The impacts of future climate change and sulphur emission reductions on acidification recovery at Plastic Lake, Ontario

Abstract

Abstract. Climate-induced drought events have a significant influence on sulphate export from forested catchments in central Ontario, subsequently delaying the recovery of surface waters from acidification. In the current study, a model chain that employed a statistical downscaling model, a hydrological model and two hydrochemical models was used to forecast the chemical recovery of Plastic Lake sub-catchment 1 (PC1) from acidification under proposed deposition reductions and the A2 emission scenario of the Intergovernmental Panel on Climate Change. Any predicted recovery in stream acid neutralising capacity and pH owing to deposition reductions were clearly offset by large acid effluxes from climateinduced drought events. By 2100, ANC is predicted to show large variations ranging between 10 and −30 µmol c L −1 . Similarly, predicted pH in 2100 is lower (>0.05 of a pH unit) than the value simulated for 2000 (pH 4.35). Despite emission reductions, the future scenario paints a bleak picture of reacidification at PC1 to levels commensurate with those of the late 1970s. The principal process behind this reacidification is the oxidation of previously stored (reduced) sulphur compounds in wetlands during periods of low-flow (or drought), with subsequent efflux of sulphate upon rewetting. Simulated catchment runoff under the A2 emissions scenario predictes increased intensity and frequency of lowflow events from approximately 2030 onwards. The Integrated Catchments model for Carbon indicated that stream DOC concentrations at PC1 will also increase under the future climate scenario, with temperature being the principal driver. Despite the predicted (significant) increase in DOC, pH is not predicted to further decline (beyond the climateinduced oxidation scenario), instead pH shows greater variability throughout the simulation. As echoed by many recent studies, hydrochemical models and model frameworks need to incorporate the drivers and mechanisms (at appropriCorrespondence to: J. Aherne (julian.aherne@ucd.ie) ate time-scales) that affect the key biogeochemical processes to reliably predict the impacts of climate change.

Comparisons of watershed sulfur budgets in southeast Canada and northeast US: new approaches and implications

“…An oxygen isotope study of the dissolved SO 4 2-in soil solution demonstrated that 32-61% of the SO 4 2-leaving the catchment had interacted with organic S in the soil (Gélineau et al 1989). Previous work at Plastic Lake (PC1) Watershed has indicated that sulfate export was strongly influenced by the presence of a large coniferSphagnum swamp (e.g., LaZerte 1993; Eimers and Dillon 2002;Eimers et al 2007;Aherne et al 2008). Stable isotopic analyses have shown that changes in SO 4 2-concentration at this watershed are associated with microbial redox processes (Eimers et al 2004a, b).…”

Assessment of impact of climate change on water resources in a hilly river basin

“…SDSM has shown advantage over other statistical downscaling approaches such as weather generators and weather typing because of its better ability in describing inter-annual variability. It has widely been used throughout the world to downscale single-site scenarios of daily surface weather variables from predictors of GCMs for assessing hydrologic responses in climate change scenarios (Dibike and Coulibaly 2005;Gagnon et al 2005;Aherne et al 2008;Combalicer et al 2010;Huang et al 2011;Goyal et al 2012). …”

Air-pollution emission control in China: Impacts on soil acidification recovery and constraints due to drought

“…The further control scenario combined with drought (scenario 3′) might reduce the SO 4 2− concentration to a level lower than in scenario 1. Recent studies also indicated that drought significantly affected SO 4 2− export from forested catchments, subsequently delaying the recovery of surface waters from acidification (Aherne et al, 2008;Evans et al, 1998;Larssen, 2005;Wright et al, 2006). Those studies emphasized that the reoxidation of sulfur stored in wetlands as sulfide caused episodic acidification during the rain events, which were strongly associated with preceding drought conditions (Aherne et al, 2008;Laudon et al, 2004).…”

“…Recently, the effects of climate change and climate variation, especially climate-induced drought, on water acidification and recovery, have attracted considerable attention (e.g., Aherne et al, 2008;Bencokova et al, 2011;Evans et al, 1998;Kerr et al, 2011;Larssen, 2005;Laudon et al, 2004;Wright et al, 2006). Historical precipitation data showed drier summers and an increased frequency of droughts across southeastern China (Ren et al, 2005).…”