Modelling acidification, recovery and target loads for headwater catchments in Nova Scotia, Canada

Abstract

Abstract. The response of twenty acid-sensitive headwater catchments in Nova Scotia to acidic deposition was investigated for the period 1850-2100 using a dynamic hydrochemical model (MAGIC: Model of Acidification of Groundwater in Catchments). To ensure robust model simulation, MAGIC was calibrated to the long-term chemical trend in annual lake observations (13-20 years). Model simulations indicated that the surface waters of all twenty catchments acidified to the 1970s but showed subsequent recovery (increases in acid neutralising capacity (ANC) and pH) as sulphate deposition decreased. However, under proposed future emissions reductions (approximately 50% of current deposition) simulated ANC and pH will not return to estimated pre-industrial levels by 2100. An ANC of 20 µmol c L −1 and pH of 5.4 were defined as acceptable chemical thresholds (or critical chemical limits) for aquatic organisms in the current study. Under the proposed emissions reductions only one catchment is predicted to remain below the critical limit for ANC by 2100; three additional catchments are predicted to remain below the critical limit for pH. Dynamic models may be used to estimate target loads, i.e., the required deposition reductions to achieve recovery within a given time. Setting target loads at approximately 30% of current depositions would allow three of the four lakes to reach the chemical criteria by 2030. In contrast to the generally good prognosis for surface waters, soils lost an average of 32% of estimated initial base saturation and recovery is estimated to be very slow, averaging 23% lower than pre-acidification levels in 2100.

Palaeolimnological assessment of lake acidification and environmental change in the Athabasca Oil Sands Region, Alberta

“…Of particular concern are the impacts of industrial activities on traditional aboriginal uses of the land, including hunting and fishing. Lake acidification is a well-known impact of acid deposition in regions of slow weathering bedrock and has occurred in eastern Canada and the USA (e.g., Schindler 1988;Charles 1991;Jeffries 1997;Stoddard et al 1999;Jeffries et al 2003;Whitfield et al 2007) and many parts of Europe (e.g., Kamari et al 1991;Henriksen et al 1992;1998;Curtis et al 2000Curtis et al , 2005. Surveys of lake water chemistry in northern Alberta carried out by another multi-stakeholder group, the Regional Aquatics Monitoring Programme (RAMP) have identified acid sensitive lakes in many parts of the region (e.g., RAMP 2008).…”

Assessment of Uncertainty in Long-Term Mass Balances for Acidification Assessments: A MAGIC Model Exercise

“…MAGIC has been widely applied in Europe and North America (Cosby et al 1985a, b;Wright et al 1994;Wright and Cosby 2003;Moldan et al 2004;Whitfield et al 2007;Aherne et al 2007 among others), mainly for estimating the potential effects of acid deposition on surface water quality. The exact mathematical formulation of the model can be found elsewhere (Cosby et al 1985a, b;Cosby et al 2001).…”

“…This in turn would influence the choice of SO 4 2-adsorption factors. Sulfate adsorption has been used in a number of previous MAGIC applications (Forsius et al 1998;Martinson et al 2003;Moldan et al 2004;Whitfield et al 2007Whitfield et al , 2011 with SO 4 2-adsorption capacities varying between 0.1 and 2.5 meq kg -1 soil. Martinson et al (2003) used the SAFE model at the Gårdsjön site and found that when adsorption of significant amounts of SO 4 2-was included in the model the fit to measured data improved.…”

“…Martinson et al (2003) used the SAFE model at the Gårdsjön site and found that when adsorption of significant amounts of SO 4 2-was included in the model the fit to measured data improved. Sulfate has been handled in various ways for different sites; some authors tend to disregard SO 4 2-desorption and assume steady state (Wright and Cosby 2003) or use small values (Whitfield et al 2007). …”

“…Both Wright and Cosby (2003) and Whitfield et al (2007) have demonstrated that MAGIC calibrations are more robust when applied for longer time scales.…”