Abstract
Ghar El Melh (Northern Tunisia) is a shallow eutrophicated lagoon (total surface area 35.6 km2) which was one of the primary sites within the MELMARINA project. It is connected to the Mediterranean through a dredged opening and receives untreated sewage from two towns and a catchment of 131 km2. During the past decade the lagoon’s water quality has deteriorated and vegetation has changed. Ruppia sp. has diminished and green macroalgae (mainly Cladophora sp.) has increased. Frequent resuspension of fine alluvial sediment has reduced both water transparency and angiosperm (Ruppia sp.) vegetation cover. Flash floods during winter deliver most of the load of sediment and nutrients from the catchment to the lagoon. Options for restoring the angiosperm cover in the lagoon have been analysed using a model system developed for the main part of the lagoon consisting of a 2-D hydrodynamic model coupled to an ecological model. The ecological model includes a combined description of eutrophication and sediment transport with rooted vegetation (Ruppia sp.), benthic macroalgae, benthic microalgae, phytoplankton and suspended matter and nutrients. A separate sediment module includes pools of nutrients, organic carbon and fine sediment. Deposition and resuspension of the sediment pools are dependent on current and wind-generated shear stress. The load of nutrients and fine sediment was estimated through calibrating the model against measured water quality data and sediment deposition rates. The anthropogenic load from July 2003 to July 2004 was 33,000 tonnes fine sediment, 182 tonnes total N and 26 tonnes total P. A net import of sediment and nutrients from the sea was simulated, driven by the relatively high concentrations of suspended matter and particulate-bound N and P measured in coastal Mediterranean water outside the lagoon. Scenario simulations indicate that the lagoon acts as a deposition area for sediment N and P for boundary concentrations down to 50% of the measured concentrations at the coast outside the lagoon. A range of simulations with decreasing load of sediment and nutrients indicate that angiosperm vegetation will slowly recover with loads of 25% of current loads, combined with increased filtration by bivalves which would decrease suspended matter concentrations and increase transparency. Elevated concentrations of suspended matter and nutrients in the sea outside the lagoon are discussed in relation to a 30-year flash flood of the Mejerda River in February 2003. Coastal erosion as well as nutrients and sediment delivered by this river probably account for a general elevation of these concentrations close to the coast.
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References
Added, A., 2001. Biochemical cycles of Org-C, Tot-N and Tot-S in the sediment of Ghar El Melh Lagoon (north of Tunisia). Journal of Marine Systems 30: 139–154.
Added, A., A. Ben Mammou & S. Abdeljaoued, 2003. Caracterisation geochemique des sediment de surface de Golfe de Tunis. Bulletin Institut National des Sciences et Technologies de la Mer, Salammbô 30: 135–142.
Andersen, O. B., 1995. Global ocean tides from ERS-1 and TOPEX/POSEIDON altimetry. Journal of Geophysical Research 100: 25249–25259.
Austin, I., T. J. Andersen & K. Edelvang, 1999. The influence of benthic diatoms and invertebrates on the erodibility of an intertidal mudflat, the Danish Wadden Sea. Estuarine, Coastal and Shelf Science 49: 99–111.
Ayache, F., J. R. Thompson, R. J. Flower, A. Boujarra, F. Rouatbi & H. Makina, 2009. Environmental characteristics, landscape history and pressures on three coastal lagoons in the Southern Mediterranean Region: Merja Zerga (Morocco), Ghar El Melh (Tunisia) and Lake Manzala (Egypt). Hydrobiologia. doi:10.1007/s10750-008-9676-6.
Beyrem, H., E. Mahmoudi & P. Aisssa, 2002. Evolution spatiale de la structure biologique des peuplements de nématodes libres de la lagune de Ghar El melh pendant l’hiver 2000. Revue de la Faculté des Sciences de Bizerte 1: 104–128.
Bouzaiane, S. & H. L. Frigui, 2003. Crues et Inondations Dans la Basse Vallée de l’Oued Mejerda – Janvier-Février 2003, Tronçon Laroussia – La Mer. Rapport Provisoire. Ministère de l’Agriculture de l’Environnement et des Ressources en Eau. Direction Générale des Ressources en Eau, Tunis.
Cornwell, J. C., D. J. Conley, M. Owens & C. Stevenson, 1996. A sediment chronology of the eutrophication of Chesapeak Bay. Estuaries 19: 488–499.
DHI, 2007a. MIKE21 & MIKE 3 flow model, hydrodynamic and transport module, scientific documentation. DHI Water Environment Health, Hørsholm.
