MERIS data for monitoring of small and medium sized humic Swedish lakes

According to the Water Framework Directive (WFD), all lakes larger than 50 ha (0,5 km2) should be monitored on a regular basis. In Sweden, chlorophyll a is one of the parameters used to classify the phytoplankton status of a lake. The possibility to use satellite based information (ENVISAT - MERIS) to measure and monitor the water quality status of Lake Bolmen and surrounding smaller lakes (>2 km2) has been investigated. The work was focused on chlorophyll a and data from 83 lakes in the investigated region has been analysed. In general, chlorophyll a (chl a) levels between 0-10 ug/l prevail in these lakes, but also more extreme levels of chla around 50 ug/l exist. Data from 5 years (2007-2011) has been analysed together with existing field data from approximately 20 lakes. The results indicate that good chl a estimates could be generated for lakes larger than 2-3 km2. This means that not all lakes required by the WFD are possible to monitor using MERIS, and future Sentinel-3-OLCI data, but that a significant contribution to the present and future monitoring program should be possible by adding earth observation data.