Water security in the UK : a pilot model-based study of current and future water security in the UK

Hydrology;Meteorology and Climatology

Centre for Ecology & Hydrology

来源: NERC Open Research Archive

【 摘 要 】

Both the NSI (XRFS) and G-BASE data sets are derived from a soil sample that has been aggregated (composited) from a number of subsamples collected over the area of a site, rather than a single point sample. In the case of NSI this is 25 cores (subsamples) from a 20-m square (McGrath and Loveland 1992) whereas G-BASE is 5 cores, also from a 20-m square (Johnson et al. 2005; Fordyce et al. 2005). If a sample is collected as a single core, and the result is compared to the NBC, it is important to be aware that short-range variation (which can be substantial) for the single core sample will be potentially much greater than for the samples from which the NBC values are derived (Lark, 2012). Soil samples used to calculate the Ni NBCs have been collected from the top 15 cm of the mineral soil profile (hence they are referred to as topsoils). When the sample is collected from a site covered with vegetation the surface organic layers does not form part of the sample collected. This is important for two reasons. Firstly, any recently deposited airborne particulates that have not yet migrated into the soil profile will not be sampled and secondly, surface organic material (litter), which has the capacity to fix some contaminants from atmospheric deposition, is not included as part of the sample. In urban areas the top 15 cm will reflect historical urban land uses and in rural agricultural areas, where relevant, will be within the ploughed horizon. Surveys targeting recent airborne pollution added to the soil will generally only collect from the top 2 cm of the profile in order to bias the soil results toward the airborne pollutant inputs. Such data has not been used in the NBC calculations.