Nitrate and ammonium levels of some water bodies and their interaction with some selected properties of soils in Douala metropolis, Cameroon

The present study examined the nitrate (NO3-) and ammonium (NH4+) levels of Rivers Wouri and Dibamba and some streams that feed them. The interaction of NO3- and NH4+ with some soil properties was also investigated. It was necessitated by the usage of these rivers for livelihood, despite the deposition of discharges into these streams. Twenty eight (28) surface water and four soil samples were collected from various sites within the Douala metropolis. The water was analysed for pH, electrical conductivity (EC), NO3-, NH4+ while the soil was analysed for particle size and cation exchange capacity (CEC). In both cases, standard methods were used. The NO3- and NH4+ levels were higher than the WHO threshold levels in some sites. Nitrate and NH4+ levels of 341.6 and 632.8 mg/l, respectively, were observed in some sites in Dibamba River despite the high level of clay in this area. The values in the Wouri River were low, contrary to the low level of clay in this area. This trend was also reflected in the streams that feed both rivers. The NH4+/NO3- molar ratio was low in areas proxy to the industries reflecting industrial source of  pollution. The continuous use of water from Rivers Wouri and Dibamba for domestic purposes is variably unsafe and needs attention.Key words: Nitrate, ammonium, water bodies/quality, soils, Douala metropolis

Contribution of some water bodies and the role of soils in the physicochemical enrichment of the Douala-Edea mangrove ecosystem

The effect of enrichment of water bodies could be of serious crises to the mangrove ecosystem. Changes in physicochemical properties of some water bodies in the Douala-Edea mangrove ecosystem was investigated alongside the potential role of soils in controlling these parameters. Water and soil samples within the Douala industrial zones were collected in February 2010 and analysed using standard methods. The concentrations of cations and chlorides (Cl-) in the rivers increased from upstream to downstream and with depth. These parameters were not distinct with other anions which showed higher fluctuations around confluences. Many anomalies were obtained in streams and wells at vicinity of the industries. Mean Cl- concentrations in streams and wells around River Wouri (135.1 and 57.9 mg/l, respectively) were higher than those around River Dibamba (59.3 and 38,2 mg/l, respectively). A low retention capacity of the soils was observed by the non significant (P > 0.05) relationship between the clay fraction and cation exchange capacity (CEC). This makes the mangrove  ecosystem vulnerable to the increase nutrient from anthropogenic activities as indicated by the occurrence of Nypa Palms (Nypa fructicans) and Water Hyacinths (Echhornia cassipes). It is therefore imminent that the Douala-Edea Mangrove Ecosystem is being degraded.Key words: Soils, water, physicochemical properties, mangrove ecosystem