CESIUM-137 SOIL SAMPLING AND INVENTORY VARIABILITY IN REFERENCE LOCATIONS - A LITERATURE SURVEY

Soil sampling design, the number of samples collected and the lateral variation of caesium-137 (Cs-137) in uneroded reference locations were extracted from previously published work. The focus was on published work which used Cs-137 reference inventory (Bq m(-2)) for qualitative or quantitative estimation of sediment redistribution (SRD) within the landscape. The objective of this study was to address one of the meth odological concerns facing the Cs-137 technique - that is, the lack of a rigorous statistical treatment of reference locations. The limited attention paid to the reference location is not justified as 'true' es timates of SRD are based on the assumption of an unbiased, independent , random probability sample estimate, commonly the arithmetic mean. Re sults from the literature survey indicated that only 11% of the refere nce locations sampled for Cs-137 expressly stated that a probability s ampling design was used (transect or systematic-aligned grid). The rem aining locations were generally sampled using a non-probability based design, more commonly known as haphazard sampling. Of the 75 reference study areas identified only 40 provided enough information to determi ne the dispersion around the mean, and from this the coefficient of va riation (CV) was calculated for all available data. The median CV was 19.3%, with 95% confidence limits of 13.0-23.4%, indicating that appro ximately 11 random, independent samples would generally be necessary t o adequately quantify the reference Cs-137 area activity with an allow able error of 10% at 90% confidence. Further analysis indicated that o nly one-third of the studies sampled a sufficient number of Cs-137 ref erence locations. This value would actually be lower as sampling frame works were based on non-probability sampling procedures. For Cs-137 re ference locations it is recommended that a probability sampling design be utilized, preferably the systematic-aligned grid method, and as a minimum first-order estimate about 11 samples should be collected for inventory estimates.