Tuesday’s Soil Ecosystem Service – Water storage
Definition: The soil water storage is acquired through interception, absorption and storage of precipitation and flooding waters. The amount of water that soaks into the soil, is retained and later slowly released is largely determined by physical soil properties such as soil depth, soil texture, structure, porosity, organic matter content and other parameters.
Processes and controlling soil properties: Soil acts as a sponge to take up and retain water. Soil water storage is the amount of water that a given soil can hold in the rooting zone and is not precipitated to the groundwater. The capacity of a soil to store water depends on many processes and properties in the soil. Organic matter, especially crop residue and decaying roots, as well as soil biota, promotes aggregation so that larger soil pores develop, allowing water to infiltrate more readily. Pore space in soil and their distribution is the conduit that allows water to infiltrate and serves as the storage compartment for water. Water holding capacity varies by soil texture (the relative proportions of sand, silt, and clay) and infiltration rates can be near zero for very clayey and/or compacted soils, or more than 250 mm per hour for sandy or very well aggregated soils. Low water storage capacity can lead to ponding on nearly level ground and runoff that leads to erosion on sloping ground.
Relations to the entire ecosystem: Water storage capacity is defined as the total amount of water that is stored in the soil within the plant’s root zone. Available water is held in soil pores by forces that depend on the size of the pore and the surface tension of water. The water in large pores is held with little force, it drains most readily, what is described with capillary action and can move water in any direction. The water in medium pores is retained after precipitations and can be absorbed by plants. The water in tiny pores between clay particles is held with strong forces and, thus, practically unavailable to plants. The plant available water (the portion of the available water in the soil that can be absorbed by a plant) refers to the amount of water held between field capacity and wilting point.
Relations to other services: Water storage ecosystem service is crucial for biomass production no matter what, food or timber, soil water retention and to local climate regulation due to transpiration and evaporation.
Land use impacts: The capacity of soils to deliver this ecosystem service is controlled by land use and soil management. In agriculture, soil cultivation strongly influences soil water storage potential. It can decrease it (e.g. soil compaction by heavy machinery) or enlarge it (e.g. by humus/soil organic matter enrichment): Regarding forest management, tree species composition dictates water storage potential due to soil biological activity, tree root systems and soil depths.
Climate change impacts: In the context of climate change, droughts are likely to occur more often and longer and thus, soil water storage ecosystem service will turn out to be crucial for both, selection of crop in agriculture as well as tree species selection in forestry. In view of floods, natural disasters, soil water holding capacity can mitigate them only to a certain extent.
Demand aspects: Due population growth, the societal demand for this service will increase as water storage is crucial for agricultural, forest and natural biomass production.
- Output: Drought control
- Provision: Soils can capture water against gravity and store it. Thus the water is available for plants as well as soil organisms at this site. The water storage capacity of soils is mainly controlled by their grain size distribution, density and humus content.
- Demand: As water storage is essential for agriculture and forestry, the demand will grow with the population. Dry periods are likely to become more frequent and severe.
- Threat: Unsustainable forestry or agricultural management practices lead to erosion, compaction, or humus loss, and thus diminish the water storage.