SYSTEMATIC APPLICATION OF UNITED-KINGDOM RIVER FLOW AND QUALITY DATABASES FOR ESTIMATING ANNUAL RIVER MASS LOADS (1975-1994)

This article describes the first effective merger of the Harmonised Mo nitoring Scheme (HMS) database of river quality and the National River Flow Archive (NRFA) for systematic estimation of UK river mass loads. Benefits and pitfalls of applying these national river flow and quali ty datasets for calculating river mass loads are described and demonst rated. The benefits of using the HMS database and the NRFA as a combin ed super-database include a synergy of information in terms of improve d precision in river mass load estimates. Special software is introduc ed for the systematic calculation off river mass aggregated loads (COR AL) for rivers grouped by coastal zones around the UK. Such an approac h necessarily establishes an audit trail of the data sources and estim ation method(s) employed, facilitating more meaningful comparisons of river mass load estimates. Possible pitfalls include the application o f a 'blanket' estimation methodology - irrespective of the hydrologica l regime at the site in question or the dynamic flow-concentration beh aviour of the determinand of interest - where a suite of site/determin and-specific estimation algorithms would make better use of the availa ble data. Other issues discussed include the need to make allowances, when interpreting time series of river mass loads, for any temporal va riations in: (1) monitoring networks; (2) quality of flow measurements ; (3) sampling regimes; and (4) methods of laboratory chemical analysi s. A focus of interest is the quality of data and information which th e United Kingdom, along with several other north-western European coun tries, provides to the Oslo and Paris Commission (OSPAR) for monitorin g the contaminant loading of the North Sea by rivers and by dumping an d incineration at sea (e.g. from ships). Time series of annual mass lo ads from the aggregated area covered by the HMS network of catchments in Great Britain, from 1975 to 1994, are presented for 12 determinands , with comments on their reliability for detecting trends. For 10 dete rminands, annual estimates are compared with previous, independently-d erived, estimates for selected years which have been submitted to OSPA R. Future monitoring and database requirements to meet the need for re liable time series of river mass loads are discussed. (C) 1998 Elsevie r Science B.V.