Anthropogenically Induced Environmental Changes in the Northeastern Adriatic Sea in the Last 500 Years (Panzano Bay, Gulf of Trieste)

Biogeosciences, 13, 5965–5981, 2016 www.biogeosciences.net/13/5965/2016/ doi:10.5194/bg-13-5965-2016 © Author(s) 2016. CC Attribution 3.0 License. Anthropogenically induced environmental changes in the northeastern Adriatic Sea in the last 500 years (Panzano Bay, Gulf of Trieste) Jelena Vidovic´1, Rafał Nawrot1, Ivo Gallmetzer1, Alexandra Haselmair1, Adam Tomašových2, Michael Stachowitsch3, Vlasta Cosovi´ c´4, and Martin Zuschin1 1Department of Palaeontology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria 2Earth Science Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 84005 Bratislava, Slovak Republic 3Department of Limnology and Bio-Oceanography, Center of Ecology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria 4Department of Geology, Faculty of Science, University of Zagreb, Horvatovac 102a, 10 000 Zagreb, Croatia Correspondence to: Jelena Vidovic´ ([email protected]) Received: 29 June 2016 – Published in Biogeosciences Discuss.: 22 July 2016 Revised: 4 October 2016 – Accepted: 16 October 2016 – Published: 1 November 2016 Abstract. Shallow and sheltered marine embayments in ur- zano Bay have a long history of adaptation to elevated trace banized areas are prone to the accumulation of pollutants, but element concentrations. little is known about the historical baselines of such marine Our study underlines the importance of using an inte- ecosystems. Here we study foraminiferal assemblages, geo- grated, multidisciplinary approach in reconstructing the his- chemical proxies and sedimentological data from 1.6 m long tory of environmental and anthropogenic changes in marine sediment cores to uncover ∼ 500 years of anthropogenic systems. Given the prolonged human impacts in coastal areas pressure from mining, port and industrial activities in the like the Gulf of Trieste, such long-term baseline data are cru- Gulf of Trieste, Italy. cial for interpreting the present state of marine ecosystems. From 1600 to 1900 AD, normalized element concentrations and foraminiferal assemblages point to negligible effects of agricultural activities. The only significant anthropogenic activity during this period was mercury mining in 1 Introduction the hinterlands of the gulf, releasing high amounts of mercury into the bay and significantly exceeding the standards on The northern Adriatic Sea is densely urbanized and polluted the effects of trace elements on benthic organisms. Nonethe- (Lotze et al., 2006; Cozzi and Giani, 2011), and the areas less, the fluctuations in the concentrations of mercury do not around the Po River, the Venice Lagoon and in the Gulf of correlate with changes in the composition and diversity of Trieste bear the highest pressure (Solis-Weiss et al., 2007; foraminiferal assemblages due to its non-bioavailability. In- Raccanelli et al., 2009). Panzano Bay, located in the north- tensified agricultural and maricultural activities in the first eastern part of the Gulf of Trieste, is a shallow and sheltered half of the 20th century caused slight nutrient enrichment embayment prone to the accumulation of pollutants, with re- and a minor increase in foraminiferal diversity. Intensified cent anthropogenic pressure coming from agricultural, mari- port and industrial activities in the second half of 20th cen- cultural, mining and industrial activities (Horvat et al., 1999). tury increased the normalized trace element concentrations The impact here started nearly 500 years ago with the on- and persistent organic pollutants (PAH, PCB) in the topmost set of mercury mining in the hinterland of the bay (Singh part of the core. This increase caused only minor changes and Turner 2009; Covelli et al., 2012), enhanced in the 20th in the foraminiferal community because foraminifera in Pan- century with intensifying agriculture and mariculture (Aleffi et al., 2006; Rampazzo et al., 2013; Finch et al., 2014), and Published by Copernicus Publications on behalf of the European Geosciences Union. 5966 J. Vidovic´ et al.: Anthropogenically induced environmental changes in the northeastern Adriatic Sea has continued until present times with increasing port and 2 Study area industrial activities (thermoelectric plant) of the city of Mon- falcone (Notar et al., 2001; Pozo et al., 2009). The Gulf of Trieste is a shallow marine basin in the north- Such intensive anthropogenic pressures have prompted a ernmost part of the Adriatic Sea, occupying an area of about growing scientific effort to estimate the effects of pollu- 500 km2, with an average water depth of 17 m and a max- tion on ecosystem composition here. Most attempts have ad- imum of about 25 m (Fig. 1). Seasonal variations of water dressed modifications of the marine habitats that occurred in temperature range from 8 to 24 ◦C at the surface and 8 to the 20th century using only geochemical (Horvat et al., 1999; 20 ◦C in the bottom layer. The salinity of the water in the gulf Faganeli et al., 2003; Acquavita et al., 2012) or biological is typically marine, ranging between 33 and 38.5 ‰ (Ogor- proxies (Solis-Weiss et al., 2007). There