Bio-optical water quality assessment susanne kratzer, piotr kowalczuk, and sławomir sagan

Abstract

1. The colour of the sea, i.e. Its spectral reflectance, depends on the absorbing and scattering properties of substances in the water. 2. The main optical in-water constituents are chlorophyll a (Chl a), coloured dissolved organic matter (CDOM) and suspended particulate matter (SPM). 3. Optical data can be obtained from sensors deployed into the water or by remote sensing imagers on aircrafts or satellites. 4. With remote sensing, the optical properties of large geographical areas can be surveyed with high temporal and spatial resolution. 5. Chl a can be used as a proxy of phytoplankton biomass, CDOM as a marker of terrestrial freshwater and decay processes of marine primary producers and SPM as an indicator of land runoff and wind-driven resuspension of sediments. 6. Remote sensing of Chl a, CDOM and SPM can assist in the evaluation of water quality, e.g. The state of eutrophication, the extent of freshwater runoff, the depth of the photic zone and the breadth of the coastal zone. 7. The bio-optical characteristics of the brackish Baltic Sea differ from those of other seas. Due to the large overall freshwater influence, CDOM is usually the dominant optical in-water constituent not only near river discharges, but also in the open waters of the Baltic Sea. 8. The CDOM concentrations in the open waters of the Baltic Sea are inversely related to the large-scale Baltic Sea salinity gradient, with CDOM absorption highest in the northern Baltic Sea and lowest in the southwestern Baltic Sea. 9. Due to the high CDOM absorption regional Baltic Sea algorithms are required to derive water quality parameters that can be used as indicators of ecosystem health.