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 km
²
) 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 km
²
) 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 km
²
. 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.