Weathering rates in Swedish forest soils

Abstract

Abstract. Soil and water acidification was internationally recognised as a severe environmental problem in the late 1960s. The interest in establishing “critical loads” led to a peak in weathering research in the 1980s and 1990s, since base cation weathering is the long-term counterbalance to acidification pressure. Assessments of weathering rates and associated uncertainties have recently become an area of renewed research interest, this time due to demand for forest residues to provide renewable bioenergy. Increased demand for forest fuels increases the risk of depleting the soils of base cations produced in situ by weathering. This is the background to the research programme Quantifying Weathering Rates for Sustainable Forestry (QWARTS), which ran from 2012 to 2019. The programme involved research groups working at different scales, from laboratory experiments to modelling. The aims of this study were to (1) investigate the variation in published weathering rates of base cations from different approaches in Sweden, with consideration of the key uncertainties for each method; (2) assess the robustness of the results in relation to sustainable forestry; and (3) discuss the results in relation to new insights from the QWARTS programme and propose ways to further reduce uncertainties. In the study we found that the variation in estimated weathering rates at single-site level was large, but still most sites could be placed reliably in broader classes of weathering rates. At the regional level, the results from the different approaches were in general agreement. Comparisons with base cation losses after stem-only and whole-tree harvesting showed sites where whole-tree harvesting was clearly not sustainable and other sites where variation in weathering rates from different approaches obscured the overall balance. Clear imbalances appeared mainly after whole-tree harvesting in spruce forests in southern and central Sweden. Based on the research findings in the QWARTS programme, it was concluded that the PROFILE/ForSAFE family of models provides the most important fundamental understanding of the contribution of weathering to long-term availability of base cations to support forest growth. However, these approaches should be continually assessed against other approaches. Uncertainties in the model approaches can be further reduced, mainly by finding ways to reduce uncertainties in input data on soil texture and associated hydrological parameters but also by developing the models, e.g. to better represent biological feedbacks under the influence of climate change.

Water Limitation in Forest Soils Regulates the Increase in Weathering Rates under Climate Change

“…The annual weathering rates calculated by ForSAFE are well within the range presented in Akselsson et al [46], which compiles weathering rates calculated by seven different methods on comparable soils in Sweden. The current annual average weathering calculated in this study, at 0.35 keq•ha −1 •year −1 , is similar to an earlier estimate at 0.33 keq•ha −1 •year −1 using the steady state model PROFILE [19].…”

Reviews and syntheses: Biological weathering and its consequences at different spatial levels – from nanoscale to global scale

“…The subaerial biofilms at this interface today remain stressful environments (Gorbushina, 2007), but ionising radiation levels are now much lower due to thickening of the Earth's atmosphere. Biomarker evidence (Brocks et al, 1999) in rocks formed 200 million years (Myr), before the increase in atmospheric oxygen, suggests that oxygen was already being produced before 2.5 Ga. Oxygenic photosynthesis by cyanobacteria is a likely source of this oxygen but there is evidence that stromatolites were abundant between 3.4 and 2.4 Ga, prior to the advent of cyanobacteria and oxygenic photosynthesis (Allen, 2016), and that Archaean microbial mats of protocyanobacteria switched between photolithoautotrophic and photoorganoheterotrophic metabolism prior to the evolution of cyanobacteria with simultaneous, constitutive expression of genes allowing both types of metabolism. It is also likely that phototrophy based on purple retinal pigments similar to the chromoprotein bacteriorhodopsin, discovered in halophilic Archaea, may have dominated prior to the development of photosynthesis (DasSarma and Schweiterman, 2018).…”

“…Models greatly improve our ability to quantify weathering rates and how they change over time. Akselsson et al (2019) present an extensive review of methods for estimating weathering rates in forest soils. These range from mass-balance budget calculations (e.g.…”

Current, steady-state and historical weathering rates of base cations at two forest sites in northern and southern Sweden: a comparison of three methods

“…Callesen et al, 2016;Brantley et al, 2017), the discrepancy in weathering rates between the two methods would be reduced since PROFILE predicted higher weathering rates with increasing depth. Furthermore, although biological processes are represented in PROFILE, the model fails to capture biological feedback mechanisms in their entirety, in particular feedbacks generated by plant uptake and mycorrhiza (Fin-lay et al, 2009(Fin-lay et al, , 2019Sverdrup, 2009;Smits and Wallander, 2017;Akselsson et al, 2019;Rosenstock et al, 2019a).…”

“…Because it is a mechanistic model, its strength is its trans-parency, while its main weakness is the difficulty in setting values of model parameters and input variables to which it may have high sensitivity. Akselsson et al (2019) concluded that the most important way to reduce uncertainties in modelled weathering rates is to reduce input data uncertainties, e.g. regarding soil texture, although there is still a need to improve process descriptions of biological weathering and weathering brakes (e.g.…”