engleski

Dynamics of organic matter in Rogoznica lake as an indication of global change

Global i.e. climate change cause the change in the characteristics and concentration of organic matter (OM) in marine system, which can lead to eutrophication. Those changes can be detected by measuring dissolved (DOC) and particulated (POC) organic carbon, as well as their surface-active fractions (SAS) [1]. In seawater, OM is a complex mixture of dissolved and particulate organic compounds (proteins, carbohydrates, lipids, humic and fluic acid), with different surface-active properties [1]. The boundary between dissolved and particulated fraction of OM is 0.7 µm, and these fractions are separated by filtration. DOC passes through filter, and represents relatively simple molecules from decomposing materials, supporting growth of microorganisms and plays an important role in the global carbon cycle through the microbial loop [2]. POC is collected on the filter, and retains evidence of its original cellular structure such as phytoplankton, zooplankton, larvae or detritus. POC is important for vertical transport of OM through the water column, being a link between surface primary production, the deep ocean, and sediments [3]. The OM (SAS) in the sea is mainly autochthonously produced by biological activity (primary production, releases of secondary metabolites under feeding pressure), while part of OM can also be allochthonously introduced (terrestrial and atmospheric origin). The Rogoznica Lake (RL) is a good study-site for monitoring of OM related to global changeRL is an isolated and unique marine environment on the eastern shore of the Adriatic Sea (43°32´N, 15°58 ´E), with strong eutrophic and euxinic (free sulfide in the water column) characteristics [4]. Due to its relative isolation (weak conection with the sea through the porous carst), small volume and stable stratification, RL allows the study of OM variability on a small spatial and time scales. The chemisty and biology of this system has been studied since 1990 [4], what is now very relevant as long-term research in context of climate change. Since the early 1990s, the volume of the anoxic layer has increased by 4- 5 times. Consequently, we noticed a trend of DOC accumulation in the bottom-anoxic layer, while its concentration is decreasing through the oxic- surface layer (0-5 m depth). In the same time SAS is increasing in the oxic surface layer and decreasing in the anoxic bottom layer, indicating certain changes in the quality of the DOC, i.e. OM in general. Furthermore, there is a evidence for POC accumulation through the water column, and an increase in the proportion of POC in the fraction of total organic carbon (TOC). On a long-term scale (1992-2021) this study will show a noticeable change in the quantity and quality of the OM in RL water column as an indication of the pronounced eutrophication probably affected by global change. ACKNOWLEDGEMENTS: This work was result of research activities within the MARRES project, IP-2018-01- 1717.

organic matter ; dissolved organic carbon ; particulated organic carbon ; surface active substances ; Adriatic sea ; global change

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