Post-mining landscape

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Recultivation of a post-mining landscape in Lusatia , 2011

As mining landscape generally in the large-scale areas of is industry during the degradation resulting or after the end or developed culture landscape designated. Conceptually, a distinction must be made between the mining landscape and the post-mining landscape. According to the technical definition, the post-mining landscape is a mining landscape that has been released from mining supervision , regardless of whether and how many technical measures have been taken to restore near-natural habitats.

In the past, mining areas were left to natural succession , which often only resulted in wasteland . Newer post-mining landscapes mostly serve subsequent uses from planned recultivation for the benefit of agriculture and forestry , but also as local recreation or nature reserves . From the start of renovation to a stable final state, post-mining landscapes go through several development phases that take very long periods of time and very high financial resources. The societal costs of post-mining landscapes are often referred to as perpetual burdens.

Problem

Dump vegetation in a post-mining landscape, Schleenhain , 2018
Rehabilitation of a post-mining landscape near Maiberg , 2007

The extraction of raw materials such as ore or coal is one of the most extreme interventions in the landscape, especially in the opencast mining process. This ventilates layers of the earth that were previously sealed off for millions of years. After removing the existing vegetation cover, the soil properties are fundamentally changed and the original landscape is completely destroyed. The Federal Mining Act (BBergG) in Germany obliges miners, among others, but also states and municipalities to recultivate destroyed land using technical and biological measures. The terms are as follows:

  • Reclamation is the proper design of the surface used by mining, taking the public interest into account.
  • Biological recultivation is the creation and promotion of soil fertility on technically prepared areas. This is done through soil cultivation, fertilization, humus enrichment , initial planting and rational agricultural or forestry subsequent use.

In the course of the renovation and recultivation work, the landscape is again being strongly reshaped. The removal of dangers has the highest priority for the release of the areas from the mountain supervision. For this purpose, measures are taken to secure embankments, improve the soil, reduce erosion and compact the soil, for example by means of targeted blasting or vibratory compaction . In principle, it must be possible to use destroyed areas in the same way as before the start of dismantling . Likewise, the requirements that miners have to meet specify how much area should be usable again for agriculture or forestry. However, the law restricts the implementation of the requirements by adding the phrase “if desired and reasonable”, so that in practice the remaining holes are often filled with water, as this is the simplest form of subsequent use.

The question arises, not only for opponents of mining, but above all for scientists, whether, in view of the difficult geological conditions in the soil, economic usability can be restored at all. For example, environmental researchers from state institutes point out that theory and practice differ widely because remedial measures are complicated, lengthy and expensive. Among other things, the Geoforschungszentrum Potsdam (GFZ) found that various renovation measures did not work because the soil was damaged too long. Rather, the question of the stability and sustainability of the ecosystem development in the emerging post-mining landscapes is still completely unresolved. Likewise, scientists, for example from the Georg-August-Universität Göttingen or the BTU Cottbus-Senftenberg , assume that the solution of the environmental problems will take decades or even centuries, and that in connection with opencast mines one should not speak of contaminated sites but of perpetual obligations .

The greatest challenge for post-mining landscapes are the tertiary substrates that come to the surface from deep layers . Basically, huge amounts of groundwater have to be pumped out in mining in order to be able to extract the required raw material deposits from the earth. As a result, for example, the groundwater level drops by many meters not only in opencast mines, but everywhere in the vicinity . This changes the water balance of entire landscapes. The pyrite contained in the rock , known as fool's gold, comes into contact with oxygen. It formed iron hydroxide and sulfate . If the production becomes unprofitable at some point and is discontinued, the water rises again and the tertiary substrates get into the water. This leads to ocher formation and sulphate pollution in rivers and lakes . When soil spoil is redeposited, pyrite comes to the surface and when it is weathered, sulfuric acid is formed. The pH values ​​of the soil or the water in opencast mines can therefore drop well below 3.5, which severely restricts the availability of nutrients . In addition, the very acidic and base-poor conditions of the soil solutions are often accompanied by a high content of heavy metals , which can reach toxic concentrations.

