Prediction of soilpHpatterns in nature areas on a national scale

Abstract

AbstractQuestionTo assess the acidification process, nationwide information about soilpHon a site level is called for. Measurements of soilpHmay be used, however there are not sufficient measurements available to map soilpHnationwide on site level. Instead we developed a soilpHmap based on vegetation data.LocationNatural terrestrial areas in The Netherlands.Methods271,693 vegetation plots were used to estimate average soilpHper plot with indicator values, based on field measurements, of plant species. By spatial interpolation averagepHvalues between the plots, with the soil type, groundwater table and vegetation management type as ancillary explanatory variables we created a soilpHmap. The map covers all terrestrial nature areas (all areas that are not built up areas, agricultural areas and infrastructural areas) in the Netherlands with a map resolution of 25 × 25 m2raster cells.ResultsThe predictedpHof the map varied between 3.0 and 8.6 with standard errors between 0.13 and 0.93. Most of the standard errors range from 0.4 to 0.55, with an average just below 0.5pHunit. Cross‐validation shows that for 33% the difference between observed and predicted is between −0.1 and 0.1pH‐unit and for 83% the difference is between −0.5 and 0.5pH‐unit. Validation shows that thepHmap is unbiased (mean error is almost zero), accurate (root mean squared error is 0.64) and nicely captures spatial patterns (r = 0.77). We applied thepHmap to assess the impact of acidification on the abiotic quality of nature areas in the Netherlands.ConclusionsThe model fit in the predicted soilpHis in good resulting in a low standard error and a high correlation. The measures taken to prevent acidic deposition causing further acidifying of nature areas can be considered as successful.