Gerhard Welp

Inhibitory effects of the total and water-soluble concentrations of nine different metals on the dehydrogenase activity of a loess soil

Abstract This study focuses on a comparison of the microbial toxicity of nine metals, including As as a metalloid and two species of Cr. A loess soil [Ap horizon, clay 15.2%, organic C 1.12%, pH(CaCl2) 7.02] was spiked with 8–12 geometrically increasing doses of the metals. The dehydrogenase assay (2-p-iodophenyl-3-p-nitrophenyl-5-phenyltetrazoliumchloride method) was combined with sorption and solubility experiments. The resulting dose-response curves and sorption isotherms were used to derive total doses that caused definite percentage inhibitions [i.e. effective doses (ED) causing a 10–90% reduction in dehydrogenase activity (dha)] as well as the corresponding toxic solution concentrations causing the same reductions in dha (i.e. effective concentrations; EC10–EC90). Based on total doses, the toxicity decreased in the following order with ED50 values (mg kg–1) given in brackets: Hg (2.0)>Cu (35)>Cr(VI) (71)>Cr(III) (75)>Cd (90)>Ni (100)>Zn (115)>As (168)>Co (582)>Pb (652). With regard to solution concentrations, toxicity decreased in the order (EC50 in mg l–1): Hg (0.003)>Pb (0.04)>Cu (0.05)>Cd (0.14)>Zn (0.19)>Cr(III) (0.62)>Ni (0.69)>Co (30.6)>As (55.5)>Cr(VI) (78.1). The retention of the metals by the soil differed strongly. Pb, Cu, and Hg exhibited the highest and Ni, As, and Cr(VI) the lowest sorption constants (Freundlich K values: 2455, 724, 348, 93, 13, and 0.06 mg kg–1, respectively). The sorptivity of the metals and their microbial toxicity in the aqueous phase were characteristically related: metals with a strong toxic action in the soil solution were adsorbed by the soil to a high degree and vice versa. Therefore, especially for metals with a high inherent toxicity, sorption is an effective way of immobilizing them and temporarily detoxifying soil.

Adsorption and solubility of ten metals in soil samples of different composition

We conducted batch experiments for ten metals [Mg, Cr(III), Fe(III), Co, Ni, Cu, Zn, Sr, Cd, Pb] and four soil samples of different composition to determine the relation of the soluble fraction (’intensity’) to an adsorbed or precipitated metal pool (’quantity’) and, thus, to investigate the buffer function of soils. The soil samples were spiked with 6 to 12 exponentially increasing metal doses added as metal nitrates. The native metal pool involved in sorption processes was characterized by an extraction with 0.025 M (NH4)2EDTA (pH 4.6). The quantity-intensity (Q/I) relations of eight metals [except Cr(III) and Fe(III)] were governed by sorption and complexation processes and can be fitted by Freundlich isotherms. Q/I relations for Cr(III) and two soils indicate a sorption maximum, which can be approximated with the Langmuir isotherm. In a calcareous soil high Cr doses induced the precipitation of a Cr oxide. The solution concentrations of Fe are primarily a function of the pH-dependent solubility of ferrihydrite. For all metals pH was the predominant factor controlling the partitioning between the solid and the liquid phase. Drastic losses in the buffer function of soils primarily occurred in the slightly acidic range. Furthermore, adsorption was also metal specific. On the basis of median Freundlich K values, adsorption increased in the order [median KF values and KF range (mg kg—1) in brackets]: Mg (2.9: 0.9—19) < Sr (4.7: 0.6—21) << Co (17.7: 1.1—143) < Zn (26.7: 1.8—301) = Ni (27.6: 2.4—120) < Cd (71: 2.5—405) << Cr(III) (329: 45—746) < Cu (352: 30—1200) < Pb (1730: 76—4110). Adsorption und Loslichkeit von zehn Metallen in Boden variierenden Stoffbestandes Schuttelversuche mit zehn Metallen [Mg, Cr(III), Fe(III), Co, Ni, Cu, Zn, Sr, Cd, Pb] und vier Bodenproben wurden durchgefuhrt, um die Beziehungen zwischen den gelosten Anteilen (“Intensitat„) und den sorbierten bzw. gefullten Anteilen (“Quantitat„) zu ermitteln und damit das Puffervermogen der Boden zu bestimmen. Die Metalle wurden als Nitratsalzlosungen mit exponentiell steigenden Konzentrationen in 6—12 Dosen zugegeben. Die bodenburtige, an Sorptionsprozessen beteiligte Metallfraktion wurde als der mit 0,025 M (NH4)2EDTA (pH 4,6) extrahierbare Anteil berucksichtigt. Die Q/I-Beziehungen von acht Metallen [ohne Cr(III) und Fe(III)] wurden durch Sorptionsprozesse und Komplexbildungen gesteuert, die sich mit Freundlich-Isothermen beschreiben liesen. Q/I-Beziehungen fur Cr und zwei von vier Bodenproben zeigten ein Adsorptionsmaximum und folgten einer Langmuir-Anpassung. In einer kalkhaltigen Bodenprobe bewirkten hohe Cr-Gaben die Ausfullung eines Cr-Oxids. Die Losungsgehalte von Fe wurden uberwiegend durch die pH-abhangige Loslichkeit des Ferrihydrits bestimmt. Bei allen Metallen hatte der pH-Wert den grosten Einflus auf Sorption und Loslichkeit. Insbesondere im schwach sauren Bereich war eine drastische Abnahme des Puffervermogens der Boden festzustellen. Daneben war das Adsorptionsverhalten stark metallspezifisch. Auf der Grundlage medianer Freundlich-K-Werte stieg die Adsorbierbarkeit in folgender Reihe an [mediane KF-Werte und KF-Bereiche (mg kg—1) in Klammern]: Mg (2.9: 0.9—19) < Sr (4.7: 0.6—21) << Co (17.7: 1.1—143) < Zn (26.7: 1.8—301) = Ni (27.6: 2.4—120) < Cd (71: 2.5—405) << Cr(III) (329: 45—746) < Cu (352: 30—1200) < Pb (1730: 76—4110).