Open pit lakes

Part of the post-mining landscape of Leipziger Neuseenland (2016); In this area there used to be the millennia-old jungle Auf der Harth and the villages of Eythra and Bösdorf
Partwitzer See with clear ocher formation, 2018
Planned post-mining landscape of the Garzweiler opencast mine in 2100, detailed planning with regard to precise mining limits and recultivation are still pending

The simplest form of subsequent use arises from the open pit . In simplesten case, it is a quarry pond , which arose during gravel mining. Its volume roughly corresponds to that of the raw material removed. If the groundwater is not to continue to be pumped out, flooding is inevitable. In this way, lakes up to 80 meters deep are created in larger opencast mines. According to a report by the Federal Environment Agency , there were more than 500 such lakes in Germany in 2017. The majority of these are currently still in production. Among these works, in addition to the final slope protection and design, the active flooding by supplying extraneous water from the drainage ditch or passive flooding by intrinsic rise of groundwater, and the achievement of an appropriate the water management requirements water quality .

In terms of their water chemistry, open pit lakes are similar to acidic volcanic lakes. Due to the weathering of sulfidic minerals, the pH values ​​in post-mining lakes are typically between 2.5 and 3.5. Few species can tolerate this extreme acidic hardness. Fish need a pH of at least 5.5 to be able to reproduce. The pH value of mussels, crabs and snails must be even higher, otherwise their shells and carapaces will dissolve. It is twice as difficult for plants. Because nutrients such as phosphorus are bound in acidic water and are not available to the plants. In addition, there is little inorganic carbon in the opencast mines that plants need for photosynthesis . Because biological components and water conditions ( trophies , food chains ) in the open-cast mining lakes behave differently from normal lakes and limit numerous uses, special attention is paid to the problem of acidification.

Without permanent processing, the remaining holes are neither suitable for fish nor for bathing for several decades. The latter is also in contrast to the regional development plans , which provided for most of the lakes to be used for swimming. According to the EU bathing water directive, this use requires a pH value greater than 6, which in almost all cases cannot be achieved without "outside" help. To counter these conditions, lime and caustic soda are added to the water for several years . Since very few quarry ponds have a natural inflow and outflow, pumps ensure the dilution and the exchange of oxygen. Thousands of tons of lime that are added to the water every year have meanwhile normalized the pH value of some lakes. Nevertheless, the neutralization - depending on the situation with lime or water from the surrounding rivers - must be continued permanently, as acid can repeatedly flow in from the soil. According to the Leibniz Institute for Freshwater Ecology and Inland Fisheries, many decades will pass before this danger is averted.

The follow-up costs of the remedial measures per open pit lake are considerable. For example, the publicly funded LMBV commissioned its first own water treatment ship in 2016 for two million euros, which fertilizes Lake Partwitz alone with around 1,100 tons of lime every month. For renaturation ecologists it is clear that not all acidic opencast mining lakes can be neutralized. This is not feasible from a financial point of view, but in some cases it is also undesirable from an ecological and nature conservation perspective.

Although bare banks and cloudy water still predominate in post-mining lakes, some successes have been recorded. Because basically every body of water contains bacteria and some fungi also survive in acidic water. Plant plankton follows them . Later, in the best case scenario, larger aquatic plants and small animals such as water fleas or rotifers settled . Nevertheless, these lakes also have to struggle with new acidification and represent an inhospitable habitat for animals and plants in the long term. In geoecology , it is currently assumed that the hydrological conditions will only stabilize after 50 or 100 years . However, the ecological value of these water landscapes cannot yet be determined and is accordingly controversial. For example, the Saxon State Ministry for the Environment and Agriculture expects the re- acidification potential of open pit lakes in Lusatia to have an impact on water quality for the next 100 to 200 years, depending on the acid reserves created by the weathering of pyrite and the transport of the acid via the groundwater path.

The experience of other institutions also shows that the models used to date for predicting stability and water quality are not reliable. Quite a few of the post-mining lakes have a pH value below 2.8 and are therefore as acidic as vinegar. In addition, due to stability problems, the areas can often only be entered to a limited extent. Specifically: Due to the risk of landslides and the poor water quality, the majority of the mining lakes are currently unusable. Above all in central Germany, numerous remaining holes that have already been rehabilitated are closed, in Lusatia this affects a total of 10,000 hectares of water.

