Ground map of Lower Saxony 1 : 50 000 - Local displacement potential - exchange frequency of soil water (1991-2020)

The map shows the average local displacement potential for non-sorbable substances (including exchange frequency of soil water per year) for the 30-year period 1991-2020. With the help of the exchange frequency (AH) of the soil water, the local displacement potential for non-absorbable or weakly absorbable substances can be described. This includes, among other things, nitrate. The AH describes how often the soil solution in the effective root zone is replaced in the course of leachate displacement. The lower the water storage and retention capacity of a soil, the greater its exchange frequency of the soil water. The variables of the soil water balance describing the exchange frequency, i.e. the ‘field capacity in the effective root space’ and the ‘leakage water rate’, form the characteristic values for the water storage capacity of a soil. Statements on the concentration and loads of non-sorbable substances cannot be mapped with the method. In the case of nitrate, deposition, denitrification and mineralisation are not taken into account. Depending on the location, they can have a significant influence on the nitrate availability and concentration in leachate. For example, in marshes, the denitrification performance is particularly high due to the high proportion of organic matter. Since the ranges of validity of the calculation formulas are limited by the slope slope, no results are provided for arable land > 3.5% slope slope and for grassland and forest > 18% slope slope. The exchange frequency per year is presented in a classified form. This parameter describes the local risk of relocation.本数据集配套的地图展示了1991-2020年这30年间，非吸附性物质（含年土壤水交换频次）的局地运移潜力平均值。 借助土壤水交换频次（AH），可表征不可吸附或弱吸附性物质的局地运移潜力，其中涵盖硝酸盐等物质。AH表征了渗流运移过程中，有效根区内土壤溶液的更换频次。土壤的蓄水持水能力越低，其土壤水交换频次越高。 用于表征交换频次的土壤水量平衡变量——即“有效根域田间持水量”与“渗漏率”——构成了土壤蓄水能力的特征参数。该方法无法表征非吸附性物质的浓度与负荷情况。以硝酸盐为例，其沉降、反硝化与矿化过程均未被纳入考量。 不同区位下，上述过程会显著影响渗滤液中硝酸盐的有效性与浓度。例如，沼泽地因有机质占比高，其反硝化能力尤为突出。 由于计算公式的有效范围受坡度限制，本数据集未提供坡度大于3.5%的耕地，以及坡度大于18%的草地与林地的相关结果。 年土壤水交换频次以分级形式呈现，该参数可表征局地物质运移风险。