DHI, 2007b. MIKE21 & MIKE 3 flow model, CSC schemes, scientific documentation. DHI Water Environment Health, Hørsholm.
DHI, 2007c. ECO Lab, short scientific description. DHI Water Environment Health, Hørsholm.
DHI, 2007d. Eutrophication model 1 including sediment and benthic vegetation. DHI Water Environment Health, Hørsholm.
DHI, 2007e. Mud transport scientific documentation. DHI Water Environment Health, Hørsholm.
Economopoulos, A. P., 1993. Assessment of sources of air, water, and land pollution (A guide to rapid source inventory techniques and their use in formulating environmental control strategies). World Health Organization, Geneva.
Flower, R. J. & J. R. Thompson (eds), 2006. MELMARINA: monitoring and modelling coastal lagoons: making management tools for aquatic resources in North Africa: final report. IC-CT-2002-10009. Environmental Change Research Centre & Wetland Research Unit Department of Geography, UCL, London.
Flower, R. J. & J. R. Thompson, 2009. An overview of integrated hydro-ecological studies in the MELMARINA Project: monitoring and modelling coastal lagoons—making management tools for aquatic resources in North Africa. Hydrobiologia. doi:10.1007/s10750-008-9674-8.
Flower, R. J., P. G. Appleby, J. R. Thompson, M. H. Ahmed, M. Ramdani, L. Chouba, N. Rose, R. Rochester, F. Ayache, M. M. Kraiem, N. Elkhiati, S. El Kafrawy, H. Yang & E. K. Rasmussen, 2009. Sediment distribution and accumulation in lagoons of the Southern Mediterranean region (the MELMARINA Project) with special reference to environmental change and aquatic ecosystems. Hydrobiologia. doi:10.1007/s10750-008-9677-5.
Ghorbel, A., 2003. Crues et Inondations de la Mejerda - Janvier-Février 2003 - Rapport de Synthèse. Republique Tunisienne, Ministère de l’Agriculture de l’Environnement et des Ressources en Eau. Direction Générales des Ressources en Eau. Direction des Eaux de Surfaces, Tunis.
Håkanson, L. & A. C. Bryhn, 2008. Modeling the foodweb in coastal areas: a case study of Ringkøbing Fjord, Denmark. Ecological Research 23: 421–444.
Harris, P., R. Fichez, J.-M. Fernandez, H. Golterman & C. Badie, 2001. Using geochronology to reconstruct the evolution of particulate phosphorus inputs during the past century in the Papeete Lagoon (French Polynesia). Oceanologica Acta 24: 1–10.
Jensen, H. S., F. Ø. Andersen, E. K. Rasmussen & A. Jensen, 1995. Phosphorus cycling in a coastal marine sediment, Aarhus Bay, Denmark. Limnology and Oceanography 40: 908–917.
Jensen, H. S., K. J. McGlathery, R. Mario & R. W. Howarth, 1998. Forms and availability of sediment phosphorus in carbonate sand of Bermuda seagrass beds. Limnology and Oceanography 43: 799–810.
Jørgensen, B. B., 1996. Case study: Aarhus Bay. In Jørgensen, B. B. & K. Richardson (eds), Eutrophication in coastal marine ecosystem. American Geophysical Union, Washington, DC: 137–155.
Kemp, W. M., R. Batuik, R. Bartleson, P. Bergstrom, V. Carter, G. Gallegos, W. Hunley, L. Karrh, E. Koch, J. Landwehr, K. Moore, L. Murray, M. Naylor, N. Rybicki, J. C. Stevenson & D. Wilcox, 2004. Habitat requirements for submerged aquatic vegetation in Chesapeake Bay: water quality, light regime, and physical-chemical factors. Estuaries 27: 363–377.
Kemp, W. M., W. R. Boynton, J. E. Adolf, D. F. Boesch, W. C. Boicout, G. Brush, J. C. Cornwell, T. R. Fisher, P. M. Gilbert, J. D. Hagy, L. W. Harding, E. D. Houde, D. G. Kimmel, W. D. Miller, R. I. E. Newell, M. R. Roman, E. M. Smith & J. C. Stevenson, 2005. Eutrophication of Chesapeake Bay: historical trends and ecological interactions. Marine Ecology Progress Series 303: 1–19.
Koch, E. W., 2001. Beyond light: physical, geological and geochemical parameters as possible submersed aquatic vegetation habitat requirements. Estuaries 24: 1–17.