Agriculture

Examples of arable land as a post-mining landscape in Ronneburg , 2007
Landslide near Nachterstedt , 2009

The recultivation of a post-mining landscape as agricultural land is also associated with considerable follow-up costs. New land can only rarely achieve the agricultural and ecological potential of its predecessors. In the meantime it is undisputed that arable land after mining does not reach the quality of the old land even after decades. Organic farming is completely impossible for a long time. In spite of all efforts, the yields on the recultivated arable land only reach the level of soils grown from similar substrates after 60 to 80 years. Until then, these fields can only be kept fertile with tons of fertilizer, as well as lime and large quantities of liquid manure .

Ideally, the incidental by relieving measures should topsoil by layers and horizons stored separately and be reused in the subsequent surface reclamation. However, the living soil layer is only 20 to 30 centimeters thick, whereas an overburden excavator has a bucket wheel diameter of twelve meters and a cutting depth of three meters. When removing and reapplying, therefore, animate topsoil and inanimate subsoil are mixed. On the recultivated sites, under the approximately one meter thick artificial topsoil layer, there is an approximately 100 meter thick zone of heaped overburden, in which all aquifers have been destroyed. Because the agricultural areas consist of soil particles that do not stick together, the entire structure is unstable and can hardly be used for up to 30 years.

Further management obstacles are caused by the fact that after the mining work has been completed, the water on the former opencast mining areas is usually higher than originally. Due to the rise in the groundwater, the surfaces become wet. One example of this is the Schlaitz deep dump . The rise in water here after the end of the recultivation measures meant that the areas created for agricultural use had to be abandoned. The expensively recultivated area was quickly declared a nature reserve and left to its own devices.

The overburden is compacted during backfilling and recultivation, but landslides and so-called settlement flows occur again and again when the rising groundwater finds its way. Embankments and dump edges are also affected. In 2009 such a mass movement devoured two houses near Nachterstedt in Saxony-Anhalt; three people died. Complex and expensive security measures followed, in which twelve semi-detached houses and 48 outbuildings were demolished. During the renovation work, another landslide occurred on June 28, 2016. The situation is similar in Saxony, where 12,672 hectares of dump areas that had already been renovated were closed by 2014 due to the risk of landslides. Just one year later it was already 23,000 hectares. Most of them are uncertain when they can be considered safe again.

The return of the groundwater not only causes stability problems. If it rises - which is the rule - above the original level, the water has to be diverted into streams and rivers via channels. Such a pump system in Hoyerswerda alone costs around half a million euros a year to maintain. The situation in the Ruhr area is even more extreme , where the perpetual costs are around 220 million euros per year. Around 30 percent of this is accounted for by groundwater retention systems, since otherwise almost a fifth of the region would be under water if it were not pumped. The core area, where most of the people live, is particularly affected. Around 180 pumps have to move over a billion cubic meters of groundwater here every year so that the area can be artificially kept dry. These pumps have to run forever, otherwise the Ruhr area would be a lake district within a few years.

But that's not enough: the groundwater that is pumped into canals or rises in recultivated fields causes iron and sulphate concentrations to get into the rivers. Central Germany is particularly affected. In Lusatia , the ossification of the Spree not only poses a serious threat to the Spreewald tourist region , but now even to the drinking water supply of Berlin . In total, the opencast mines in Saxony, Brandenburg, Saxony-Anhalt and Thuringia damaged 41 groundwater bodies. Twelve of them have been so badly destroyed that they do not meet the EU requirements. Nothing about that will change in the foreseeable future. Between 1992 and 2016, the federal and state governments have already invested 10.2 billion euros in the rehabilitation of the post-mining landscape in the Lusatian and Central German lignite district . A further 1.2 billion euros are planned for the years 2018 to 2022.

forestry

Part of a renatured post-mining landscape of the former Inden opencast mine , 2010
Afforestation of the post-mining landscape at the Graureihersee , 2013

The reforestation of a post-mining landscape is one of the most expensive and longest renovations. In order to reforest a forest, machines have to cover the areas of the former open-cast mines with a clay-sand layer of at least two meters, level, lime and fertilize the areas, enrich the soil with nitrogen and humus over several years and then usually Plant saplings up to two years old. However, these are often the less demanding pines and birches - or even invasive species such as the fast-growing black locust . The high material and financial commitment leads in all cases to high economic losses, since the costs for the renovation neither flow back through the sale of the forestry recultivated areas after mining, nor through the proceeds from the sale of wood.

