Overall concept south of Kreuzstauden in Grießenbacher Moos Biotope design measures as part of the creation of eco-account areas

Objective: Creation of wetland habitats and the rewetting of fen peat. Thus, the project shows an example of successful peatland protection and makes a significant contribution to climate adaptation. The importance of fens in the natural balance can be measured on the basis of four factors:

1. Storage function as a nitrogen depot with up to 75 tonnes of nitrogen per hectare and metre of peat thickness, and as a carbon sink with up to 686 tonnes of carbon per hectare and metre of peat thickness (Kuntze 1973, Göttlich 1990, cited in Lenz 1994); the aim is to maintain a high retention capacity for non-sorbable substances such as nitrate (nitrogen depot),

2. Filter function by fixing carbon, nitrogen, phosphorus or organic compounds, quasi a "renewable activated carbon filter", which has a purifying effect on the groundwater,

3. retention function or "sponge function" in phases of heavy rainfall runoff and thus a certain reduction of flood runoff peaks; this can be seen especially in the wet winter months in the almost extensive overwatering,

4. habitat function for rare plant and animal species.

The planning area "south of Kreuzstauden" covers a total of 10.1 ha including the so-called "district area". It represents an extension and sensible rounding off of the measure of the Landshut district (approx. 25 %), which was initially selectively created on the Fl.Nr. 900/4 in the northeast and was planned over again in 2008. The remaining 75 hectares were created in seven construction phases and serve as a compensatory measure according to § 1a BauGB for the commercial areas developed south of the motorway. Between 2001 and 2012, a secondary habitat was created, which is based on the landscape structure of the flood channels or "Seigen" and offers meadow-breeding bird species as well as rare plant communities, e.g. whistling grass meadows and wet meadows but also calcareous grasslands, development opportunities in the otherwise intensively used natural area of the Lower Isar Valley. The area has been developed as part of a private, commercial eco-account. Regular monitoring of the biotope design and maintenance measures was carried out twice a year. In 2012, ownership and monitoring were transferred to the lower nature conservation authority in the Landshut district office.

The planning area is part of an overarching concept within the framework of the large-scale nature conservation project "Moor and meadow breeding protection in the Mettenbacher and Grießenbacher Moos", which is carried out by the district of Landshut as project sponsor. The 480 hectare area of the large-scale nature conservation project on the northern edge of the Isar valley still has peat thicknesses of 1 to 3 metres. The importance of the project area for nature conservation results from the high potential of endangered and rare species and their habitats, its outstanding function for the protection of abiotic resources (soil, groundwater, atmosphere) and its location and function as a "core area of the state-wide biotope network" (location on the migration axis and bird migration corridor of the Isar valley). Despite existing impairments (initial state of large-scale arable land use), there is a high potential for site development through rewetting and the promotion of extensively used areas with permanent vegetation.

Low moors can represent both significant material sinks and material sources for climate-relevant gases. While intact fens fix e.g. carbon and nitrogen in large quantities due to their inhibited mineralization, a drainage of fen soils leads to the release of considerable amounts of NOX, N2O and CO2.
Intact fens are one of the rarest habitats in all of Bavaria. There are only 9 he in 1914 mapped fen areas left. In Bavaria the portion amounts to 2,3
n of the state area. In the project area of the "Grießenbacher und Mettenbacher Moos", which covers a total of 480 ha, peat thicknesses of over 1 m still exist on two thirds of the area, over 2 m in a quarter and over 3 m in a small area in Grießenbeck'schen Forst. This means that the peat thicknesses are significantly higher than in the other valley-edge reservoirs of the Lower Isar Valley. The objective is to preserve the basic functions of an intact lowland moor or to restore them through local rehabilitation of lowland moor soils.

The project area "Grießenbacher und Mettenbacher Moos" is home to a large number of rare and endangered species. Among the animal species, the project area has a nationwide significance. In particular, the leading meadow breeding species, the curlew, has above-average breeding populations. While the species is declining throughout Bavaria, its occurrence within the project area has remained stable in recent years. About 17 of the curlew population of all of Lower Bavaria breeds within the project area. For the overall project "Moor - and meadow breeding protection in the Grießenbacher and Mettenbacher Moos" three main objectives are mentioned:

1. Local rehabilitation of low moor sites by rewetting the moor body in hydrologically delimited areas with a moor thickness of at least 1 m; that is, introduction of water or impoundment only in sub-areas that are bounded all around by ditches and thus do not affect the surrounding agricultural land.

2. Restitution of fen habitats: Restoration of calcareous fens and stream valley meadows through soil removal on sites close to groundwater in order to create site conditions for plant communities of the original calcareous fens, establishment of stands through transfer of mown material, targeted measures for species enrichment, here e.g. the establishment of the fragrant leek.

3. Improve habitat structure for meadow-nesting birds, e.g. through grassland extensification, conversion of arable land to grassland, structural enrichment, rewetting and deconstruction of paths. About 17 of the curlew population of Lower Bavaria breed within the project area. By the measure could be resettled in the area south Kreuzstauden e.g. the redshank.

The 10 ha large implementation area is located in the zone 11 "Eastern meadow breeding core area", the so-called "Unterköllnbacher Moos". The following measures were implemented in the specific area "south of Kreuzstauden":
- Diversion or impoundment and discharge of water from the adjacent ditch to the east,
- Creation of (shallow) channels and troughs for water distribution in the area,
- Lowering of the terrain surface in the course of a soil exchange and reintegration of the peat with targeted rewetting,
- Inoculation with hay scrub from neighboring supply biotopes.

In detail, the terrain "south of Kreuzstauden" was lowered on average by 0.6 to 1.2 m to 369.80 to 370.40 m above sea level. The peat layers and cohesive layers underneath were selectively reinstalled. In addition, the water brought in from the Oberköllnbacher or Unterköllnbacher moss and the seepage water from the moss properties adjacent to the ditch course is now being selectively introduced into the district area in the northeast (rewetting). As part of the overall design, the water supply was increased to 75 er mean flow and impounded in extensive swale areas. These "Seigen" are temporarily overwatered, in the winter months partly over large areas up to 50 er total area. With a water depth of about 10 cm to max. 30 cm, these are so-called wading areas. Diverse reed communities develop. The water evaporates in the summer months - the hollows partially dry out - and also seeps very slowly into the groundwater. Valuable feeding habitats are created for the meadow-nesting bird species that occur here (= priority development measure for nature conservation). At the same time, the peat body remains moist and does not mineralise.

In the construction sections BA I - BA IV, very shallow ridges are formed between the swale areas, which temporarily dry out in the summer months, through which the water seeps. These ridges have been deliberately formed from Quaternary sandy-gravelly to silty material. The slopes of the embankments are so flat that they can be cultivated with agricultural machinery. Here, hay seeding was used to initiate the development of fragrant meadows and calcareous grasslands.

The project implementation focused on the combination of abiotic and biotic objectives such as soil and water conservation, climate protection and the development of meadow-breeding habitats. The 10 ha large area shows as a building block in the NATURA 2000 area already five years after completion visible results and is exemplary for further implementation measures.