Shifting stoichiometry: Long‐term trends in stream‐dissolved organic matter reveal altered C:N ratios due to history of atmospheric acid deposition

Abstract

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Determining patterns in the composition of dissolved organic matter in fresh waters according to land use and management

“…This displays a similarly pattern to those reported between DOC and nitrate in a range of other studies (e.g. Evans et al 2006;Taylor and Townsend 2010;Rodriguez-Cardona et al 2021) and between DON and TDN in the global analysis of Wymore et al (2021). Given the range of scales covered in each of these studies, and in the research presented here, these patterns may well be ubiquitous in fresh waters, representing a transition from N (or P) limitation in low nutrient status waters, typically natural or semi-natural, to systems which are highly enriched with N and System stoichiometry then shifts as systems move along this transition in response to external forcing or mitigation efforts in catchments.…”

“…The high degree of variability in the relationship between DON and TDN at lower TN concentrations (< 1.3 mg N l −1 ) observed in that global analysis is echoed in the data presented in this study, suggesting no single landscape control on the composition of the N pool in streams. Rather, local landscape characteristics such as land management, plant species composition, topography, soil characteristics, and wetland cover in natural or semi-natural catchments, as well as relative rates of N deposition (Helliwell et al 2007) or recovery from acidification (Rodriguez-Cardona et al 2021) exert catchmentspecific controls on N speciation, shifting C:N ratios in the riverine DOM pool and altering its likely ecosystem functional role. Helliwell et al (2007), for example, report upward shifts in nitrate leading relative to DOC flux to streams moving from low to high N deposition areas, while Rodriguez-Cardona et al (2021) report changes in DOC:DON stoichiometry of the stream DOM pool as systems recover from atmospheric acid deposition.…”

“…Rather, local landscape characteristics such as land management, plant species composition, topography, soil characteristics, and wetland cover in natural or semi-natural catchments, as well as relative rates of N deposition (Helliwell et al 2007) or recovery from acidification (Rodriguez-Cardona et al 2021) exert catchmentspecific controls on N speciation, shifting C:N ratios in the riverine DOM pool and altering its likely ecosystem functional role. Helliwell et al (2007), for example, report upward shifts in nitrate leading relative to DOC flux to streams moving from low to high N deposition areas, while Rodriguez-Cardona et al (2021) report changes in DOC:DON stoichiometry of the stream DOM pool as systems recover from atmospheric acid deposition. Wymore et al (2021) also report instances where systems approaching a near natural state may be in fact dominated by oxidised N species rather than elevated DON contributions.…”

Mycorrhizal fungi alleviate acidification‐induced phosphorus limitation: Evidence from a decade‐long field experiment of simulated acid deposition in a tropical forest in south China

“…Soil acidification due to acid rain/deposition remains a widespread environmental issue that can cause acute nutritional imbalances in the soils and adversely affect the functions and service of natural ecosystems (Breemen et al, 1984;De Vries & Breeuwsma, 1987;Dietze & Moorcroft, 2011;Rodríguez-Cardona et al, 2022). For example, in Europe and North America, the two recognized high acid rain centers (Johnson et al, 2018;Likens & Butler, 1981), acid rain has caused a decline of sugar maple (Acer saccharum) and red spruce (Picea rubens) stands due to soil Ca 2+ depletion (Battles et al, 2014;DeHayes et al, 1999;Sullivan et al, 2013) and significantly reduced Mg 2+ nutrition in Norway spruce (Picea abies) forests (de Wit et al, 2010;Lomský et al, 2012).…”

Groundwater metabolome responds to recharge in fractured sedimentary strata

“…Particularly the composition of dissolved organic matter (DOM) and its fate in groundwater reservoirs are rather obscure. DOM signatures are essential for assessing groundwater ecosystem functioning and vulnerability to land use, water resource exploitation, and climate change-driven threats (Drake et al, 2020; Humphrey et al, 2016; Phillips et al, 2012; Riedel & Weber, 2020; Rodell et al, 2018; Rodríguez-Cardona et al, 2022; United Nations Office for Disaster Risk Reduction (UNDRR), 2021; Wada et al, 2012). Groundwater DOM sources, composition, persistence, and transformation reflect biogeochemical processes below-ground (Kaiser & Kalbitz, 2012; J.…”