SummarySterilized soil is often used, for example in degradation studies, sorption experiments, microbiological tests and plant test systems, to distinguish between microbial processes and abiotic reactions. The most commonly used technique for sterilization is autoclaving of the soil. Another technique is irradiation with highlevel gamma radiation (g-radiation). One major drawback of sterilization procedures is the possible alteration of the structure of soil components, for example the organic matter. A change in the chemical structure of the soil organic matter can cause different reactions in the above-mentioned experiments and hence interfere with the aim of clearly distinguishing between biotic and abiotic processes. Two soils (Gleyic Cambisol and Orthic Luvisol) were sterilized by two g-irradiation procedures (4 kGy hour À1 for 9 hours and 1.3 kGy hour À1 for 27 hours) and repeated autoclaving at 121°C. Gentle physical aggregate fractionation of the sterilized soils revealed a decrease in the aggregation of the soil, which was reflected in an increase of the clay fraction. Subsequent analysis of the aqueous phase revealed much more dissolved organic matter (DOM) in the g-sterilized and autoclaved soils than in the untreated soils. Ultraviolet (UV) and fluorescence spectra of the DOM showed a decrease in the aromaticity and polycondensation of the dissolved organic carbon (DOC). 13 C cross-polarization/magicangle spinning nuclear magnetic resonance ( 13 C-CP/MAS NMR) spectra of the unfractionated soils and their respective soil fractions before and after sterilization showed that the most important change occurred in the carbohydrate and N-alkyl region, the main components of microorganisms. In general, the impact of the sterilization method was stronger for autoclaving. The g-sterilized soils and fractions displayed both fewer and smaller changes in the soil organic matter.
We provide an overview of the Rur hydrological observatory, which is the main observational platform of the TERENO (TERrestrial ENvironmental Observatories) Eifel/Lower Rhine Valley Observatory. The Rur catchment area exhibits distinct gradients in altitude, climate, land use, soil properties, and geology. The Eifel National Park is situated in the southern part of the Rur catchment and serves as a reference site for the hydrological observatory. We present information on general physical characteristics of the Rur catchment and describe the main features of the multi-scale and multi-compartment monitoring framework. In addition, we also present some examples of the ongoing interdisciplinary research that aims to advance the understanding of complex hydrological processes and interactions within the Rur catchment.
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