HR: 17:10h
AN: OS34B-04    [Abstracts]
TI: Benthic Nutrient Fluxes in the Black Sea - Historical Legacy of Eutrophication
AU: * Friedrich, J
EM: Jana.Friedrich@awi.de
AF: Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, Bremerhaven, 27570, Germany
AB: The broad and shallow western Black Sea shelf suffered from pollution, eutrophication and overfishing from the 1960s to the early 1990s and experienced severe changes in the ecosystem structure and functioning as a result. Eutrophication has been imposed on the western shelf largely by external point sources which are the major inflowing rivers Danube, Dniestro and Dnipro by their nutrient load. Recurrent widespread bottom water hypoxia during 20 years caused deterioration of the benthic system. After the collapse of the centrally planned industries and agriculture in the eastern European countries in the early 1990s, resulting in decreasing nutrient discharge by the rivers, the ecosystem is now responding to the decrease in anthropogenic pressures. It is not known however, how resistant the benthic and pelagic ecosystems are to further stress and what the thresholds are. Climate changes introduce further stress to the shelf ecosystems by temperature rise and by changes in the freshwater supply from the rivers. An important internal source for eutrophication, often ignored though, is recycling of nutrients from organic matter deposited on the seafloor. Benthic nutrient fluxes measured in 1995, 1997, 1998 and 2006 on the western Black Sea shelf did not decrease during that period of time despite the recovery of the pelagic system. Release of nutrients from the sediments along with a tight benthic-pelagic coupling on the shallow shelf continues to fuel benthic and pelagic productivity decades after outside pressures on the shelf ecosystem in the form of river nutrient input have decreased. This underlines the importance of the benthic system as the memory of past eutrophication. Our recent survey further indicates that from the biogeochemical point of view the state of the benthic system along the Romanian and Ukrainian Black Sea coast is nevertheless improving as bottom water hypoxia is much less prevalent and severe than a decade ago. Benthic flux experiments in a red algal field showed that a healthy benthic ecosystem with macrophytes and macrozoobenthos in balance releases less organic and inorganic nutrients to the sediment overlaying water than a disturbed system without macrobenthic life. Our experiments further indicate that a recovered benthic system with opportunistic species may fulfil ecosystem functions comparable to a pristine system. Our results will help to identify the thresholds for resilience of the benthic and pelagic ecosystems on the western Black Sea shelf. Integrating these new and existing data on sources and sinks of nutrients in the western shelf of the Black Sea into budget models may assist in developing ecological management scenarios for western Black Sea shelf.
DE: 0410 Biodiversity
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0442 Estuarine and nearshore processes (4235)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly