A new approach to deriving ‘best-estimate’ chemical fluxes for rivers draining the LOIS study area

A central objective of the LOIS Community Research Programme was to provide estimates of the land]ocean flux of chemical species from the LOIS study area. In the absence of detailed information on the concentration of most of the dissolved and particulate-associated chemical constituents, it has proved necessary to make use of the relatively infrequent samples collected in the UK Harmonised Monitoring Scheme, in order to estimate chemical fluxes for the LOIS rivers. In these circumstances, standard procedures may provide unreliable results, and a new approach has been developed to derive improved estimates of chemical flux from the LOIS study area. This approach is based on the generation of detailed synthetic time series of concentration, which are used to estimate the likely errors associated with different flux calculation procedures, especially those resulting from differences in the timing of chemographs and hydrographs during storm events. The approach was applied on a river by river and determinand by determinand basis to identify and to employ the best methods for computing fluxes of 45 chemical determinands from the LOIS study area during the period 1992]1996.