is however, a grow- elec et al., 1991). ing tendency towards integrated assessments of its present The water enters the gulf in the southeast and continues to state (Cibic et al., 2007; Melis and Covelli, 2013; Franzo the northwest, following the general anticlockwise circula- et al., 2015), but until today there have been no multidisci- tion pattern of the Adriatic Sea. However, the water circula- plinary studies assessing the long-term history of the envi- tion in the gulf is mostly controlled by tides (range ∼ 0.5 m), ronmental changes in the northeastern Adriatic and thus cap- winds (strong northeastern Bora) and seasonal variations of turing its preindustrial, undisturbed state. freshwater inflow. The Isonzo/Socaˇ and Timavo rivers are the Such a historical record requires an integrated geochem- most significant sources of freshwater to the Gulf, with aver- ical and paleoecological approach. Benthic foraminifera, age inflows of about 100–130 m3 s−1 each (Ogorelec et al., among the most abundant microorganisms in shallow and 1991). marginal marine environments, are often used in paleoe- The Gulf of Trieste generally shows mesotrophic to olig- cological studies. This is because they are highly sensitive otrophic conditions, with episodic eutrophication events, ac- to short-term environmental changes (Schönfeld, 2012) and companied by summer thermal stratification of the water col- have a high preservation potential, thus providing an excel- umn (Ogorelec et al., 1991; Horvat et al., 1999; Turk et al., lent temporal record of ecosystem states over the past hun- 2007). dreds to thousands of years (Yasuhara et al., 2012). The main sediment supply comes from the Isonzo River in The present multidisciplinary study is designed to provide the north and from the weathering of the Paleogene flysch de- a high-resolution historical record of environmental changes posits outcropping along the southern coast of the gulf. The in Panzano Bay, to obtain information on the state of the sediment accumulation rates are approximately 1 mm yr−1 in ecosystem prior to the onset of the most intensive impact the central part of the gulf and increase to about 2.5 mm yr−1 and to evaluate the effects of anthropogenic activities in the towards the mouth of the Isonzo River, located in Panzano bay. We obtained geochemical data and foraminiferal as- Bay (Ogorelec et al., 1991; our unpublished data). Surface semblages from a 1.6 m long sediment core containing a sediments in this area are mostly silty clays and clayey silts centennial-scale record of environmental and anthropogenic (Zuschin and Piller, 1994) occupied by a high biomass epi- changes. The core covers approximately the last 500 years, as fauna (Zuschin et al., 1999). indicated by radiocarbon calibrated AAR dating of the mol- The Gulf of Trieste is affected by many sources of organic lusk shells. and inorganic pollutants, coming from agricultural and in- Taking into account the history of potential anthropogenic dustrial activities in the hinterland, as well as from tourist stressors in Panzano Bay, we assess the following hypothe- and maricultural activities along its coasts (Notar et al., 2001; ses: (1) agricultural and maricultural activities produce up- Covelli et al., 2006). Panzano Bay is one of the highly im- core increases in the concentrations of organic matter, nutri- pacted areas, with organic pollution coming from mussel ents and trace elements, (2) mining activities and thermoelec- farms located along the eastern part of the Gulf of Trieste tric plants generate a progressive enrichment of mercury and (Melaku Canu and Solidoro, 2014) and industrial and port persistent organic pollutants and (3) increased pollutants al- areas of the city of Monfalcone, including a thermoelectric ter the taxonomic composition of foraminiferal assemblages plant and several coal, petroleum and other cargo handling and cause a decline of species abundance and diversity. piers (Fig. 1). The Monfalcone thermoelectric plant con- To test these hypotheses, we evaluate the pollution in the sists of four thermoelectric generator sets powered by coal bay using geochemical proxies (major, minor and trace el- and fuel oil that became operative in 1965 (The Monfalcone ements, nutrients, persistent organic pollutants) and quan- Thermoelectric Plant, 2016). Finally, there is substantial Hg tify the composition and diversity of foraminiferal assem- pollution originating from the Idrija mercury mine in the hin- blages. Finally, we reconstruct the chronology of environ- terlands and delivered to the bay through the Isonzo river mental changes in Panzano Bay over the last 500 years and flow (Horvat et al., 1999; Notar et al., 2001). Idrija, situated underline the applicability of our results to disturbed shallow 50 km west of Ljubljana (Slovenia), was the second-largest coastal ecosystems elsewhere. Hg mine in the world, operating for nearly 500 years until its definite closure in 1995 (Faganeli et al., 2003; Covelli et al., 2012). During this period, over 5 million tons of Hg ore Biogeosciences, 13, 5965–5981, 2016 www.biogeosciences.net/13/5965/2016/ J.

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