Bioverfügbare Fraktionen von Arsenat, Kupfer und Nickel: Ergebnisse chemischer Extraktionsmethoden

In der Bundes-Bodenschutzverordnung sind für ausgewählte Metalle Vorsorgewerte festgeschrieben, bei deren Überschreiten „die Besorgnis einer schädlichen Bodenveränderung besteht“. Für deren Ableitung wurden die jeweiligen Gesamtgehalte im Boden (Königswasser-Aufschluss) verwendet. Allerdings ist für den Wirkungspfad Boden – Organismen der Zusammenhang zwischen Gesamtgehalten und einem potenziellen Effekt auf Mikroorganismen, Pflanzen und Invertebraten gering. Eine realistische Bewertung der Metallgehalte sollte deshalb die Bioverfügbarkeit von Metallen im Boden berücksichtigen. Um die geignetste Metallfraktion zur Bewertung der Bioverfügbarkeit von Metallen zu identifizieren, werden wir in unserem Projekt Ergebnisse verschiedener chemischer Extraktionsverfahren mit den Daten von mehreren ökotoxikologischen Tests auf den chronischen Effekt auf verschiedene Organismen miteinander korrelieren. In diesem Beitrag werden die Ergebnisse der chemischen Extraktionen präsentiert. Für die Untersuchungen wurden elf Böden ausgesucht, die einen großen Bereich der Eigenschaften von mitteleuropäischen Böden abdecken (z. B. 0.9‑23.3 % organischer Kohlenstoff; 5-36 % Ton). Teilproben wurden mit acht Konzentration der kationischen Metalle Kupfer und Nickel sowie dem Oxyanion Arsenat versetzt. Nach einer Woche Inkubationszeit wurden die Extraktionen durchgeführt. Diese umfassen neben dem Königswasser-Aufschluss, Extraktionen mit unterschiedlichen Salzlösungen (Ca(NO3)2 angepasst an die Ionenstärke des Bodens, 0.01 M CaCl2, and 1 M NH4NO3), mit Komplexbildner (DTPA/CaCl2) und mit schwach konzentrierter Säure (043 M HNO3). Die Extraktionsstärke der verschiedenen Methoden folgt bei den meisten Böden und Metallen der Reihenfolge HNO3 > DTPA > NH4NO3 > CaCl2. Die extrahierte Menge an Metall variert zwischen den Böden und hängt von deren Eigenschaften ab. Diese Einflussfaktoren werden weiter untersucht. Die Daten sollen dann zusammen mit den ökotoxikologischen Untersuchungen genutzt werden, um die Bioverfügbarkeit der einzelnen Metallfraktionen zu bewerten und zukünftig bei der Ableitung von Vorsorgewerten berücksichtigen zu können

Effects of Tillage and Nitrogen Fertilizers on CH4 and CO2 Emissions and Soil Organic Carbon in Paddy Fields of Central China

Quantifying carbon (C) sequestration in paddy soils is necessary to help better understand the effect of agricultural practices on the C cycle. The objective of the present study was to assess the effects of tillage practices [conventional tillage (CT) and no-tillage (NT)] and the application of nitrogen (N) fertilizer (0 and 210 kg N ha−1) on fluxes of CH4 and CO2, and soil organic C (SOC) sequestration during the 2009 and 2010 rice growing seasons in central China. Application of N fertilizer significantly increased CH4 emissions by 13%–66% and SOC by 21%–94% irrespective of soil sampling depths, but had no effect on CO2 emissions in either year. Tillage significantly affected CH4 and CO2 emissions, where NT significantly decreased CH4 emissions by 10%–36% but increased CO2 emissions by 22%–40% in both years. The effects of tillage on the SOC varied with the depth of soil sampling. NT significantly increased the SOC by 7%–48% in the 0–5 cm layer compared with CT. However, there was no significant difference in the SOC between NT and CT across the entire 0–20 cm layer. Hence, our results suggest that the potential of SOC sequestration in NT paddy fields may be overestimated in central China if only surface soil samples are considered

Spatial patterns of microbial diversity and activity in an aged creosote-contaminated site

