Edzard Hangen

Projected loss of soil organic carbon in temperate agricultural soils in the 21st century: effects of climate change and carbon input trends

Climate change and stagnating crop yields may cause a decline of SOC stocks in agricultural soils leading to considerable CO2 emissions and reduced agricultural productivity. Regional model-based SOC projections are needed to evaluate these potential risks. In this study, we simulated the future SOC development in cropland and grassland soils of Bavaria in the 21st century. Soils from 51 study sites representing the most important soil classes of Central Europe were fractionated and derived SOC pools were used to initialize the RothC soil carbon model. For each site, long-term C inputs were determined using the C allocation method. Model runs were performed for three different C input scenarios as a realistic range of projected yield development. Our modelling approach revealed substantial SOC decreases of 11–16% under an expected mean temperature increase of 3.3 °C assuming unchanged C inputs. For the scenario of 20% reduced C inputs, agricultural SOC stocks are projected to decline by 19–24%. Remarkably, even the optimistic scenario of 20% increased C inputs led to SOC decreases of 3–8%. Projected SOC changes largely differed among investigated soil classes. Our results indicated that C inputs have to increase by 29% to maintain present SOC stocks in agricultural soils.

Influence of Soil Pore Length upon Portable X-ray Fluorescence Spectrometer Measurements of Elements in Soils

To approximate the measurement accuracy of laborious lab approaches, soil inventories using field portable XRF (pXRF) spectrometers should take distorting parameters into account. Besides soil moisture, the length of water-filled soil pores may also affect X-ray intensity. Following the Arya-Paris approach of soil pore bundles, soil pore lengths were calculated for 20 riparian soil samples based on effective pore diameters obtained at specified pressure heads of the water retention curve. When contrasted against pXRF signals of lead, zirconium, and potassium, soil pore length information showed an explanation comparable to soil moisture values. Presumably, the bases and walls of soil pores are successively exposed to the excitation source during dewatering. Though its laborious determination, soil pore length calculation is based on comparatively static parameters, which may circumvent adverse effects occurring at moisture determination at steel-ring samples, such as artificial macropores in the course of sampling and transport or shrinkage of porosity due to pressure application.

Präferenzielle Wasser- und Luftbewegung in heterogenen aufgeforsteten Kippenböden im Lausitzer Braunkohletagebaugebiet (Teilprojekt 19)

In diesem Projekt wurde das vermutete Auftreten von praferenziellem Fluss im mit Kiefern forstlich rekultivierten Kippenboden des Versuchssstandorts „Barenbruck“ untersucht. Dazu erfolgte zunachst eine qualitative Beschreibung bevorzugter Flieswege durch ein Farbtracer-Infiltrationsexperiment. Gleichzeitig wurde ein Unterflur-Zellenlysimeter konstruiert und installiert, mit dem die raumliche Verteilung der Flussraten auch quantitativ erfasst werden kann. Fur den Farbtracerversuch wurde eine 1,25 m × 2,5 m Flache unter den 16-jahrigen Kiefern mit einer Jodidlosung (15 g L−1) 8 Stunden lang (7,5 mm h−1) bespruht. Beim nachfolgenden schichtweisen Bodenabtrag und durch Ausnutzung der Jod-Starke-Reaktion zeigten sich violett gefarbte Bodenzonen, in die Jodid-Tracerlosung gelangt sein muss. Die grafische Auswertung der in 10 cm Tiefenabstanden aufgenommenen flachenhaften Farbmuster zeigte, dass der Tracer nach Passieren der Streuschicht nur auf weniger als 20 % der Flache den Mineralboden erreichte. In der Graswurzelzone waren die markierten Bereiche relativ gleichmasig und auf etwa 60 % der Flache verteilt. Darunter konzentrierte sich die Verlagerung des Farbtracers auf einzelne „fingerartige“ Fliesbahnen bis in 1,5 m Tiefe. Zwischen der raumlichen Verteilung der Infiltrationszonen und derjenigen des Grades der potenziellen Benetzbarkeit konnte kein Zusammenhang gefunden werden. In der durchwurzelten Zone bis etwa 60 cm Tiefe scheint die Lage praferenzieller Flieszonen eher mit der raumlichen Struktur des Wurzelsystems zu korrelieren. Der Versuch zeigt, dass auf diesem Standort das Phanomen „Fingerfluss“ eine raumlich heterogene Sickerwasserbewegung induzieren kann. Das Zellenlysimeter zur quantitativen Erfassung der Flussraten wurde 110 cm unterhalb des ungestorten Kippenbodens von der Seite her hydraulisch eingepresst. Die Instrumentierung des Lysimeterbodens umfasst Gerate zur Messung des Bestandesniederschlags sowie die Kombination von Tensiometern und Bodenluftdruck-Sensoren.

