Dan Berggren

The role of organic matter in controlling aluminum solubility in acidic mineral soil horizons

Abstract Despite the ecological importance of potentially phytotoxic Al, its solubility control in acidic mineral soils remains unresolved. We examined the solubility of Al in mineral horizons of two acidic forest soils (Inceptisol and Spodosol) in southern Sweden using a series of batch experiments. Dissolution of Al was found to consist of a rapid solubilization of reactive solid phase Al, which quickly reached an equilibrium state, superimposed on a slow dissolution of less reactive Al-containing phases (e.g., primary Al-silicates). Titration experiments in the pH range 3.2–4.7 using an equilibration time of 5 days showed that at pH ∗ K SO = 8.85 at 8° C ) . Under such conditions, the Al solubility could be explained qualitatively by equilibrium complexation reactions with soil organic matter. Quantitatively, our results could be reproduced reasonably well using the mechanistic model WHAM, which describes the binding of Al by humic substances in organic soils. This suggests that the pool of organically bound soil Al controls the Al solubility in suspensions of strongly acidic soils. Due to the kinetically constrained release of Al from primary and secondary minerals, the amount of organically bound Al, and therefore the Al solubility in the suspensions, gradually increases with time. Consequently, a quantitative evaluation of Al solubility data from long-term batch experiments should consider both equilibrium and kinetic processes.

Contributions of Oi, Oe and Oa horizons to dissolved organic matter in forest floor leachates

The aim of this study was to identify the role of organic matter of the Oi, Oe and Oa layers for leaching of dissolved organic matter (DOM) from the O horizon in a podsolised forest soil in southern Sweden. Solid state C-13 cross polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy and C-14 measurements were used to analyse organic matter in solid material and water extracts from the Oi, Oe and Oa horizons, soil leachates collected below the Oe and Oa horizons and throughfall. The DOM in soil leachates from the Oe horizon had a C-14 content that was higher than the water extractable organic matter (WEOM) from the Oi horizon but equal to the C-14 content in the WEOM from the Oe horizon. The C-14 contents in WEOM and DOM from the Oe and Oa horizons were all equal. These results suggest that the DOM leaving the Oe horizon to a large extent had its origin within the Oe horizon itself. NMR spectroscopy showed that WEOM was higher in O-alkyl and lower in aromatic carbon than DOM in soil leachates.

Long-term N addition effects on the C mineralization and DOC production in mor humus under spruce

This study was based on laboratory incubations of mor humus from two N fertilized stands of Norway spruce in Sweden (Skogaby and Strasan), which had received repeated N additions (100 kg N ha(-1) yr(-1) as (NH4)(2)SO4 at Skogaby and 35, 73 and 108 kg ha(-1) yr(-1), as NH4NO3 at Strasan) during 8 and 24-29 years, respectively. The aim was to investigate long-term N effects on the mineralization of C and production of DOC. Mor humus (Oe and Oa) was incubated in columns at 20 degreesC for 49 days. Columns were leached once a week with artificial throughfall solution, which was analyzed for DOC, total N, NH4+-N and NO3--N. Prior to each leaching event, CO2 evolution from the columns was determined. C-to-N ratios in the N-treated Oe layers at Strasan (21-24) and Skogaby (24) were significantly lower than those of the controls (Strasan, 32; Skogaby, 28). The cumulative amount Of CO2-C showed a significant treatment effect in the Oe layer at Skogaby, i.e. 18 and 29 mg C g(-1) C in the N treatment and control, respectively. At Strasan, the cumulative CO2-C was significantly lower in the N3 treatment compared to the control in both layers (33 compared to 74 mg C g(-1) C in the Oe layer and 16 compared to 35 mg C g(-1) C in the Oa layer). Neither the DOC nor the DON production showed any significant treatment effects at the two sites. However, DOC was lower in the fertilized Oe layer at Skogaby throughout the incubation. The leaching of DON was highest in the Oe layers at both sites, and DON increased with time at Skogaby while there was a decreasing trend at Strasan. The DOC-to-DON ratio tended to be lower in the fertilized Oe layers at both sites. The NH4+ leaching at Skogaby decreased in the N-treated Oe and Oa layers. At Strasan, NH4+ from the Oe layer increased in N2 and control. The NO3- leaching was low and constant in both Skogaby layers. At Strasan, NO3- increased in the Oe layer of N1. Cumulative CO2 was positively correlated to C-to-N ratio (r(2) = 0.71, p < 0.01) and to cumulative DOC (r(2) = 0.63, p < 0.05) in the Oe layer at Strasan. Our conclusion was that long-term N additions caused decreased C-to-N ratios and decreased CO2 evolution rates. The correlation between CO2 and C-to-N ratio in the Oe layers at Strasan may be due to a changed quality of the fertilized forest floor material and presence of more N efficient microorganisms. (Less)

