The moss grass Coleanthus subtilis (Tratt.) Seidl is a rare, diminutive grass which grows on wet muddy bottoms of drained water bodies displaying a high degree of water level dynamics, such as fishponds or water reservoirs. Due to the temporal character of its habitat, C. subtilis has a very short life cycle of only a few weeks.

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Abstract:Two different models (WBS FLAB, WaSiM-ETH) were used in the project HochNatur (flood prevention and nature conservation in the Weißeritz catchment in the Eastern Ore Mts. -Erzgebirge) to determine risk areas with quick runoff processes and to simulate the discharge. It was done in different scales, in the mesoscale Weißeritz catchment as well as two selected subcatchments with different natural and urban conditions, the Weißbach subcatchment with a well-structured landscape, the Höckenbach subcatchment with a greater part of arable land. On the basis of selected scenarios, the effect of land use changes on the runoff generation processes of an area and on the hydrograph is described. Land use changes are able to reduce the portion of quick runoff components, the water erosion and the discharge. The effect occurs especially in smaller catchments and with short heavy rains (events with a frequency of occurrence of 5-50 years). Depending on the present situation the changes have to include areas of more than 25% of the catchments area to cause a significant effect. It became apparent that nature conservation and flood prevention agree well in their requirements with the land use. A rich structured landscape proved to be extraordinarily positive for both, flood prevention and nature conservation.

Within the framework of the project "Flood Prevention and Nature Conservation in the Weisseritz area" ("HochNatur"), a method including landscape metrics was developed and applied to assess and to compare different land use scenarios with regard to flood prevention and nature conservation. For the analysis, two sub-catchments strongly differing in land use within the Weisseritz catchment (Eastern Erzgebirge, Saxony, Germany) were selected. The first step of the evaluation procedure was a biotope assessment using three assessment criteria (naturalness, substitutability, rareness/endangerment). However, the biotope assessment did not yield any information about spatial distribution or the structural composition of the landscape. Therefore, landscape metrics were applied to analyse the structural and biotope type diversity at the landscape scale. Different landscape metrics (Shannon/Weaver diversity index, mean patch size index, Interdispersion/Juxtaposition index) and a weighting system were used to compare the different land use scenarios and the current state. The analysed catchment areas differ substantially in terms of their current state and potential measures regarding flood prevention and nature conservation depending on the location and distribution of biotope types. It was demonstrated that this method can be used for small catchment areas regardless of their land use for assessing, analysing and comparing different land use scenarios for a specific area.

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