Field of Action Soils

freshly ploughed fieldClick to enlarge
The different impacts of climate change affect soil characteristics and functions.
Source: joeEsco/photocase.com

Impacts of Climate Change

Table of Contents

Soils are the world's largest terrestrial reservoir of organic carbon. They store around four times as much carbon as the above-ground vegetation and more than twice as much as the atmosphere. At the same time, many of the processes that take place in the soil are dependent on temperature and moisture. If climate conditions change, it has a direct impact on the ability of soils to perform their important functions.

 

Temperature

Climate change is already affecting the soil. As temperatures in the atmosphere rise, so does the soil temperature. This has consequences for the soil, regardless of whether it is used for agriculture or forestry, in urban areas or with near-natural vegetation.

Elevated temperatures accelerate the chemical and biological processes in the soil and influence the growth processes of vegetation. With sufficient moisture and heat, the biological activity in the soil is high. If organic soil matter is converted more rapidly, more nutrients are available to stimulate plant growth. This increases the water requirements of the plants, which are also increased by the prolongation of vegetation periods. If the soil has a sufficient water content, this process leads to higher crop yields. However, if there is not enough water available, drought damage to the plants occurs and crop yields fall.

Increased biological activity changes the balance of humus decomposition and build-up. The humus content of the soil can decrease in the long term. Humus is the totality of organic matter in the soil, which is composed of all dead plant and animal matter in and on the soil and its organic transformation products. Humus is an important storage medium for nutrients and water. When humus is decomposed, the proportion of organically bound carbon in the soil decreases and the greenhouse gas CO2 is released. Soils are thus becoming increasingly important as a source of carbon dioxide.

If climate change leads to the degradation of organic substances, the pollutants stored in the soil are mobilised. The previously bound substances can be removed with the seepage water through increased precipitation and/or fumigated at the surface by higher temperatures.
If summers become warmer and drier and winters milder, the evaporation rate increases. This can lead to less rainwater seeping into the soil and the groundwater recharge decreasing. A particularly large amount of harmful greenhouse gases can be released if organic substances are decomposed in peatlands due to the falling groundwater level.

 

Precipitation

Due to climate change, precipitation patterns are changing. In the spring and summer months there are now more frequent periods of high temperatures and low precipitation, while in the winter months precipitation increases.

More frequent and longer dry periods in the summer half of the year lead to increased drying of the soil and encrustation of the topsoil. This weakens the important filtering function of the soil. The trend towards lower soil water supplies puts plants under drought stress. The soil water contents modeled by the DWD show a declining trend over the last 40 years on average in Germany in May and July.

The continued decline in soil moisture may increase the need for irrigation in agriculture, require the cultivation of other varieties and species, or lead to lower yields and - in extreme situations - even desertification, which has a global impact on food production.

Reduced soil water content is also a problem in urban areas. As the number of hot days increases due to climate change, the cooling effect of the evaporation capacity of trees and other vegetation is of growing importance. However, this cooling capacity can only be achieved if there is sufficient water supply to the floor.

However, in the winter months there is an increase in precipitation. This increases the risk of soil irrigation in the future. This can reduce the stability of the soil structure and increase the risk of compaction, which is especially true for arable soils when driving and working. If the number of frost days decreases at the same time, an increase in precipitation during the winter leads to a change in soil structure and silting up of soil surfaces. This results in stagnant moisture and increased surface runoff, since the water cannot seep away in sufficient quantities, which, in turn, can promote flooding.

With the changed framework conditions, the nature of the soil changes and thus its properties as a filter, habitat and location for food production. Negative developments that can result are a reduced storage capacity of the soil for nutrients and therefore less fertility or poorer filtering of pollutants (e.g. from rainwater). In addition, soil biodiversity can be reduced and the nutrient balance can shift.

