Wolfgang Schaaf

Spatial variability of potential water repellency in a lignitic mine soil afforested with Pinus nigra

Reclaimed mine soils in Lusatia/Germany are heterogeneous sandy sediment mixtures, which often contain significant portions of lignite (brown coal). Water-repellent aliphatic organic compounds may cause preferential finger-type flow in mine soils. The objective of this study was to analyse the significance, spatial scales, and spatial variability of potential water repellency in a lignitic mine soil. The mine site was located northeast of the city of Cottbus, Germany. A soil block of 2.5-m length, 1.25-m width, and 1.5-m depth was divided into squares of 0.25-m edge length from where 25 soil cores of 636 cm3 were sampled at each 0.1-m depth increment. After drying the samples at 60°C for 4 days, the Water Drop Penetration Time (WDPT) test was carried out using 30 water drops per sample. The frequency distributions of the classified potential water repellency were analyzed (i) locally, within a sample, (ii) horizontally, within a layer, and (iii) vertically, within the soil block. The WDPT values of most samples were either smaller than 5–10 s or larger than 10 min. Such ‘bipolar’ distribution occurred for the whole block, as well as locally, i.e., the WDPT varied between repellent and not repellent from drop to drop at distances of about 1 cm. The persistence of potential water repellency seems somewhat larger in the subsoil (0.5–1.5-m depth) than in the ameliorated topsoil (0–40-m depth). However, hardly any spatial structures are obvious since severely repellent, as well as not repellent, soil material occurs throughout the soil profile and intra- was as large as inter-sample variability. To a large degree, the spatial variability of water repellency seems to reflect a situation that resulted from partially mixing of different overburden sediments. The small-scale variability of the potential water repellency may probably be correlated with the spatial distribution of lignite, minerals, and more-or-less lignite-coated sand particles. These spatial patterns of repellency may, in particular, affect water and solute movement in mine soils.

Nutrient supply of forest soils in relation to management and site history

Internal and external factors like forest management practices and atmospheric deposition may have large influences on the nutrient supply of forest soils. Examples are given for the effects of tree species, harvesting, site history, changes of species and specific soil conditions, nitrogen deposition, and forest growth dynamics. It is concluded from these examples that all of these factors may contribute to soil acidification in forest ecosystems under humid temperate climatic conditions.

Magnesium deficiency in forest ecosystems.

1. Introduction R.F. Huttl, W. Schaaf. 2. Visual Mg-Deficiency Symptoms (Coniferous, Deciduous Trees) and Threshold Values (Foliar, Soil) P. Ende, F.H. Evers. 3. Temporal and Spatial Development of Mg Deficiency in Forest Stands in Europe, North America, New Zealand G. Landmann, et al. 4.1 Biogeochemistry of Mg in Forest Ecosystems K.H. Feger. 4.2. Tree Physiology S. Slovik. 4.3. Influence of Magnesium Supply on Tree Growth K. Makkonen-Spieker, H. Spiecker. 5. Causes of Magnesium Deficiency in Forest Ecosystems K. Katzensteiner, G. Glatzel. 6.1 Soil Chemistry S. Augustin, et al. 6.2. Tree Nutrition M. Kaupenjohann. 6.3. Structural Aspects of Mg-Deficiency S. Fink. 6.4. Fine Root Development S. Raspe. 7. Evaluation of Different Mg Fertilization Strategies W. Schaaf. 8. Concluding Remarks R.F. Huttl.

Temporal and spatial development of soil solution chemistry and element budgets in different mine soils of the Lusatian lignite mining area

Lignite and pyrite contents in the dump materials of the Lusatian opencast mining district in East Germany result in high acidification and salinization potentials. These extreme conditions require considerable amounts of alkaline materials like ash or lime to enable recultivation and revegetation. Investigations at chronosequence sites on different mining substrates show characteristic developments of the soil solution chemistry. Processes like weathering of primary and formation of secondary mineral phases, acid production and buffering, and their impacts on both the solid and the liquid soil phase result in high temporal and spatial dynamics especially in the initial phase of soil and ecosystem development. To study these processes we continuously collected soil solutions from different soil depths at seven sites with two representative soil substrates. All sites were afforested with pine and cover stand ages from 1 to 60 yr. The results show that actual pyrite oxidation occurs at the youngest sites on lignite and pyrite containing substrates leading to extremely low pH values and high Fen+ and SO42- concentrations. The considerable acid production causes weathering of aluminium silicates resulting in high Aln+ concentrations. Ca2+ concentrations are unexpectedly high even at low pH showing no correlation to amelioration amounts or depths. Therefore it seems most probable that these mining substrates contain geogenic Ca sources. The transport of dissolved weathering products is limited due to low leaching rates enabling formation of secondary phases which control the actual composition of the soil solution. Depth gradients of the soil solution composition at the chronosequence sites point to a gradual transport and leaching of these secondary phases from the soil profiles. Soil solution composition and dynamics at lignite and pyrite free sites show completely different patterns and have a higher potential for successful sustainable recultivation.