Forest soils require loose humus soil. However, the heap substrates are often spilled from conveyor belts from a great height, with the soil material being compacted upon impact. This can lead to a lack of water and waterlogging, which leads to a lack of oxygen in the root area. The increased surface runoff on the compacted soils causes water erosion and the formation of ditches. In addition, raw heap soil is usually free from mycorrhizal fungi , which only slowly migrate back in and decline again if host plants are missing for a long time. These fungi are among the most important factors in primary succession on mining heaps. Most of the woody species that rely on the symbiosis with fungi cannot colonize the Halde site without mycorrhiza. Even tree species that form a symbiosis with mycorrhizal fungi show higher failure rates if these are absent in the soil.

Also due to soil compaction, dump soils can often only store small amounts of water available to plants. In the warm season of the year, the exposed heap floors dry out considerably when the sun is shining, and cracks run through them. The evaporation is intensified by high wind speeds, since the surface roughness of the cleared post-mining landscape is only slight due to the lack of vegetation. The plants on these locations are therefore exposed to considerable drought stress. In addition, the plants can be mechanically destabilized by wind. The soils are at great risk from wind erosion. If the roots come into contact with tertiary substrates as they grow in the lower layers, the trees die suddenly even years later.

The afforestation of open-cast mining areas is associated with considerable difficulties due to the unfavorable site conditions described. In order to circumvent this, up to one meter of topsoil is often applied to the dump floors with great technical and financial effort over the more or less sterile overburden layers . At the same time, in addition to regular watering, lime and NPK fertilizer must be added. Continuous fertilization and re-liming is necessary for years to ensure the survival of the trees in the long term. Between the listed factors, which are problematic in themselves, there are additional interactions with negative effects on plant growth, which lead to high failure rates of young plants.

According to several environmental researchers, the loss of forest areas cannot be compensated. Even the minimum goal of establishing new forests of at least the same area has not yet been achieved in any federal state. Despite the undisputed further development of the recultivation technology, it had to be determined that the recolonization of the recultivated forest areas is not possible for all species. The question of the long-term success of the remediation methods used today, as well as the question of the stability of the resulting dump forests and the question of the sustainability of the ecosystem development in the landscapes that have been greatly changed by opencast mining, is still unresolved. Ultimately, recultivation will not be able to replace the loss of old forest ecosystems in the foreseeable future.

Military training areas

In principle, post-mining landscapes are not suitable as military training areas according to the guidelines for the sustainable use of exercise sites in Germany by the Federal Ministry of Defense . For these purposes, the site must offer various types of use. Often 60 percent of the restricted areas are forest; the rest of the outdoor area, mostly dunes or heather. The forest places special and unique demands on operational and combat management. In the outdoor areas, diverse forms of design of the near-natural cultural landscape of the respective region should be concentrated.

The wooded areas are used for training in typical combat behavior such as camouflage, protection and cover. For this purpose, according to the specifications of the Federal Ministry of Defense, the forest should be both large-scale and small-scale parcels and developed in the form cultivated in Central Europe. The open area is of particular importance for the conduct of operations, but must also have cover. Post-mining landscapes do not meet any of these properties. The unstable open-pit lunar landscapes are even unsuitable as shooting or target bombing test sites, since the impact of the impacts does not allow any comparison to natural terrain in crisis regions.

Nature reserves

In Germany, recultivation has been in the foreground in the rehabilitation of post-mining landscapes since the late 1980s. The demands on the areas of the newly created landscapes are "usage demands". Since the beginning of the 21st century, ecologists and planners have developed a large number of concepts that are characterized by different objectives and measures. Thereby, proponents of classic subsequent uses (bathing lake, agriculture and forestry) and proponents of spontaneously settling flora and fauna on former mining areas face each other. The latter call for a promotion of renaturation instead of general recultivation (“forest instead of forest”) as compensation and replacement for the destruction of pre-mining landscapes .

Although renaturation ecology is a young scientific discipline, there is increasing recognition that recultivation will not be able to replace the loss of old forest ecosystems in the foreseeable future, and that new land seldom offers the agricultural and ecological potential of its predecessors. However, areas that have been destroyed by renaturation cannot be completely restored to the state before the damage. Among other things, the biodiversity on the renatured areas remains lower than before the disturbance, and the carbon cycle and nitrogen cycle also show lower values ​​after the renaturation than the original ecosystems . The restoration of areas that have been damaged by human use is therefore no substitute for preventive protection of ecosystems.

Stages of development

A technical distinction is made between mining landscapes and post-mining landscapes:

  • Mining landscape is the landscape during and after mining activity , but before release from mining supervision .
  • Post-mining landscape is the mining landscape released from mining supervision, regardless of whether and how many technical measures to restore near-natural habitats have taken place.

Mining landscapes, including the areas directly as well as indirectly influenced by mining activity, go through several phases from the point in time of the pre-mining landscape to a "stable final state":

Landscape
development stage		 Landscape
development phase		 Landscapes
(selection)
Pre-mining stage of
development		 Cultural landscape Forest
landscape meadow landscape
arable landscape
settlements
Mining stage of
development		 Exposure Lowering of the groundwater level.
Destruction of the vegetation cover.
Devastation.
Removal of spoil
Extraction and
operation phase		 Increase in devastation.
Development of spoil heaps.
Development of residual holes
Recultivation and
rehabilitation phase
(post-mining landscape)		 Slope
flattening Leveling
Melioration
Fertilization
Sowing
Afforestation
Flooding
Post-mining
development stage
( post-mining landscape)		 early succession
initial phase
(up to about 5 years)		 often strong morphodynamics
beginning soil development
unstable hydrological conditions
first pioneering plants
permanent succession
(about 50 to 100 years)		 declining geomorphological process dynamics
humus formation
development soil water balance
stabilization of water balance in lakes
formation of plant and animal communities
high biodiversity and settlement dynamics
advanced succession
(from 50, mostly 100 years)		 Stabilization and equilibrium
phase mostly low morphodynamics
Continuation of soil-forming processes
Setting of stable hydrological conditions
Establishing stable populations

Literature (selection)

