Due to their special hydrological conditions, near-natural peatlands fulfil a large number of important ecological functions and thus provide remarkable ecosystem services. Especially in the densely populated urban space, these soils worthy of protected status are exposed to various use interests and are threatened by a loss of their ecosystem services. In the course of climate change, this situation will be further exacerbated.
While the near-natural Berlin peat soils take up only 1 % to 2 % of the Berlin state area, their ecosystem services are considerable compared to the mineral soils in the urban city landscape. Within the meaning of the Federal Soil Protection Act, near-natural peat soils fulfil the natural soil functions in a particularly sustainable manner. This includes in particular their function as a habitat for humans, animals, plants and soil organisms as well as their capacity to absorb and store water, nutrients and other substances. Thus the Berlin peatlands form nutrient sinks for carbon, phosphor and nitrogen, buffer immitted pollutants and thus at the same time protect the groundwater. Due to their capacity to store and retain water, peatlands have a compensating effect during flooding. Moreover, in hot and dry periods during summer they have a microclimatic cooling effect due to evaporation. Besides the water level, near-natural, peat-forming plant communities and also anthropogenic influences determine the natural regeneration of the peat soils. Peatlands are unique archives of natural and cultural history, as they permanently conserve the pollen, plants and animals as well as settlement traces and cultural relics from earlier times.
Most of the Berlin peatlands were protected as protected areas (nature protection areas and landscape protection areas) because of their significance as a biotope and as a habitat for endangered species, due to their function for the ecosystem and also as testimonies to the landscape history. The peatlands in the Spandau Forest, Grunewald and Köpenick as well as the Tegeler Fließ and the Berlin Müggelspree fulfil the criteria of the EU Habitats Directive and are part of the European protected area system Natura2000.
On March 13, 2012, the Berlin Senate adopted the Berlin Biodiversity Strategy. It aims both to preserve valuable remainders of pristine and culturally shaped nature in Berlin and to allow for a wider, dynamic scope for nature development within all land uses.
Berlin habitats consist of relics of the original natural landscape such as peatlands and near-natural sections of watercourses and of the historical cultural landscape such as meadows and infertile grassland. The diversity of habitats brings a great wealth of plant and animal species, but many of them are endangered because their habitats are often in bad condition. Efforts to preserve the diversity of habitats and species are therefore imperative. Particularly in times of climate change, Berlin aims to preserve significant parts of its peatlands as wetlands and thus as a habitat of species typical of peatlands and wetlands.
Due to their high levels of soil organic matter, peatlands represent important carbon storages for the global carbon cycle. For this reason, they play an important role in the debate in connection with climate change. Even though these ecosystems make up only three percent of the world’s land surface (Parish et al. 2008), they store approx. one third of the total organic carbon (TOC) (Post et al. 1982). All of the carbon © stored globally in peatlands is estimated to exceed 500 billion tons, which is equivalent to more than half of the amount residing in the atmosphere in the form of carbon dioxide (CO2) (Houghton 2007, Limpens et al. 2008). The phase of mire formation, and with it the storage of C, began in Berlin, as in the rest of Central Europe, mainly with the end of the last Ice Age (Succow & Joosten 2001).
The activity of biota in peat soils is much reduced by high water levels all year round that cause low levels of oxygen so that dead parts of plants are not fully decomposed. As a result, they are deposited as peat layers, which are sometimes several metres thick (Koppisch 2001a). Compared to mineral soils, these peat soils can generally store vast amounts of C, often greatly in excess of 1,000 t per hectare (Möller et al. 2014). Through these high proportions of carbon stored and fixed in peat soils, peatlands make a meaningful contribution to climate protection, and thus have had a major role in the cooling of the global climate (Frolking et al. 2001, Akumu & McLaughlin 2013). Due to their capacity to capture and fix atmospheric CO2 (carbon dioxide), the ‘global cooling effect’ of peatlands accounts for approx. 1.5 to 2 °C over the past 10,000 years (Holden 2005).
Growing peatlands with high water levels still accumulate C up to the present day. However, peatlands are increasingly being aerated by drainage and decreasing water levels caused by agricultural land use and forestry, groundwater extraction for drinking water, or climate-change-induced reductions in rainfall. This leads to an intensification of the activity of soil biota and therefore to peat decomposition and mineralisation. Peatlands change from C sinks into C sources, releasing considerable amounts of CO2 (Koppisch 2001b). For example, Drösler et al. (2013) specify the current greenhouse gas emissions from drained peatlands with 0--34 t CO2 equivalents per hectare and year depending on land use, which accounts for a proportion of up to 5 % of the total emissions nationwide.
The climate protection service is expressed by the total C stored in all of Berlin’s peatlands (their ‘historical’ C pool). The amount of C stored may vary considerably from one peatland to another. Based on their natural diversity (hydrology, geomorphology, etc.) during peatland formation, different soil horizons were formed, consisting of varying peat thicknesses and varying contents of organic C. Thus, peatland or mire types can be categorised according to their formation conditions, for example, as percolation mires, which can store up to ten times more carbon than flat peatlands such as a ‘water rise mire’ (Zauft et al. 2010). In addition to differences in peat thickness, there are considerable differences also in peat qualities (peat-forming plants, degree of decomposition, etc.). This is reflected in the substrate-specific C storages and bulk densities of single soil horizons, and likewise is also reflected in the amounts of stored C (Rosskopf & Zeitz 2009).
In the framework of the project "Berlin’s Peatlands and Climate Change" (Berlin Environmental Relief Programme II) of the Humboldt University of Berlin, Soil Science and Site Science Division ("research project" in the following), in the past years Berlin’s peatlands were for the first time comprehensively mapped using a uniform procedure. Subsequently, an indicator and assessment system for different ecosystem services of peat soils for urban spaces was developed using the example of Berlin. In this context, the use of peat soil data that provide information on the state, functional capacity and biotope quality and thus possess a high indicator value is a distinctive feature. The soil-scientific peatland mapping now forms the basis of a systematic assessment of the ecological state of Berlin’s peat soils and identifies environmental relief potentials and development goals, in particular with respect to their climate protection services.