Swiss concept of soil protection

The maintenance of soils as a basis for sustaining life is an important subject of Swiss environmental policies. A prominent instrument to achieve this goal is the Ordinance of 1998Relating to Impacts on the Soil (OIS). In 13 articles a guiding framework for the protection of the soil is given. For a better understanding of the legal background, SAEFL has published specific commentaries. They explain the intention of the legislator and thus contribute to a consistent and mutual implementation of the soil regulations in practice. Comments are made on respective articles, on the Swiss concept of soil protection and also on the guide, trigger and cleanup values for hazardous substances in the soil. The commentaries are available in German, French and English languages. The extent of the Commentaries (including OIS and excerpts of the Swiss Federal Law of 1983 Relating to the Protection of the Environment) is 44 pages. Mail-address: sol@huwal.admin.ch     

Particle-size distribution of PAH in the air of a remote Norway spruce forest in northern Bavaria

The aim of the present study was to elucidate thedistribution of particulate polycyclic aromatichydrocarbons (PAH) in the air of a remote Norwayspruce (Picea abies (L.) karst.) stand.The study encompassed a total of twenty differentcongeners. Particles in ambient air were alternativelycollected by two different Berner cascade impactors atthe field site in Northern Bavaria over a 14-weeksperiod from the end of April through to the end ofJuly 1994 and subsequently analyzed for their PAHcontent. The concentrations of total suspendedparticulate matter (TSP) ranged from 9–31 μg m^-3,suggesting that the field site is an area with a lowlevel of airborne particles. There was a negativerelationship of total particle concentrations with theamount of canopy precipitation due to particle washout at precipitation events. The distribution of theparticle masses on the different size fractions witha maximum in the 1-μm range is typical for remoteareas and indicates a medium-range transport. Theaerosol-bound PAH load decreased from spring sampleswith 2–4 ng m^-3 to values <1 ng m^-3 in the summersamples. Concurrently, the proportion of low molecularweight congeners in the total PAH load declined.Frequently, the highest PAH concentrations (referringto the air) were found in the 0.1–3 μm sizeseparates (accumulation mode). The results suggestthat apart from PAH input to the soil with litter, dryand wet deposition of aerosol particles is animportant pathway of PAH contamination of acid forestsoils in the Fichtelgebirge mountain range.     

Suitability of S factor algorithms for soil loss estimation at gently sloped landscapes

The reliability and the estimation technique of the S factor limit the use of the Universal Soil Loss Equation (USLE) at a regional scale. The accuracy of the S factor principally depends on the digital elevation model (DEM) accuracy and the precision of algorithms. Few studies were conducted on the accuracy of the S factor for a gently rolling landscape at a regional scale. We select a rectangular study site of 1.3 km² in northern Germany as a case study to explore the effects of algorithm, horizontal resolution and vertical precision of DEM as well as terrain on the S factor. Horizontal resolution includes 1 m, 5 m, 10 m, 25 m, 50 m and 100 m. We use the following eight algorithms: maximum slope gradient, maximum downhill slope gradient, second-order finite difference, third-order finite difference, third-order finite difference weighted by reciprocal of squared distance, third-order finite difference weighted by reciprocal of distance, frame finite difference and simple difference. The results are as follows: (1) the algorithms affect the accuracy of the S factor at any given resolution of DEM, in particular more obvious for the lower DEM resolutions; (2) the accuracy of the S factor decreases as horizontal resolution decreases; (3) the most suitable algorithm is maximum downhill slope gradient for 1 m, and maximum slope gradient for the 5 m to 100 m resolution; (4) vertical precision also affects the accuracy of the S factor. However, vertical precision almost does not change the order of rank of the S factor with eight different algorithms at any given resolution of DEM; (5) the more complex the terrain is, the worse the accuracy of the S factor is represented. Among all the affective factors, horizontal resolution is the most important for the accuracy of the S factor. Selecting the most suitable algorithm is the best way for reducing the errors of the S factor when applying the USLE.     

Dynamics of mineral components in the forest floor of an acidic beech (Fagus sylvatica L.) forest

Seasonal changes of the mineral components Na, K, Mg, Ca, Mn, Fe, Al, Si and ash were investigated in the L1 horizon of an acidic beech (Fagus sylvatica L.) forest using litterbags (1 mm and 45 μm mesh-size) buried for up to 467 days in the forest floor. The element dynamics in this surface horizon were compared with the concentration and the total amount stored in a complete sequence of horizons (L1, L2, F1, F2 and H) taken from a moder profile in the Solling area. In the 1 mm litterbags with free access of the mesofauna, the concentrations of all cations were increased in comparison to the 45 μm treatment. This increase was highly significant, especially with regard to Fe and Al. The concentrations of these two cations were closely related to Si during the decomposition of fresh leaf litter in the L1 horizon. Si is the dominant element of ash in the litterbags and down the profile. The total amounts stored in the forest floor revealed that the Fe and Al input considerably exceeded the input by litter fall, and dry and wet deposition due to incorporation of mineral soil material. The input of soil material was also indicated by a decrease in the molar Si/Al ratio from 17 to 6 and in the relation of nutrient cations to ash from 30% to 2.5%.     