 

Biodiversity in soil

The services of the soil and its organisms are vital for agriculture and forestry and thus for our nutrition, our well-being and for economic reasons. Studies by the Helmholtz Centre for Environmental Research and the German Centre for Integrative Biodiversity Research indicate that the increasing drought in summer also has negative effects on the biomass of small soil animals, which decompose organic matter in the soil and maintain soil fertility. Increased temperatures and reduced precipitation can therefore reduce the biomass and impair the nutrient cycle in the soil. This effect increases with intensive land use.

 

Soil Erosion

In addition, changes in precipitation patterns may increase the two types of soil erosion: Deflation (wind erosion) is often observed on dried-out topsoil when strong winds remove sand and dry soil. Particularly in the northern coastal states, wind plays a role as a cause of erosion on the rather sandy soils. Water erosion, on the other hand, occurs when rainwater does not seep away quickly enough, but instead runs off at the surface and carries soil material away with it. This is a problem especially on terrain with relief and a light soil. Soil erosion primarily means a reduction in soil thickness and a loss of the topsoil, which is particularly rich in nutrients and humus. Removed soil material is relocated in the area and can be discharged into neighboring waters. There, diffuse inputs of substances, especially phosphorus, lead to undesired water eutrophication, i.e. an increase in the concentration of plant nutrients that promote the growth of algae and cyanobacteria.

Climate change and its associated temperature increase will also shift the development phases of plants, including agricultural crops. The resulting changes in land cover are likely to increase the risk of erosion. Gaps in the vegetation caused by drought and dried-out soil surfaces have erosion-promoting effects.

 

Extreme Weather Events

Extreme weather events contribute to many of the climate impacts on soils already described. Wind, storms and heavy rainfall increase the risk of erosion; they influence soil structures and change soil functions.

Heavy precipitation, in combination with more frequent changes of frost and dew, can promote water erosion, especially in southern and southwestern Germany, and encourage debris flows, landslides and rock falls. However, in the north and northeast, increasing wind speeds and more frequent dry periods increase the risk of wind erosion.
Both variants can result in local and regional flood events, waterlogging or flooding.

The melting of large amounts of inland ice and the expansion of warming seawater are causing sea levels to rise, which increases the starting level for storm surges. Therefore, salt water can penetrate into the interior of the country and enter the fresh water of groundwater and surface waters. This changes the soils and thus the conditions for forestry and agriculture, as the salt water is absorbed and salinises the soil. This can also lead to the loss of tidal flats and salt marshes, possibly even beaches.

 

Adaptation to Climate Change

Ecosystem Measures

Measures of the ecosystem approach consist of protecting soils in a sustainable manner and preserving them in their natural state. Above all, sustainable and good agricultural practice is important in this context as agriculture represents the largest intervention in the balace of nature in terms of area. More than half of the area of Germany is used for agriculture.

Agriculture can contribute to soil protection through a climate-sensitive selection of varieties and species as well as adapted crop rotations, sowing dates, fertilisation, soil cultivation and tilling methods. For example, site-adapted crop rotation can ensure continuous soil cover throughout the year. Permanently ploughless conservation tillage preserves the natural soil structure and reduces the risk of erosion and compaction.

So far, there is no comprehensive erosion monitoring in Germany. Soil erosion monitoring, which is carried out on existing permanent observation plots (BDF) in individual federal states, is the only transnational measuring network for long-term recording of soil erosion in Germany. Its procedure and intensity are not uniform. Despite the lack of representative monitoring data, hazard potentials can be derived at the federal level by means of modelling. (Source: Monitoringbericht 2019)

The preservation of the humus content is particularly important. Humus is an important storage medium for nutrients and water and reduces the summer dryness of the soil. In addition, the soil stores carbon in humus, thereby reducing the amount of the climate-relevant greenhouse gas carbon dioxide in the atmosphere.

Land use changes and unsustainable use and management contribute to soils losing their carbon sink function and becoming a source of greenhouse gases. Moor soils are "hot spots", because the storage and release potential from organic soils is significantly higher and more persistent than from mineral soils. In addition, the hydromorphic mineral soils (soils characterised by groundwater: gleye, marshlands, alluvial soils) are also of particular relevance. A decisive contribution to both climate protection and soil conservation is to maintain, restore or sustainably improve the C sink function of soils as far as possible.

