Ecosystem monitoring of the fresh water lake IJsselmeer

dr Hans Van der woerd⁽¹⁾and dr Steef Peters⁽¹⁾

⁽¹⁾ IVM, De Boelelaan 1087, 1081 HV Amsterdam, Netherlands

Abstract

The IJsselmeer is the largest fresh water lake in the Netherlands with a surface area of 1300 km2 and an average depth of 4,4 meter. Due too high nutrient loadings in this lake and bottom processes serious eutrophication problems occurred in the past. Some of those remain till the present day. In some periods a strong growth of cyanobacteria (Microcystis) occurs that causes ecological and economical damage. Understanding and monitoring of three algal groups (green algae, cyanobacteria, and diatoms) is therefore of major concern to the water authorities.

Over the last years a large investment has been made to provide all the necessary in-situ measurement and algorithms for interpretation of the SeaWiFS and MERIS images of Lake IJsselmeer: Data sets were collected of the Specific Inherent Optical Properties of algal blooms at the IJsselmeer, together with field spectra on R(0-) from PR-650 and other standard water quality parameters. A detailed water quality (DBS) model was adapted and prepared for inter-comparison with RS and in-situ measurements.

From the combination of SeaWiFS images, DBS model output, maps of monthly mean CHL were made and compared with local measurements. The project results indicated that this integration has great potential. The remote sensing and model results showed a remarkable consistency in the evolution of CHL patterns in Lake IJsselmeer for the year 1999.

MERIS has the potential to map CHL with improved accuracy and with greater detail. Moreover it is able to resolve additional important parameters (Cyano-phycocyanine) and CDOM. We will present the first MERIS results of lake IJssel and discuss their quality and prospect for monitoring of water quality in large inland fresh water lakes.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry