The British Geological Survey's Geochemical Baseline Survey of the Environment (G-BASE) project (Johnson et al., 2005) started to systematically collect stream sediments as part of its UK regional geochemical mapping programme in the late 1960s (see History of G-BASE).
Fine stream sediments from small streams are used to define the regional geochemical baseline as sediments derived from the drainage catchment above the sampling site generally give an excellent approximation of the concentrations of the chemical elements in the surface environment.
In excess of 105 000 stream sediments have been collected from Great Britain and Northern Ireland with some 85% of the area being sampled — only southern England remains unsampled — Distribution of G-BASE stream sediments map.
The western part of Northern Ireland was systematically sampled using G-BASE methodology in the mid 1990s (Flight et al., 1995) and the whole country completed as part of the Tellus Project 2004–2007 (Smyth, 2007).
Systematic sampling southwards across England ceased in 2007. On-going rural stream sediment sampling continues in England around the perimeter of Greater London as part of the London Earth Project and in Scotland as part of the Clyde Basin Urban Super Project (CUSP).
Stream sediment is sieved at site through a nylon sieve to <150 µm and collected from small (low order) streams at a high average sampling density of 1 site every 1–2 km2 (see Johnson, 2005; Johnson et al., 2008).
This high density of sampling enables the regional geochemical baseline to be interpreted at a local scale. Stream water samples and heavy mineral panned concentrates are also collected from each site.
Since the project commenced 'total' element concentrations have been determined, firstly by direct current optical emission spectroscopy (DCOES) and more recently X-ray fluorescence spectrometry (XRFS). The current methodology, a combination of wavelength-dispersive (WD) and energy-dispersive (ED) XRFS delivers results for some 50 chemical elements.
The stream sediment results have been published in a series of geochemical atlases (see Geochemical maps and atlases) in which the results for the most recent atlases are presented as interpolated geochemical images. Central and eastern England stream sediment data for a selected number of elements is presented as an pdf geochemical atlas.
A geochemical atlas of the Tellus stream sediment data (Northern Ireland) is in preparation.
Sediment is collected from the active drainage channel of 1st or 2nd order streams. The sediment is wet sieved firstly through a 2 mm nylon screen then a 150 µm nylon sieve. The fine stream sediment is collected in a KraftTM paper bag. Sampling density varies according to land use and drainage pattern but averages at one sample every one to two square kilometre.
Sediments are dried initially by air drying then freeze drying before being pulverised in agate ball mills. Samples are pelletised ready for XRFS analyses at the BGS laboratories in Keyworth, UK. A combination of emission and dispersive techniques gives a wide range of elements (Ag, Al, As, Ba, Bi, Br, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Ge, Hf, I, K, La, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Rb, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Te, Th, Ti, Tl, U, V, W, Y, Zn and Zr)
Geochemical data, including the G-BASE stream sediment results are available under licence from the British Geological Survey. There is a data licencing and handling charge plus a charge of £0.50 per data record (with discount for large numbers). Some or all of these charges can be waivered for academic use of the data. Contact BGS Enquiries.
Excess sample powders have already found use in many research projects. These are archived at the National Geoscience Data Centre (NGDC), British Geological Survey, Keyworth, Nottingham, UK. Information concerning the availability of the Tellus Northern Ireland geochemical data can be found at Tellus data licensing.
BGS data are protected by NERC copyright, Tellus data are protected by Crown Copyright.
Flight, D M A , Christie, J L , Lister, T R, Simpson, P L, and Smith, B. 1995. Results of a pilot geochemical survey, Northern Ireland. Geological Survey of Northern Ireland Technical report, No. GSNI/95/6, Geological Survey of Northern Ireland, Belfast. March 1995.
Johnson, C C. 2005. 2005 G-BASE field procedures manual. British Geological Survey, 65pp. (IR/05/097) (Unpublished).
Johnson, C C, Breward, N, Ander, E L, and Ault, L. 2005. G-BASE: Baseline geochemical mapping of Great Britain and Northern Ireland. Geochemistry: Exploration, Environment, Analysis, 5 (4), 347–357.
Johnson, C C, Flight, D M A, Ander, E L, Lister, T R, Breward, N, Fordyce, F M, and Nice, S E. 2008. The collection of drainage samples for environmental analyses from active stream channels. In: B. de Vivo, H.E. Belkin and A. Lima (Editors), Environmental Geochemistry: Site characterisation, data analysis and case histories. Elsevier, Oxford, pp. 59–92.
Smyth, D. 2007. Methods used in the Tellus Geochemical Mapping of Northern Ireland. British Geological Survey Open Report, OR/07/022.