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16Drained peatlands are hotspots of carbon dioxide (CO 2 ) emissions from agriculture. As a consequence of both drainage-17 induced mineralisation and anthropogenic mixing with mineral soils, large areas of former peatlands under agricultural use 18 now contain soil organic carbon (SOC) at the boundary between mineral and organic soils and/or underwent a secondary 19 transformation of the peat (e.g. formation of aggregates). However, low carbon organic soils have rarely been studied since 20 previous research has mainly focused on either mineral soils or true peat soils. The aim of the present study was to evaluate 21 the soil organic matter (SOM) vulnerability of the whole range of organic soils including very carbon rich mineral soils (73 g 22) and to identify indicators for mineralisation of such anthropogenically disturbed organic soils. 23Using a large sample pool from the German Agricultural Soil Inventory, 91 soil samples were selected covering a broad 24 range of soil and site characteristics. Fen and bog samples were grouped into disturbance classes according to their 25 pedogenetic features. Potential CO 2 production by aerobic incubation was then measured. Specific basal respiration rates 26 (SBR) per unit SOC showed the highest potential emissions for heavily disturbed fen (12.1 ± 5.0 µg CO 2 -C g SOC -1 h -1 ) and 27 moderately disturbed bog samples (10.3 ± 5.2 µg CO 2 -C g SOC -1 h -1 ). Surprisingly, SOM vulnerability increased with an 28 increasing degree of disturbance and a decreasing SOC content, indicating positive feedback mechanisms as soon as peat 29 soils are disturbed by drainage. Furthermore, with increasing degree of disturbance the variability of the SBR increased 30 drastically, but correlations between soil properties and SBR could not be identified. Respiration rates increased more 31 strongly with an increasing degree of disturbance in bog than in fen samples. Peat properties that positively influenced the 32 turnover of SOM in less disturbed soil samples were mainly pH value and nitrogen content, while phosphorus was important 33 for the mineralisation of increasingly disturbed samples and bog peat in general. Furthermore, a narrow carbon-to-nitrogen 34 ratio correlated strongly with potential emissions. Given the high potential of CO 2 emissions from organic soils with a low 35 SOC content, mixing with mineral soil does not seem to be a promising option for decreasing emissions. 36Biogeosciences Discuss.,

Background Peatlands only cover a minor fraction of the global terrestrial surface, but due to drainage, they are major contributors to carbon dioxide (CO2) emissions from soils. Previous studies have shown that hydrological conditions, nutrient availability and anthropogenic disturbance play an important role in the mineralisation of organic matter. Furthermore, microbial turnover depends on peat quality, which is determined by its botanical origin and degree of transformation under natural conditions. Aims The objective of this study was to shed light on the interdependence between mineralisation rates, secondary transformation of peat and chemical composition by examining the differences between bog and fen peat and between strongly degraded topsoil and well‐preserved subsoil. Methods Bog and fen peat from ten different peatlands under grassland use in Germany were analysed for their chemical composition using standard 13C nuclear magnetic resonance (NMR) spectroscopy and wet chemical extractions for fibre analysis. The radiocarbon age was determined as well. The results were combined with CO2 fluxes from a previous incubation study. Results Topsoils had higher shares of proteins and lipids, and lower shares of carbohydrates and aromatics than subsoils. Bog peat subsoils were characterised by higher shares of carbohydrates and lower shares of aromatics than fen peat subsoils. Topsoils were more similar to each other in their chemical composition than the subsoils. Considering all samples, aromatics and phenolics were negatively correlated with CO2 fluxes. Measured CO2 fluxes from topsoils were significantly higher than from subsoils. However, no influences of chemical composition on CO2 fluxes were detected when examining topsoils and subsoils separately. Even though aromatics and phenolics showed positive relationships with radiocarbon age, differences in age alone were unable to explain the higher amounts of these compounds in the subsoil. Conclusions The results imply that chemical composition of topsoil peat is not the reason for higher mineralisation rates compared to subsoil peat, but rather a consequence of decomposition and transformation. Thus, peat mineralisation of drained organic soils under agriculture might not slow down over time due to gradually decreasing peat quality but could increase further.

<p>Halting and reversing soil degradation as well as protection and sustainable use of soil as a resource are part of the United Nations Sustainable Development Goals. Despite the vital significance and essential functions of soil, massive amounts of fertile soil worldwide are lost due to improper land use. In Germany, approximately 66 ha of soil are damaged partly or completely in their soil functions daily. The main issues are soil erosion, land area claims for housing estate and transportation, and pollution. Until now, precise spatial location and assessment of the loss of valuable soil in terms of fertility and productivity has not been quantifiable and therefore not controllable.</p><p>In the SOIL-DE project, indicators to evaluate the functionality, potential, intensity of use, and vulnerability of soils are developed in order to be able to assess the quality and value of soils, both in retrospective and under current agricultural use. The aim of this survey is (i) to detect the loss of land over the past ten years in high spatial accuracy, (ii) to determine the fertility of the soil and (iii) to identify risk areas, i.e. regions with particularly high soil loss rates and high soil profitability. The threat to soil, the fertility and impairment of soil functions by changes in land use, are to be recorded nationwide and statewide. Therefore, the evaluation of time series from satellite images is used in combination with official soil information at different spatial resolution, as well as digital elevation models and climatic data. In this study, different rating systems are investigated including e.g. the Muencheberg Soil Quality Rating (ZALF), biotic potential yield, resistance to erosion, filter, buffer and transformation function, and runoff regulation. First results will be presented.</p>