An attempt to evaluate the biogeochemical budget of the Nador Lagoon (Morocco)

1. DINatm= 0 (assumed) VP = 20.3 VE = -150 VP • VESE =0 • VEYE =0 VE VR = -31.83 VR SR = -1084 VSystem = 575106 m3 S System = 37 psu • t = 33 days VQ = 146.5 VR DINR = -91.51 DINSystem=5.75 mM DDIN = -26695 VQ DINQ = 62532 VG = 10.0 SOcean= 36.4 psu SR = 36.67 psu System V sys, A sys System V sys, S sys System V sys, Y sys DINOcean= 0 DINR = 2.87 VG DING = 0 Ocean • S ocean Ocean Ocean • Y ocean Land Land Land VO = 5 VO DINO = 0 (assumed) VQ, VG,VO • VQ SQ, VG SG, • VOSO = 0 • VQ YQ, VG YG, • VOYO = 0 VX (S Ocean S System)= 1084.4 VX = 6216.5 Fluxes in 106 psu-m3 yr-1 VX (DIN Ocean -DIN System)= -35744.87 • VX = -(VRSR- VGSG ) /( SOcn -SSys) VR = -(VQ+VP+VE+VG+VO) Fluxes in 103 mole yr-1 • Y = -VQYQ - VGYG - VOYO - VRYR - VX(Yocn - Ysys) Eaux marines Eauxcourantes Eaux usées DIPatm= 0 (assumed) Eaux de la nappe VR DIPR = -39.79 VR SR = -1084 DIPSystem = 1.83 Mm • DDIP = +1574 VQ DIPQ = 2743 VG DIPG = 0 DIP Ocean = 0.66 mM DIPR = 1.25 mM VO DIPO = 0 (assumed) VX (DIP Ocean -DIP System)= -7263.3 Fluxes in 103 mole yr-1 An attempt to evaluate the biogeochemical budget of the NadorLagoon (Morocco) FirdaousHalim1, GianmarcoGiordani. 2, Maria Snoussi1 1 University Mohamed V, Faculty of Sciences, Department of Earth Sciences, Avenue IbnBattota, B.P. 1014, Rabat, Morocco. Firdaous.halim@gmail.com 2 Department of Environmental Sciences, University of Parma, Italy. Giordani@nemo.unipr.it INTRODUCTION Coastal lagoons are among the most productive ecosystems but also the most exposed aquatic ecosystems to current and foreseen changes. The Nador lagoon, which is classified as RAMSAR site represents important sources of food and habitats for many species.However, the demand for space and natural resources has increased tremendously over the last decades due to increasing population, expanding agriculture, rapid urbanization and economic development around the lagoon. This paper aims to attempt a preliminary estimation of the biogeochemical budget of water, salt and nutrients (N and P) in the Nador lagoon. STUDY SITE The lagoon of Nador is located on the Mediterranean coast of Morocco (2º 45'-2º 55', 35º 10' N). It has a NW-SE oval shape and covers an area of about 115 km², with a depth not exceeding 8 m. The lagoon is separated from the sea by a narrow sandy barrier and opens into the Mediterranean through a single inlet which has undergone several modifications. In fact, during the last fifty years, the inlet evolved along the barrier in various positions along the sandy bar and with a changing cross-section (Guelorget et al., 1987). Very recently, an artificial inlet has been created in order to improve the water circulation and quality within the system. The Nador system is microtidal. Tidal amplitudes range from about 0.1 m at neap tide to about 0.5 m at spring tide (Erimesco, 1961; Brethes and Tesson, 1978). The dominant direction of the winds is W-SW from November to May, and E-NE from May to October (Tesson, 1977). Average salinity varies from 36.2 to 39 psu over the year. The climate is semi-arid with two pronounced seasons: the summer condition from May to October with an average temperature of 22.5°C and the winter season from November to April with an average temperature of 14°C (Hilmi, 2005). The rainfall is irregular and varies from 150 to 450 mm/year. The average evaporation ranges between 840 mm in winter and 1130 mm in summer (Lefebvre et al., 1997). The lagoon receives drainage mainly from Selouane and BouAreg streams that flows into the lagoon only in rainy season and from several canals used for the irrigation of the BouAreg plain, which represents the most important agricultural area of the Mediterranean coast of Morocco. Frisoni et al. (1982) have estimated the mean continental runoff between 40 to 200.106 m3/year and groundwater inputs to 18.106 m3/year. About 800 000 people inhabit the area around the lagoon (RGPH 2004), concentratedmainly in the Nador city. The main activities are agriculture and livestock. Besides, the lagoonsustains an important fishactivity for the local communities. The main sources of pollution are from agriculture and urban areas. Apartfrom the urban effluents of the city that are partly (70%) treated, all the sewageisdirectlydischargedinto the lagoonwithoutanytreatment. The total dischargewasestimatedfrom 8 000 to 13 000 m3 per day (RADEEN-NADOR). METHODOLOGY In order to establish budgetary calculations, data for water and salinity are available from various sources (Tesson,1977; Lefebvre,1997 ; Frisoni et al.,1982; Guelorget et al.,1987; Kharmiz,1989; Abouhala et al.,1995; DAFIR, 1997 ; Hilmi,2003; Hilmi,2005 and Bloundi,2005). The dissolved N and P data in the lagoon and the near Sea are available from (Abouhala et al.,1995 and Bloundi,2005), based on samples collected twice a month between June 1991 and May 1992 at 5 stations (Abouhala et al.,1995); and 69 water surface samples collected between July 2000 and September 2004 at about fifty stations (Bloundi,2005). Data on groundwater are obtained from (Frisoni et al., 1982 and Lefebre et al.1997). DIN represents NO3 + NO2 + NH4. The LOICZ Toolbox for the calculation of the BGC budget has been applied to estimate the fluxes of water, salt, P and N using a simple box model. NUTRIENT (Y)BUDGET WATER BUDGET SALT BUDGET • VPSE =0 • VPYE =0 • SR = ( SOcn +SSys) /2 • YR = ( YOcn +YSys) /2 VRSR VRYR VR VX VX= ( YOcn -YSys) RESULTS DIP BALANCE CALCULATION DIN BALANCE CALCULATION WATER & SALT BALANCE CALCULATION Conclusion In accordance with the assumptions of the model, the Nador lagoon acted as sink for DIN as DDIN was negative, and as source for DIP since DDIP was positive. The rates of nonconservative DIP and DIN fluxes can be used to estimate the apparent rate of nitrogen fixation minus denitrification (nfix-denit) as the difference between observed and expected DDIN. The annual Estimated N fixation-denitrification was estimated to be approximately: - 1,2 mmol m-² d-1.Thus the system appears to be denitrifying at a substantial rate. The calculation of the Net Ecosystem Metabolism (NEM), that is, the difference between organic carbon production (p) and respiration (r) within the system (p-r), is calculatedassuming again that organic oxidation is the primary source of nonconservative DIP flux. This rate is estimated as the Redfield ratio of the reacting organic matter (C:P = 106:1) (p-r) = -3,97 mmol m-² d-1. This negative value indicates a net mineralization of organic matter and that the Nador lagoon is a net heterotrophic system. The LOICZ budgeting model is a very useful tool to state the trophic status of the lagoon and foresee its evolution in the context of climate change. However, in the case of the Nador lagoon, the lack of time series of the basic variables didn't allow to have reliable results. The budgeting should then be considered as very preliminary and interpreted with caution. Remerciements This preliminaryworkwascarried out thanks to the scientific support of Gianmarco Giordani and thenfinancial support of START. Final workshop - START Project Maghlag. Tunisia / Bizerte 25-27 June 2012