Wolfgang Tappe

Ammonia oxidation in nitrosomonas at NH3 concentrations near km: Effects of pH and temperature

Abstract Nitrosomonas europaea from continuous pure cultures was incubated with 26.4 μ M NH 3 (= 0.37 mg NH 3 -N l −1 ) at various NH 4 + concentrations, pH values and temperatures. Measured rates of nitrite formation were significantly influenced by pH. Likewise unexpectedly, the maximum ammonia oxidation rate occurred between pH 6.7 and 7.0. Temperature had an even stronger effect on the rate of ammonia oxidation than the availability of NH 3 . It is concluded that the assumption of a strict dependence of the rate of ammonia oxidation on substrate concentration is an unjustified oversimplification. Among the mechanisms which could explain ammonium uptake and oxidation near or below pH 7.0, the formation of NO from HNO 2 is considered.

Diffuse atrazine pollution in German aquifers.

Until its prohibition in Germany in 1991, atrazine was the mostfrequently applied herbicide in maize cultivation. Moreover, it was used in orchards andvineyards and as a total herbicide on non-cultivated grounds (railways, factory grounds).Later on, atrazine was substituted mainly by terbutylazine. Terbutylazine and terbutrynare the only s-triazines presently permitted in Germany. Nevertheless, atrazine and itsmetabolite desethylatrazine are by far the most abundant herbicides detected in near surfacegroundwater. This might be due to wash-outs from the pools of atrazine and its metabolitesfrom the soil into the groundwater or continuing illegal applications. Samples takenfrom maize fields in 1994 showed that 6.2% of 471 fields tested were treated with atrazinedespite the prohibition of its use. Nevertheless, the overall trend is in fact a slow decreasein atrazine concentrations where it is detected in groundwater and, simultaneously often aslight increase in desethylatrazine concentrations. But this is not the case forall sampling points, and increasing concentrations in several aquifers are observedas well. Factors governing the adsorption, degradation, persistence and the possible transferinto the aquifer and the current situation concerning atrazine occurrence in German aquiferswill be discussed.

A terrestrial observatory approach to the integrated investigation of the effects of deforestation on water, energy, and matter fluxes

Integrated observation platforms have been set up to investigate consequences of global change within a terrestrial network of observatories (TERENO) in Germany. The aim of TERENO is to foster the understanding of water, energy, and matter fluxes in terrestrial systems, as well as their biological and physical drivers. Part of the Lower Rhine Valley-Eifel observatory of TERENO is located within the Eifel National Park. Recently, the National Park forest management started to promote the natural regeneration of near-natural beech forest by removing a significant proportion of the spruce forest that was established for timber production after World War II. Within this context, the effects of such a disturbance on forest ecosystem functioning are currently investigated in a deforestation experiment in the Wüstebach catchment, which is one of the key experimental research sites within the Lower Rhine Valley-Eifel observatory. Here, we present the integrated observation system of the Wüstebach test site to exemplarily demonstrate the terrestrial observatory concept of TERENO that allows for a detailed monitoring of changes in hydrological and biogeochemical states and fluxes triggered by environmental disturbances. We present the observation platforms and the soil sampling campaign, as well as preliminary results including an analysis of data consistency. We specifically highlight the capability of integrated datasets to enable improved process understanding of the post-deforestation changes in ecosystem functioning.

Degradation of Sulfadiazine by Microbacterium lacus Strain SDZm4, Isolated from Lysimeters Previously Manured with Slurry from Sulfadiazine-Medicated Pigs

ABSTRACT Sulfadiazine (SDZ)-degrading bacterial cultures were enriched from the topsoil layer of lysimeters that were formerly treated with manure from pigs medicated with 14C-labeled SDZ. The loss of about 35% of the applied radioactivity after an incubation period of 3 years was attributed to CO2 release due to mineralization processes in the lysimeters. Microcosm experiments with moist soil and soil slurries originating from these lysimeters confirmed the presumed mineralization potential, and an SDZ-degrading bacterium was isolated. It was identified as Microbacterium lacus, denoted strain SDZm4. During degradation studies with M. lacus strain SDZm4 using pyrimidine-ring labeled SDZ, SDZ disappeared completely but no 14CO2 was released during 10 days of incubation. The entire applied radioactivity (AR) remained in solution and could be assigned to 2-aminopyrimidine. In contrast, for parallel incubations but with phenyl ring-labeled SDZ, 56% of the AR was released as 14CO2, 16% was linked to biomass, and 21% remained as dissolved, not yet identified 14C. Thus, it was shown that M. lacus extensively mineralized and partly assimilated the phenyl moiety of the SDZ molecule while forming equimolar amounts of 2-aminopyrimidine. This partial degradation might be an important step in the complete mineralization of SDZ by soil microorganisms.