The preservation of moor soils and grassland is of great relevance for climate protection. Grassland uprooting releases a considerable amount of the carbon stored in the soil into the atmosphere in the form of greenhouse gases. In addition, for soils under grassland, both the risks of dehydration and of soil erosion by water and wind are significantly reduced. During heavy rainfall, rainwater can penetrate better into permanently overgrown grassland soils.

Grassland area in Germany decreased between 1991 and 2013 and has been increasing slightly since 2014. Since 2015, EU directives have made it mandatory to maintain permanent grassland, according to which the conversion of permanent grassland into arable land is generally only permitted after approval and in most cases only possible if new permanent grassland is established elsewhere. In areas designated under the Fauna-Flora-Habitat Directive (FFH areas), permanent grassland is even strictly prohibited from being converted or altered. However, newly created grassland does not have the same importance for climate protection or biodiversity, as it is usually species-poor.

Technical measures

Vehicles and machinery in agriculture, forestry and the construction industry have become increasingly powerful and, in most cases, heavier in recent decades. If vehicles or machines roll over floors, weight-dependent pressure is generated. If the pressure under the tires is greater than the stability of the soil, the soil particles are compressed more tightly. This compaction of the soil impacts the soil quality. On the one hand, agricultural yields are reduced however, on the other, the living conditions for soil organisms deteriorate, and the infiltration of rainwater into the soil can be restricted.

Vehicles and equipment that drive over open ground can be adapted in such a way that the total mass and the specific surface pressure are better distributed, and thus the load-bearing capacity of the ground is less strained. One possible measure is to use wide tires with low internal pressure and large contact area. In addition, the use of lighter machines with less payload mass is beneficial for soil protection.

The stability of the soil can also be improved by reducing the working depth and intensity. Therefore, ploughless loosening of the soil not only helps to maintain intact soil life, but also preserve a stable soil structure. In addition, ploughless tillage reduces fuel costs and helps prevent soil erosion as protective crop residues remain on the soil surface.

Appropriate adaptation measures must be taken at both regional and local levels.

Legal, political and management measures

In order to protect the soil, it is important to focus soil protection policy more strongly on soil-related climate protection and adaptation measures. This also includes taking greater account of the climate protection function of soils in legislation and in planning and approval procedures.

Numerous specific measures can strengthen soil protection. Here are some selected examples:

  • Protection of soils, in particular those with a very high C storage capacity or high C reserves from overbuilding within the framework of planning and approval procedures
  • Sustainable use of arable land, in particular through: ensuring a balanced humus balance; preventing the loss of organic matter due to water and wind erosion; preventing soil damage compaction.
  • Grassland areas can be permanently protected and preserved as CO2 reservoirs by including them in appropriate funding programs and legal regulations.
  • The reduction of land consumption in settlement and traffic development, as well as land unsealing contribute to keeping soils free for rainwater infiltration and reducing the risk of flooding.
  • The unsealing and recultivation contributes to an improved urban climate.
  • Land reserves in built-up areas can contribute to maintaining the biomass production potential and the CO2 storage function of soils.
  • Areas with little or no vegetation can be converted into compensation areas for construction projects or into urban green spaces.
  • Land use planning should secure peatlands and, if possible, regenerate drained peatlands.

Since adaptation strategies require a sound information base, further knowledge must be gained on the possibilities of climate adaptation in the soil sector. In order to be able to assess the consequences of climate change on soil functions, information on soil, land use and regional climate changes is also necessary. Climate change related soil monitoring could be an important source of information here. Against this background, the 2nd DAS Progress Report states that a climate impact soil monitoring network should be implemented and established in the long term. The aim of this instrument is the nationwide collection, monitoring and documentation of the actual state of soils in Germany, as well as the changes resulting from climate change. To this end, the network will provide easy access to soil-related measurement data for users in science and administration and will network and coordinate the activities of measuring point operators and users.

sources: