal Name: Global Change Biology; Journal Volume: 28; Journal Issue: 1; Related Information: CHORUS Timestamp: 2023-08-27 08:47:35 %K %MOSTI ID: 10363629 %PMedium: X %TShifting stoichiometry: Long‐term trends in stream‐dissolved organic matter reveal altered C:N ratios due to history of atmospheric acid deposition %XAbstract

Dissolved organic carbon (DOC) and nitrogen (DON) are important energy and nutrient sources for aquatic ecosystems. In many northern temperate, freshwater systems DOC has increased in the past 50 years. Less is known about how changes in DOC may vary across latitudes, and whether changes in DON track those of DOC. Here, we present long‐term DOC and DON data from 74 streams distributed across seven sites in biomes ranging from the tropics to northern boreal forests with varying histories of atmospheric acid deposition. For each stream, we examined the temporal trends of DOC and DON concentrations and DOC:DON molar ratios. While some sites displayed consistent positive or negative trends in stream DOC and DON concentrations, changes in direction or magnitude were inconsistent at regional or local scales. DON trends did not always track those of DOC, though DOC:DON ratios increased over time for ~30% of streams. Our results indicate that the dissolved organic matter (DOM) pool is experiencing fundamental changes due to the recovery from atmospheric acid deposition. Changes in DOC:DON stoichiometry point to a shifting energy‐nutrient balance in many aquatic ecosystems. Sustained changes in the character of DOM can have major implications for stream metabolism, biogeochemical processes, food webs, and drinking water quality (including disinfection by‐products). Understanding regional and global variation in DOC and DON concentrations is important for developing realistic models and watershed management protocols to effectively target mitigation efforts aimed at bringing DOM flux and nutrient enrichment under control.

%0Journal Article