01.12.6 Efficiency of Soils in the Fulfillment of the Natural Soil Functions and the Archival Function
Maps 01.12.1 to 01.12.5 constitute an initial evaluation of the efficiency of the soils with regard to the individual natural soil functions and the archival function. For the consideration of soil protection aspects in primary land-use planning, it is useful, however, to bring these evaluations together for an overall evaluation. The goal of the present map is therefore not only to evaluate the efficiency of the soils with regard to these individual functions, but also as a whole. Sections which have a high overall importance with regard to their performance and functionality and hence for soil protection are thus to be particularly emphasized.
A general problem for the combination of all five soil functions is the fact that within each of the individual soil functions, the same soil qualities are judged differently, and to some extent even oppositely. Thus for example, the habitat function for the natural vegetation evaluates damp/wet, near-natural and rare sites as high, i.e. it favors extreme sites, the yield function of which for cultivated plants is, however, evaluated as the lowest. Among the sites evaluated as high for the archival function for natural history are very dry dune sites, while the filtration and buffering function, the regulatory function for the water balance, and the yield function class the same sites as very low.
Another problem is that due to the evaluation methodology chosen for the individual functions, sections of very different sizes have been evaluated as medium or high for the particular functions. Thus, large parts of the city area have been evaluated “high” with regard to the buffering and filtration function, for example, while with regard to the archival function, only very few sections show a high efficiency. The result is that while in principle the five soil functions each carry equal weight in the final evaluation, some soil functions, primarily the buffering and filtration function as and the regulatory function for the water balance, affect the final result more strongly than others.
The three-level evaluations of the individual functions constitute the basis for the final evaluation. An evaluation of low (1), medium (2), or high (3) for each soil function thus exists for every section in the city. As possible criteria for the combined evaluation, the individual evaluations were both added up, and also the number of times that each section was evaluated as high for a soil function was counted.
Several possible methods were tested alternatively for the evaluation of the efficiency of the soils in the fulfillment of the natural soil functions.
In the procedure that was ultimately used, both the frequency of the highest evaluation level (3) and the sum of the evaluations were taken into account for the overall evaluation (cf. Table 1). All soil functions have an equal influence on the overall evaluation; no weighting was carried out.