Base cation reservoirs in soil control the buffering capacity of lakes in forested catchments

Abstract

The acidification of forest soils and surface waters and their relatively poor recovery record following reductions in atmospheric sulphur emissions is a major ongoing environmental problem, particularly in northeastern North America. The slow recovery of surface water is widely hypothesized to result from depletion of reservoirs of base cations in soil. This is concordant with the theory that the acid-neutralizing capacity (ANC) of lakes is likely proportional to the size of the exchangeable base cation reservoirs present in surrounding watershed soils. However, data describing these linkages are still nonexistent in the literature. Here we show that lake ANC is highly predictable (r 2 = 0.75) based on the size of the exchangeable Ca 2+ reservoir in soil in 21 catchments representative of soil and lake conditions encountered in northeastern North America. This finding indirectly supports the hypothesis that the poor recovery of surface water from acidification is governed by the size of base cation reservoirs present in catchment soils. The size of the base cation reservoir in soil is thus a strong indicator of the acid-base status of both soils and surface waters.Résumé : L'acidification des sols forestiers et des eaux de surface ainsi que leur récupération relativement mitigée malgré une diminution des dépôts atmosphériques de soufre représentent toujours un important problème environnemental, particulièrement dans le nord-est de l'Amérique du Nord. La faible récupération des eaux de surface a été principalement attribuée à la diminution des réservoirs de cations basiques dans les sols. Cela suppose que la capacité des eaux de surface à neutraliser les apports acides (CNA) est proportionnelle à la taille des réservoirs de cations basiques échangeables dans les sols des bassins versants. Bien que cette hypothèse paraisse plausible, elle n'a pas encore été démontrée. Dans cette étude, nous démontrons que la CNA des lacs peut être prédite avec succès (r 2 = 0,75) à partir de la taille du réservoir échangeable de Ca 2+ pour 21 bassins versants forestiers représentatifs des conditions lacustres et édaphiques rencontrées dans le nord-est de l'Amérique du Nord. Cette découverte supporte indirectement l'hypothèse selon laquelle la faible amélioration de la CNA des eaux de surface est contrôlée par la taille des réser-voirs échangeables de cations basiques présents dans le sols. Ces derniers sont donc des indicateurs fiables du statut acido-basique non seulement des sols mais aussi des eaux de surface.Houle et al. 474

Soil weathering rates in 21 catchments of the Canadian Shield

“…The PROFILE BC WRs were first compared with the lake BC concentrations taken from Houle et al (2006). Also, estimates of annual catchment BC exports were obtained by multiplying BC lake concentrations by the estimated annual runoff obtained from the FORHYM model for each of the 21 catchments divided by the terrestrial area of the catchments.…”

Assessment of sugar maple tree growth in relation to the partitioning of elements in xylem along a soil acidity gradient

“…Wood and soil samples were collected in six watersheds of the Quebec Lakes Network (Houle et al, 2004(Houle et al, , 2006 …”

“…Notably, these Al wood fractions increased at lower concentrations of soil base cations. Considering that soil base cation reservoirs were shown to contribute largely to the acid neutralizing capacity of forest soils (Houle et al, 2006), it is thus coherent that tree uptake of Al is lessened as base cations reduce the proportion of soil exchange sites being occupied by Al. The negative relation between wood Al and soil pH is consistent with the known enhanced solubility of Al following acidification of forest soils (Ulrich et al, 1980).…”

Modelling and mapping critical loads and exceedances for the Georgia Basin, British Columbia, using a zero base-cation depletion criterion

“…Furthermore, AC leach,CL refers to the rate of soil acid-cation leaching once the critical zero base-cation depletion load is achieved. This quantity is equivalent to critical acid-neutralizingcapacity (ANC) leaching in conventional SSMB terminology (Ouimet et al 2006), such that AC leach,CL = -ANC leach . All terms are in units of eq ha -1 y -1 .…”

“…The risk of harmful effects on natural ecosystems increases when incoming pollutants exceed the critical load (CL) of ecosystems, such as aciddeposition induced soil acidification and base-cation depletion (Nilsson & Grennfelt 1988;Posch et al 2005). Soil acidification and subsequent base-cation depletion in upland (forest) soils in relation to acid precipitation and other factors such as forest harvesting have been reviewed by Watmough & Dillon (2001, Huntington (2005), Duchesne & Houle (2006), Houle et al (2006) and Kreutzweiser et al (2008) for the North American context. Changes in soil base-cation content, however, are not easily relatable to external stressors.…”