Defining the trophic status of Maltese (Central Mediterranean) coastal waters through the computation of water quality indices based on satellite data

Abstract

The Maltese Islands have to comply with onerous EU legislation in order to protect the integrity of their water resources in a comprehensive manner. To date, operational monitoring of water quality parameters within the Maltese coastal waters is almost non-existent. This present study was carried out to compute and map values for the CSI023(+) and modified TRIX indices, using satellite and model data for the entire Maltese Fisheries Management Zone (FMZ); and to identify trends in such index values and relate these to anthropogenic activities, geolocation, bathymetry and seasonal factors. Temporal analyses of ocean colour and index values revealed the following seasonal trend, in decreasing order of value: winter, autumn, spring, and summer. Ocean colour and TRIX index values indicate that, overall, chlorophyll-a values for the 2002-2011 period and 2013-2014 period are consistent with those of oligotrophic, poorly productive waters, with a high water quality. CSI023(+) values for the 2002-2011 period indicated that the Maltese marine area shows a statistically insignificant trend of variation in chlorophyll-a values, possibly due to the low spatial resolution of the ocean colour dataset used. Statistical analyses shows that bathymetry and west/east geolocation have an influence on the trophic status of the Maltese FMZ. Water quality indices computation from satellite and model data enables the fulfilment of the mandatory, contemporary water quality monitoring requirements Malta has and enables the formulation of water quality management recommendations. This research can be integrated in an operational online system as a decision-making tool.