Soil Acidification Induced by Ammonium Sulphate Addition in a Norway Spruce Forest in Southwest Sweden

The contributions of different acidifying processes to the total protonload (TPL) of the soil in control plots (C) and ammonium sulphate treatedplots (NS) were studied in a Norway spruce stand in Southwest Sweden during 1988–1998. The annual deposition of inorganic nitrogen and sulphate was on average 18 kg N and 20 kg S ha-1. In addition the NS treated plots received 100 kg N and 114 kg S ha-1 annually. The amounts of nutrients added to the ecosystem by wet and dry deposition and the leaching at 50 cm depth were calculated. The net atmosphericproton load, the proton load by nitrogen transformations in the soil, the sulphate sorption/desorption in the soil and the excess base cation accumulation in biomass were calculated. There was no leaching of inorganic nitrogen from control plots during the study period. The net atmospheric proton deposition, originating from sulphuric and nitric acid deposition, was the main contributor to TPL in control plots. The addition of ammonium sulphate increased the leaching of ammonium, nitrate, sulphate, magnesium and calcium but not of potassium. The TPL in NS plots was about ten times that in control plots. The nitrogen transformation processes were the main contributors to TPL to NS soil, in the beginning by ammonium uptake and later also by nitrification. The pH decreased by 0.4 units in the mineral soil. The between-year variation in TPL during the eleven year period in C plots (200–1500 molc ha-1 yr-1) and in NS plots (1000–13000 molc ha-1 yr-1) was mainly dependent on the sorption or release of sulphate. Both in C and NS, the TPL was buffered mainly by dissolving solid aluminium compounds, most probably some Al(OH)3 phase.

Retention of deposited NH+ 4‐N and NO− 3‐N in coniferous forest ecosystems in Southern Sweden

The main aim of the study was to investigate the retention pattern of atmospherically deposited NH+ 4 plus NO− 3 in podsolized forest soils in southern Sweden during the period 1985–1994. Nitrogen budgets were calculated for 37 coniferous forest sites dominated by Norway spruce (Picea abies (L.) Karst.) or Scots pine (Pinus sylvestris L.). Total deposition of NH+ 4 plus NO− 3 was obtained by adding bulk deposition and dry deposition. Dry deposition was calculated by using regional data on air concentrations of paniculate and gaseous N compounds and previously established deposition velocities in stands of Norway spruce and Scots pine. Nitrogen leaching was obtained by combining measured NH+ 4 and NO− 3 concentrations with the amount of percolating soil water. The latter was chiefly estimated from the Cl− balance, assuming that the flux in throughfall was equal to the Cl− flux in the soil water. Nitrogen uptake by the trees was estimated by inserting data on diameter growth in empirical biornass functions ...

