Understanding the patterns and processes underlying water quality and pollution risk in West-Africa River using self-organizing maps and multivariate analyses.

Rivers are dynamic systems in complex interactions with their surrounding environments. Reliable and fast interpretation of water quality is therefore needed for sustainable river management. Unfortunately, water quality and environmental status interactions have not yet been documented sufficiently in West-Africa. This study explored the spatial-latitudinal and seasonal features of water quality along the Sô River Basin (SRB, West Africa) using self-organizing map (SOM) and principal component analysis. Twenty-two water quality variables were measured in the surface layer at 12 different sampling sites during a twenty-four-month period from July 2016 to June 2018. The results revealed three water quality groups, following an upstream-downstream pollution gradient: (1) upstream and middle reach sites with high dissolved oxygen and Secchi disk depth values, which are more suitable for the aquatic biota; (2) downstream sites with high concentrations of ammonium, biochemical oxygen demand, and heavy metals especially in flood period, reflecting both high organic and heavy metal pollution; and (3) brackish downstream sites characterized by less heavy metal and organic pollutions. No significant variation was observed between seasons. However, the SRB relatively suffered from higher risks of heavy metal contamination and organic pollution in wet seasons. Although hydroclimatic processes affect the water quality, anthropogenic inputs of point and non-point sources were identified and discussed as a more prominent factor contributing to variation in the water quality condition. These results offer insights into the water quality dynamics in river-estuary system as well as potential pollution sources, crucial for defining sanitation, and management measures.

Checklist of the fresh and brackish water snails (Mollusca, Gastropoda) of Bénin and adjacent West African ecoregions.

Currently no comprehensive checklist of fresh and brackish water gastropods from Bénin exists, and those for adjacent West African areas are outdated. Yet, such checklists provide essential biodiversity information and a consistent taxonomic and nomenclatural framework for that biodiversity. Here a first checklist of the fresh and brackish water gastropods from Bénin and adjacent West African ecoregions is presented, based on an extensive literature review and field surveys between September 2014 and June 2019 in six major fresh and brackish water ecosystems in Bénin. This inventory includes information on synonymy, species distribution in West Africa, habitats, and conservation status. The fresh and brackish water gastropod fauna includes 60 species, belonging to 28 genera and 16 families. Pachychilidae, Ampullariidae, Neritidae, and Bulinidae were the most diverse families with 9, 8, 7, and 7 species, respectively. However, literature and field data indicated that 23 species observed in West African basins that extend to Bénin do not occur in the territory of Bénin. These species were not detected in our field surveys, most likely because they are rare at collecting sites. Of the 60 species included, five are classified as "Data Deficient", 43 as "Least Concern", two as "Nearly Threatened", one as "Vulnerable", and six as "Endangered" by the IUCN, whereas the remaining three species were not evaluated. Because the taxonomy of fresh and brackish water gastropods in West Africa is still largely based on morphology, comparative molecular and taxonomic studies may result in substantial revisions of this checklist over the coming years.

Genetic characterization of Benin's wild populations of Sarotherodon melanotheron melanotheron Rüppell, 1852.

The Cichlid fish Sarotherodon melanotheron is typically found in West and Central African estuaries and lagoons. It represents a good candidate for promoting tilapia farming in brackish waters. Understanding the genetic diversity in its populations from the hydrographical basins of Southern Benin is primordial before designing selective breeding programs. For this purpose, 202 samples collected from four rivers of Southern Benin and were genotyped using 15 polymorphic microsatellite DNA markers. Each river was split up into three sampling sites. We found significant global linkage disequilibrium across the genome of natural populations of this tilapia species overall the loci. However, when the loci that display aberrant Wright's (FIS and FST) were removed from the data, a linkage disequilibrium was detected for the remaining 11 loci and became compatible with the null hypothesis. Null alleles explained at least 20.58% of FIS variation. We found a significant isolation by distance across subsamples. Effective population size averaged 210 individuals, with a range from 36 to 517 individuals. Assuming that 79% of heterozygote deficits are explained by sib mating lead to a rough estimate of rsm = 0.4 of mating rate between full sibs within S. melanotheron subpopulations. The fish size correlated positively and significantly with the observed FIS (r = 0.58; p value = 0.04806). Reproduction system (endogamy) in S. melanotheron could explain the strong heterozygote deficit observed. Our results provide technical guidance for efficient management of this tilapia species' genetic resources for breeding programs in fresh and brackish waters.

[Use of the self-organizing map (SOM) for the characterization of macrobenthic populations]. / Caractérisation des peuplements de macroinvertébrés benthiques à l'aide de la carte auto-organisatrice (SOM).

Macrobenthic organisms are much used nowadays as bio-indicators for their ability to reflect different disturbances of aquatic ecosystems. However, they have never been used to assess the ecological status of the lagoons of Benin. The current study aims at revealing the ecological state of the lagoon of Porto-Novo through the study of changes in the settlement of benthic organisms collected in this lagoon. The sampling was carried out from July 2007 to June 2009 on a frequency of four seasons of collection per year. The self-organizing map (SOM) of Kohonen has been used for various patterns of distribution of collected organisms. A discriminant analysis (AFD) has allowed the identification of the parameters that govern the patterns observed in this environment. Four groups of macrobenthic communities emerged that were well predicted (75%). The distribution of benthic macro invertebrates of this lagoon is therefore zonal, seasonal and discriminated by variables of mineralization and sediment grain size. The difference in taxonomic richness corresponds to environmental conditions of stations appearing more or less stable and highlighting a gradient of the stress on organisms. Places with unstable conditions are affected by human activities due to their proximity to homes that are enriched in organic matter. These places are full of polluted-tolerant species such as the Gastropods Potamididae, Cirratulidae Polychaetes, Diptera Chironomidae and Oligochaeta. The macrobenthic fauna, which is well differentiated in the groups, is then subjected to human disturbance.