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Pebesma EJ

71 p in Dutch   1992

Toon Nederlands

English Abstract
Chloride and nitrate concentrations in groundwater are mapped on a national scale using classification, point kriging, stratified point kriging and stratified block kriging. A soil map aggregated to six main soil types (peat, sand, marine clay, fluvial clay, old clay and loam) is used as classification criterion. Zinc and cadmium concentrations in groundwater are mapped on a national scale using stratified block kriging. The results are presented as 95% confidence intervals of the predictions. When spatial dependence between measurements is observed, kriging interpolation results in more spatially differentiated maps than those obtained by classification. For mapping on a national scale block kriging seems more appropriate than point kriging because of the large uncertainties that result from the latter. Stratification preceding kriging is needed because of important differences between the strata. High concentrations along the coast characterise the chloride concentration maps. Block averages indicate a difference between high sand areas with chloride concentrations below 50 mg/l and areas near the coast with chloride concentrations above 50 mg/l. All methods used for mapping nitrate produce overlapping confidence intervals. The upper side of the confidence intervals show high tendencies on areas with high sand soils. In the provinces Noord-Brabant and Limburg (South East Holland) some areas have block averaged zinc and cadmium concentrations higher than the background value (a-level). The confidence intervals do not exclude b- or c-levels (signal and danger levels, respectively).


RIVM - Bilthoven - the Netherlands - www.rivm.nl

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RIVM - Bilthoven - Nederland - www.rivm.nl

( 1992-11-30 )