30 Years of N Fertilisation in a Forest Ecosystem - The Fate of Added N and Effects on N Fluxes

We investigated the fate of added N and its effect on N fluxes in a long-term nitrogen fertilisation experiment. Ammonium nitrate was added annually (30 years) at mean rates of 0 (N0), 35 (N1), 73 (N2) and 108 (N3) kg N ha−1 yr−1 to a spruce forest in Sweden, which initially showed signs of N deficiency. Net N mineralisation and N leaching were measured in situ together with soil N pools. We used the PnET-CN model to model the maximum sustainable net N mineralisation rate. The short-term fate of added N was studied by addition of 15NH4Cl. In N1 and N2 most of the added N (80–120%) was retained in the system, compared to 45% in N3. A major fraction was retained in the organic horizons (58–79%). The internal N fluxes had increased considerably as a result of the N additions. Net N mineralisation in N1 had increased by a factor 10 and litterfall N flux by a factor 4. The PnET-CN model could not mimic the fast changes in tree growth and N mineralisation, but the maximum N mineralisation rate seems realistic. The ratio of actual to maximum mineralisation rate indicates that the N1 treatment now is close to N saturation, and nitrate was occasionally found in soil solution from the B-horizon in N1. The N retained was probably to a great extent immobilised directly by mycorrhizal fungi, as indicated by the high amounts of 15N found in the L and F layers and by the great fraction of 15N found in amino sugars compared to amino acids.

The solubility of aluminium in two swedish acidified forest soils : An evaluation of lysimeter measurements using batch titration data

This paper presents aluminium (Al)-solubility data for two acid forest soils (Inceptisol and Spodosol), obtained in connection with lysimeter measurements (tension-cup and zero-tension lysimeters) and batch equilibrium experiments. The solubility of Al obtained in the batch experiments was used as a reference to test whether Al3+in soil solutions collected by the lysimeters was in equilibrium with secondary forms of solid-phase Al (Al(OH)3or organically bound Al). The relation between pH and Al3+activity found for the zero-tension lysimeter solutions collected from the Inceptisol agreed well with that obtained in the batch experiment. This suggests that Al3+in the lysimeter solutions were in, or close to, equilibrium with the solid phase, whether this was organically bound Al (A horizon) or an Al(OH)3phase (B horizon). For the tension-cup lysimeters, solutions obtained from the Inceptisol B and Spodosol Bs1 horizons were generally close to equilibrium with respect to secondary solid-phase Al (apparently Al(OH)3; average ion activity product was 109.3and 108.8, respectively), whereas the Inceptisol A and Spodosol Bh solutions were not. The Al solubility in Inceptisol A and Spodosol Bh horizons was consistently higher than that obtained in the batch equilibrium experiment, indicating that the sampled solution partly originated from the underlying horizons. Thus, tension-cup lysimeters should be used with care in soils (or in parts of soil profiles) having steep solute concentration gradients because the soil volume from which the sample is drawn with this lysimeter type seems to be poorly defined.

Characterization of jarosite-natrojarosite in two northern Scandinavian soils

Abstract Jarosite-type minerals, MFe 3 (SO 4 ) 2 (OH) 6 (MK, jarosite; MNa, natrojarosite), were studied in two Sulfic Cryaquepts developed in sulfidic sediments deposited in the Baltic between 7000 and 4000 BP. The jarosites were characterized by X-ray diffraction (XRD) and a selective dissolution technique. Selective dissolution showed that the K/Na molar ratio in the jarosites was 0.32–1.27, and the XRD patterns indicated that the jarosite and natrojarosite components formed solid solutions. Saturated pastes of soil samples were equilibrated for different periods (6 hours to 8 days) in order to estimate solubility product constants ( K so ) for the jarosite and natrojarosite. Estimated values of K so for jarosite (10 −94.1 − 10 −94.2 ) corresponded well with literature values for pure or nearly pure synthetic jarosite. For natrojarosite only one determination or K so was found in the literature. The discrepancy between this value and the K so values obtained in the present study (10 −93.1 − 10 −93.9 ) is about four orders of magnitude, which is too large to be explained as an effect of solid solution formation. Thus we suggest that the literature value is not valid for the pedogenic natrojarosite in these soils, i.e., it is less soluble than the value indicates. We hypothesize that natrojarosite forms mainly where the supply of K limits jarosite formation, e.g. under conditions where marine or brackish water has a minor influence. The weathering of silicate minerals might be the main source of K and Na in such a case. By contrast, in coastal areas concentrations of K, Na and SO 4 are high, and jarosite formation probably is limited by Fe oxidation. In such environments mainly jarosite is formed owing to its more rapid formation kinetics.