Influence of decomposition of roots of tropical forage species on the availability of soil nitrogen

Immobilization of mineral N induced by decomposition of roots of four tropical forage species (Stylosanthes guianensis, Centrosema sp., Andropogon gayanus and Brachiaria decumbens) in an Oxisol was studied under laboratory conditions. Root materials had a high lignin content (12–20%) but total polyphenol content was small (<0.8%). Roots, at 2.5 and 5.0 g kg⁻¹, and 10 mg N kg⁻¹ of -labelled ammonium sulphate (20.3 at.%) were thoroughly mixed with the soil which was maintained at field capacity for 117 d. Decomposition of the roots (as monitored by CO₂ evolution) was initially rapid and the legume materials (S. guianensis, Centrosema sp.) with their lower C-to-N ratio and lignin content, decomposed more quickly than the grass roots (A. gayanus, B. decumbens). After 8 d of incubation the rate of CO₂ evolution decreased and was similar for all root materials. CO₂ evolution from the decomposing roots in all cases fitted closely (R²>0.99) a double exponential equation defining two compartments of root carbon of differing susceptibility to decomposition. The equation predicted that between 43% (Centrosema) and 62% (Brachiaria) of root carbon would not be decomposed even at infinite time under incubation conditions. Mineral N in the soil was immobilized rapidly at the start of the incubation, and the immobilization was greatest with the higher rate of application of root material. Although the C-to-N ratio of legume roots was narrower their higher degradability stimulated greater immobilization of soil mineral N than the grass roots. The results are discussed with reference to N immobilization and carbon sequestration in planted pastures of tropical South America.     

Measuring soil microbial biomass using an automated procedure

Here we outline the development of the first automated procedure for measuring soil microbial biomass carbon (biomass C) by Fumigation-Extraction (FE) and on which this Citation Classic is based. The method (and its later variations) has been used widely since it was published. It gives essentially the same results as the Fumigation-Incubation (FI) method on which it was based and which it has now largely replaced. Analysis of the current data clearly showed that the calibration value to convert extracted organic C to biomass C (k_EC = 0.45) using FE is still valid and that there was no need for a change. We also review some of the previous discussions about the method and outline future prospects for microbial biomass measurements in soil microbial ecology.     

Rate of soil‐aggregate formation under different organic matter amendments—a short‐term incubation experiment

To improve soil structure and take advantage of several accompanying ecological benefits, it is necessary to understand the underlying processes of aggregate dynamics in soils. Our objective was to quantify macroaggregate (> 250 μm) rebuilding in soils from loess (Haplic Luvisol) with different initial soil organic C (SOC) contents and different amendments of organic matter (OM) in a short term incubation experiment. Two soils differing in C content and sampled at 0–5 and 5–25 cm soil depths were incubated after macroaggregate destruction. The following treatments were applied: (1) control (without any addition), (2) OM₁ (addition of OM: preincubated wheat straw [< 10 mm, C : N 40.6] at a rate of 4.1 g C [kg soil]^–1), and (3) OM₂ (same as (2) at a rate of 8.2 g C [kg soil]^–1). Evolution of CO₂ released from the treatments was measured continuously, and contents of different water‐stable aggregate‐size classes (> 250 μm, 250–53 μm, < 53 μm), microbial biomass, and ergosterol were determined after 7 and 28 d of incubation. Highest microbial activity was observed in the first 3 d after the OM application. With one exception, > 50% of the rebuilt macroaggregates were formed within the first 7 d after rewetting and addition of OM. However, the amount of organic C within the new macroaggregates was ≈ 2‐ to 3‐fold higher than in the original soil. The process of aggregate formation was still proceeding after 7 d of incubation, however at a lower rate. Contents of organic C within macroaggregates were decreased markedly after 28 d of incubation in the OM₁ and OM₂ treatments, suggesting that the microbial biomass (bacteria and fungi) used organic C within the newly built macroaggregates. Overall, the results confirmed for all treatments that macroaggregate formation is a rapid process and highly connected with the amount of OM added and microbial activity. However, the time of maximum aggregation after C addition depends on the soil and substrate investigated. Moreover, the results suggest that the primary macroaggregates, formed within the first 7 d, are still unstable and oversaturated with OM and therefore act as C source for microbial decomposition processes.     

Effects of DEM horizontal resolution and methods on calculating the slope length factor in gently rolling landscapes

The USLE is used world-wide to predict soil loss on the field scale from sheet and rill erosion. The slope length (L) factor is derived as its topographical factor. The accuracy of L factor determines the precision of soil loss estimation with USLE. Uncertainties on L factor are caused by DEM resolution and the choice of the processing algorithm. In the present study we made two comparisons to evaluate the effects of DEM horizontal resolution and processing algorithm on the accuracy of the L factor in gently sloped landscapes: one is between the grid cumulating method (GC) and the contributing area method (CA) using D8 flow-routing algorithm, the other is among single (D8, Rho8) and multiple (FD8, FRho8 and DEMON) flow-routing algorithms for processing the contributing area method. In two comparisons, 5 m, 10 m, 25 m, 50 m and 100 m DEM of a 0.88 km² catchment in the lowland of Northern Germany were applied. The results indicate that L factor calculated with any of the six methods is sensitive to horizontal resolution, which strongly affects the accuracy. With decreasing resolution, correlations of L_{CA_Rho8} and L_{CA_D8}, L_{CA_FD8} and L_{CA_D8}, L_{CA_FD8} and L_{CA_Rho8} increase while those between DEMON and the other flow-routing algorithms do not change significantly. With decreasing resolution, the difference between L_{GC_D8} and L_{CA_D8} is enlarged, while differences between any two flow algorithms using CA did not change significantly. The L factor variation between any two methods is larger on the upslope than the flat valley for the 5 m and 10 m DEM while terrain characteristics are not visible on the 25 m, 50 m and 100 m DEM. The L factor also depends on the computation method. L_{GC_D8} is approximately half of L_CA. It is concluded that DEM horizontal resolution is very important for L factor calculation. The most suitable calculation method is L_{GC_D8} for gently rolling landscapes. This study can be used for selecting a suitable method and DEM resolution for accurate calculation of L factor and soil loss in gently rolling landscapes.