Trophic status assessment of Central Eastern Adriatic Sea using water quality variables and loading capacity concept for estuaries.

The temporal and spatial variability of pollution pressures of the coastal waters resulting from river discharges is the main cause of eutrophication along the coastline. This study aims to assess the water quality and trophic state of Kastela Bay and the river Jadro estuary located in the Croatian central Adriatic Sea. The trophic assessment is classified using the composite trophic status index (TRIX), originally developed for Italian coastal waters and modified for the eastern central Adriatic Sea using data series from 2012 to 2019 from 13 stations. The impact coming from the river Jadro estuary is analyzed using the loading capacity concept to examine the exchange flows and loading dynamics of nutrients discharged in the Kastela Bay. The results show that the trophic index is larger within the river Jadro estuary and maintains the increased values in the surface layer throughout Kastela Bay. The presented loading capacity concept, accounting for the exchange flows in transitional waters, may help better understand the trophic dynamics of the receiving waters. The loading capacity is changing with the river flow and daily loads from measurements can be used to assess the pattern of impairment.