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

Abstract

Long-term (1860-2010) catchment mass balance calculations rely on models and assumptions which are sources of uncertainty in acidification assessments. In this article, we report on an application of MAGIC to model acidification at the four Swedish IM forested catchments that have been subject to differing degrees of acidification stress. Uncertainties in the modeled mass balances were mainly associated with the deposition scenario and assumptions about sulfate adsorption and soil mass. Estimated base cation (BC) release rates (weathering) varied in a relatively narrow range of 47-62 or 42-47 meq m -2 year -1 , depending on assumptions made about soil cation exchange capacity and base saturation. By varying aluminum solubility or introducing a dynamic weathering feedback that allowed BC release to increase at more acidic pHs, a systematic effect on predicted changes in acid neutralizing capacity (DANC ca. 10-41 leq l -1 ) and pH (ca. DpH = 0.1-0.6) at all sites was observed. More robust projections of future changes in pH and ANC are dependent on reducing uncertainties in BC release rates, the timing, and extent of natural acidification through BC uptake by plants, temporal changes in soil element pools, and fluxes of Al between compartments.

Recovery of Soil Water, Groundwater, and Streamwater From Acidification at the Swedish Integrated Monitoring Catchments

“…3), which to some extent compensated for the decreased SO 4 2-concentrations. At Gårdsjön, the mean Cl -concentrations were in the range 400-500 leq l -1 in all aqueous media, while at Aneboda they increased from the recharge areas (&100 leq l -1 ) toward the stream (200-300 leq l -1 , Table 3), indicating the presence of an unknown local Cl -source (see Köhler et al 2011). At Kindla, the mean Cl -concentrations were in the range 50-80 leq l -1 in all aqueous media.…”

“…In this assessment, we have used the total deposition values by Köhler et al (2011) covering the years 1996-2009 for all IM sites except Gammtratten where the measurements started in 1999. The input of major ions in wet and dry deposition was estimated from bulk deposition and throughfall.…”

“…Dry deposition was estimated by subtracting wet deposition from total deposition. For a more detailed description of the methodology see Köhler et al (2011). Long-term average climatic data from 1961 to 1990 (Raab and Vedin 1995) and, within brackets (precipitation), for the study period …”

“…Model simulations of streamwater chemistry based on lumped data from hydraulically different compartments of the catchment may thus be flawed. Further discussion of this issue is presented in this volume by Futter et al (2011), Köhler et al (2011), andWinterdahl et al (2011).…”

Simulating damage for wind storms in the land surface model ORCHIDEE-CAN (revision 4262)

“…Furthermore, storm-induced disturbances are likely to provide feedbacks on climate through direct effects such as increasing greenhouse gas emissions (Lindroth et al, 2009), increasing surface albedo (Planque et al, 2017), and decreasing local cloud 10 frequency (Teuling et al, 2017) as well as indirect effects such as increased natural disturbances, a reduced logging rate in subsequent years, increased weathering, and increased C, N and cation leaching (Futter et al, 2011;Köhler et al, 2011).…”