Changing hydro-ecological dynamics of rivers and deltas of the Western Indian Ocean : anthropogenic and environmental drivers, local adaptation and policy response

This paper details common characteristics of the rivers flowing into the Western Indian Ocean as well as their specificities, the changes affecting their hydro-ecological rhythms, and their consequences downstream, especially in the deltas. In the river systems of the Western Indian Ocean, the flood pulse is the engine of productivity through the direct relationship between flood extent and ecosystem production. Large scale land conversions and the construction of dams create salt water intrusion and catchment degradation. On a multi-decadal time scale, the current approach is not sustainable. Coastal wetland systems are rapidly losing their value: between 1997 and 2011 swamps and floodplains lost 64% of their surface area, while tidal marshes and mangroves lost 22% globally

Dossier : Des recherches participatives dans la production des savoirs liés à l’environnement – Recherches participatives en Tanzanie : un observatoire local pour un dialogue autour de la gestion des territoires et de l’eau

Un observatoire local participatif a été mis en place à partir de 2001 dans le District du Rufiji en Tanzanie, à l’initiative d’un projet de développement et d’une équipe de recherche. Ce dispositif a permis la collecte et le partage de données environnementales (sur l’eau, la pluie, la pêche, l’agriculture et l’alimentation) entre les différents acteurs de la gestion de l’eau et du territoire. Les modalités de collecte, de mise en commun et de discussion des résultats au cours d’ateliers organisés régulièrement sont décrites dans cet article. À partir de cette expérience de recherche participative, menée dans un contexte où le dialogue entre paysans et gouvernement local est peu fréquent, tendu, voire conflictuel, nous discutons des enjeux, des intérêts et des écueils des recherches participatives

Recherches participatives en Tanzanie : un observatoire local pour un dialogue autour de la gestion des territoires et de l’eau

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Carbon stable isotopes suggest that hippopotamus‐vectored nutrients subsidize aquatic consumers in an East African river

© 2015 McCauley et al. The common hippopotamus, Hippopotamus amphibius, transports millions of tons of organic matter annually from its terrestrial feeding grounds into aquatic habitats. We evaluated whether carbon stable isotopes (δ13C) can be used as tracers for determining whether H. amphibius-vectored allochthonous material is utilized by aquatic consumers. Two approaches were employed to make this determination: (1) lab-based feeding trials where omnivorous river fish were fed a H. amphibius dung diet and (2) field sampling of fish and aquatic insects in pools with and without H. amphibius. Lab trials revealed that fish fed exclusively H. amphibius dung exhibited significantly more positive δ13C values than fish not fed dung. Fish and aquatic insects sampled in a river pool used for decades by H. amphibius also exhibited more positive δ13C values at the end of the dry season than fish and insects sampled from an upstream H. amphibius-free reference pool. Fish sampled in these same pools at the end of the wet season (high flow) showed no significant differences in δ13C values, suggesting that higher flows reduced retention and use of H. amphibius subsidies. These data provide preliminary evidence that δ13C values may be useful, in certain contexts, for quantifying the importance H. amphibius organic matter

Carbon stable isotopes suggest that hippopotamus‐vectored nutrients subsidize aquatic consumers in an East African river

© 2015 McCauley et al. The common hippopotamus, Hippopotamus amphibius, transports millions of tons of organic matter annually from its terrestrial feeding grounds into aquatic habitats. We evaluated whether carbon stable isotopes (δ13C) can be used as tracers for determining whether H. amphibius-vectored allochthonous material is utilized by aquatic consumers. Two approaches were employed to make this determination: (1) lab-based feeding trials where omnivorous river fish were fed a H. amphibius dung diet and (2) field sampling of fish and aquatic insects in pools with and without H. amphibius. Lab trials revealed that fish fed exclusively H. amphibius dung exhibited significantly more positive δ13C values than fish not fed dung. Fish and aquatic insects sampled in a river pool used for decades by H. amphibius also exhibited more positive δ13C values at the end of the dry season than fish and insects sampled from an upstream H. amphibius-free reference pool. Fish sampled in these same pools at the end of the wet season (high flow) showed no significant differences in δ13C values, suggesting that higher flows reduced retention and use of H. amphibius subsidies. These data provide preliminary evidence that δ13C values may be useful, in certain contexts, for quantifying the importance H. amphibius organic matter