Cleaner air reveals growing influence of climate on dissolved organic carbon trends in northern headwaters

Abstract

Surface water browning, the result of increasing concentrations of dissolved organic matter (DOM), has been widespread in northern ecosystems in recent decades. Here, we assess a database of 426 undisturbed headwater lakes and streams in Europe and North America for evidence of trends in DOM between 1990 and 2016. We describe contrasting changes in DOM trends in Europe (decelerating) and North America (accelerating), which are consistent with organic matter solubility responses to declines in sulfate deposition. While earlier trends (1990–2004) were almost entirely related to changes in atmospheric chemistry, climatic and chemical drivers were equally important in explaining recent DOM trends (2002–2016). We estimate that riverine DOM export from northern ecosystems increased by 27% during the study period. Increased summer precipitation strengthened upward dissolved organic carbon trends while warming apparently damped browning. Our results suggest strong but changing influences of air quality and climate on the terrestrial carbon cycle, and on the magnitude of carbon export from land to water.

Rapid improvement of lake acid–base status in Atlantic Canada following steep decline in precipitation acidity

“…The causes for the widely observed DOC increased in temperate and boreal lakes are still debated and not within the scope of the present study. It has been suggested that decreasing ionic strength in the soil solution (mainly due to the widespread sulfate decrease) is responsible for an increase in DOC solubility thus increasing its exportation to surface water (Monteith et al 2007;Lawrence and Roy 2021;de Wit et al 2021). In this context, the increasing DOC concentration (and thereby, contribution of organic acids to the inorganic acid anions) could be a consequence of decreasing acid deposition and should then be considered to be part of the "recovery" process instead of slowing it down, although it may likely slow down the rate of ANC and AlcG increases.…”

Constraining the Carbon Budget of Peat Ecosystems: Application of Stoichiometry and Enthalpy Balances

“…The change in atmospheric S deposition is not independent of other C pathways and decreases in S deposition across the Northern Hemisphere have been related to increases in loss of DOC in rivers from peat headwaters (de Wit et al, 2021;Montieth et al, 2007); this has also been observed within this study catchment (Clark et al, 2005). If decreasing S deposition is leading to increased loss of DOC from peat catchments, this not only means an increase in the direct loss of C from peatlands but also that deep peat formation may be limited via Equation 14or Equation 22.…”

Surface Water under Growing Anthropogenic Loads: from Global Loads to Regional Consequences: A Review

“…Montaith et al [45] believe that this process is related to the role of humic acids at the recovery of the chemical composition of lake waters after their acidification over the past two to three decades. Lately many researchers explained this phenomenon by the additional effect of climate warming [9,27,48,61].…”