Merging Field and High-Resolution Satellite Chlorophyll Data in Mediterranean Coastal Waters: Setbacks and Benefits (original) (raw)

2018

Abstract

med 2018, 11-12 December 2018, Frascati, Rome, ItalyIn addition to their ecological and environmental value, coastal areas are of major economic and social importance. Therefore, they are one of the marine environments most affected by anthropogenic pressures, in the form of high population densities and intense human activities. Anthropogenic pressures produce an excess of nutrients which are delivered to coastal waters, triggering phytoplanktonic growth and the eutrophication process, thus decreasing water quality. Several policies have been enacted in Europe with the aim of restoring and protecting waters, such as the Water Framework Directive (WFD; 2000/60/EC) and the Marine Strategy Framework Directive (MSFD; 2000/60/EC). This aim involves combatting the negative effects of eutrophication, which necessitates the assessment of its impact through chlorophyll-a concentration. Until now, these assessments have been based mainly on field data. However, satellite data of the new generation high-resolution missions are now readily available, such as that of Sentinel-2 (10-60m) of the European Space Agency. Therefore, an opportunity is given to assimilate field and satellite data to model the structure and functioning of coastal waters. Our aim is to set up an operational system for monitoring the quality of coastal waters based on the synergy between satellite observations and in situ data. As a first step to achieve it, we present here a case study from the Catalan coast, which is representative of the NW Mediterranean coast. In this area, under the National Catalan Coastal Water Monitoring Program, chlorophyll-a concentration is sampled monthly or quarterly at 268 stations, located along 400km of coastline and at three distances from the shore (0, 1000 and 5000m). The objective of this study is to merge this field data with the same kind of data provided by Sentinel-2. Specifically, we are interested to check whether the data from these two sources 1) agree between them from 2015 to 2018, and 2) can be assimilated into a regional model. The main setbacks to be solved in this case study are related to the higher spatial variability of Mediterranean coastal waters compared with other coastal areas due to their specific characteristics. This variability is intensified near the coastline (<500m from the shore), where the chlorophyll algorithm should be adjusted for turbid and clear neighbouring areas and corrected for sea bottom interferences, especially sea grasses and macro algae. Results will allow us to 1) improve the scientific knowledge regarding the structure and functioning of the Catalan coastal zone, 2) provide an improved assessment of eutrophication for this area, and 3) suggest recommendations related to the zone¿s management. At the same time, the findings will be useful for fulfilling the requirements of the WFD, in relation with the Biological Quality Element Phytoplankton, and of the MSFD, in relation with the Descriptor 5 - Eutrophication. Therefore, these results will be very valuable for the involved administrations: the Catalan Water Agency, the Spanish Environmental Ministry and the European Commission. Future work will provide chlorophyll maps of the Catalan coast in an operational way and extend the procedure to provide full coverage of Mediterranean coastal watersPeer Reviewe

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