This study addresses the different biogeochemical parameters that control the dynamics of Hg, which is a less-studied metal in the Ebrié Lagoon. During two hydrological seasons, the dry season and ...the rainy season, we regularly sampled and analysed various compartments (e.g. sediments and fishes (
Tilapia
sp.)) of the lagoon. Thus, the physicochemical parameters were measured in situ (e.g. temperature, pH, salinity, redox potential and dissolved oxygen, total dissolved organic carbon, nitrates and sulphates), and the microbiological parameters (e.g. cultivable cells, total enzymatic activity and catabolic activity) were measured to establish the seasonal variations in the links between Hg and biogeochemical parameters through multivariate statistical analyses. The bioavailability of Hg from an unpolluted site was studied by comparing the ratios of fish and sediment. The results indicated that the seasons influenced the different biogeochemical factors, although for some factors, the variations were not significant. This influence was more pronounced in the dry season than in the rainy season. The impact of microbial activities and organic matter on Hg dynamics was observed in all seasons. However, other factors, such as pH, temperature, salinity, Eh and sulphates, influenced the dynamics of Hg only in the dry season.
Climate change has had strong impacts on water resources over the past decades in Côte d’Ivoire, but these impacts on hydrological extremes remain largely unknown in most watersheds. Thus, this work ...aimed to evaluate the trends and breakpoints in extreme discharge characteristics of five watersheds in Côte d’Ivoire over the period 1970 to 2017. Seven indexes were selected, namely the 5-day maximum flow (QX5-days), peak discharge (Qmaxan), maximum monthly discharge (VCX30), annual minimum discharge (Qminan), average monthly discharge (QMNA), discharge day rate (VCN7), and characteristic of low discharge (WFD). The analysis was done using the modified Mann–Kendall (MMK) test and the standard normal homogeneity test at a 5% significance level for heterogeneous and homogeneous periods of data. The results for the heterogeneous and homogeneous periods were similar, with a predominance of non-significant trends for high discharge, except for the VCX30 index, which showed a significant upward trend at Kahin station. A decreasing trend for QX5-days was found at Loboville station. The variables Qminan, QMNA, VCN7, and WDF show significant upward trends of 33%, 16%, 50%, and 33% for the heterogeneous stations, respectively. A significant breakpoint in almost all variables was obtained, with a strong decrease after 2008. Some differences between the results from the heterogeneous and homogeneous periods of data were found and discussed. This study can help in understanding the behaviour of past hydrological extremes in the study area and in planning for further studies in the future.
The Sassandra Basin, like most regions of Côte d’Ivoire, is increasingly affected by droughts that involve many environmental, social and economic impacts. This basin is full of several amenities ...such as hydroelectric dams, hydraulic and agricultural dams. There is also a strong agricultural activity. In the context of climate change, it is essential to analyze the occurrence of droughts in order to propose mitigation or adaptation measures for water management. The methodological approach consisted initially in characterizing the dry sequences by the use of the SPI (Standardized Precipitation Index) and secondly in determining the probabilities of occurrence of successive dry years using by Markov chains 1 and 2. The results indicate that most remarkable droughts in terms of intensity and duration occurred after the 1970s. A comparison of Markov matrices 1 and 2 between the period considered 1953–2015 with the periods 1953–1970 and 1971–2015 shows a profound change in the distribution of droughts at the different station. Thus, the probability of having two successive dry years is greater over the period 1970–2015 and is accentuated to the Southern and Northern regions (probabilities ranging from 71% to 80%) of the basin. Over the 1970–2015 period, the probability of obtaining three successive dry years is significantly high in this watershed (between 20% and 70%).
Climate change is impacting water users in many sectors: water supply, farming, industry, hydropower, fishing, housing, navigation and health. Existing situations, like population growth, movement of ...populations from rural to urban areas, poverty and pollution can aggravate the impacts of climate change. The aim of the study is to evaluate the vulnerability of different water user groups to climate change and define communities’ adaptation strategies in the Comoe River Basin. Information was collected on communities’ concerns and perception on changes in climate and potential adaptation measures and strategies. Results show that 95 % of the sample in the study communities had heard of it and are aware that climate change is occurring. They have been experiencing changes in economic activity and cropping pattern, reduced water level in rivers, crop failure, delay in cropping season, new pests and diseases, food insecurity, drop in income and decline in crop yield. Results also show that communities employ various adaptation strategies including crops diversification, substitution and calendar redefinition, agroforestry, borrowing from friends and money lenders and increasing fertilizer application.
Extreme rainfall events are meteorological hazards that cause great damage and many casualties in the world. This paper examines the trends in extreme rainfall from 10 sub-daily time series and 44 ...daily time series in Côte d’Ivoire. Rainfall data were converted into indices. In total, six (6) indices were used for daily extreme rainfall and one (1) index for sub-daily extreme rainfall (15 to 240 min). Two statistical tests for trend detection were used to evaluate the possible trend in these precipitation data. The first is a Mann-Kendall non-parametric trend test, used to evaluate the existence of monotonic trends. The second is a linear regression method, based on a parametric approach to trend detection. Results show that very few statistically significant decreasing trends can be detected at the sub-daily and daily timescales. Some decreasing trends in extreme rainfall events were localized in the south and southeast. These results could enhance the implementation of adaptation systems to flood risk.
A study of the unconfined Continental Terminal aquifer in Abidjan District, located in a coastal sedimentary basin in Southern Côte d’Ivoire (West Africa), is conducted. This aquifer is the principal ...source of drinking water for the city of Abidjan. The water quality of the aquifer is affected by anthropogenic sources of pollution, such as scattered deposits of solid and liquid waste of all kinds. Additionally, the proliferation of gas stations, including potential tank leakage, must be considered in the event of an accident. To ensure the effective protection and management of the Abidjan groundwater, this work assesses the groundwater contamination risk of the Abidjan aquifer by hydrocarbons such as benzene. To achieve this objective, a numerical groundwater model that included the geological and hydrogeological data of the Abidjan aquifer was constructed with FEFLOW 7.1. A predictive simulation of groundwater flow coupled with the transport of dissolved benzene deposited on the soil surface at the N’Dotré and Anador gas stations was performed. The initial concentrations of dissolved benzene were 43.12 mg/L and 14.17 mg/L at the N’Dotré and Anador sites, respectively. The results revealed that a threshold concentration of 0.001 mg/L was reached after 44 years and two months at borehole ZE11, which is located four kilometers downgradient from the source. The maximum peak concentration of 0.011 mg/L was reached at this point after 47 years and two months. In this region, 14 other boreholes could be threatened by dissolved benzene pollution based on the simulation.
This study aims to assess future trends in monthly rainfall and temperature and its impacts on surface and groundwater resources in the Bandama basin. The Bandama river is one of the four major ...rivers of Côte d’Ivoire. Historical data from 14 meteorological and three hydrological stations were used. Simulation results for future climate from HadGEM2-ES model under representative concentration pathway (RCP) 4.5 and RCP 8.5 scenarios indicate that the annual temperature may increase from 1.2 °C to 3 °C. These increases will be greater in the north than in the south of the basin. The monthly rainfall may decrease from December to April in the future. During this period, it is projected to decrease by 3% to 42% at all horizons under RCP 4.5 and by 5% to 47% under RCP 8.5. These variations will have cause an increase in surface and groundwater resources during the three periods (2006–2035; 2041–2060; 2066–2085) under the RCP 4.5 scenario. On the other side, these water resources may decrease for all horizons under RCP 8.5 in the Bandama basin.
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