ALBERT

Description: For the design and the assessment of river restoration projects, it is important to know to what extent the elimination of reactive nitrogen (N) can be improved in the riparian groundwater. We investigated the effectiveness of different riparian zones, characterized by a riparian vegetation succession, on nitrate (NO3−) removal from infiltrating river water in a restored and a still channelized section of the River Thur, Switzerland. Functional genes of denitrification (nirS and nosZ) were relatively abundant in groundwater from willow bush and mixed forest dominated zones, where oxygen concentrations remained low compared to the main channel and other riparian zones. After flood events, a substantial decline in NO3− concentration (〉50 %) was observed in the willow bush zone, but not in the other riparian zones closer to the river. In addition, the characteristic enrichment of 15N and 18O in the residual NO3− pool (by up to 22 ‰ for δ15N and up to 12 ‰ for δ18O) provides qualitative evidence that the willow bush and forest zones were sites of active denitrification and, to a lesser extent, NO3− removal by plant uptake. Particularly in the willow bush zone, during a period of water table elevation after a flooding event, substantial input of organic carbon into the groundwater occurred, thereby fostering post-flood denitrification activity that reduced NO3− concentration with a rate of ~21 μmol N l−1 d−1. Nitrogen removal in the forest zone was not sensitive to flood pluses, and overall NO3− removal rates were lower (~6 μmol l−1 d−1). Hence, discharge-modulated vegetation-soil-groundwater coupling was found to be a~key driver for riparian NO3− removal. We estimated that, despite higher rates in the fairly constrained willow bush hot spot, total NO3− removal from the groundwater is lower than in the extended forest area. Overall, the aquifer in the restored section was more effective and removed ~20 % more NO3− than the channelized section.

Description: Soil formation is the result of a complex network of biological as well as chemical and physical processes. Mainly the role of soil microbes is of high interest in this respect, as they are responsible for most transformations and drive the development of stable and labile carbon and nutrient pools in soil, which facilitate the basis for the subsequent establishment of plant communities. Glacier forefields, which provide a chronosequence of soils of different age due to the continuous retreat of the ice layer as a consequence of the increasing annual temperature since the last centuries, are a nice play ground to study the interaction of bacteria, fungi and archaea with their abiotic environment at different stages of soil formation. In this review we give insights into the role of microbes for soil development on the basis of investigations which have been performed at the Damma glacier in Switzerland in the frame of two international network projects Big Link (http://www.cces.ethz.ch/projects/clench/BigLink/) and DFG SFB/TRR 38 (http://www.tu-cottbus.de/ecosystem/). The review focusses on the microbiology of three major steps of soil formation including weathering of the parental material, the development of basic nutrient cycles, the formation of soil crusts and biofilms as initial microbial network structures and the occurrence of plants respectively the setup of plant communities.

Description: For the design and the assessment of river restoration projects, it is important to know to what extent the elimination of reactive nitrogen (N) can be improved in the riparian groundwater. We investigated the effectiveness of different riparian zones, characterized by a riparian vegetation succession, for nitrate (NO3−) removal from infiltrating river water in a restored and a still channelized section of the river Thur, Switzerland. Functional genes of denitrification (nirS and nosZ) were relatively abundant in groundwater from willow bush and mixed forest dominated zones, where oxygen concentrations remained low compared to the main channel and other riparian zones. After flood events, a substantial decline in NO3− concentration (〉 50%) was observed in the willow bush zone but not in the other riparian zones closer to the river. In addition, the characteristic enrichment of 15N and 18O in the residual NO3− pool (by up to 22‰ for δ15N and up to 12‰ for δ18O) provides qualitative evidence that the willow bush and forest zones were sites of active denitrification and, to a lesser extent, NO3− removal by plant uptake. Particularly in the willow bush zone during a period of water table elevation after a flooding event, substantial input of organic carbon into the groundwater occurred, thereby fostering post-flood denitrification activity that reduced NO3− concentration with a rate of ~21 μmol N l−1 d−1. Nitrogen removal in the forest zone was not sensitive to flood pulses, and overall NO3− removal rates were lower (~6 μmol l−1 d−1). Hence, discharge-modulated vegetation–soil–groundwater coupling was found to be a key driver for riparian NO3− removal. We estimated that, despite higher rates in the fairly constrained willow bush hot spot, total NO3− removal from the groundwater is lower than in the extended forest area. Overall, the aquifer in the restored section was more effective and removed ~20% more NO3− than the channelized section.

Description: Soil formation is the result of a complex network of biological as well as chemical and physical processes. The role of soil microbes is of high interest, since they are responsible for most biological transformations and drive the development of stable and labile pools of carbon (C), nitrogen (N) and other nutrients, which facilitate the subsequent establishment of plant communities. Forefields of receding glaciers provide unique chronosequences of different soil development stages and are ideal ecosystems to study the interaction of bacteria, fungi and archaea with their abiotic environment. In this review we give insights into the role of microbes for soil development. The results presented are based on studies performed within the Collaborative Research Program DFG SFB/TRR 38 (http://www.tu-cottbus.de/ecosystem ) and are supplemented by data from other studies. The review focusses on the microbiology of major steps of soil formation. Special attention is given to the development of nutrient cycles on the formation of biological soil crusts (BSCs) and on the establishment of plant–microbe interactions.