Kohlenoxydvergiftung in geschlossenen Garagen

The Science of Nature -     

DOM-Flocculation: A suitable approach for separating free and DOM-bound herbicides?

Dissolved organic matter (DOM) in soil solution is considered to interact with herbicides enhancing their mobility and promoting subsequent leaching. Batch experiments were conducted to test if free and DOM-bound herbicides can be separated by a DOM-flocculation technique with Cu as a coagulant. DOM was extracted from the H and A horizons of two soils (Terric Histosol, Cumuli-Calcaric Cambisol) and from the O horizon of a forest soil (Humic Cambisol). DOM-solutions (100 mL) were fortified with the herbicides terbuthylazine and pendimethalin (100 μg active ingredient each) and equilibrated for 14 hours. After DOM-flocculation with Cu (addition of 0,5 mM CuCl₂) herbicide recovery was determined in the supernatant solutions and in the precipitate of Humic Cambisol-DOM, respectively. Recovery of the herbicides from pure water was 85–99% and was not influenced by the addition of Cu. At low pH (4,8–5,3) DOM-flocculation of different DOM-extracts was insufficient and varied in a range of 18 – 90%. Herbicide recovery from DOM-solutions decreased moderately for terbuthylazine (60–90%) and strongly for pendimethalin (5 – 30%). In general, the addition of Cu caused no further reduction of herbicide recovery from supernatant solutions, except for Humic Cambisol-DOM. The effects of Cu-addition were most evident for pendimethalin (strongly reduced concentration in the supernatant solutions) and were considered to be caused by a flocculation of DOM-bound moieties. Flocculation of Humic Cambisol-DOM increased from 18 – 24% at pH 5 to > 95% at pH 8. However, at this pH the formation of Cu(OH)₂ as a sorbing subcomponent of the flocculated matter lead to an overestimation of DOM-bound pendimethalin. Calculating this side effect 6% of pendimethalin added was DOM-bound. Only traces of terbuthylazine (< 1%) were found in the solid matter of flocculated Humic Cambisol-DOM. To sum up, the new approach to separate freely dissolved herbicides from DOM-bound moieties not fully corresponded to our expectations. DOM-flocculation was found to depend strongly on pH-environment influencing not only DOM-herbicide interactions but also the clear separation of DOM-bound herbicides from herbicides in solutions.     

A new conceptual model for the fate of lignin in decomposing plant litter

Lignin is a main component of plant litter. Its degradation is thought to be critical for litter decomposition rates and the build-up of soil organic matter. We studied the relationships between lignin degradation and the production of dissolved organic carbon (DOC) and of CO2 during litter decomposition. Needle or leaf litter of five species (Norway spruce, Scots pine, mountain ash, European beech, sycamore maple) and of different decomposition stage (freshly fallen and up to 27 months of field exposure) was incubated in the laboratory for two years. Lignin degradation was followed with the CuO method. Strong lignin degradation occurred during the first 200 incubation days, as revealed by decreasing yields of lignin-derived phenols. Thereafter lignin degradation leveled off. This pattern was similar for fresh and decomposed litter, and it stands in contrast to the common view of limited lignin degradation in fresh litter. Dissolved organic carbon and CO2 also peaked in the first period of the incubation but were not interrelated. In the later phase of incubation, CO2 production was positively correlated with DOC amounts, suggesting that bioavailable, soluble compounds became a limiting factor for CO2 production. Lignin degradation occurred only when CO2 production was high, and not limited by bioavailable carbon. Thus carbon availability was the most important control on lignin degradation. In turn, lignin degradation could not explain differences in DOC and CO2 production over the study period. Our results challenge the traditional view regarding the fate and role of lignin during litter decomposition. Lignin degradation is controlled by the availability of easily decomposable carbon sources. Consequently, it occurs particularly in the initial phase of litter decomposition and is hampered at later stages if easily decomposable resources decline.     

A correlation between the fate and non-extractable residue formation of 14C-metalaxyl and enzymatic activities in soil

Extracellular, oxidative soil enzymes like monophenol oxidases and peroxidases play an important role in transformation of xenobiotics and the formation of organic matter in soil. Additionally, these enzymes may be involved in the formation of non-extractable residues (NERs) of xenobiotics during humification processes. To examine this correlation, the fate of the fungicide ¹⁴C metalaxyl in soil samples from Ultuna (Sweden) was studied. Using different soil sterilization techniques, it was possible to differentiate between free, immobilized, and abiotic (“pseudoenzyme”-like) oxidative activities. A correlation between the formation of metalaxyl NER and soil organic matter content, biotic activities, as well as extracellular phenoloxidase and peroxidase activities in the bulk soil and its particle size fractions was determined. Extracellular soil-bound enzymes were involved in NER formation (up to 8% of applied radioactivity after 92 days) of the fungicide independently from the presence of living microbes and different distributions of the NER in the soil humic subfractions.     

My land? Your land? Scotland?—understanding sectoral similarities and differences in Scottish land use visions

Understanding agreement and differences between land use visions forms a first step for assessing and comparing alternative pathways towards a sustainable future. This study presents an analysis of 20 semi-structured interviews with representatives of the principal land use sectors in Scotland. The aim was to understand what, in their ideal vision, they would want rural Scotland to look like in 2050. Inductive content analysis was used to identify similarities and differences amongst interviewees. There was general agreement on the following: the importance of the environment; the wish for more partnerships, dialogue and collaboration; the desire for society to be more engaged and aware about land use; and a strong need for short-, medium- and long-term policies helping to achieve these goals. The most notable differences relate to land ownership and governance. The outcomes form a basis for further facilitated discussions, emphasising common ground and exploring where, how and to what degree land use sectors can prepare and plan in the light of uncertainties posed by Brexit and climate change. The method was effective for understanding commonalities and differences between stakeholder groups and is transferable to other countries or regions.