Restoration of polluted sites via in situ bioremediation relies heavily on the indigenous microbes and their activities. Spatial heterogeneity of microbial populations, contaminants and soil chemical parameters on such sites is a major hurdle in optimizing and implementing an appropriate bioremediation regime. We performed a grid-based sampling of an aged creosote-contaminated site followed by geostatistical modelling to illustrate the spatial patterns of microbial diversity and activity and to relate these patterns to the distribution of pollutants. Spatial distribution of bacterial groups unveiled patterns of niche differentiation regulated by patchy distribution of pollutants and an east-to-west pH gradient at the studied site. Proteobacteria clearly dominated in the hot spots of creosote pollution, whereas the abundance of Actinobacteria, TM7 and Planctomycetes was considerably reduced from the hot spots. The pH preferences of proteobacterial groups dominating in pollution could be recognized by examining the order and family-level responses. Acidobacterial classes came across as generalists in hydrocarbon pollution whose spatial distribution seemed to be regulated solely by the pH gradient. Although the community evenness decreased in the heavily polluted zones, basal respiration and fluorescein diacetate hydrolysis rates were higher, indicating the adaptation of specific indigenous microbial populations to hydrocarbon pollution. Combining the information from the kriged maps of microbial and soil chemistry data provided a comprehensive understanding of the long-term impacts of creosote pollution on the subsurface microbial communities. This study also highlighted the prospect of interpreting taxa-specific spatial patterns and applying them as indicators or proxies for monitoring polluted sites

Cation exchange capacities of soil organic matter fractions in a Ferric Lixisol with different organic matter inputs

Soil organic matter (SOM) has an important effect on the physicochemical status of highly weathered soils in the tropics. This work was conducted to determine the contribution of different SOM fractions to the cation exchange capacity (CEC) of a tropical soil and to study the effect of organic matter inputs of different biochemical composition on the CEC of SOM. Soil samples were collected from a 20-year-old arboretum established on a Ferric Lixisol, under seven multipurpose tree species: Afzelia africana, Dactyladenia barteri, Gliricidia sepium, Gmelina arborea, Leucaena leucocephala, Pterocarpus santalinoides, and Treculia africana. Fractions were obtained by wet sieving and sedimentation after ultrasonic dispersion. Relationships between CEC and pH were determined using the silver thiourea-method and were described by linear regression. The CEC of the fractions smaller than 0.053 mm was inversely related to their particle size: clay (< silt silt (0.02–0.053 mm), except for the soils under T. africana, D. barteri, and L. leucocephala, where the CEC of the fine silt fraction was highest or comparable to the CEC of the clay fraction. The clay and fine silt fractions were responsible for 76–90% of the soil CEC at pH 5.8. The contribution of the fine silt fraction to the CEC at pH 5.8 ranged from 35 to 50%, which stressed the importance of the fine silt fraction for the physicochemical properties of the soil. Differences in CEC between treatments for the whole soil and the fractions could be explained by the differences in carbon content. Except for the intercept for the clay fraction, SOM had a significant (P<0.001) contribution to both the intercepts (=estimated CEC at pH 0) and slopes (=pH-dependent charge) of the CEC–pH relationships for the whole soil and the fractions. The CEC of SOM at pH 5.8 varied between 283 cmolc kg−1 C for particulate organic matter, and 563 cmolc kg−1 C for the fine silt fraction. The biochemical composition of the organic inputs did not have an important effect on the CEC of SOM. In total, SOM was responsible for 75–85% of the CEC of these soils

A new method for the simultaneous measurement of Ph-dependent cation exchange capacity and ph buffering capacity

The pH dependent cation exchange capacity (CEC) and pH buffering capacity (pH BC) are two crucial properties in soil fertility management of variable charge soils. However, they are rarely measured, since most of the existing methods are cumbersome and time-consuming. We propose a new method, based on the silver-thiourea (AgTU) method, for the simultaneous measurement of pH dependent CEC and the pH BC. In general, this method consists of first increasing the pH of the soil to about pH 7 and then gradually acidifying the soil by titrating with HNO3, while measuring pH and CEC after each equilibration. This way, both CEC at different pH values and the pH BC are measured on the same sample, without the multiple washing steps needed in other procedures. Various aspects of the proposed method were tested and the results obtained were compared with the ion adsorption method. The modified AgTU method obtains field relevant results and is suitable for the routine analysis of large numbers of samples