Spatial variability of potential water repellency in a lignitic mine soil afforested with Pinus nigra

Reclaimed mine soils in Lusatia/Germany are heterogeneous sandy sediment mi xtures, which often contain significant portions of lignite (brown coal). W ater-repellent aliphatic organic compounds may cause preferential finger-ty pe flow in mine soils. The objective of this study was to analyse the signi ficance, spatial scales, and spatial variability of potential water repelle ncy in a lignitic mine soil. The mine site was located northeast of the cit y of Cottbus, Germany. A soil block of 2.5-m length, 1.25-m width, and 1.5- m depth was divided into squares of 0.25-m edge length from where 25 soil c ores of 636 cm(3) were sampled at each 0.1-m depth increment. After drying the samples at 60 degreesC for 4 days, the Water Drop Penetration Time (WDP T) test was carried out using 30 water drops per sample. The frequency dist ributions of the classified potential water repellency were analyzed (i) lo cally, within a sample, (ii) horizontally, within a layer, and (iii) vertic ally, within the soil block: The WDPT values of most samples were either sm aller than 5-10 s or larger than 10 min. Such 'bipolar' distribution occurr ed for the whole block, as well as locally, i.e., the WDPT varied between r epellent and not repellent from drop to drop at distances of about 1 cm. Th e persistence of potential water repellency seems somewhat larger in the su bsoil (0.5-1.5-m depth) than in the ameliorated topsoil (0-40-m depth). How ever, hardly any spatial structures are obvious since severely repellent, a s well as not repellent, soil material occurs throughout the soil profile a nd intra- was as large as inter-sample variability. To a large degree, the spatial variability of water repellency seems to reflect a situation that r esulted from partially mixing of different overburden sediments. The small- scale variability of the potential water repellency may probably be correla ted with the spatial distribution of lignite, minerals, and more-or-less li gnite-coated sand particles. These spatial patterns of repellency may, in p articular, affect water and solute movement in mine soils. (C) 2001 Elsevie r Science B.V. All rights reserved.