Abstract
Long-term data series (1971–2015) of physical and biogeochemical parameters were analyzed in order to assess trends and variability of oceanographic conditions in the northern Adriatic Sea (NAS), a mid-latitude shallow continental shelf strongly impacted by river discharges, human activities and climate changes. Interpolation maps and statistical models were applied to investigate seasonal and spatial variability, as well as decadal trends of temperature, salinity, chlorophyll-a and nutrients. This analysis shows that sea surface temperature increased by +0.36% year−1 over four decades. Annual mean flow of the Po River markedly changed due to the occurrence of periods of persistent drought, whereas the frequency of flow rates higher than 3000 m3 s−1 decreased between 2006 and 2015. Moreover, we observed a long-term decrease in surface phosphate concentrations in Po River water (−1.34% year−1) and in seawater (in summer −2.56% year−1) coupled, however, to a significant increase in nitrate concentration in seawater (+3.80% year−1) in almost all seasons. These changes indicate that the nutrient concentrations in the NAS have been largely modulated, in the last forty years, by the evolution of environmental management practices and of the runoff. This implies that further alteration of the marine environment must be expected as a consequence of the climate changes.
Highlights
Continental shelf areas are strongly threatened by climate change and by their interaction with a large variety of disturbances of anthropogenic origin
The northern Adriatic Sea (NAS), which constitutes the northernmost continental shelf of the Mediterranean Sea, is an important example of a marine system dynamically influenced by anthropogenic pressures
Oceanographic properties (T and S), Chl-a and nutrient concentrations were analyzed on both spatial and temporal scales, in order to assess the seasonal variability of spatial patterns, as well as the long-term trends in the NAS
Summary
Continental shelf areas are strongly threatened by climate change and by their interaction with a large variety of disturbances of anthropogenic origin. Modifications of oceanographic characteristics and of circulation patterns, sea level rise and coastal erosion interact with anthropogenic discharges of the nutrients and of organic matter, often leading to eutrophication problems and to changes in the structure of marine ecosystems, including the spreading of alien species [1,2,3,4,5]. This issue is critical considering that an important portion of the human population (625 million year 2000; global population of 6.1 billion) lives in coastal zones and use their ecosystem services [6]. Significant changes in plankton community composition, macrobenthos distribution, spreading of non-indigenous species, total biomass of target demersal fishes and small pelagic fish catches have been reported here by different authors [10,13,14,15]
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