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Berlin Environmental Atlas

01.12 Soil Functions (Edition 2013)

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01.12.3 Buffering and Filtration Function

Description

The buffering and filtration function describes the ability of the different soils to slow substances down in their ecosystemic material flow (buffering function), or to withdraw them permanently from this cycle (filtration function). It is based on the ability of the soils to capture or neutralize substances by physico-chemical adsorption and reaction, and by metabolism in the soil.

An essential aspect of this is the ability to capture immitted pollutants on their way through the soil into the groundwater. The basis for the evaluation is the respective water permeability of the soil, its binding power for heavy metals, its binding capacity for nutrients and pollutants, and its filtering distance to the adjoining groundwater. Buffering counteracts the acidification of the soil by means of the reaction of alkaline cations. Filtration mechanically filters solid substances out of the percolation water, and binds dissolved substances, primarily by means of the binding powers of organic matter and clay. This ability is determined by various physical, chemical and biological soil qualities. The soil has different filtration and buffering capacities for different substances and substance groups, such as plant nutrients, organic compounds, acidifiers or heavy metals.

Soils with a high filtration and buffering capacities can accumulate pollutants to a high degree. The pollutants taken up are generally not broken down, but remain in the soil up to the point of exhaustion of its buffering and filtration capacity, when they are passed through to the groundwater. With continual immission, the danger therefore exists that these soils will function as pollutant sinks, and that soil burdens will appear which can, for example, make agricultural or horticultural uses impossible in these sections.

An additional aspect is the capacity of the soil to store carbon in the form of organic matter or peat. Disturbances and destruction of the soil lead to organic matter loss and hence to a release of carbon dioxide (CO2) from the soil into the atmosphere. Bog and mire soils are particularly carbon-rich, and hence fulfill the buffering and filtration function in the carbon cycle with great efficacy.

Methodology

For the evaluation of the filtration and buffering functions, the evaluations are taken from the results of the data ascertained for each section on organic matter content (cf. Map 01.06.5), nutrient-storage capacity/ pollutant-binding capacity(cf. Map 01.11.6), binding power for heavy metals (cf. Map 01.11.10) and filtration capacity (cf. Map 01.11.9); furthermore the depth to groundwater (cf. Map 02.07) is used.

Fig. 1: Diagram for the evaluation of the buffering and filtration functions
Fig. 1: Diagram for the evaluation of the buffering and filtration functions

The buffering and filtration function of the soils is evaluated according to Table 1. This involves adding up the evaluations for nutrient storage capacity/ pollutant binding capacity, binding power for heavy metals and filtration capacity, with 1 (= low) to 3 (= high) points each, and correcting by a factor for the evaluation of the depth to groundwater. In this way, the filtration distance, too, is taken into account, along with the abilities of the soil to bind substances, since pollutants are carried into the groundwater more quickly at groundwater-proximate sites than at groundwater-remote sites.

Regardless of nutrient-storage/ pollutant-binding capacity, binding power for heavy metals or depth to groundwater, the soil associations with the highest buffering capacity for the carbon balance (3) are weighted as high. The small stages do not affect the evaluation. The overall evaluation of the buffering and filtration function of the soils is accomplished according to the three levels low, medium and high (1 - 3).

Tab. 1: Evaluation of the buffering and filtration functions
Sum of the evaluations of the criteria
filtration capacity
+
Nutrient-storage/ pollutant-binding capacity
+
Binding power for heavy metals
Depth to groundwater Buffering capacity for the carbon balance Evaluation of the buffering and filtration functions
      Evaluation Designation
3-5 < 2 m   1 low
  2-5 m   1 low
  > 5 m   2 medium
6-7 < 2 m   1 low
  2-5 m   2 medium
  > 5 m   3 high
8-9 < 2 m   2 medium
  2-5 m   3 high
  > 5 m   3 high
    high 3 high
Tab. 1: Evaluation of the buffering and filtration functions (Gerstenberg 2013)

Map Description

Loamy soils have a high buffering and filtration function with low water permeability, a neutral-to-basic pH value which reduces the mobility of heavy metals, and a high cation exchange capacity, due to their high clay and organic matter contents and great depths to groundwater. These requirements are met primarily by the soils on the Teltow and Barnim boulder-marl plateaus. As a rule, these are luvisol - arenic cambisol - podzoluvisol soil associations, with near-natural uses, undisturbed by anthropogenic aggradation, and frequently used for agricultural or small gardening (cf. Fig. 2).

The sandy soils of the end and push moraines and dune sands consisting of cambisol - dystric cambisol - spodo-dystric cambisol associations with near-natural use, or with sandy-soil aggradations caused by residential construction, receive an evaluation of medium. While the sands have of relatively high water permeability, their greater distance to groundwater enhances their filtration distance.

The sandy soils of the glacial spillway and of the glacial streams and depressions with only a short filtration distance of the pollutants to the groundwater table have only a slight ability to filter pollutants and to buffer substances. These are soils whose development is determined by the groundwater, such as gleyic and bog-mire associations with near-natural use, or with sandy aggradations in the inner-city section with loose lithosols, regosols, and calcaric regosol soil associations.

Soil associations with boggy soils under woods, or grasslands, have a high buffering and filtration capacity with respect to carbon; they are primarily found in the glacial spillway and in the glacial-stream channels.

Area share of the buffering and filtration functions per use class (incl. impervious sections without streets and waters, not all uses, are shown)
Fig. 2: Area share of the buffering and filtration functions per use class
(incl. impervious sections without streets and waters, not all uses, are shown)

Excel
[Statistical base of Figure 2 is also available as Excel-File (MS-Excel is required).]

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