Inland valleys are agro-ecosystems whose study is necessary not only for agricultural and agro-pastoral perspectives but also for the management of natural crises such as floods and droughts. This cannot be done by ig...Inland valleys are agro-ecosystems whose study is necessary not only for agricultural and agro-pastoral perspectives but also for the management of natural crises such as floods and droughts. This cannot be done by ignoring the catchment area which circumscribes them. The present study aims at evaluating the geomorphological parameters of the basin and their influence on the hydrological functioning of the Okpara catchment in general and the lowlands in particular for a good management of the said basin. To do so, an SRTM image was exploited thanks to GIS and Remote Sensing tools to analyze the morphometric properties of this watershed with ArcGIS 10.3 software. Through the results of this study, it can be seen that the Okpara watershed is very elongated, the relief is not very uneven with a dense hydrographic network characterized by low peak flood flows. The watershed is characterized by a permeable geological formation that favours a good infiltration of surface water and limits runoff. Thus, for a good management of the catchment area from these lowlands at the head of the hydrographic network, it is important to undertake actions to improve the storage capacity and to restore the flow channels.展开更多
Surface watercourses are areas of very high ecological and heritage value. Macroinvertebrates are bioindicators of the health of aquatic ecosystems. The aim of this study was to assess the effects of dewatering and re...Surface watercourses are areas of very high ecological and heritage value. Macroinvertebrates are bioindicators of the health of aquatic ecosystems. The aim of this study was to assess the effects of dewatering and re-watering cycles on benthic macroinvertebrate (BMI) communities. Two data collections were carried out at two stations (Okpara 1 and Okpara 2) on the Okpara river before and after dewatering. Thus, 8 samples of benthic macroinvertebrates and 12 physico-chemical parameters (T°C, pH, Transparency, Depth, Conductivity, Dissolved Oxygen that were measured in situ, and BOD5, COD, NH<sub>4</sub><sup>+</sup>, NO<sub>3</sub><sup>-</sup>, NO<sub>2</sub><sup>-</sup> and PO<sub>4</sub><sup>3-</sup>) were assayed in the laboratory. Canonical Correspondence Analysis (CCA) was used to match physico-chemical data to MIB families. Shannon and Piélou diversity indices were used to determine the effects of dewatering on MIBs. The increase in temperature values of pH, BOD5, COD, NH4</sub>+</sup>, NO3</sub>-</sup>, NO2</sub>-</sup> and PO4</sub>3-</sup>, after re-watering indicates the effect of dewatering on the quality of Okpara aquatic ecosystems. The benthic macrofauna collected consisted of 62.42% insects, 0.65% crustaceans, 6.48% molluscs, 0.72% worms and 0.14% arachnids. Whereas after re-watering, 21.67% insects, 0% crustaceans, 0.22% molluscs, 7.56% worms and 0.29% arachnids were recorded. Insects, crustaceans and molluscs were more abundant before dewatering than after. This was revealed by low abundances and taxonomic richness, as well as low Shannon index values of samples collected after re-watering.展开更多
This work presents mainly, the seasonal variation of pollution by nutrients and suspended solids thresholds between the old urban core and the peripheral areas of the city of Parakou on the Okpara basin. The city of P...This work presents mainly, the seasonal variation of pollution by nutrients and suspended solids thresholds between the old urban core and the peripheral areas of the city of Parakou on the Okpara basin. The city of Parakou has been experiencing strong demographic and socio-economic growth for about two decades. A total of sixty wastewater samples from twelve sampling sites were collected in 2016 according to the AFNOR