Coastal protection assessment: a tradeoff between ecological, social, and economic issues

Marine coastal ecosystems are crucial to human populations in reducing disaster risk. Least Developed Countries are particularly vulnerable to the effects of climate change, such as sea-level rise and storm surges. The Mauritanian coast, West Africa, ranks among the most vulnerable worldwide to sea-level rise, and coastal communities in the National Park of Banc d’Arguin (PNBA) are particularly at risk. Here, we assessed the service of coastal protection in PNBA by (1) mapping the coastal marine ecosystems with Sentinel-2 imagery and determining their spatial wave height attenuation rates; (2) assessing the vulnerability of villages and natural habitats to coastal hazard risk; and (3) assessing the applicability of coastal protection measures in the PNBA. We found that a total of 83% of the populated coastline presents a moderate to high risk of flooding and erosion, with Iwik and R’Gueiba being the most threatened villages in the PNBA. As for the ecological risk, two low-elevated islands, which support breeding colonies of birds, are particularly vulnerable to sea-level rise. However, in other areas, the rupture in the dune cord created new lagoons that present valuable ecological and economic interests like the Lagoon of Bellaat. Improving the comprehension of wave attenuation provided by coastal habitats, combined with identifying the vulnerability and applicability of coastal protection measures, is essential for achieving the Sendai Framework for Disaster Risk Reduction goals. In the PNBA, relocation of identified villages at risk is probably the best cost-effective solution with the least disturbance to both breeding and wintering birds. Protection of coastal ecosystems will also ensure a continued provision of other ecosystem services, including food supply for sea dependent populations, and contribute to achieving the Paris Agreement and Sustainable Development Goals

Seagrass connectivity on the west coast of Africa supports the hypothesis of grazer-mediated seed dispersal

Population connectivity influences the distribution of genetic diversity and divergence along a species range, as the likelihood of extinction or differentiation increases in isolated populations. However, there is still poor understanding of the processes mediating interpopulation dispersal in marine species that are sessile and lack planktonic life stages. One such case is the seagrass species Halodule wrightii, which produces basal seeds, although detached plants can drift. Along the tropical western coast of Africa, this species occurs in distant discontinuous habitats, raising the question of how interpopulation dispersal is mediated. The species is a key source of ecosystem functions including feeding large migratory grazers. This study aims to infer whether genetic differentiation of the seagrass H. wrightii along the western coast of Africa supports a hypothesis of predominant transportation of rafting seagrass by ocean currents, versus the hypothesis of biotic vectors of dispersal. Additional hypotheses were addressed concerning range-wide clonality and genetic diversity, assessed with microsatellite markers on populations of the west coast of Africa from Mauritania to Angola. Population genetic diversity and structure were compared with predictions from biophysical models of dispersal by oceanographic currents. The genetic data revealed low divergence among most populations, in strong contrast with predictions of very low probability of connectivity mediated by currents along the western African coastline. Moderate to high genotypic diversity showed important seed recruitment, but genetic and genotypic diversities were lower at range edges. Populations north and south of the equator were differentiated, and remarkably, so were neighboring equatorial populations despite their proximity. These results reveal independent sources of colonization of meadows in these islands, which are major habitat for migratory grazing green turtles, also supporting the hypothesis of biotically mediated seed transport. The importance of seagrass for conservation of endangered macrofauna has been widely reported; here we report evidence supporting the reciprocal role, that macrofauna protection can also plays a role in long-term survival and reproductive success of seagrass.Fundação para a Ciência e Tecnologia - FCTinfo:eu-repo/semantics/publishedVersio

