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Berlin Environmental Atlas

01.12 Soil Functions (Edition 2002)

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01.12.3 Buffering and Filtration Function

Description

The Buffering and Filtration Function describes the ability of the different soil associations to bind immitted pollutants moving through the soil toward the groundwater table. The basis for the evaluation of the single soil associations is their respective water permeability, their binding capacity for heavy metals, their binding capacity for nutrients and pollutants, and their filtration distance toward the adjoining groundwater.
The buffering and filtration quality of a soil represents its ability to bind substances by physical-chemical adsorption, reaction and/or biological substance restructuring in the soil, or to neutralize them. Buffering counteracts the acidification of the soil by means of the reaction of alkaline cations. Filtration mechanically filters solid substances out of the percolating water, and binds dissolved substances, primarily by means of the binding powers of humus 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 as a rule are 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.

Methodology

For the evaluation of the filtration and buffering function, the evaluations arrived at from the data ascertained for nutrient storage capacity/ pollutant binding capacity (cf. 01.11.6), binding capacity for heavy metals (cf. 01.11.10), filtration capacity (cf. 01.11.9), and also the depth to groundwater (cf. 02.07), have been used for every section.

Figure 1 - Thumbnail
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Figure 1: Scheme for the evaluation of the buffering and filtration function

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. 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).

Table 1: Evaluation of the filtration and buffering function of the soils on the basis of evaluations of Nutrient Storage Capacity / Pollutant Binding Capacity, Binding Power for Heavy Metals, Filtration Capacity, and Depth to Groundwater
Sum of the evaluations of the criteria filtration capacity
+
nutrient storage / pollutant binding capacity
+
binding capacity for heavy metals
Depth to groundwater Filtration and buffering function
    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
Tab. 1: Evaluation of the filtration and buffering function of the soils on the basis of evaluations of Nutrient Storage Capacity / Pollutant Binding Capacity, Binding Power for Heavy Metals, Filtration Capacity, and Depth to Groundwater (Lahmeyer 2000)

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 humus contents and great depths to groundwater. These requirements are met primarily by the soils on the Teltow and Barnim glacial-till plateaus. As a rule, these are soil associations with para-braunerde, sandy-wedge braunerde and pale leached soils with near-natural uses, without disturbances due to anthropogenic dumping.
The sandy soils of the end and push-moraines and dune-sands consisting of braunerde, rusty soil and podzol-braunerde associations with near-natural use or sandy-soil dumping 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 gley and mire associations with near-natural use, or the sandy dumped soils in the inner-city area with loose syrosem, regosol, and para-rendzina soil associations.

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