Individual evidence

  1. ↑ Sustainable recreational use and tourism in post-mining landscapes - Definitions p. 19. Federal Agency for Nature Conservation, accessed on March 24, 2019
  2. ^ Mining post- mining landscape Spektrum.de , accessed on March 24, 2019
  3. ↑ Societal costs of lignite (p. 6 f.) Greenpeace , accessed on March 25, 2019
  4. ↑ Financial provisions in the lignite sector (p. 48 f.) Forum Ecological-Social Market Economy , accessed on March 25, 2019
  5. ↑ A question of coal Die Welt from September 30, 2016, accessed on March 25, 2019
  6. ↑ Wolfgang R. Roth roof: Handbook of engineering geology and geotechnical engineering. Springer-Verlag, 2002, pp. 625-640.
  7. ↑ [ https://www.umweltbundesamt.de/publikationen/poster-boden-des-jahres-2019-kippenboden ] Federal Environment Agency , accessed on April 26, 2019
  8. ↑ Baden in the brown coal mine Süddeutsche Zeitung of July 7, 2014, accessed on March 26, 2019
  9. ↑ Recultivation: The problems lie beneath the surface Heinrich Böll Foundation of July 7, 2017, accessed on March 26, 2019
  10. ↑ Wilderness potential in the Lusatian post-mining landscape Deutsche Umwelthilfe , accessed on March 26, 2019
  11. ↑ Thorough Destruction of the Climate Reporter from October 22, 2015, accessed on March 26, 2019
  12. ↑ Meike Kirscht: Recultivation of opencast mining areas with various soil additives and tree species. Dissertation, 2001, p. 1 f. Georg-August-Universität Göttingen, accessed on March 26, 2019
  13. ^ Lignite mining: groundwater in danger Frankfurter Rundschau of October 22, 2015, accessed on March 26, 2019
  14. ↑ Meike Kirscht: Recultivation of opencast mining areas with various soil additives and tree species. Dissertation, 2001, p. 1 f. Georg-August-Universität Göttingen, accessed on March 26, 2019
  15. ↑ Umweltforschungsplan FKZ 29822240 Umweltbundesamt, accessed on March 26, 2019
  16. ↑ Renaturation in the Handelsblatt opencast mine , accessed on March 26, 2019
  17. ↑ Life conquers acidic waters NTV Wissen dated July 10, 2017, accessed on March 27, 2019
  18. ↑ Umweltforschungsplan FKZ 29822240 Umweltbundesamt, accessed on March 26, 2019
  19. ↑ Life conquers acidic waters NTV Wissen dated July 10, 2017, accessed on March 27, 2019
  20. ↑ Umweltforschungsplan FKZ 29822240 Umweltbundesamt, accessed on March 26, 2019
  21. ^ "Klara" supplies the lake with lime Sächsische Zeitung from September 2, 2016, accessed on March 27, 2019
  22. ↑ Umweltforschungsplan FKZ 29822240 Umweltbundesamt, accessed on March 26, 2019
  23. ↑ The Miner's Enemy Returns Climate Reporter of November 27, 2017, accessed on March 25, 2019
  24. ↑ Sabine Tischew: Renaturation after brown coal mining. Springer-Verlag, 2013, p. 25 f.
  25. ↑ Renaturation in the Handelsblatt opencast mine , accessed on March 26, 2019
  26. ^ Art landscapes instead of nature BUND , accessed on March 27, 2019
  27. ↑ For an orderly exit from lignite (p. 12.) BUND, accessed on April 5, 2019
  28. ^ Art landscapes instead of nature BUND , accessed on March 27, 2019
  29. ↑ Recultivation: The problems lie beneath the surface Heinrich Böll Foundation of July 7, 2017, accessed on March 26, 2019
  30. ↑ Deep dump Schlaitz Landesverwaltungsamt Saxony-Anhalt, accessed on 29 March 2019
  31. ↑ Information on the dismantling of the houses in the Nachterstedter LMBV settlement , accessed on March 28, 2019
  32. ^ Nachterstedt: Another landslide on Lake Concordia Mitteldeutsche Zeitung of June 28, 2016, accessed on March 28, 2019
  33. ↑ Recultivation: The problems lie beneath the surface Heinrich Böll Foundation of July 7, 2017, accessed on March 26, 2019
  34. ↑ For an orderly exit from lignite (p. 12.) BUND, accessed on April 5, 2019
  35. ↑ Recultivation: The problems lie beneath the surface Heinrich Böll Foundation of July 7, 2017, accessed on March 26, 2019
  36. ↑ Why the Ruhr area would be a lake district without pumps DerWesten , accessed on March 26, 2019
  37. ^ Verockerung der Spree Der Tagesspiegel , accessed on March 26, 2019
  38. ↑ Fight against opencast mining consequences RBB24 of October 17, 2018, accessed on March 26, 2019
  39. ↑ Recultivation: the problems lie beneath the surface Heinrich Böll Foundation of July 7, 2014, accessed on March 26, 2019
  40. ↑ Sabine Tischew: Renaturation after brown coal mining. Springer-Verlag, 2013, p. 290.
  41. ↑ Thorough Destruction of the Climate Reporter from October 22, 2015, accessed on March 26, 2019
  42. ^ Art landscapes instead of nature BUND, accessed on March 27, 2019
  43. ↑ Meike Kirscht: Recultivation of opencast mining areas with various soil additives and tree species. Dissertation, 2001, p. 1 f. Georg-August-Universität Göttingen, accessed on March 26, 2019
  44. ↑ Federal Ministry of Defense: Guideline for the sustainable use of exercise areas in Germany by the Federal Minister of Defense. Bonn / Berlin, 2002, p. 8 f.
  45. ↑ Federal Ministry for Economic Affairs and Energy: Project report. Renewable energy. Projects in the opencast mining regions. Berlin, 2018, p. 96 f.
  46. ↑ Wolfram Pflug: Lignite mining and recultivation. Springer-Verlag, 2013, p. 177.
  47. ↑ Reinhard Barbl: Recultivation versus Renaturation. The spontaneous development of vegetation in the area of ​​tension between nature conservation and planned subsequent use. BHM - Berg- und Hüttenmännische monthly books (148/10), 2003, pp. 412–417.
  48. ↑ David Moreno-Mateos et al .: Anthropogenic ecosystem disturbance and the recovery debt . In: Nature Communications . tape 8 , 2017, doi : 10.1038 / ncomms14163 .
  49. ^ Art landscapes instead of nature BUND, accessed on March 27, 2019
  50. ↑ Meike Kirscht: Recultivation of opencast mining areas with various soil additives and tree species. Dissertation, 2001, p. 1 f. Georg-August-Universität Göttingen, accessed on March 26, 2019
  51. ↑ Sustainable recreational use and tourism in post-mining landscapes - Definitions p. 19. Federal Agency for Nature Conservation, accessed on March 27, 2019
  52. ↑ Sabine Tischew: Renaturation after brown coal mining. Springer-Verlag, 2013, pp. 25–26.