Thème :
Riverine and atmospheric nutrient and particulate material inputs to the southwestern Mediterranean Sea
Présentation :
Studies of river and estuarine modifications at global or regional scales remain lacking and assessing impacts of some river or estuarine syndromes on aquatic resources is considered a first priority. In the southwestern Mediterranean Sea, atmospheric inputs of nutrients are becoming the main external source due to declining river discharge in recent decades following reservoir construction and changes in irrigation. Information on riverine and atmospheric inputs of materials is still scarce in the Mediterranean basin particularly for Algerian coastal catchments. Annaba’s coastal region is subject to atmospheric deposition under the main influences of European airflows (October-March) and African air masses with high dust loads (April-September). This region is among the wettest areas in Algeria and receives inputs from two important Algerian rivers, namely the Mafragh River and the Seybouse River. Although the wet atmospheric deposition of dissolved nutrients has been recognized as significant in the Mediterranean Sea, data on nutrient wet deposition on Algerian coasts are almost nonexistent. In addition, little is known about nutrient and material transport from Algerian coastal catchments. The present project is based on an extensive riverine and rainwater data collection during six years in the Annaba coastal area of the southwestern Mediterranean. We present the distribution and fluxes of dissolved nutrients [silicates Si(OH)4), dissolved inorganic nitrogen components (ammonia: NH4; nitrate: NO3; nitrite: NO2), dissolved organic nitrogen (DON), total dissolved nitrogen (TDN), phosphate (PO4), polyphosphate (P2O5), dissolved organic phosphorus (DOP), total dissolved phosphorus (TDP)] and particulate material [suspended particulate material (SPM), Chlorophyll a (Chl a), particulate organic carbon (POC), Particulate organic nitrogen (PON), particulate organic phosphorus (POP) and particulate biogenic silica (BSi)] into the Annaba Bay from the Mafragh and Seybouse Rivers together with the wet atmospheric deposition of dissolved nutrients. To our knowledge, this is the first assessment of the wet deposition of dissolved nutrients and of particulate biogenic silica, particulate organic carbon, suspended particulate matter and chlorophyll a in southwestern Mediterranean waters, including Algerian coastal waters. Our main objectives were to: (1) assess the relative contributions of riverine and wet atmospheric inputs of dissolved nutrients (Nitrogen, Phosphorus, Silicon) into Annaba Bay, (2) determine the relative importance of the dissolved and particulate matter transferred into the bay through the two rivers outlets and (3) assess differences in the material deliveries of the two rivers, which are differently affected by human activities.
Thème :
The zooplankton from the southeastern Mediterranean Sea: composition, abundance and biomasse
Présentation :
Coastal marine areas are of important ecological, economic and social interest and are very sensitive to anthropogenic activities. Fluctuations of rivers and sewage discharge into coastal zone induce high temporal and spatial variability of environmental factors and food conditions, which controls the metabolism, feeding behav¬ior and production of the planktonic populations. The zooplankton plays a key role in the marine food web, which constitute the major diet component of numerous peligic fishes (sardines and anchovy) and other marine consumers. Studies on the dynamic of Mediterranean zooplankton are sparse or lacking, and still far from be¬ing understood, and ba¬sic exploratory research is still needed. Concerning the zooplankton biomass, only few reviews were performed in the western and the eastern basins, and comparisons remain uneasy because of the lack of standardized sam¬pling methods and data treatment. Moreover, most investigations were carried out in various areas with specific objectives and various strategies, types of nets and mesh sizes, and different sampling depths. Since the pioneering works of Rose (1925) and Ber¬nard (1955), which were limited to the zooplankton from Algiers, very few studies have been performed in Alge¬rian coastal waters, and very little is known regarding the zooplankton community. Although there have been several studies on the phytoplankton, physical and chemical characteristics of Annaba Bay, there have only been two studies of the surface zooplankton from this area by Ounissi et al. (1998) and Khélifi-Touhami et al. (2007), who exam¬ined the copepod structure of Annaba Bay and the adja¬cent Tunisian coast. There are, however, no data on the annual distribution of zooplankton abundance, biomass, diversity and species composition. Among the published studies, there are differences in the sampling equipment, time of collection, and sampling depth of zooplankton abundance and biomass, which makes any comparison difficult. Annaba Bay is a singular coastal area (southwestern Mediterranean Sea) that receives large diffusive inputs from the Seybouse and Mafragh estuaries and has also been subjected to severe pollution problems induced by direct domestic and industrial wastes. The estuaries’ plumes are relatively limited to only several ki¬lometers, but under the flooding period, the dilution zone due to their freshwater input can reach the entrance of the bay in the north western part. From the marine side, the entrance of Annaba Bay is submitted to the Modified Atlantic Water (MAW) intrusion, which may renew and disseminate the estua¬rine and land inputs. The objectives of this project are (i) to analyze the zooplankton composition and abundance of Annaba Bay, under estuarine influences and (ii) to compare our findings with previous studies on the zooplankton structure of the bay that were conducted 20 and 10 years ago in order to reveal possible populations and environmental change and to (iii) to develop a comprehensive leaflet for the Copepoda as the major component of the marine zooplankton This study provide for the first time both com¬plete annual cycle of zooplankton in the northeastern Algerian coasts and information about the zooplankton biomass. In addition, this study may facilitate the com¬parison between different Mediterranean coastal areas, as the zooplankton was sampled by WP2 net (200 μm mesh size) and its biomass was expressed in dry weight, fol¬lowing the methods mostly used for marine zooplankton studies.