engleski

Long-term (30 years) study of dissolved organic matter in the northern Adriatic sea; an indication of global changes and the bios variations

Long-term data sets from freshwater, estuarine and marine ecosystems provide a unique information on complex dynamics within the ecosystems themselves, especially when they respond to anthropogenic pressure and climate change. Today, they become even more important since they play a key role in comprehensive discussions and conclusions concerning the climatic and anthropogenic pressure. The importance of long-term research in the aquatic environment is crucial for many reasons, such as: the interpretation of main processes within ecosystems, detecting the occurrence of complex conditions which might be indiscernible in short-time scale, documenting physical, chemical and biological phenomena and discovering the complexity of interactions as well as dynamics and the population ecology. Therefore, long-term research is an ideal basis for the evaluation and creation of legislation focused on environmental quality and pollution control, and monitoring and prediction of climate change. In this paper an unique time series of dissolved organic carbon (DOC) and its surface active fraction (SAS) that were collected between 1989 and 2020 with monthly or bimonthly temporal resolution along the transect Po River delta - Rovinj in the northern Adriatic (NA) will be presented. The organic matter (OM) shows very pronounced changes in its amount and properties. [1, 2] During the investigated years the periods of high and low carbon content change may be noticed with evident changes in reactivity regarding to SAS type content. The changes indicate altering episodes of eutrophication and oligotrophication, embedded to an overall oligotropication trend in the considered period. Observed changes on a long-term scale are dominantly due to (a) annual fluctuations of freshwater input, mainly driven by the Po River, (b) water circulation and alteration of water masses in the Adriatic Sea, being as a consequence of the Adriatic-Ionian Bimodal Oscillating System (BiOS), [1–3] and (c) unusual phenomena such as mucilaginous algal blooms, red tides, gelatinous zooplankton blooms, [4, 5] which contribute to eutrophication characterized by anomalous accumulation of organic carbon in the sea. The BiOS is responsible for advection of either highly saline ultraoligotrophic Levantine Intermediate Water from the Eastern Mediterranean or nutrient- richer less saline Western Mediterranean waters that reflects on OM amounts (DOC, SAS) and properties at different phase lags of -1 to -4 years. Acknowledgments. Financial support of Croatian Science Foundation projects SPHERE-1205, MARRES1717, ADIOS-1995, and EcoRENA-4764 is highly acknowledged.

organic matter ; northern Adriatic ; environment ; dissolved organic carbon

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