|Title||Gradients of Anthropogenic Nutrient Enrichment Alter N Composition and DOM Stoichiometry in Freshwater Ecosystems|
|Publication Type||Journal Article|
|Year of Publication||2021|
|Authors||Wymore, AS, Johnes, PJ, Bernal, S, Brookshire, ENJack, Fazekas, HM, Helton, AM, Argerich, A, Barnes, RT, Coble, AA, Dodds, WK, Haq, S, Johnson, SL, Jones, JB, Kaushal, SS, Kortelainen, P, López-Lloreda, C, Rodríguez-Cardona, BM, Spencer, RGM, Sullivan, PL, Yates, CA, McDowell, WH|
|Journal||Global Biogeochemical Cycles|
|Keywords||dissolved organic carbon, Dissolved organic matter, dissolved organic nitrogen, freshwater ecosystems, HBR-DataOnly, itrogen cycle, LTER-HBR, stoichiometry, total dissolved nitrogen|
A comprehensive cross-biome assessment of major nitrogen (N) species that includes dissolved organic N (DON) is central to understanding interactions between inorganic nutrients and organic matter in running waters. Here, we synthesize stream water N chemistry across biomes and find that the composition of the dissolved N pool shifts from highly heterogeneous to primarily comprised of inorganic N, in tandem with dissolved organic matter (DOM) becoming more N-rich, in response to nutrient enrichment from human disturbances. We identify two critical thresholds of total dissolved N (TDN) concentrations where the proportions of organic and inorganic N shift. With low TDN concentrations (0–1.3 mg/L N), the dominant form of N is highly variable, and DON ranges from 0% to 100% of TDN. At TDN concentrations above 2.8 mg/L, inorganic N dominates the N pool and DON rarely exceeds 25% of TDN. This transition to inorganic N dominance coincides with a shift in the stoichiometry of the DOM pool, where DOM becomes progressively enriched in N and DON concentrations are less tightly associated with concentrations of dissolved organic carbon (DOC). This shift in DOM stoichiometry (defined as DOC:DON ratios) suggests that fundamental changes in the biogeochemical cycles of C and N in freshwater ecosystems are occurring across the globe as human activity alters inorganic N and DOM sources and availability. Alterations to DOM stoichiometry are likely to have important implications for both the fate of DOM and its role as a source of N as it is transported downstream to the coastal ocean.