What can element budgets of false-time series tell us about ecosystem development on post-lignite mining sites?

Abstract The post-lignite mining landscape in Lusatia, Germany, is dominated by sandy substrates of Tertiary and Quaternary sediments. Lignite and pyrite contents of varying amounts can result in extremely phytotoxic site conditions. To establish pine stands on these sites, large amounts of CaO were used for amelioration. The development of these ecosystems in 2–60–year–old pine stands on two typical substrates in a ‘false-time series’ approach was studied. Continuous measurements of weather data, soil tensions and soil water contents, together with regular sampling of rainwater and soil solutions at different soil depths, were used to calculate element fluxes through the ecosystems and outputs from the soil. Soil solution compositions indicate very high spatial and temporal dynamics. Over time, sharp depth gradients are formed as a result of amelioration and due to soil forming processes. Acid production by pyrite oxidation, weathering of primary minerals, precipitation of secondary salt and mineral phases, and leaching of salts down the profile are the dominating processes at the lignite and pyrite containing sites. These processes result in long-term soil and site conditions that are very different from pre-mining conditions or compared to non mined soils of the region. Soil solutions are mainly composed of Ca T , Al T , Fe T , and SO 4T depending on soil pH and pyrite content. The dynamics in lignite- and pyrite-free sands are much less pronounced and overall show much lower concentrations. The element outputs from the systems on pyritic substrates can reach very high levels.

Soil solution chemistry and element budgets of three scots pine ecosystems along a deposition gradient in North-Eastern Germany

Since 1993 we are studying three Scots pine ecosystems along a deposition gradient in north-eastern Germany (formerly GDR). Dramatic reductions of pollutant emissions are reported for the period since 1989/90. S-deposition is high at the sites Roesa and Taura (25 kg S ha−1yr−1) compared to Neuglobsow. Inputs of basic cations, especially Ca, by alkaline dust immissions decrease in the order Roesa > Taura > Neuglobsow. The soil solution data show high concentrations of Ca and SO4 at Roesa decreasing drastically along the deposition gradient. The elevated pH values reflect the impact of alkaline dust deposition particularly in the organic surface layer at Roesa. The site Taura received less base cation deposition and is marked by the lowest pH values throughout the soil profile combined with increased Al concentrations in the solution of the mineral soil. Thus, the composition of the soil solutions clearly reflects the different deposition regimes of the past. The element budgets show that large amounts of base cations, sulfur, and, at Taura, also aluminum are actually released from the soils that were previously stored.

Soil solution chemistry of two reclamation sites in the Lusatian lignite mining district as influenced by organic matter application

Due to a large reclamation (recultivation) demand in the Lusatian lignite mining district, efficient strategies for the rehabilitation of abandoned mine sites are needed. A field study was conducted for comparing the effects of three different fertilizer treatments (mineral fertilizer, sewage sludge and compost) on soil solution chemistry of both a lignite and pyrite containing spoil as well as a lignite and pyrite free spoil. The lignite and pyrite containing spoil was ameliorated with fly ash from a lignite power plant (17–21 t ha−1 CaO), whereas the lignite and pyrite free site received 7.5 t ha−1 CaO in form of limestone. Fertilizer application rates were: mineral fertilizer 120 N, 100 P and 80 K kg ha−1. 19 t ha−1 sewage sludge and 22 t ha−1 compost were applied. Soil solution was sampled in 20, 60 and 130 cm depth for the period of 16 months. Solution was collected every fortnight and analysed for pH, EC, Ca2+, Mg2+, K+, Na+, Fen+, Aln+, Mn2+, Zn2+, NO3−, NH4+, SO42−, Cl−, PO43−, Cinorg and DOC. Lignite and pyrite containing spoil differed clearly from lignite and pyrite free spoil regarding soil solution concentrations and composition. Acidity (H+) produced by pyrite oxidation led to an enhanced weathering of minerals and, therefore, to at least 10 fold higher soil solution concentrations compared to the lignite and pyrite free site. Major ions in solution of the lignite and pyrite containing site were Ca2+, Mg2+, Fen+, Aln+ and SO42−, whereas soil solution at the lignite and pyrite free site was dominated by Ca2+, Mg2+ and SO42−. At both sites application of mineral fertilizer led to an immediate but short term (about 1 month) increase of NO3−, NH4+ and K+ concentrations in soil solution down to a depth of 130 cm. Application of sewage sludge caused a long term (about 16 months) increase of NO33− in the topsoil, whereas NO3− concentrations in the subsoil were significantly lower compared to the mineral fertilizer plot. Compost application resulted in a strong long-term increase of K+ in soil solution, whereas NO3− concentrations did not increase. Concentrations of PO43− in soil solution depend on solution pH and were not correlated with any treatment.

Element budgets of two afforested mine sites after application of fertilizer and organic residues

The effects of mineral fertilizer, sewage sludge and compost application on soil solution chemistry and element fluxes at two mine spoils were studied in a field trial. The two sites differed in substrate composition: (a) a pyrite and lignite containing spoil (WEB site); and (b) a pyrite and lignite free spoil (SEE site). Soil solution was continuously sampled at 20 and 130 cm soil depth over a 2-year period, and analyzed for all major elements, pH, and electrical conductivity. At the WEB site, major elements in soil solution at 20 cm depth were Ca, Mg, Al and SO4-S. In the unameliorated subsoil, Fe was detected in high concentrations. Pyrite oxidation caused massive element fluxes of up to 6 t Fe ha−1 year−1 and 14 t SO4-S ha−1 year−1. At the SEE site, major elements in soil solution were Ca, Mg and SO4-S. Maximum element fluxes measured 1 t Ca ha−1 year−1 and 1 t SO4-S ha−1 year−1. Application of mineral fertilizer and organic residues increased NO3, NH4, K, and Cl concentrations and fluxes. Thirty to 40% of the applied mineral fertilizer was leached below 20 cm within 4 weeks. Sewage sludge application led to N fluxes in 20 cm depth of 56 kg N ha−1 (2 years)−1 at the SEE site and 94 kg N ha−1 (2 years)−1 at the WEB site, equivalent to 5 and 10% of N applied with sewage sludge, respectively. At the SEE site, NO3-N fluxes were increased down to 130 cm soil depth after application of sewage sludge. At both sites, compost plots showed lower N fluxes (25 and 14 kg N ha−1) compared with the control plots (35 and 24 kg N ha−1). In contrast, potassium fluxes were significantly increased after compost application. However, the overall effects on soil solution chemistry from application of mineral fertilizer and organic residues were small relative to the effects from mining only.

Soil microcosm experiments to study the effects of waste material application on nitrogen and carbon turnover of lignite mine spoils in Lusatia (Germany)

The lignite and pyrite containing spoil substrates of the Lusatian mining district are marked by very high acidity and salt concentrations due to pyrite oxidation and by a very low content of pedogenic organic matter and nutrients. The effects of fly ash application to neutralize the produced acid and of organic waste material application to improve the ecological soil functions were studied considering the carbon and nitrogen cycling. Nineteen, 38 and 57 t ha−1 sewage sludge and 22, 44 and 66 t ha−1 compost were applied to ameliorated lignite and pyrite containing substrate. An automated soil microcosm system was used to analyse the solid, gaseous and liquid phases. Almost 9% of total N applied with sewage sludge (620, 1240 and 1860 t N ha−1 applied) were lost over a period of 150 days mainly as NO3-N. The total N losses from compost treatments were three times lower (2.8–3.1% of applied Nt) and occurred in similar quantities as NH4-N and NO3-N. Only sewage sludge treatments showed slightly increased N2O emissions at the beginning of the experiment. CO2 emissions determined the carbon losses of all treatments. The C losses amounted to 3.2–4.7% and 1.5–2.7% of Ct applied with sewage sludge and with compost, respectively.

Short Communication Actual cation exchange capacity in lignite containing pyritic mine soils

The actual cation exchange capacity (CEC act ) in sandy mine soils from Tertiary sediments increases with the lignite contents of the substrates. Therefore, lignite is important for nutrient storage and availability in these soils. Base saturation varies over a wide range of 4 - 100% according to soil pH. For the determination of CEC act , the high contents of soluble salts typical for these substrates have to be considered for reliable results.