Soil heterogeneity at the field scale: a challenge for precision crop protection

Crop protection seldom takes into account soil heterogeneity at the field scale. Yet, variable site characteristics affect the incidence of pests as well as the efficacy and fate of pesticides in soil. This article reviews crucial starting points for incorporating soil information into precision crop protection (PCP). At present, the lack of adequate field maps is a major drawback. Conventional soil analyses are too expensive to capture soil heterogeneity at the field scale with the required spatial resolution. Therefore, we discuss alternative procedures exemplified by our own results concerning (i) minimally and non-invasive sensor techniques for the estimation of soil properties, (ii) the evidence of soil heterogeneity with respect to PCP, and (iii) current possibilities for incorporation of high resolution soil information into crop protection decisions. Soil organic carbon (SOC) and soil texture are extremely interesting for PCP. Their determination with minimally invasive techniques requires the sampling of soils, because the sensors must be used in the laboratory. However, this technique delivers precise information at low cost. We accurately determined SOC in the near-infrared. In the mid-infrared, texture and lime content were also exactly quantified. Non-invasive sensors require less effort. The airborne HyMap sensor was suitable for the detection of variability in SOC at high resolution, thus promising further progress regarding SOC data acquisition from bare soil. The apparent electrical conductivity as measured by an EM38 sensor was shown to be a suitable proxy for soil texture and layering. A survey of arable fields near Bonn (Germany) revealed widespread within-field heterogeneity of texture-related ECa, SOC and other characteristics. Maps of herbicide sorption and application rate were derived from sensor data, showing that optimal herbicide dosage is strongly governed by soil variability. A phytoassay with isoproturon confirmed the reliability of spatially varied herbicide application rates. Mapping areas with an enhanced leaching risk within fields allows them to be kept free of pesticides with related regulatory restrictions. We conclude that the use of information on soil heterogeneity within the concept of PCP is beneficial, both economically and ecologically.

Adsorption von Pflanzenschutzmitteln und DOC an Saugkerzen aus Glas und Keramik

Bei der Gewinnung von Bodenlosung mittels Saugkerzen konnen die Konzentrationen geloster Stoffe in Abhangigkeit vom Kerzenmaterial durch Ad- und Desorptionsprozesse stark verandert werden. Zum Vergleich der bislang uberwiegend ublichen Keramik-Saugkerzen mit neuartigen Saugkerzen aus Borosilikatglas wurden wassrige Losungen von Pflanzenschutzmitteln (PSM) und DOC durch diese Kerzentypen geleitet. Dabei zeigte sich, dass die Adsorption der PSM Pendimethalin, Terbuthylazin, Metolachlor und Chlortoluron (Konzentrationen: 2, 20 und 200 μg 1−1) an Saugkerzen aus Borosilikatglas z. T. erheblich geringer war als an Saugkerzen aus Keramik. Wahrend bei der Perkolation durch die Keramik-Saugkerzen im Mittel 10% (1,1—31%) der Wirkstoffe adsorbiert wurden, betrugen die Verluste bei den Glas-Saugkerzen im Mittel nur 3,1% (0—11%). Die Unterschiede zwischen den beiden Saugkerzentypen nahmen mit steigender Hydrophobie der PSM-Wirkstoffe und sinkender Losungskonzentration deutlich zu. So wurden bei einer Losungskonzentration von 2 μg 1−1 in den Keramik-Saugkerzen 31% des gelosten Pendimethalins adsorbiert, wahrend die Verluste in den Glas-Saugkerzen mit 7,7% deutlich geringer waren. Entsprechende Adsorptionstests mit bodeneigenem gelostem organischem Kohlenstoff (DOC) fuhrten zu ahnlichen Ergebnissen. Vom DOC verschiedener Bodenextrakte wurden in den Glas-Saugkerzen durchschnittlich 2,4% adsorbiert, wahrend die Keramik-Saugkerzen bis zu 50% der gelosten organischen Substanz retardierten. Da bodeneigene geloste organische Substanzen bedeutende Sorbenten und Carrier fur Pflanzenschutzmittel darstellen, wird durch die weitgehende Neutralitat des Glas-Materials gegenuber PSM und DOC die Eignung dieses Werkstoffs fur die Gewinnung von Saugkerzen-Losungen in Pflanzenschutzmittel-Studien nachdrucklich unterstrichen.

