Bernhard Manderscheid

Is acidification still an ecological threat

There has been a significant reduction in anthropogenic acid deposition in Europe and North America, and now we need to gauge the rate and extent of ecosystem recovery. Stoddard et al. have reported a widespread aquatic recovery from acidification in European ecosystems in response to a fall in sulphate deposition. But many sites in central Europe are showing a significant delay in aquatic recovery from acidification, or even no recovery at all, and only some of them show biological recovery of waters or a recovery from soil acidification. Ecosystem management still needs to consider the consequences of acidification.

Spatial and temporal variation of soil solution chemistry and ion fluxes through the soil in a mature Norway Spruce (Picea abies (L.) Karst.) stand

In this study we investigated the spatial and temporal variation in soil solution chemistry and of water and ion fluxes through the soil in a forest ecosystem. Our aim was to evaluate the relevance of these variations for the accuracy of average areal soil solution concentrations and ion fluxes with seepage at 90 cm depth.Twenty spatially distinct ‘subcompartments’ of approximately 1 m2 were established within a mature stand of Norway spruce and ceramic suction lysimeters were installed at depths of 20, 35 and 90 cm. A tensiometer was placed close to each suction lysimeter, and one throughfall sampler was established for each subcompartment.Soil solution samples were analysed for major ions (H+, Na+, K+, Ca2+, Mg2+, Mn2+, Fe3+, Al3+, Cl-, NO3-, SO42-. We calculated water fluxes for each subcompartment separately by a numeric simulation of the soil water flux close to the lysimeters. The ion fluxes at each lysimeter were calculated by multiplying the simulated water fluxes with the ion concentrations on a fortnightly base. Averaging these 20 independent ion fluxes gave the areal average flux and an estimate of its statistical accuracy. The spatial variation of ion concentrations in the soil solution was high with coefficients of variance ranging from 5% to 128%. Part of the spatial variation was related to stem distance. Temporal variation of the concentrations was less than spatial for most ions. The spatial variation of water and ion fluxes with seepage was also substantial; for example the fluxes of SO42- -S calculated for each subcompartment ranged from 21 to 119 kg ha-1 yr-1, with an arithmetic average of 47 kg ha-1 yr-1. For H2O, Mg2+, Cl-, and SO42- , the spatial heterogeneity of seepage fluxes was largely explained by the heterogeneity of throughfall fluxes. No such relationship was found for nitrogen.Despite using 20 replicates, the 95% confidence intervals of the average annual areal fluxes with seepage were found to be 20–30% for most ions.

Effects of reduced atmospheric deposition on soil solution chemistry and elemental contents of spruce needles in NE—Bavaria, Germany

The decrease in anthropogenic deposition, namely SO42- and SO2, in European forest ecosystems during the last 20 years has raised questions concerning the recovery of forest ecosystems. The aim of this study was to evaluate if the long term data of element concentrations at the Fichtelgebirge (NE-Bavaria, Germany) monitoring site indicates a relationship between the nutrient content of needles and the state of soil solution acidity. The soil at the site is very acidic and has relatively small pools of exchangeable Ca and Mg. The trees show medium to severe nutrient deficiency symptoms such as needle loss and needle yellowing. The Ca and Mg concentrations in throughfall decreased significantly during the last 12 years parallel to the significant decline in the throughfall of H+ and SO42- concentrations. Soil solution concentrations of SO42-, Ca and Mg generally decreased while the pH value remained stable. Aluminum concentrations decreased slightly, but only at a depth of 90 cm. Simultaneously a decrease in the molar Ca/Al and Mg/Al ratios in the soil solution was observed. Ca and Mg contents in the spruce needles decreased, emphasizing the relevance of soil solution changes for tree nutrition. The reasons for the delay in ecosystem recovery are due to a combination of the following two factors: (1) the continued high concentrations of NO3— and SO42— in the soil solution leading to high Al concentrations and low pH values and, (2) the decreased rates of Ca and Mg deposition cause a correlated decrease in the concentration of Ca and Mg in the soil solution, since little Ca and Mg is present in the soils exchangeable cation pools. It is our conclusion that detrimental soil conditions with respect to Mg and Ca nutrition as well as to Al stress are not easily reversed by the decreasing deposition of H+ and SO42—. Thus, forest management is still confronted with the necessity of frequent liming to counteract the nutrient depletion in soils and subsequent nutrient deficiencies in trees.

