Effects of simulated marine heat waves on sediment biogeochemistry of a Baltic coastal lagoon
1
Department of Life and Environmental Sciences, University of Cagliari, Ing. Tommaso Fiorelli, 1, Cagliari, CA - 09126, Italy
2
, IMC Foundation - International Marine Centre, Loc. Sa Mardini, Torregrande, OR - 09170, Italy
3
Department of Marine Sciences, University of Gothenburg, Box 461, Gothenburg, - 40530, Sweden
4
Marine Research Institute, Klaipeda University, Universitero al. 17, Klaipeda, - 92294, Lithuania
Coastal lagoons can be considered "sentinel systems" for detecting climate change impacts. Indeed, extreme events like marine heat waves (MHWs) can severely impact coastal lagoons at all levels of the ecological organization. In coastal lagoons the benthic compartment plays a crucial role in ecosystem functioning and is a good indicator of ongoing changes. Despite this, MHWs effects on sediment biogeochemistry of coastal lagoons are poorly known. We investigated the effects of MHWs of different magnitudes (+2°C and +6°C) on benthic processes of a brackish, semi-enclosed coastal lagoon facing the Baltic Sea. Intact cores of either sandy or muddy sediment from the Curonian lagoon (Lithuania) were exposed to 5-day lasting heatwaves in benthocosms. During the experiment, we measured gas and nutrient fluxes through incubation techniques. At the end of the MHWs, the top 2 cm of each core was analysed to determine the biochemical composition and the degradation rates of sedimentary organic matter (OM). Our results show that both MHWs altered the benthic processes and the OM nutritional quality in both sandy and muddy sediments. In sandy sediments MHWs increased oxygen flux to the sediment and ammonium release, indicating enhanced oxidative processes and metabolic demand. There, the sedimentary protein contents increased by 32-33% after both events. On the other hand, in muddy sediments carbohydrate (CHO) contents decreased by ca. 43%, with a 57% reduction in CHO turnover time during the severe MHWs, suggesting an accelerated degradation of organic matter. Our results pinpoint that MHWs could concur to cause a possible “oligotrophication” of the lagoon sediments, ultimately disrupting the lagoon functioning.
This study was conducted attending PhD program in Life, Environmental and Drug Sciences (UniCa, Cycle XXXVIII), funded by DM 352/2022 (Next Generation EU-PNRR) and IMC Foundation).
Ecosistemi e cambiamento climatico