A quality-control method for physical and chemical monitoring data. Application to dissolved oxygen levels in the river Loire (France)

A quality-control method is proposed for examining continuous physical and chemical measurements, including temperature, dissolved oxygen, pH and elec trical conductivity. Firstly, measurement consistency is evaluated by vario us modelling approaches: internal series structure, inter-variable relation s or relations with external variables, spatial coherence and deterministic models. Secondly, outliers or systematic errors are detected using classic al statistical tests. The method was evaluated for dissolved oxygen concent rations (DO) in the river Loire at Dampierre over a 5-year period (1990-199 4), using data records containing fictitious errors, and raw data for the y ear 1995. The results demonstrate the effectiveness and advantages of a mul timodel approach. In the case of dissolved oxygen for example, slow continu ous drifts are always detected in under 4 days. (C) 2001 Published by Elsev ier Science B.V.