Cameroon estuary complex, Cameroon

C.E. Gabche and S.V. Smith

Water and salt balance

The Cameroon estuary complex has three main rivers (Mungo, Wouri and Dibamba) with input directly into the estuary.  The volume of runoff  (V_Q) calculated from mean discharge (Table 1) gives total volumes of 120x10⁶ m³ d^-1; 20x10⁶ m³ d^-1and 170x10⁹ m³ d^-1 for annual, dry and rainy seasons, respectively.  River runoff, rainfall and evaporation with seasonal values (where available) are given in Table 1.

Total evaporation (V_E) for the dry season and rainy seasons is calculated with the assumption of mean monthly values of 100 mm for the 1,500 km² Cameroon estuary area.  This gives a mean evaporation of 5x10⁶ m³ d^-1 for both the dry and rainy seasons.  The precipitation (V_P) values for the dry and rainy seasons are obtained from rainfall for Douala.  These gave mean monthly values of 40 mm and 390 mm for the dry and rainy seasons, respectively (Table 1).  The mean precipitation values are 2x10⁶ m³ d^-1 and 20x10⁶ m³ d^-1 for the dry and rainy seasons, respectively.  Salinity values with seasonal variations at different depths and various stations (fresh, estuarine and marine) of the Cameroon estuary complex are given in Table 2.  Areas of high input of freshwater have low salinity with higher values at the Cameroon estuary due to salt water intrusion. V_G (groundwater inflows) and V_o (other inflows) like sewage are assumed to be zero.  The water exchange time (t) was 315 and 48 days in the dry and rainy seasons, respectively.

Balance of nonconservative materials

 DIP balance

The population of Douala city within the estuary estimated at 1.4 million inhabitants. The human waste is discharged directly into the system hence wastewater loading is considered an important contributor to nutrient loading to the estuary.  DIP equivalent of the domestic sewage from the population was estimated based in McGlone et al. (2000).

 Nonconservative flux of DIP (DDIP) was calculated for the Cameroon estuary. DIP fluxes are presented in Table 3.  The system is a net sink of DIP both in the dry and rainy seasons.   

 DIN balance

Waste load for DIN from the human population was considered (McGlone et al. 2000).   DIN fluxes are summarized in Table 3.   The system is a net sink in the dry season and a net source in the rainy season for DIN.

 Table 3.  Water, salt and nutrient budgets for the Cameroon estuary complex.

Stoichiometric calculation of aspects of net system metabolism

The net ecosystem metabolism (NEM = p-r) can be estimated as negative of the DDIP flux multiplied by the C:P ratio of the reacting organic matter.   If the dominant reacting material is plankton, the particulate C:P ratio is about 106:1; (p-r) is +1 mmol m^-2 d^-1 in the dry season and +2 mmol m^-2 d^-1 in the rainy season.  If it is dominantly mangrove, then the ratio may be as high as 1000:1 which gives a (p-r) of +10 mmol m^-2 d^-1 in the dry season and +20 mmol m^-2 d^-1 in the rainy season.  The system seems to be autotrophic for both seasons.

The net nitrogen fixation minus the denitrification (nfix–denit) is expressed as the difference between observed and expected DDIN.  Expected DDIN is DDIP multiplied by the N:P ratio of the reacting particulate organic matter.  The system appears to be a net nitrogen fixing; (nfix-denit) = +0.1 mmol m^-2 d^-1 in the dry season and +0.6 mmol m^-2 d^-1 in the rainy season.

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Last Updated 21 May 2006 by DPS