Satellite-based products for monitoring optically complex inland waters in support of EU Water Framework Directive

The need to restore and protect waterbodies from further degradation has resulted in formulation of the European Union Water Framework Directive 2000/60/EC (WFD). The directive aims to harmonize European legislation on water; and member states shall establish a programme for monitoring the status of all waterbodies larger than 0.5 km(2), in order to ensure future quality and quantity of inland waters. The biological and physical-chemical status and ecological potential should be assessed and action plans for a sustainable management and protection of freshwater resources should be established. In practice, this means that extensive and expensive sampling programmes are needed. The ecological status of a waterbody can be described by various biological and physical-chemical quality elements, and several of these important ecological parameters can be monitored by space-based instruments: (1) phytoplankton biomass; (2) chlorophyll-a concentration; (3) water transparency; and (4) frequency and intensity of blooms. The objective of this article is to demonstrate how Environmental Satellite/Medium Resolution Imaging Spectrometer and future Sentinel-3/Ocean Land Colour Instrument data can be effectively used to complement traditional water monitoring programmes by adding information with significantly improved spatial coverage and temporal detail to support the WFD status assessment process. Examples are provided for five large European lakes (Peipsi, Vortsjarv, Vanern, Vattern, Malaren). Time series based on satellite data and data collected within national and regional monitoring programmes were compiled and compared, to demonstrate good agreement between the two techniques, but also to discuss natural differences and limitations. Furthermore, the ecological status class based on satellite and in situ data for each waterbody was calculated and analysed.