Growth-inhibitory effects of sulfonamides at different pH: Dissimilar susceptibility patterns of a soil bacterium and a test bacterium used for antibiotic assays

The ionic speciation of sulfonamides is pH-driven and this may be crucial for their bioavailability and sorption to soil constituents, as well as for their uptake into bacterial cells. The inhibition behaviour of a bacterial test strain (Pseudomonas aeruginosa; DSM 1117), which was grown in the presence of different concentrations of 8 sulfonamides at pH values from 5 to 8, could be predicted by models that take the speciation of sulfonamides in- and outside of bacterial cells into account. Assuming a pH of 7.5 inside the cells (pH homeostasis), the strongest inhibition was predicted for the lowest external pH and for sulfonamides with the lowest pK(a) values. Growth experiments with Ps. aeruginosa basically reflected this predicted behaviour. However, Pantoea agglomerans -- a bacterial strain isolated from arable soil -- behaved surprisingly different regarding its pH dependency: all sulfonamides showed the strongest effects at pH 7 to 8 instead of being most effective at lowest pH, although the pK(a) dependencies followed the same pattern. Experimental and modeling results could be brought into good agreement for P. agglomerans if the cell-internal pH was admitted to approximate the external pH instead of implying pH homeostasis for modeling calculations. Thus, besides the actual concentration of sulfonamides, the pH dependent mode of reaction of different bacteria to sulfonamides may additionally govern the population dynamics in soils.

Dissipation of bentazone, pyrimethanil and boscalid in biochar and digestate based soil mixtures for biopurification systems

Biopurification systems, such as biofilters, are biotechnological tools to prevent point sources of pesticide pollution stemming from on-farm operations. For the purification processes pesticide sorption and mineralization and/or dissipation are essential and both largely depend on the type of filling materials and the pesticide in use. In this paper the mineralization and dissipation of three contrasting (14)C-labeled pesticides (bentazone, boscalid, and pyrimethanil) were investigated in laboratory incubation experiments using sandy soil, biochar produced from Pine woodchips, and/or digestate obtained from anaerobic digestion process using maize silage, chicken manure, beef and pig urine as feedstock. The results indicate that the addition of digestate increased pesticide mineralization, whereby the mineralization was not proportional to the digestate loads in the mixture, indicating a saturation effect in the turnover rate of pesticides. This effect was in correlation with the amount of water extractable DOC, obtained from the digestate based mixtures. Mixing biochar into the soil generally reduced total mineralization and led to larger sorption/sequestration of the pesticides, resulting in faster decrease of the extractable fraction. Also the addition of biochar to the soil/digestate mixtures reduced mineralization compared to the digestate alone mixture but mineralization rates were still higher as for the biochar/soil alone. In consequence, the addition of biochar to the soil generally decreased pesticide dissipation times and larger amounts of biochar led to high amounts of non-extractable residues of pesticide in the substrates. Among the mixtures tested, a mixture of digestate (5%) and biochar (5%) gave optimal results with respect to mineralization and simultaneous sorption for all three pesticides.

Field scale boscalid residues and dissipation half-life estimation in a sandy soil.

The aim of this study was to analyze the environmental fate of the fungicide boscalid in a sandy soil. Boscalid was applied in spring 2010/11 to a cropland site in western Germany. Three years after second application 65 undisturbed soil samples were taken. Boscalid was extracted using accelerated solvent extraction (ASE). Boscalid contents in the plough horizon ranged between 0.12 and 0.53 with a field mean of 0.20 ± 0.09 μg kg(-1). These contents were considerably lower compared to calculation using literature DT50 values, whereby a concentration of 16.89 μg kg(-1) was expected assuming a literature DT50 value of 345 days. Therefore, the measured field boscalid concentration only yields 1.2% of the expected value. To test whether the unknown extraction efficiency, losses from spray drift and interception can explain the mismatch between calculated and measured concentrations all these uncertainties were taken into account into calculations, but field concentrations and DT50 were still lower as expected. Leaching to deeper horizons was also studied but could not explain the discrepancy either. Moreover, a short-term incubation experiment using (14)C labelled boscalid revealed also shorter DT50 values of 297-337 compared to the 345 days taken from literature. However, this DT50 value is still considerably larger compared to the 104-224 days that were calculated based on the field experiment. Our results indicate that boscalid dissipation under field conditions is much faster at agricultural sites with sandy soil type as expected from laboratory incubation experiments.

Nitric oxide production in Nitrosomonas europaea under Aerobic and anoxic conditions

The trace gas nitric oxide (NO) substantially influences the chemistry of the troposphere. Depending on the mixing ratio, NO contributes to both, the net formation or degradation of ozone. Besides denitrification, nitrification plays a substantial role regarding the NO release from soils.

Continuous cultivation of nitrosomonas europaea with complete biomass retention

A bioreactor (360 mL working volume) was developed for continuous axenic cultivation of bacteria with internal retention of biomass. Nitrosomonas europaea was cultivated in this system at a constant ammonia input of 0.57 mmol NH4CI L−1 h−1. Since only cell-free filtrate left the reactor at a rate equivalent to the input rate, Nitrosomonas biomass was accumulating. After four weeks of operation, the biomass concentration reached a stable maximum of 2.7 × 109 cells mL−1 (equivalent to 400 mg dry matter per liter) and the growth rate approached zero. In this state, the ammonia input met the energy required for maintenance. The calculated specific maintenance energy demand was 0.02 mg NH3-N mg DM−1 h−1. Cell volumes decreased from an arithmetic mean volume of 0.6 μm3 at μmax to 0.25 μm3 at zero growth. Nutrient additions to the non growing culture resulted in a shift of the whole population to bigger cell volumes thus indicating homogeneity of the population at zero growth.