Flood risks in the city of Nouakchott (Mauritania)

peer reviewedAfter the drought and the desertification that affect strongly Mauritania during the years 70 and 80, the city of Nouakchott knew a spectacular demographic development. The city has widely expanded and the newcomers constructed their houses in marginal zones without planning. Several districts have been installed either in areas of salty soils as sebkha, either in sandy zones. This work permitted to analyze the relation between rains and floods, to monitor the evolution of the urban growth of Nouakchott between 1978 and 2006 and its impact on the vulnerability of the population, to map the flood risk zones and to delimit the present unviable sectors if no planning measure would be taken. Was also studied the coastal area evolution and particularly coastline modification during the period 1978-2006, by using photographs and remote sensing. The results of the work constitute an excellent tool for helping the decisions makers. It's a reliable tool for the assessment and the management of the flood risks in Nouakchott.Après la sécheresse et la désertification qui ont fortement frappé la Mauritanie dans les années 70 et 80, la ville de Nouakchott a connu un développement démographique spectaculaire. La ville s'est agrandie considérablement et les nouveaux arrivants ont construit leurs maisons dans des zones marginales sans aménagement préalable. Plusieurs quartiers se sont installés soit dans des zones dépressionnaires à sols salés sous forme de sebkha, soit dans des zones dunaires fortement ensablées. Ce travail a permis d'analyser la relation entre pluies et inondations, l'évolution de la croissance urbaine de la ville de Nouakchott entre 1978 et 2006 et son impact sur la vulnérabilité de la population. La cartographie des zones à risque d'inondations ainsi que la délimitation des secteurs non viables à l'habitat à l'heure actuelle a été établie au cas où aucune mesure d'aménagement ne serait prise. En outre, nous avons également étudié l'évolution géomorphologique du trait de côte du littoral de Nouakchott, durant la période 1978-2006, au départ de photographies et d'images satellitaires. Les résultats de ce travail constituent un outil d'aide à la décision dans le domaine d'évaluation et de gestion des risques d'inondation dans la ville de Nouakchott

Etalement urbain des villes en Afrique subsaharienne et vulnérabilité croissante face au risque d’inondation : l’exemple de Nouakchott (Mauritanie)

Après la sécheresse et la désertification qui ont fortement frappé la Mauritanie dans les années 1970 et 1980, la ville de Nouakchott a connu un développement démographique spectaculaire. En effet, la population de la capitale mauritanienne est passée de 134 704 habitants en 1977 à 899 887 habitants recensés en mars 2013. Depuis 2000, Nouakchott voit sa population augmenter de 125 personnes par semaine ; une croissance absolue jamais atteinte par le passé. La ville s’est donc agrandie considérablement et les nouveaux arrivants ont construit leurs maisons dans des zones marginales sans aménagement préalable. Plusieurs quartiers se sont installés soit dans des zones dépressionnaires à sols salés sous forme de sebkha, soit dans des zones dunaires fortement ensablées. Sur base de l’analyse de la relation entre pluies et inondations, nous avons pu déterminer que ces dernières n’étaient plus dues à des événements pluviométriques extrêmes mais bien à un aménagement du territoire non contrôlé

Impacts of climate change and anthropization on groundwater resources in the Nouakchott urban area (coastal Mauritania)

International audienc

Étalement urbain et vulnérabilité croissante face au risque d’inondation : l’exemple de Nouakchott (Mauritanie)

peer reviewedAprès la sécheresse et la désertification qui ont fortement frappé la Mauritanie dans les années 1970 et 1980, la ville de Nouakchott a connu un développement démographique spectaculaire. En effet, la population de la capitale mauritanienne est passée de 134 704 habitants en 1977 à 899 887 habitants recensés en mars 2013. Depuis 2000, Nouakchott voit sa population augmenter de 125 personnes par semaine ; une croissance absolue jamais atteinte par le passé. La ville s'est donc agrandie considérablement et les nouveaux arrivants ont construit leurs maisons dans des zones marginales sans aménagement préalable. Plusieurs quartiers se sont installés soit dans des zones dépressionnaires à sols salés sous forme de sebkha, soit dans des zones dunaires fortement ensablées

Méthodes exactes pour la détermination d'un plus long chemin DG-consistant dans des réseaux biologiques

National audienc