Soil weathering rates in 21 catchments of the Canadian Shield

Abstract

Abstract. Soil mineral weathering represents an essential source of nutrient base cation (Ca, Mg and K) for forest growth in addition to provide a buffering power against precipitation acidity for soils and surface waters. Weathering rates of base cations were obtained for 21 catchments located within the temperate and the boreal forest of the Canadian Shield with the geochemical model PROFILE. Weathering rates ranged from 0.58 to 4.46 kmol c ha −1 yr −1 and their spatial variation within the studied area was mostly in agreement with spatial variations in soil mineralogy. Weathering rates of Ca and Mg were significantly correlated (r = 0.80 and 0.64) with their respective lake concentrations. Weathering rates of K and Na did not correlate with lake concentrations of K and Na. The modeled weathering rates for each catchment were also compared with estimations of net catchment exportations. The result show that modeled weathering rates of Ca were not significantly different than the net catchment exportations while modeled weathering rates of Mg were higher by 51 %. Larger differences were observed for K and Na weathering rates that were significantly different than net catchment exportations being 6.9 and 2.2 times higher than net exportations, respectively. The results for K were expected given its high reactivity with biotic compartments and suggest that most of the K produced by weathering reactions was retained within soil catchments and/or above ground biomass. This explanation does not apply to Na, however, which is a conservative element in forest ecosystems because of the insignificant needs of Na for soil microorganisms and above ground vegetations. It raises concern about the liability of the PROFILE model to provide reliable values of Na weathering rates. Overall, we concluded that the PROFILE model is powerful enough to reproduce spatial geographical gradients in weathering rates for relatively large areas as well as adequately predict absolute weathering rates values for the sum of base cations, Ca and Mg.

The importance of atmospheric base cation deposition for preventing soil acidification in the Athabasca Oil Sands Region of Canada

“…The median base cation weathering rate was just 17 mmol c m −2 yr −1 and more than 80% (52 of 63) of the sites had a base cation weathering rate b40 mmol c m −2 yr −1 . These weathering estimates are at the lower end of weathering estimates for soils in other parts of Canada: base cation weathering rates for the soil rooting zone of 3-13 mmol c m −2 yr −1 (Nova Scotia: Whitfield et al, 2006); 58-446 mmol c m −2 yr −1 (Quebec: Houle et al, 2012); 21 -79 mmol c m −2 yr −1 (Ontario: Koseva et al, 2010); 0.1-8000 mmol c m −2 yr −1 (Saskatchewan: Whitfield and Watmough, 2012); and 19-351 mmol c m −2 yr −1 (British Columbia: Mongeon et al, 2010). Weathering rates in this study were estimated using PROFILE, which like all methods used to estimate base cation weathering rates, is associated with some uncertainties (Hodson and Langan, 1999).…”

Impact of Climate Change on Soil Hydro-Climatic Conditions and Base Cations Weathering Rates in Forested Watersheds in Eastern Canada

“…described in previous studies (Houle et al, 2012b;Augustin et al, 2015aAugustin et al, , 2016. In this region, the Canadian Shield is composed of bedrocks formed during the Precambrian, which consists mainly of igneous (granite, syenite, anorthosite) and metamorphic (gneiss, granitic gneiss, paragneiss) rocks.…”

“…The geochemical model PROFILE is widely used to evaluate chemical and geochemical processes involved in forest soils and watersheds (Koptsik et al, 1999;Duan et al, 2002;Duchesne and Houle, 2006;Sverdrup, 2009;Erlandson Lampa et al, 2020). Previous works have shown that PROFILE is enough powerful to reproduce spatial geographical gradients in WRs for relatively large areas with contrasted mineralogy (Houle et al, 2012b;Augustin et al, 2016), while yielding reliable BC WRs (Jönsson et al, 1995). Since soil temperature and moisture both greatly affect the chemical, physical, and biological processes that are occurring in soils, it is essential to better understand how climate change will affect resulting future soil conditions.…”

Wetlands and low‐gradient topography are associated with longer hydrologic transit times in Precambrian Shield headwater catchments

“…The Precambrian Shield in Canada is dominated by catchments with areas of hundreds or thousands of square kilometres and numerous smaller, but important, headwater catchments (Craig & Johnston, ; Creed, Beall, Clair, Dillon, & Hesslein, ; Houle et al, ). Glaciation from the last ice age has led to significant surface‐exposed bedrock outcrops and thin soil resting on top of Precambrian bedrock (Gunn, Steedman, & Ryder, ).…”