Lauersen, M., F. Gertz, J. W. Hansen, J. P. Nielsen & J. Lissner, 2004. Environmental condition in the fjords 2003. Ringkøbing Fjord and Nissum Fjord (in Danish). County of Ringkøbing Journal 8-56-3-28-02.
Luzak, C., M. A. Janquin & A. Kupka, 1997. Simple standard procedure for the routine determination of organic matter in marine sediment. Hydrobiologia 345: 87–94.
Mammou, A. B., 2006. Aménagements hydrauliques des basins exoréiques de la Tunisie. Impact sur le flux sédimentaire et la stabilité du littoral. In CIESM, 2006. Fluxes of small and medium-size mediterranean rivers: impact on coastal areas. CIESM Workshop Monograph 30, CIESM, Monaco: 55–66.
Moussa, M., L. Baccar & R. Ben Khemis, 2005. La lagune de Ghar El Melh: Diagnostic écologie et perspectives d’aménagement hydraulique. Revue Des Sciences de l’au 18: 13–26. Special.
Orth, R. J., M. L. Luckenbach, S. R. Marion, A. Kenneth, A. More & D. J. Wilcox, 2006. Seagrass recovery in the Delmarva Coastal Bays, USA. Aquatic Botany 84: 26–36.
Poulos, S. E. & M. B. Collins, 2002. Fluviatile sediment fluxes to the Mediterranean Sea: a qualitative approach and influence of dams. In Jones, S. J. & L. E. Frostick (eds), Sediment Flux to Basins: causes, controls and consequences, Vol. 191. Geological Society, London: 227–245. (Special Publication).
Ramdani, M., N. Elkhiati, R. J. Flower, J. R. Thompson, L. Chouba, M. M. Kraiem, F. Ayache & M. H. Ahmed, 2009. Environmental influences on the qualitative and quantitative composition of phytoplankton and zooplankton in North African coastal lagoons. Hydrobiologia. doi:10.1007/s10750-008-9678-4.
San Diego-McGlone, M. L., S. V. Smith & V. F. Nicolas, 2000. Stoichiometric interpretations of C:N:P ratios in organic waste materials. Marine Pollution Bulletin 40: 325–330.
Scheren, P. Å. G. M., B. Kroeze, F. J. J. O. Jonssen, L. Hadrijk & K. J. Ptosinski, 2004. Integrated water pollution assessment of the Elsié Lagoon, Ivory Coast, West Africa. Journal of Marine Systems 44: 1–17.
Shili, A., E. B. Trabelsi & N. Ben Maïz, 2002. Benthic macrophyte communities in the Ghar El Melh lagoon (Northern Tunisia). Journal of Coastal Conservation 8: 135–140.
Souissi, S., O. Daly Yahia-Kéfi & M. N. Daly Yahia, 2000. Spatial characterization of nutrient dynamics in the Bay of Tunis (south-western Mediterranean) using multivariate analysis: consequences for phyto- and zooplankton distribution. Journal of Plankton Research 22: 2039–2059.
Thompson, J. R., R. J. Flower, M. Ramdani, F. Ayache, M. H. Ahmed, E. K. Rasmussen & O. S. Petersen, 2009. Hydrological characteristics of three North African coastal lagoons: insights from the MELMARINA project. Hydrobiologia. doi:10.1007/s10750-008-9680-x.
Van Haren, R. F. J. & S. Kooijman, 1993. Application of a dynamic energy budget to Mytilus edulis (L.). Netherlands Journal of Sea Research 31: 119–133.
Zahar, Y., A. Ghorbel & J. Albergel, 2008. Impacts of large dams on downstream flow conditions of rivers: aggradation and reduction of the Medjerda channel capacity downstream of the Sidi Salem dam (Tunisia). Journal of Hydrology 351: 318–330.
Acknowledgements
The MELMARINA Project was financed by the EU Framework V INCO-Med Programme (Grant ICA3-CT2002-10009). The authors acknowledge the assistance of all the partner institutions in the project. Particular thanks are extended to those who participated in the field programme at Ghar El Melh and to Mr. R. Oueldi of Ghar El Melh town.
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Guest editors: J. R. Thompson & R. J. Flower
Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons
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Rasmussen, E.K., Petersen, O.S., Thompson, J.R. et al. Model analyses of the future water quality of the eutrophicated Ghar El Melh lagoon (Northern Tunisia). Hydrobiologia 622, 173–193 (2009). https://doi.org/10.1007/s10750-008-9681-9
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DOI: https://doi.org/10.1007/s10750-008-9681-9