High Resolution Mapping of Soil Properties Using Remote Sensing Variables in South-Western Burkina Faso: A Comparison of Machine Learning and Multiple Linear Regression Models.

Accurate and detailed spatial soil information is essential for environmental modelling, risk assessment and decision making. The use of Remote Sensing data as secondary sources of information in digital soil mapping has been found to be cost effective and less time consuming compared to traditional soil mapping approaches. But the potentials of Remote Sensing data in improving knowledge of local scale soil information in West Africa have not been fully explored. This study investigated the use of high spatial resolution satellite data (RapidEye and Landsat), terrain/climatic data and laboratory analysed soil samples to map the spatial distribution of six soil properties–sand, silt, clay, cation exchange capacity (CEC), soil organic carbon (SOC) and nitrogen–in a 580 km2 agricultural watershed in south-western Burkina Faso. Four statistical prediction models–multiple linear regression (MLR), random forest regression (RFR), support vector machine (SVM), stochastic gradient boosting (SGB)–were tested and compared. Internal validation was conducted by cross validation while the predictions were validated against an independent set of soil samples considering the modelling area and an extrapolation area. Model performance statistics revealed that the machine learning techniques performed marginally better than the MLR, with the RFR providing in most cases the highest accuracy. The inability of MLR to handle non-linear relationships between dependent and independent variables was found to be a limitation in accurately predicting soil properties at unsampled locations. Satellite data acquired during ploughing or early crop development stages (e.g. May, June) were found to be the most important spectral predictors while elevation, temperature and precipitation came up as prominent terrain/climatic variables in predicting soil properties. The results further showed that shortwave infrared and near infrared channels of Landsat8 as well as soil specific indices of redness, coloration and saturation were prominent predictors in digital soil mapping. Considering the increased availability of freely available Remote Sensing data (e.g. Landsat, SRTM, Sentinels), soil information at local and regional scales in data poor regions such as West Africa can be improved with relatively little financial and human resources.

Leaching of veterinary antibiotics in calcareous Chinese croplands.

Veterinary antibiotics reach the soil environment by manure application, where they accumulate or are prone to vertical translocation. We assumed that a high pH value at slightly calcareous soil properties should retain tetracyclines and fluoroquinolones even at high manure loads, whereas it should facilitate leaching of sulfonamides. Hence, we investigated the transport of manure-added antibiotics in a soil developed from calcareous parent material on a farm in peri-urban Beijing, China. Leachate was collected from zero-tension samplers, installed at 40cm depth under undisturbed soil, which was treated according to (i) routine farm practice and (ii) worst-case conditions (high antibiotic concentrations, irrigation imitating heavy rainfall). Additionally, the soil depth distribution of pharmaceuticals at the end of the leaching experiment was analysed. Under routine farm practice, sulfamethazine was repeatedly detected in the leachate with a maximum concentration of 0.12μgL(-1). All applied substances were still detected in soil after 53days, suggesting that there was no overall rapid and complete dissipation. Worst-case conditions enhanced vertical translocation; all leachate samples contained sulfonamides (up to 653μgL(-1) sulfamethazine), and even tetracyclines were found in the leachate once, with doxycycline reaching the highest concentration (0.19μgL(-1)). The concentrated simultaneous occurrence of sulfonamides with the bromide tracer in leachate samples pointed to preferential flow as underlying transport process. The high pH values did not prevent the single leaching event for tetracyclines and hardly affected overall leaching behaviour. The applied fluoroquinolones were not significantly translocated below 4cm depth, irrespective of irrigation and high manure addition.

Bioavailability of copper, cadmium, zinc, and lead in tropical savanna soils assessed by diffusive gradient in thin films (DGT) and ion exchange resin membranes.

