Boron in the major UK rivers entering the North Sea

Boron in the major UK rivers entering the North Sea is predominantly in 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 relationship of the type [B]=a∗flowb, where a and b are constants. In this equation, the a term varies from river to river in relation to the boron concentration at baseflow while the b term is of similar value for all the rivers (around −0.5 to −0.6). The spatial variations are directly linked to the degree of sewage discharge and the dilution associated with (i) rainfall events and (ii) the length of river reach from the pollutant source. Boron concentrations exhibit simple chemically conserved water mixing behaviour. However, deviations between chloride and boron indicate secondary chloride supplies from storm runoff, increased boron contamination for part of the sampling period on one river (the Nidd) and possibly significant atmospheric inputs for the less polluted 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 relatively low rainfall component (about 25% for the cleaner rivers and much lower values for the more polluted rivers). These preliminary estimates also indicate that about 92% of the riverine fluxes comes from the Humber rivers compared to the more northerly rivers. For the Humber, preliminary estimates indicate that about 60% of the flux is associated with detergent-related sources: historical mining activity may also provide an important source (e.g. mine drainage and land contaminated with fly ash and associated material disposal). This illustrates the usefulness of boron as a tracer for non-biodegradable compounds from anthropogenic sources.