|Paper title||Earth Observation-based cyanobacterial bloom index testing for ecological status assessment in the coastal and transitional waters of the Baltic and Black Seas|
|Form of presentation||Poster|
Algal blooming is one of the factors with the greatest impact on the quality, functioning, and ecosystem services of waterbodies, and can frequently occur in the coastal regions (O'neil et al., 2012). The observed increase in cyanobacterial blooms in European seas is attributed to severe eutrophication and a subsequent change in nutrient balance caused by anthropogenic nutrient enrichment, in particular from urban areas, agriculture and industry (Kahru et al., 2007, Vigouroux et al., 2021). The EU Marine Strategy Framework Directive (MSFD) is the main initiative to protect the seas of Europe that requires to minimize human-induced eutrophication (MSFD, 2008). The majority of indicators developed under MSFD Descriptor 5 Eutrophication are based on in situ monitoring data, and only recently, the Earth-Observation (EO) data has started to be proposed as a valuable source of information for monitoring, ecological status assessment and indicator development (Tyler et al., 2016). Recently, HELCOM proposed a pre-core indicator Cyanobacteria Bloom Index (CyaBI) that evaluates cyanobacterial surface accumulations and cyanobacteria biomass, describes the symptoms of eutrophication caused by nutrient enrichment, and exclusively is based on EO satellite data (Antilla et al., 2018). The indicator was developed using the Baltic Sea as a testing site, and is focused on the open sea areas (HELCOM, 2018). However, anthropogenic pressures, unbalanced and intensive land use, and climate change increasingly affect coastal and transitional waters representing water continuum from inland waters towards sea. These regions are more exposed to ongoing eutrophication and the severe cyanobacteria blooms are evident (Vigouroux et al., 2021). Therefore, the aim of this study is to test the applicability of pre-core indicator CyaBI for the coastal and transitional waters of the two enclosed seas located at different latitudes: the Baltic and the Black Sea. We also hypothesize that the intensive cyanobacteria blooms significantly alter the short-term environmental conditions of the Seas in terms of the Sea Surface Temperature (SST) changes.
The Baltic and the Black Sea are the world’s largest brackish water ecosystems, which exhibit many striking similarities as geologically young post-glacial water bodies, semi-isolated from the ocean by physical barriers. Both Seas are exposed to similar anthropogenic pressures, such as increasing urbanization, water pollution by heavy industries, intense agriculture, overexploitation of fish stocks, abundant sea traffic and port activities, oil spills, etc. In both seas, increasing attention is being paid to the search for scientifically based solutions to improve the state of the marine environment.
In our study, we have used time series of the Medium Resolution Imaging Spectrometer (MERIS) on-board Envisat at 300 m, and the Ocean and Land Colour Instrument (OLCI) on-board Sentinel-3 at 300 m spatial resolution for the estimation of chlorophyll-a (Chl-a) concentration. Chl-a concentration was retrieved after the application of the FUB processor, which was developed by the German Institute for Coastal Research (GKSS), Brockmann Consult, and Freie Universität Berlin, and is designed for European coastal waters. In case of MERIS images, the FUB processor uses Level 1b top-of-atmosphere radiances to retrieve the concentrations of the optical water constituents. A good agreement (R2=0.69, RMSE=14.44, N=56) was found between Chl-a derived from MERIS images after application of FUB processor and in situ measured Chl-a concentration during the validation in the coastal waters of the Lithuanian Baltic Sea (more details in Vaičiūtė et al., 2012). Although the FUB processor is originally designed for MERIS images, we have tested its performance in case of OLCI images. Chl-a concentration derived from OLCI data after FUB processor application and measured in situ were in agreement with R2=0.72, RMSE=4.2, N=31. CyaBI index was calculated following the methodology described in Antilla et al. (2018). In this study, we used Terra/Aqua MODIS standard Level 2 SST products with a spatial resolution of around 1 km—obtained from the NASA OceanColor website—to analyse the spatial patterns and changes in SST at the presence of cyanobacteria surface accumulations.
In this presentation, we will demonstrate the first results of ecological status assessment using pre-core CyaBI indicator in the Lithuanian Baltic and Ukrainian Black Seas. We will discuss the potential of using CyaBI for the ecological status assessment in the coastal and transitional waters, and for the seas located at different latitudes. We also will provide significant insights about the integration of SST data for the ecological status assessment considering the Descriptor 5 of MSFD and the Water Framework Directive.
The research was funded by the Lithuanian-Ukrainian bilateral cooperation in the field of science and technology under project "Measuring the marine ecosystem health: concepts, indicators, assessments – MARSTAT (contract no. S-LU-20-1)".