Spatial heterogeneity of soil solution chemistry in a mature Norway spruce (Picea abies (L.) Karst.) stand

The determination of the average soil solution concentrations in forest soils is hindered by the spatial heterogeneity of the soil conditions and the stand structure on all scales. The aim of this paper is to investigate the spatial heterogeneity of the soil solution chemistry within a mature stand of Norway spruce and to evaluate the implication of this heterogeneity for the sampling design for soil solutions.The site is a 140 years old Norway spruce stand of 2.5 ha located in the German Fichtelgebirge at 800 m elevation on granitic, deeply weathered bedrock. At 35 cm soil depth, 59 ceramic suction lysimeters (5 cm length, 2 cm diameter) were installed in a systematic grid of 25 · 25 m and soil solution was sampled at 3 dates in June and July 1994. The solutions were analysed for major cations and anions.Semi-variance of the concentrations at a given date revealed no systematic spatial patterns. The coefficients of variance of the element concentrations were between 36 and 298% with highest values for NH4+-N. The implications of the observed heterogeneity for the appropriate number of replicates was investigated by Monte Carlo simulations. As an example, the probability that the measured average concentration of SO42−-S is outside a ±10% range (related to the ‘true’ 59 lysimeter average) is about 68% if only 3 replicates would have been used, 41% with 10 replicates and 25% with 20 replicates. Due to the generally large spatial heterogeneity of the soil solution chemistry in forest soils the number of lysimeters used must be carefully adjusted to site conditions and the specific question.

Long-Term Development of Element Budgets in a Norway Spruce ( Picea Abies (L.) Karst.) Forest of the German Solling Area

To evaluate ecosystem response to changing atmospheric deposition, element budgets were established over the period from 1973 to 1991 for a Norway Spruce (Picea abies (L.) Karst.) site. Budgets for Na+, Cl−, Ca2+, Mg2+, N, S and H+ were based on total deposition and seepage water fluxes. The deposition of Ca2+, Mg2+, particularly, of S and H+ decreased with time, while calculated N deposition remained constant at a high level. The decrease in Ca2+ deposition led to a reduction of Ca2+ fluxes with seepage water. The decrease of Mg2+ deposition did not have an effect on the output fluxes of Mg2+. The reversibility of soil and seepage water acidification by reduced S deposition was delayed by the release of previously accumulated soil SO42−. The highest NO3− fluxes were observed during the period of 1986 to 1988; NO3− fluxes in general demonstrated a considerable annual and periodic variation. Total N accumulation in the ecosystem amounted to nearly 590 kg ha−1 yr−1 during the observation period. The major sink of N in the spruce site is the aggrading humus layer. The results emphasize the need for measurements over several years to make conclusions regarding the function of ecosystems in response to atmospheric deposition.

Spatial heterogeneity and temporal dynamics of soil water tension in a mature Norway spruce stand

In ecosystem research great effort is made in measuring soil water tension, because this is a critical calibration variable for modelling soil water fluxes. In this paper the spatial heterogeneity and temporal dynamics of soil tensions and their consequences for the determination of water fluxes are investigated. Studies were carried out at a Norway spruce stand in the Fichtelgebirge (NE Bavaria). Standard tensiometers were installed at three soil depths (20 each) on the whole experimental plot, as well as 45 microtensiometers as a dense grid in a small soil pit. Microtensiometry at the centimetre scale showed that, depending on rain intensity and initial soil water tension, even a soil without discernible macrostructure may show preferential water infiltration. At the stand scale the variability of soil hydraulic properties and tree root distribution causes substantial heterogeneity of soil water tension, as observed by standard tensiometers. A functional relationship between increasing spatial heterogeneity of tensiometer readings and increasing soil water tension was found, which was particularly pronounced after longer dry periods. Also at low soil water tension, where spatial heterogeneity was low, the calculation of water fluxes from tensiometer values was critical, owing to the fact that small differences in measuring soil water tension resulted in big differences in calculated water fluxes. At high soil water tension in summer the spatial heterogeneity of tensiometer readings was extremely high. At our experimental site, since 30% of the total rain in summer falls in events having a precipitation rate greater than 5 mm h -1 , preferential water and solute flow was an important phenomenon. We conclude that the validation of calculated water fluxes using measured soil water tension at the stand scale is not an appropriate tool, because of measurement difficulties, considerable spatial heterogeneity, especially in dry periods, and the great variability of soil hydraulic properties.

Seasonal modelling of catchment water balance: A two-levle cascading modification of TOPMODEL to increase the realism of spatio-temporal processes

A general problem of hydrological modelling is parameter identification for the driving processes. To examine the long-term dynamics of the water balance of a small (4.2 km 2 ) forested catchment in south-east Germany (Lehstenbach), TOPMODEL has been adapted as a two-level cascading. approach. Only the lower cascade is allowed to respond dynamically. This modified TOPMODEL version accounts for the observations that surface runoff only takes place in a small portion of the catchment and that water flow in large portions of the catchment occurs through groundwater aquifers with a lateral recharge to the downslope regions. Water from an upper catchment region is transferred to a lower storage. The border between the two areas is represented as a topographic index (ATB) threshold that can be varied in the model. The best fits are obtained if only 60% of the catchment area is allowed to react dynamically. A substantial improvement of the runoff description has been achieved by a moderate increase of model complexity. Results of a Monte Carlo simulation showed that the model structure has a flat global optimal solution. In order to quantify the boundary conditions, we combined direct estimates of tree and understorey transpiration, maps of tree age and understorey cover to estimate empirically the total catchment evapotranspiration. The context of a dynamic hydrological model allows an evaluation of ecological data in the context of catchment scale dynamics. Vapour pressure deficit can be assumed to be the major driver of vegetation-atmosphere water transfer. Soil moisture does not affect tree transpiration in this catchment. The results show that transpiration measurements can be scaled to the catchment scale in spite of variations between sites of up to 100%.

Investigating soil and groundwater quality at different scales in a forested catchment: the Waldstein case study

The impact of anthropogenic depositions on soil and groundwater quality has been the subject of numerous studies in the last two decades. However, the problem of linking results and models at different scales remains to be solved. A case study has been performed in the Fichtelgebirge region in South-East Germany. Data from this case study has been used to analyse scale dependences of spatial variance, autocorrelation lengths, and the interdependence of soil hydrological and soil chemical parameters. For soil suction, spatial variability increases stepwise with scale. Three different sources of variation could be identified, predominating at different ranges of scale, making a deterministic mapping feasible. Local SO4 deposition explained much of the spatial pattern of SO4 concentration in soil solution and in catchment runoff observed at different scales. This is mainly due to the fact that the sorption capacity of the soils in this region has been exceeded. Decreasing SO4 deposition in the long term run is likely to enhance the influence of the soil, and reduces the correlation between deposition and soil solution concentration. NO3 showed minimum variation at the county scale. This seems to be a reasonable representative elementary area for mapping regional NO3 concentration patterns. For protons and Cl, neither observed spatial patterns nor the scale dependence of spatial heterogeneity could be explained adequately.

Describing soil SO42− dynamics in the solling roof project with two different modelling approaches

The release of previously stored soil SO42− is tightly connected with the reversibility of soil and water acidification. Thus soil SO42− dynamics have to be included when predicting the reversibility of acidification. Our aim was to compare two modelling approaches: The model MAGIC (Cosby et al., 1985) describes SO42− dynamics with the Langmuir sorption isotherme. In the SO-MODEL (Prenzel, 1991) a precipitation/ dissolution of jurbanite is defined.Even though it was possible to calibrate both models to lysimeter data of the Solling D1 site in 1 m depth, the prognosis for SO42− concentrations in the soil solution differed significantly. While MAGIC predicted the observed gradual decrease of SO42− concentration with decreasing deposition, the SO-MODEL calculated stable concentrations up to the year 2026 followed by a sudden drop. Because the prognosis established with the SO-MODEL is incompatible with observed field data, we concluded that the predicted SO42− dynamic of the SO-MODEL was unrealistic.

Spatial variability of sulfate isotherms in forest soils at different scales and its implications for the modeling of soil sulfate fluxes

To predict reversibility of soil and water acidification under conditions of decreasing S-input into forested ecosystems, the amount of reversibly bound SO42- in the soil as well as its desorption behavior must be considered. This study investigated variability of sulfate isotherms and their spatial scaling. The Langmuir isotherm parameters in two forested catchments (one deciduous, one coniferous stand) and their spatial distribution at two different scales (site and catchment scale) were investigated. The soil samples (250 cm(3)) were taken in a systematic grid with spatial distances ranging from 20 x 20 m to 300 X 300 m, Isotherm parameters, soil pH, dithionite- and oxalate-extractable iron and aluminum, crystalline iron oxide, and ent were determined. Significant relationships were found between sulfate sorption isotherm parameters and soil chemical properties for each site. It would be useful to be able to replace the experimental determination of isotherm parameters with the less costly measurements of soil chemical properties such as pH, Al- and Fe-oxides, and C-org content of the soils. Regression analysis, however, resulted in different parameters for each site. Thus, at sites where this relation is unknown, isotherms have to be determined via soil extraction procedures and cannot be predicted by soil chemical properties. To determine the average isotherms with an accuracy of +/- 0.2 mu mol g(-1) SO42- (sorb), a sample size of 55 for the site scale and up to 106 for the catchment scale is required. The semivariance of the isotherm parameters revealed no spatial patterns. The influence of isothenll variability on the prediction of SO42--fluxes with seepage was investigated using the chemical equilibrium model MAGIC. Forecast accuracy depends on proper consideration of the variability of sulfate sorption in a catchment.