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Organic matter from biological soil crusts induces the initial formation of sandy temperate soils
(2014)
Different development stages of algae-dominated and moss-dominated biological soil crusts (BSCs) were sampled on a natural sand dune (b17 years old) and on an experimental sand dune (b8 years old) along a catena, including gradients of vegetation cover, location on the slope, as well as composition and thickness of BSC organisms in northeastern Germany. The accumulation of BSC-derived organic carbon (OC)was determined for bulk materials and fractions less than 63 μm. The OC composition was characterized by solid-state 13C NMR spectroscopy and the carbohydrate-C signature. 14C contents were determined to assess the origin and dynamics of OC. From the radiocarbon contents, two OC pools were differentiated: recent BSC-derived and lignite-derived “old” OC. Downward movement of OC into the underlying substratewas found only undermoss-dominated BSCs at the old sand dune. BSC-derived OC was mainly composed of carbohydrate-C and, to a lesser extent, alkyl C and N-alkyl C, with considerably higher contributions of alkyl C in the young dune, indicating differences in the composition of extracellular polymeric substances produced by the BSCs with age. This is consistent with higher proportions of water-soluble OC of moss-dominated BSCs at the old dune, which is leached in the underlying substrate and initiates soil formation. Because of the channeling effect of mosses, OC depth translocation along with suspended colloidal substances contribute to OC accumulation in substrates.
Ecosystems in transition: interactions and feedbacks with an amphasis on the initial development
(2014)
In this Special Issue of Biogeosciences on “Ecosystems in transition: Interactions and feedbacks with an emphasis on the initial development”, we bring together research on ecosystems undergoing state transitions, including artificially created and naturally formed sites, most of them in an initial
stage of development. State transitions of an ecosystem may occur either when a formerly stable system state is disturbed or when a developing system gradually achieves new functions during succession. This special issue presents a collection of observational and experimental studies that focus on processes occurring during state transitions in the development of ecosystems and provide insights into the feedback mechanisms controlling
them. These state transitions are studied at multiple scales, ranging from the pore scale to the catchment scale. The contributions
collected in this issue can be divided into two main groups: (i) studies dealing with state transition occurring in initial ecosystems without active human interference, and (ii) studies dealing with active restoration of ecosystems after severe disturbances.
Watersheds are often insufficiently known and have to be explored indirectly e.g. by means of geophysical methods. Therefore, important parts of the system often remain 'black boxes'. In addition, natural systems are characterized by huge complexity and heterogeneity. To overcome these disadvantages artificially created watersheds may play an important role in ecosystem research. They offer the chance to investigate systems with well defined boundary conditions and inner structures. Furthermore, artificial watersheds might be an important link between lysimeter research and investigations at the landscape scale. The artificial catchment "Chicken Creek" ('Huehnerwasser') is one of the world's largest man-made catchments for scientific purposes. It was established in 2005 with an area of 6 ha (450 m x 150 m) including a small lake. The site is located in the Eastern German lignite mining district near Cottbus, about 150 km southeast of Berlin. The watershed was constructed by Vattenfall Europe Mining AG as the operator of the still active lignite open-cast mine Welzow-South. Construction work was done by means of large mining machines in co-operation with the Brandenburg University of Technology at Cottbus. The inner structure of this new landscape element is relatively simple: A clay layer was dumped as a barrier for seepage water overlaid by a 3 m sandy layer consisting of Quaternary substrate from Pleistocene sediments. The surface of the site has been flattened and the area was fenced to prevent disturbances. Neither amelioration nor any reclamation measures were carried out afterwards. The site has been left for an unrestricted natural succession. In 2007 the Transregional Collaborative Research Centre (SFB/TRR 38) as a joint project between 3 Universities (BTU Cottbus, TU Munich and ETH Zurich) was launched and is funded by the German Research Foundation (DFG). The project group investigates the initial genesis of ecosystems with the Chicken Creek catchment as its main research site. A comprehensive monitoring programme is investigating the development of hydrological, pedological, geomorphologic and biological patterns and processes. It is planned to establish a structure and process model for this catchment to describe the initial development phase of an ecosystem in detail. Furthermore, the site will be the basis for (hydrological) model validation