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 electrical conductivity. Firstly, measurement consistency is evaluated by various modelling approaches: internal series structure, inter-variable relations or relations with external variables, spatial coherence and deterministic models. Secondly, outliers or systematic errors are detected using classical statistical tests. The method was evaluated for dissolved oxygen concentrations (DO) in the river Loire at Dampierre over a 5-year period (1990–1994), using data records containing fictitious errors, and raw data for the year 1995. The results demonstrate the effectiveness and advantages of a multi-model approach. In the case of dissolved oxygen for example, slow continuous drifts are always detected in under 4 days.