The technique of diffusion gradient in thin films (DGT) for assessing bioavailable metals has not been tested under field conditions. We assessed the relationships of DGT- and cation exchange resin-membrane-measured concentrations of Cd, Cu, Pb, and Zn with plant uptake of the metals under greenhouse and field conditions. In the greenhouse, the effective concentrations of Cu, Pb, and Zn by DGT correlated significantly with uptake by sorghum (Sorghum bicolor), but cation exchange resin-membrane-measured concentrations of Cd, Pb, and Zn did not correlate with sorghum uptake. In the field, the DGT-measured concentrations of Cd, Pb, and Zn were not linearly related to uptake Cd, Pb, and Zn by lettuce (Lactuca sativa) except for Cu uptake (r = 0.87, p < 0.05). Similarly, it was only the resin-membrane-extractable Pb that correlated with Pb uptake by lettuce (r = 0.77; p < 0.05). However, fitting non-linear regression models improved the plant metal uptake predictions by DGT-measured bioavailable Cd, Cu, Pb, and Zn under field conditions. In conclusion, the DGT technique was fairly predictive of bioavailability in the greenhouse, but not in the field.

Parallels of secondary grassland succession and soil regeneration in a chronosequence of central-Hungarian old fields

This study deals with spontaneous regeneration of fen and steppe meadows and corresponding soil properties on extensively managed ex-arable fields. Our first main aim was to analyse the nature of relations between various vegetation and soil parameters and time since abandonment and to determine the time needed for regeneration. Our second major goal was to determine the main environmental factors influencing regeneration success. Time since abandonment of the studied areas was determined with military maps, aerial photographs and the help of local rangers. Stands which were presumably not ploughed for over 150 years were taken as a reference. Vegetation surveys and soil sampling were carried out in 307 plots with different soil moisture conditions. The correlation with time was tested for relevant vegetation and soil parameters. The influence of different parameters on the species composition was tested with a generalized linear mixed model. We found that vegetation and soil parameters approach the level of long-term (permanent) grassland in a similar asymptotic curve. Numerous characteristic target vegetation species and legally protected species have colonized the old fields. The time frame needed for regeneration can be stated to be 20–40 years for the majority of sites, but the proportion of favourable species in the resulting grasslands is divergent. The most important finding among soil properties was a pronounced negative effect of plant available phosphorus on the species composition of regenerating grassland. We conclude that relying on spontaneous recolonization for grassland restoration in central Hungary is promising, particularly on sites which were not fertilized intensively with phosphorus prior to abandonment.

Tracing copper derived from pig manure in calcareous soils and soil leachates by 65Cu labeling.

Copper is used as a growth promoter in animal husbandry, resulting in high Cu concentrations in animal manure. We tested whether Cu would be mobilized in soils receiving excessive loads of manure, both from recently added and from aged fractions. To discriminate between these Cu sources, manure was labeled with (65)Cu. After soil application of 0, 15, and 30 Mg manure ha(-1), leachate was collected in free-draining lysimeters (40 cm depth) under undisturbed soil over a 53 day period. Determining the total amounts of Cu and the fractions of (65)Cu in leachate and the soil profile enabled us to trace the translocation of Cu derived from labeled manure. More than 84% of the applied Cu was retained in the top 2 cm of soil. Less than 0.01% of the applied Cu was detected overall in the leachate. Of this amount, however, 38% (± 8.9 SE) was leached within 8 days after application. The total Cu concentration in leachates (32-164 μg L(-1)) frequently exceeded the Chinese groundwater quality standard of 50 μg L(-1). The added (65)Cu, however, accounted for less than 3.6% of the total Cu leaching load, suggesting that Cu from older sources and/or geological background controls contamination, regardless of current land management.

Chemische Eigenschaften und Prozesse

Viele Regelungsfunktionen von Boden beruhen auf biogeochemischen Prozessen und werden deshalb von den chemischen Eigenschaften der Boden beeinflusst. Beispiele hierfur sind die Speicherung und Nachlieferung von Nahrstoffen, die Sorption und der Abbau von Schadstoffen sowie die Pufferung von Saureeintragen. Chemische Prozesse an Grenzflachen sind dabei von herausragender Bedeutung. Etwa 40–60 % des Bodenvolumens bestehen aus Poren, die je nach aktueller Bodenfeuchte mit Wasser (Bodenlosung) und Gasen (Bodenluft) gefullt sein konnen. Die feste Bodensubstanz besteht uberwiegend aus Mineralen und kleineren Anteilen organischer Substanzen. In diesem porosen System aus mineralischen und organischen Bodenpartikeln, Gasen, wassrigen Losungen und Organismen bilden sich enorm grose und chemisch reaktive Grenzflachen aus. An diesen Grenzflachen konnen Ionen und Molekule adsorbiert, komplexiert, oxidiert, reduziert, ausgefallt oder chemisch umgewandelt werden. Dieses Kapitel bietet eine Einfuhrung in wichtige chemische Eigenschaften und Prozesse, die das Verhalten von Nahr- und Schadstoffen in Boden kontrollieren.