Platinum, Palladium and Rhodium in a Bavarian Roadside Soil

As constituents of automobile exhaust catalysts platinum, palladium and rhodium are emitted by mechanical abrasion. Their deposition and vertical displacement in the soil was investigated along an east-west oriented transect at the Franken expressway (highway 73), Germany. With increasing distance to the road the concentrations of platinum, palladium and rhodium decreased exponentially. The influence of wind effects as well as of guard rails upon the lateral distribution of the three elements was clearly reflected. In view of a rising traffic density the pollution by platinum, palladium and rhodium becomes more important.

3D-Wurzelverteilung Sechzehnjähriger Schwarzkiefern in einem Kippenboden im Vergleich mit markierten Fließwegen

Preferential flow may possibly affect the water and solute budgets of afforested mine soils ecosystems. Root channels of trees can form preferential flow paths. The 3D-spatial distribution of root biomass of a Pinus nigra stand was investigated and compared with the distribution of preferential flow paths, visualized by staining patterns of a dye tracer. The experiment was carried out on a lignitic reclaimed spoil in the Lusatian mining district afforested with a 16-years old stand of Pinus nigra. An area of 250 × 125 cm was sampled at a 25 × 25 cm grid in 10 cm depth increments down to 150 cm soil depth using a 636 cm3 steel cylinder. All the roots, irrespective of vitality, were separated from the soil and subdivided into five diameter classes. The 1D vertical distribution of the dry total root biomass of the soil block showed a maximum of about 1200 g/m3 in the upper 40 cm, which corresponds to the depth of the flue-ash amelioration horizon. Only at isolated spots, roots could be found down to 80 cm soil depth. Highest root biomass was generally in the diameter class > 1 mm. The small-scale heterogeneity of root biomass did not directly correspond with the tree stem locations. For this experiment, a correlation between the distribution of root biomass and the location of flow paths could not be found by visual inspection. The location and formation of preferential flow paths may additionally be affected by other parameters, such as soil water repellency or coal fragments.

Signatures of chlorinated dioxins and furans along the exposure path – The relation between vegetation and soil

Polychlorinated dibenzo-p-dioxins and dibenzo-furans (PCDD/Fs) belong to the most toxic persistent organic environmental pollutants. Therefore, knowledge about their fate along the exposure path is of special concern. In order to comprehend the transfer of PCDD/Fs across different environmental compartments, PCDD/F concentrations in plants and in soil were evaluated. Pairs of soil and plant samples were selected according to the shortest distance between sampling points. At 15 sites PCDD/F concentrations in spruce needles and in forest humus layers where compared. Summer conditions were evaluated on the basis of 8 sites with ryegrass- and grassland topsoil samples. Autumn conditions were addressed using 7 sites with curly kale and topsoil samples under grassland. Correlation analyses of the PCDD/F congener profiles for plant- and soil samples were conducted. The correlations were compared to influencing site (e.g. local temperature) and spatial as well as temporal offset parameters. No governing parameter that decisively influenced the similarity between plant and soil signature became evident. By means of the toxicity factors of TEQ-WHO, tetra- and penta-PCDD/F homologues were assigned to the group of low-chlorinated homologues (lcH), and hexa-, hepta- and octa-PCDD/F homologues to the high-chlorinated homologues (hcH). lcH and hcH are presumed to differ in solubility, volatility and rate of degradation. The ratio of lcH/hcH revealed characteristic fingerprints that enabled the differentiation of the individual PCDD/F-plant and -soil pairs. Spruce-humus pairs showed a close relation during winter exposure times, while the lower summer concentrations were not reflected in the humus layer. Kale was exposed at the beginning of the season with elevated PCDD/F immissions, and showed a closer relation to grassland topsoil than did ryegrass. lcH/hcH proved as a simple criterion that can reveal related PCDD/F fingerprints of different environmental compartments despite signal attenuation due to decomposition, volatilization and particulate transport.

A Comparison of Five Different Techniques to Measure Hydraulic Conductivity of a Riparian Soil in North Bavaria, Germany

Abstract Soil saturated hydraulic conductivity (Ks) is a predominant input factor when forecasting the vertical transport of contaminants through the soil or when estimating the flood retention capacity of the soil. Displacement of contaminants in the soil over extended periods of time can be attributed mainly to matrix flow, whereas flow through macropores becomes significant under untypically wet conditions, e.g., during spills or rain storms. To obtain matrix conductivities for a soil, the effects of macropores should be excluded. However, the Ks values of a soil profile are unlikely to be reflected solely by pedotransfer tables based on soil texture and bulk density. In this study, we examined five different methods (pedotransfer table, soil core, borehole permeameter, particle-size distribution curve, and instantaneous profile) to determine Ks values for a mercury-contaminated riparian soil for subsequent simulation of long-term mercury displacement toward groundwater. We found that the determined Ks values increased in the following order: borehole permeameter