Modelling the solid–solution distributions of protons, aluminium, base cations and humic substances in acid soils

Abstract

WHAM, an equilibrium chemical model for soils, waters and sediments, centred on a discrete-site/ electrostatic model of humic substances (HS), has been used to analyse batch titration data for organic and mineral horizons of acid soils. In most cases, tolerable fits were obtained by optimizing the soil contents of HS and aluminium, while keeping the model parameters (site densities, equilibrium constants, electrostatic terms) fixed. The optimized contents agreed reasonably with those estimated by chemical extraction. For some mineral soil samples, low in HS and high in aluminium, fitting of the titration data was improved by assuming the formation and dissolution of AI(OH)3 and adjusting its solubility product. Solid-solution distributions of base cations (Na+, Mg2+, K + , Ca2+, NH: ) could be explained by non-specific counterion accumulation, with a small degree of selectivity. The WHAM sub-model for fulvic acid sorption accounted approximately for observed aqueous-phase concentrations of organic carbon and organically-complexed aluminium.

Groundwater Al dynamics in boreal hillslopes at three integrated monitoring sites along a sulphur deposition gradient in Sweden

“…Due to the low number of observations the representativity of these data can be (Tipping et al, 1995;van Hees et al, 2001;van Hees and Lundstrom, 2000). This overall pattern of increasing Al t accompanied by increasing TOC and decreasing pH was seen in both acidified and pristine sites in other studies (Mulder et al, 1991;Pellerin et al, 2002).…”

Aquatic DOC export from subarctic Atlantic blanket bog in Norway is controlled by seasalt deposition, temperature and precipitation

“…Aquatic concentrations (and fluxes) of DOC in headwater streams are the result of catchment processes where DOC is produced from fresh and humified organic materials (Michalzik et al 2001), sorbed and desorbed from solid phases by metal complexation and acidity (Neff and Asner 2001;Tipping et al 1995), and displaced and leached by vertical and lateral water movement (Boyer et al 1996;Ledesma et al 2015). Atmospheric deposition of sulfate (Monteith et al 2007) and chloride (Moldan et al 2012) can lower DOC concentrations by suppressing organic matter solubility.…”

Humic Ion-Binding Model VII: a revised parameterisation of cation-binding by humic substances

“…Examples include 71 the acidification of soils [7][8][9][10][11][12][13][14] and surface waters [15] , trace metal behaviour in soils [16][17][18][19][20][21][22] , surface 72 waters [23][24][25][26][27][28][29][30][31] and groundwaters [32] , lake sediment diagenesis [33,34] , rare earth geochemistry [35-73 37] , iron and manganese geochemistry [38][39][40][41] , radionclide geochemistry [42][43][44][45] , organic matter 74 solubility in soils [46,47] , catchment modelling [48,49] , interactions of metals with biota [50,51] , 75 ecotoxicology [52][53][54][55][56][57][58][59] and Critical Loads …”