The discharge of acidic mine drainage waters onto a hillslope in Dalarna, central Sweden, has lead to the contamination of the podzol soils with Cu, Fe, Ni, Pb, Zn and sulfate. Samples from contaminated and reference soils have been collected for chemical and mineralogical analyses. Jarosite is identified by x-ray diffraction analysis as a precipitate in the upper horizons (A, E, B) of the contaminated soils, where the soil acidity (pHKCₗ ∼ 2.6) promotes jarosite stability. The sequential chemical extraction of soil samples indicates that, in the reference A horizon, Cu, Pb, Ni and Zn are bound primarily to cation exchange sites and organic matter. In the A horizon of the contaminated soils closest to the rock dump, metal partitioning is dominated by the Fe oxide fractions, despite the high organic matter content; Pb is almost completely bound to crystalline Fe oxides, possibly adsorbed to Fe oxides or occuring in a jarosite solid solution. In the reference B and C horizons, Cu, Ni and Zn are primarily adsorbed/coprecipitated in the Fe oxide fractions, while Pb remains with a large fraction bound to organic matter. In the Fe-rich B horizon of the contaminated soils, the partitioning of the metals in cation exchange sites and to organic matter has greatly increased relative to the reference soils, resulting from the mobilization of organo-metal complexes down the profile.

The weathering release rate of base cations (BCw) from soil minerals is fundamentally important for terrestrial ecosystem growth, function, and sensitivity to acid deposition. Understanding BCw is necessary to reduce or prevent damage to acid-sensitive natural systems, in that this information is needed to both evaluate the effectiveness of existing policies, and guide establishment of further policies in the event they are required. Yet BCw is challenging to estimate. In this study, major sources of uncertainty associated with a process-based model (PROFILE) commonly used to estimate weathering rates were quantified in the context of efforts to quantify BCw for upland forest sites across the continental USA. These include uncertainty associated with parameterization of mineral content where horizon data are not available, stoichiometry of individual minerals, and specific surface area of soil and individual soil minerals. Mineral stoichiometry was not an important influence on BCw estimates (uncertainty < 1%). Characterizing B horizon mineralogy by averaging A and C horizons was found to be a minor (< 5%) contributor to uncertainty in some areas, but where mineralogy is known to vary with depth the uncertainty can be large. Estimating mineral-specific surface areas had a strong influence on estimated BCw, with rates increasing by as much as 250%. The greatest uncertainty in BCw estimates, however, was attributed to the particle size class-based method used to estimate the total specific surface area upon which weathering reactions can take place. The resulting uncertainty in BCw spanned multiple orders of magnitude at individual sites, highlighting this as the greatest challenge to ongoing efforts to produce robust BCw estimates across large spatial scales in the USA. Recommendations for improving estimates of BCw to support robust decision making for protection against terrestrial acidification are provided.

Microbial removal of C and N in soil-based wastewater treatment involves emission of CO₂, CH₄, N₂O, and N₂ to the atmosphere. Water-filled pore space (WFPS) can exert an important control on microbial production and consumption of these gases. We examined the impact of WFPS on emissions of CO₂, CH₄, N₂O, and N₂ in soil microcosms receiving septic tank effluent (STE) or effluent from a single-pass sand filter (SFE), with deionized-distilled (DW) water as a control. Incubation of B and C horizon soil for 1 h (the residence time of wastewater in 1 cm of soil) with DW produced the lowest greenhouse gas (GHG) emissions, which varied little with WFPS. In B and C horizon soil amended with SFE emissions of N₂O increased linearly with increasing WFPS. Emissions of CO₂ from soil amended with STE peaked at WFPS of 0.5–0.8, depending on the soil horizon, whereas in soil amended with SFE, the CO₂ flux was detectable only in B horizon soil, where it increased with increasing WFPS. Methane emissions were detectable only for STE, with flux increasing linearly with WFPS in C horizon soil, but no clear pattern was observed with WFPS for B horizon soil. Emissions of GHG from soil were not constrained by the lack of organic C availability in SFE, or by the absence of NO₃ availability in STE, and addition of acetate or NO₃ resulted in lower emissions in a number of instances. Emission of ¹⁵N₂ and ¹⁵N₂O from ¹⁵NH₄ took place within an hour of contact with soil, and production of ¹⁵N₂ was much higher than ¹⁵N₂O. ¹⁵N₂ emissions were greatest at the lowest WFPS value and diminished markedly as WFPS increased, regardless of water type and soil texture. Our results suggest that the fluxes of CO₂, CH₄, N₂O, and N₂ respond differently to WFPS, depending on water type and soil texture.

Batch adsorption experiments were carried out with samples from an A-, Bh- and C-horizon of contaminated sandy soil of podzolic character from the Kempen region at the Dutch-Belgian border. Cadmium sorption was studied on 3 soil samples at 3 different pH-levels (3.6, 4.3 and soil buffered pH) and 3 different additions of zinc (0–40 mg l⁻¹).Adsorption of cadmium by acid sandy soils can be fitted by a Freundlich adsorption isotherm. Although zinc competes with cadmium for the sorption sites, we observe a two to three times stronger competition effect of the proton cation, which is explained by the chemical properties of both ions. The cadmium adsorption coefficient KF decreases considerably by an increase of the proton activity used in the sorption experiments. Organic matter content explains for a large part the variation of KF of te three soil samples. Desorption data do not fit the proposed regression model for adssorption. Not all the cadmium, intitially present in the polluted soil, will fylly desorb reversibly. Thus, part of the cadmium may be irreversible bound.

The nitrite reductase (nirS and nirK) and nitrous oxide reductase-encoding (nosZ) genes of denitrifying populations present in an agricultural grassland soil were quantified using real-time polymerase chain reaction (PCR) assays. Samples from three separate pedological depths at the chosen site were investigated: horizon A (0–10 cm), horizon B (45–55 cm), and horizon C (120–130 cm). The effect of carbon addition (treatment 1, control; treatment 2, glucose-C; treatment 3, dissolved organic carbon (DOC)) on denitrifier gene abundance and N₂O and N₂ fluxes was determined. In general, denitrifier abundance correlated well with flux measurements; nirS was positively correlated with N₂O, and nosZ was positively correlated with N₂ (P < 0.03). Denitrifier gene copy concentrations per gram of soil (GCC) varied in response to carbon type amendment (P < 0.01). Denitrifier GCCs were high (ca. 10⁷) and the bac:nirK, bac:nirS, bac:nir ᵀ , and bac:nosZ ratios were low (ca. 10⁻¹/10) in horizon A in all three respective treatments. Glucose-C amendment favored partial denitrification, resulting in higher nir abundance and higher N₂O fluxes compared to the control. DOC amendment, by contrast, resulted in relatively higher nosZ abundance and N₂ emissions, thus favoring complete denitrification. We also noted soil depth directly affected bacterial, archaeal, and denitrifier abundance, possibly due to changes in soil carbon availability with depth.