- Bioavailability and isotopic composition of CO2 released from incubated soil organic matter fractions (2014)
- The stabilization of soil organic matter (SOM) is triggered by three main mechanisms: (i) low bioavailability due to aggregation, (ii) recalcitrance due to the chemical structure, and (iii) association of the SOM with mineral surfaces. In the present study we used particle size SOM fractions (sand, silt and clay), derived from the Ah soil horizon from a Norway spruce forest in Southern Germany, to study the effects of different stabilization mechanisms on the bioavailability of soil organic carbon (SOC) in a one year incubation experiment. The respired CO2 was hourly recorded, additionally 13CO2 was analysed 20 times and 14CO2 three times during the incubation experiment. To better differentiate between particulate OM (POM) and mineral associated OM (MIN), the incubated fractions and bulk soil were separated according to density (1.8 g cm� 3) after the incubation experiment. 13C-CPMAS NMR spectroscopy was used to study the chemical composition of the incubated samples. We demonstrate a clear increase in SOM bioavailability due to aggregate disruption, as the calculated theoretical CO2 evolution of the SOM fractions recombined by calculation was 43.8% higher in relation to the intact bulk soil. The incubated sand fraction, dominated by POM rich in O/N-alkyl C, showed a prolonged bioavailability of SOC moieties with mean residence times (MRT) of 78 years. Interestingly, the silt fraction, dominated by highly aliphatic, more recalcitrant POM, showed low mineralization rates and slow MRT’s (192 years) close to values for the clay fraction (171 years), which contained a large amount of mineral-associated SOM. The recorded 13/12CO2 signatures showed a high depletion in 13C during the initial stage of the incubation, but an enrichment of the respired 13CO2 of up to 3.4& relative to the incubated SOM was observed over longer time periods (after 3 and 4 days for bulk soil and sand, respectively, and after 14 days for silt and clay). Therefore, we found no evidence for a 13C enrichment of SOM as driven by metabolic isotopic fractionation during microbial SOM mineralization, but an indication of a change in the isotopic composition of the C-source over time.
- High impact: early pastoralism and environmental change during the Neolithic and Bronze Age in the Silvretta Alps (Switzerland/Austria) as evidenced by archaeological, palaeoecological and pedological proxies (2015)
- The beginnings of the continuous human presence and of pastoral activities in the high mountainous region of Central Europe have recently become a frequently discussed topic in both archaeology and palaeoecology. In extreme environments such as the high Alpine main ridge and adjacent areas, highly adaptive subsistence strategies were required to exploit natural resources available in the subalpine and alpine zones. Such strategies were determined by changing environmental, social, and economic conditions. To investigate the relationships between settlement dynamics, human impact, and Holocene climatic changes, we studied the valleys of the Silvretta Massif in the central Eastern Alps between the Paznaun (Austria) and Lower Engadine valleys (Switzerland). We are presenting new archaeological, palaeoecological, and pedological evidence of continuous human activities from the Early Neolithic Period to the Bronze Age (~ 5,500–800 BC). This evidence sheds new light on the beginnings of intensifi ed human impact on the high mountainous landscape, i.e. activities beyond Mesolithic hunting along the timberline. Archaeological data suggest a shift in subsistence strategies from hunting to herding at the end of the Neolithic Period (~2,800–2,500 BC). While palaeoecological data confirm this trend, they also indicate potentially earlier human and livestock impact through forest clearances by fire and grazing from about 4,200 BC onwards. In addition to archaeological sites and peat bogs, soils in high-altitude regions prove to be appropriate archives indicating former vegetation cover, shifts of timberline altitudes as well as disturbance of soil formation by human activity such as by slash-and-burn and by livestock grazing.