standards, between the months of March and April in the dry season, then August, September and October in the rainy season. The descriptive statistic of data (minima-maxima) indicates variations of the parameters as follows: The temperature varies between 27.05 and 30.82, the water is a highly variable pH in the dry season (5.84 < pH < 9.14;mean = 7.17) and wet (6.28 < pH < 9.38;mean = 7.45). The reduction potential is lower in rainy season (-89.50 5 respectively reach the highest ratio (55 mg/L O2 and 232.08 mg/LO2) in the dry season than in the wet season (12.00 mg/L O2 and 202.40 mg/L O2). Nitrates have reached a maximum of 12.60 mg/L in the rainy season against 5.40 mg/L in the dry season. For nitrite, yielded 3.34 mg/L against 0.45 mg/L for conversely, phosphates are at 6.45 mg/L in the dry season against 2.32 mg/L in the rainy season. The mean concentrations of suspended solids are between 40 mg/L in the rainy season and 0.52 mg/L in the dry season. From the physico-chemical characterization and the chi-square independent test, this work shows mainly two results: On the one hand, apart from phosphates, concentrations of nitrates, nitrites and suspended solids on the Okpara basin in Parakou, are higher in the rainy season than in dry season. This can be explained by the variability of soil leaching and thus shows a relative link between the quality of surface water and the hydrogeomorphic basin conditions shown by the independence test (0.456 < CC < 0.856). In addition, pollutant concentrations vary according to a decreasing gradient between the former urban core, the periphery zone and the exit of the peripheral zone.展开更多
Physiographic differences and conditions of use of water resources in anthropogenic basins explain the variability of risk to surface water. Based on the multi-criteria analysis of Saaty, the present work proposes an ...Physiographic differences and conditions of use of water resources in anthropogenic basins explain the variability of risk to surface water. Based on the multi-criteria analysis of Saaty, the present work proposes an assessment of the vulnerability of surface water through a three-factor accessibility index: the slope, the subdivision rate and the drainage density of the basin. It is observed that the topographic (slope) and urbanistic (subdivision) conditions are the most important (weighting of 59%, 34%) in front of the hydrographic condition (drainage 6%) with an overall consistency of 2%. Thus, in the Okpara basin in the city of Parakou, the analysis of the vulnerability of surface waters by the accessibility index highlights two groups. The Ganré and Kokouro basins with about 30% of their areas in the low and moderate classes and the Wonka and Dama basins in the very strong class at more than 50% of their areas.展开更多
This work presents recent data on the physico-chemical properties and the trophic status of Kpassa reservoir at eighteen locations from August 2014 to February 2015. Seventeen physico-chemical parameters were measured...This work presents recent data on the physico-chemical properties and the trophic status of Kpassa reservoir at eighteen locations from August 2014 to February 2015. Seventeen physico-chemical parameters were measured and data obtained were statistically analyzed. The descriptive statistics showed their variations (minima-maxima) as follows: pH (4.65 - 7.30), temperature (25.1°C - 29.9°C), dissolved oxygen (1 - 5.79 mg/L), oxydability (0.32 - 10.88 mg O<sub>2</sub>/L), electrical conductivity (55 - 77 μS/cm<sup>𕒵</sup>), TDS (76 - 94 mg/L), turbidity (15.70 - 274.40 NTU), transparency (0.24 - 1.55 m), suspended matter (3 - 92 mg/L), total phosphorus (0.25 - 1.90 mg/L), orthophosphate (0.08 - 0.61<sup> </sup>mg/L), nitrate (undetected 5.50 mg/L), nitrite (undetected 0.79 mg/L), ammonia (undetected 0.36 mg/L), chlorophyll a (7.20 - 2334.6 μg/L), silica (4.34 - 15.67 mg/L) and N/P ratio (0.08 - 42.62). These parameters were mainly influenced by agricultural activities and climatic conditions. The restriction or the removal of the use of chemical fertilizers in agricultural activities in Kpassa reservoir basin was recommended. The highest values of Pearson and Spearman correlations were observed across TDS and conductivity (0.967;0.951), turbidity and oxydability (0.924;0.665), turbidity and chlorophyll a (0.884;0.663), turbidity and suspended matter (0.982;0.793), suspended matter and transparency (𕒴.781;𕒴.819), suspended matter and nitrate (𕒴.813;𕒴.839), suspended matter and oxydability (0.919;0.602) and suspended matter and chlorophyll a (0.879;0.656). Carlson’s trophic state index (TSI) values varied between 36 and 66 showing that Kpassa reservoir was eutrophic in August and mesotrophic to oligotrophic during the other months of the sampling period. ANOVA and Kruskal-Wallis test indicated that there were no significant differences between sampling stations.展开更多
文摘Inland valleys are agro-ecosystems whose study is necessary not only for agricultural and agro-pastoral perspectives but also for the management of natural crises such as floods and droughts. This cannot be done by ignoring the catchment area which circumscribes them. The present study aims at evaluating the geomorphological parameters of the basin and their influence on the hydrological functioning of the Okpara catchment in general and the lowlands in particular for a good management of the said basin. To do so, an SRTM image was exploited thanks to GIS and Remote Sensing tools to analyze the morphometric properties of this watershed with ArcGIS 10.3 software. Through the results of this study, it can be seen that the Okpara watershed is very elongated, the relief is not very uneven with a dense hydrographic network characterized by low peak flood flows. The watershed is characterized by a permeable geological formation that favours a good infiltration of surface water and limits runoff. Thus, for a good management of the catchment area from these lowlands at the head of the hydrographic network, it is important to undertake actions to improve the storage capacity and to restore the flow channels.
文摘Surface watercourses are areas of very high ecological and heritage value. Macroinvertebrates are bioindicators of the health of aquatic ecosystems. The aim of this study was to assess the effects of dewatering and re-watering cycles on benthic macroinvertebrate (BMI) communities. Two data collections were carried out at two stations (Okpara 1 and Okpara 2) on the Okpara river before and after dewatering. Thus, 8 samples of benthic macroinvertebrates and 12 physico-chemical parameters (T°C, pH, Transparency, Depth, Conductivity, Dissolved Oxygen that were measured in situ, and BOD5, COD, NH<sub>4</sub><sup>+</sup>, NO<sub>3</sub><sup>-</sup>, NO<sub>2</sub><sup>-</sup> and PO<sub>4</sub><sup>3-</sup>) were assayed in the laboratory. Canonical Correspondence Analysis (CCA) was used to match physico-chemical data to MIB families. Shannon and Piélou diversity indices were used to determine the effects of dewatering on MIBs. The increase in temperature values of pH, BOD5, COD, NH4</sub>+</sup>, NO3</sub>-</sup>, NO2</sub>-</sup> and PO4</sub>3-</sup>, after re-watering indicates the effect of dewatering on the quality of Okpara aquatic ecosystems. The benthic macrofauna collected consisted of 62.42% insects, 0.65% crustaceans, 6.48% molluscs, 0.72% worms and 0.14% arachnids. Whereas after re-watering, 21.67% insects, 0% crustaceans, 0.22% molluscs, 7.56% worms and 0.29% arachnids were recorded. Insects, crustaceans and molluscs were more abundant before dewatering than after. This was revealed by low abundances and taxonomic richness, as well as low Shannon index values of samples collected after re-watering.
基金NICHE-BEN-167 project focused financial support to the implementation of field activities and analysis of samples.
文摘This work presents mainly, the seasonal variation of pollution by nutrients and suspended solids thresholds between the old urban core and the peripheral areas of the city of Parakou on the Okpara basin. The city of Parakou has been experiencing strong demographic and socio-economic growth for about two decades. A total of sixty wastewater samples from twelve sampling sites were collected in 2016 according to the AFNOR standards, between the months of March and April in the dry season, then August, September and October in the rainy season. The descriptive statistic of data (minima-maxima) indicates variations of the parameters as follows: The temperature varies between 27.05 and 30.82, the water is a highly variable pH in the dry season (5.84 < pH < 9.14;mean = 7.17) and wet (6.28 < pH < 9.38;mean = 7.45). The reduction potential is lower in rainy season (-89.50 5 respectively reach the highest ratio (55 mg/L O2 and 232.08 mg/LO2) in the dry season than in the wet season (12.00 mg/L O2 and 202.40 mg/L O2). Nitrates have reached a maximum of 12.60 mg/L in the rainy season against 5.40 mg/L in the dry season. For nitrite, yielded 3.34 mg/L against 0.45 mg/L for conversely, phosphates are at 6.45 mg/L in the dry season against 2.32 mg/L in the rainy season. The mean concentrations of suspended solids are between 40 mg/L in the rainy season and 0.52 mg/L in the dry season. From the physico-chemical characterization and the chi-square independent test, this work shows mainly two results: On the one hand, apart from phosphates, concentrations of nitrates, nitrites and suspended solids on the Okpara basin in Parakou, are higher in the rainy season than in dry season. This can be explained by the variability of soil leaching and thus shows a relative link between the quality of surface water and the hydrogeomorphic basin conditions shown by the independence test (0.456 < CC < 0.856). In addition, pollutant concentrations vary according to a decreasing gradient between the former urban core, the periphery zone and the exit of the peripheral zone.
文摘Physiographic differences and conditions of use of water resources in anthropogenic basins explain the variability of risk to surface water. Based on the multi-criteria analysis of Saaty, the present work proposes an assessment of the vulnerability of surface water through a three-factor accessibility index: the slope, the subdivision rate and the drainage density of the basin. It is observed that the topographic (slope) and urbanistic (subdivision) conditions are the most important (weighting of 59%, 34%) in front of the hydrographic condition (drainage 6%) with an overall consistency of 2%. Thus, in the Okpara basin in the city of Parakou, the analysis of the vulnerability of surface waters by the accessibility index highlights two groups. The Ganré and Kokouro basins with about 30% of their areas in the low and moderate classes and the Wonka and Dama basins in the very strong class at more than 50% of their areas.
文摘This work presents recent data on the physico-chemical properties and the trophic status of Kpassa reservoir at eighteen locations from August 2014 to February 2015. Seventeen physico-chemical parameters were measured and data obtained were statistically analyzed. The descriptive statistics showed their variations (minima-maxima) as follows: pH (4.65 - 7.30), temperature (25.1°C - 29.9°C), dissolved oxygen (1 - 5.79 mg/L), oxydability (0.32 - 10.88 mg O<sub>2</sub>/L), electrical conductivity (55 - 77 μS/cm<sup>𕒵</sup>), TDS (76 - 94 mg/L), turbidity (15.70 - 274.40 NTU), transparency (0.24 - 1.55 m), suspended matter (3 - 92 mg/L), total phosphorus (0.25 - 1.90 mg/L), orthophosphate (0.08 - 0.61<sup> </sup>mg/L), nitrate (undetected 5.50 mg/L), nitrite (undetected 0.79 mg/L), ammonia (undetected 0.36 mg/L), chlorophyll a (7.20 - 2334.6 μg/L), silica (4.34 - 15.67 mg/L) and N/P ratio (0.08 - 42.62). These parameters were mainly influenced by agricultural activities and climatic conditions. The restriction or the removal of the use of chemical fertilizers in agricultural activities in Kpassa reservoir basin was recommended. The highest values of Pearson and Spearman correlations were observed across TDS and conductivity (0.967;0.951), turbidity and oxydability (0.924;0.665), turbidity and chlorophyll a (0.884;0.663), turbidity and suspended matter (0.982;0.793), suspended matter and transparency (𕒴.781;𕒴.819), suspended matter and nitrate (𕒴.813;𕒴.839), suspended matter and oxydability (0.919;0.602) and suspended matter and chlorophyll a (0.879;0.656). Carlson’s trophic state index (TSI) values varied between 36 and 66 showing that Kpassa reservoir was eutrophic in August and mesotrophic to oligotrophic during the other months of the sampling period. ANOVA and Kruskal-Wallis test indicated that there were no significant differences between sampling stations.
