BORON IN THE MAJOR UK RIVERS ENTERING THE NORTH-SEA

Boron in the major UK rivers entering the North Sea is predominantly i n dissolved form and concentrations show large variations in time and space. The time-dependent feature relates to seasonal patterns linked to flow. Boron concentrations are well described by a power relationsh ip of the type [B] = aflow(b), where a and b are constants. In this e quation, the a term varies from river to river in relation to the boro n concentration at baseflow while the b term is of similar value for a ll the rivers (around -0.5 to -0.6). The spatial variations are direct ly linked to the degree of sewage discharge and the dilution associate d with (i) rainfall events and (ii) the length of river reach from the pollutant source. Boron concentrations exhibit simple chemically cons erved water mixing behaviour. However, deviations between chloride and boron indicate secondary chloride supplies from storm runoff, increas ed boron contamination for part of the sampling period on one river (t he Nidd) and possibly significant atmospheric inputs far the less poll uted rivers. Preliminary estimates of riverine fluxes to the North Sea are of the order of 1.6 Gg-B/year and the calculations indicate a rel atively low rainfall component (about 25% for the cleaner rivers and m uch lower values for the more polluted rivers). These preliminary esti mates also indicate that about 92% of the riverine fluxes comes from t he Humber rivers compared to the more northerly rivers. For the Humber , preliminary estimates indicate that about 60% of the flux is associa ted with detergent-related sources: historical mining activity may als o provide an important source (e.g. mine drainage and land contaminate d with fly ash and associated material disposal). This illustrates the usefulness of boron as a tracer for non-biodegradable compounds from anthropogenic sources. (C) 1998 Elsevier Science B.V.