Université de Liège; Faculty of Sciences; Department of Astrophysics, Geophysics and Oceanography; Chemical Oceanograpy Unit
Borges, Alberto Vieira
Frankignoulle, Michel
Fonds National de la Recherche Scientifique (FNRS), sponsor
Abstract
The Scheldt estuary is probably one of the most polluted estuaries in Europe. It is bordered by highly populated and industrialised towns (Lille, Gent, Brussels and Antwerp). Industry, untreated waste water and agriculture introduce in the rivers and the estuary high loads of organic matter and nutrients.
Previous studies (Frankignoulle et al. 1996; 1998) reported very high values of the partial pressure of CO2 (pCO2), up to 9400 ppm, which represents 2500% of atmospheric equilibrium (present day atmospheric pCO2 is around 370 ppm). Abril et al. 2000 showed that about 60% of this CO2 originates from bacterial production and about 40% from nitrification. Moreover, it has been estimated that organic carbon inputs in the estuary are mostly anthropogenic, with 55% from industries and 38% from domestic waste (Wollast 1982). This estuary is then heavily impacted by human activities, but with the European directive 91/271/CEE and its application with the construction in a few years of a treatment plant in Brussels, we expect to observe an improvement in the water quality of this ecosystem.
The project, started in January 2002 in collaboration with the Chemical Oceanography and Water Geochemistry Laboratory of the Université Libre de Bruxelles. It deals with the continuous measurement of surface pCO2, salinity and water temperature in the maximum turbidity zone of the Scheldt estuary, at Ste Anna Station, located in Antwerp. Weekly sampling is carried out for the determination of dissolved oxygen, Total Alkalinity, Total Suspended Matter (TSM), Chlorophyll a, Dissolved Organic Carbon (DOC), as well as dissolved inorganic and organic nutrients, such as: Total Phosphorus (TP), Total Dissolved Phosphorus (TDP), Phosphate and Dissolved organic Phosphate (PO4/DOP), Total Particulate Phosphorus (TPP), Total Particulate Inorganic Phosphorus (TPIP), Dissolved Silica (DSi), Biogenic Silica (Bsi) and Dissolved Nitrogen (NO3/NO2/NH4).
This will allow us to understand the seasonal and inter-annual variations of inorganic and organic carbon, and, nutrients in the estuary, which, presently, are not well constrained. Also it should allows us to estimate the carbon and nutrients transfer from the inner estuary to the outer estuary (plume) of the Scheldt. Finally we should be able to follow the incidence, in a few years time, of the urban wastewater plant of Brussels on both ecosystems: the inner estuary, presently heterotroph and the Scheldt plume, where recurrent and massive blooms of Phaeocystis sp. occur, that are probably associated with high inputs of nitrate originating from the inner estuary (due mainly to high nitrification rates).
Abril, G.; Borges, A.V. (2004). Carbon dioxide and methane emissions from estuaries, in: Tremblay, A. et al.Greenhouse gases emissions from natural environments and hydroelectric reservoirs: fluxes and processes. Environmental Science Series, : pp. 187-207
Borges, A.V. et al. (2004). Gas transfer velocities of CO2 in three European estuaries (Randers Fjord, Scheldt, and Thames). Limnol. Oceanogr. 49(5): 1630-1641. https://dx.doi.org/10.4319/lo.2004.49.5.1630
Borges, A.V. et al. (2004). Variability of the gas transfer velocity of CO2 in a macrotidal estuary (the Scheldt). Estuaries 27(4): 593-603
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