Studies on the effects of Hippopotamus amphibious vectored subsidies on the ecology of aquatic ecosystem

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Sokoine University of Agriculture


A study was conducted along the Great Ruaha River (GRR) at Ruaha National Park (RNP) for a period of two months (November to December 2013) with the main aim of assessing the effects of Hippopotamus amphibious vectored subsidies on the chemistry of river ecosystems and the ecology of aquatic resident within these systems. The study was done by measuring river water nutrients, physical water chemistry parameters, and stable isotope analysis of aquatic consumers. Study sites were identified in two basic treatment types: river pools containing hippos and those showing no evidence of hippo occupancy. Response parameters that were measured included total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), dissolved organic carbon (DOC), nitrate (NO3), and ammonia (NH3). Total dissolved nitrogen, total dissolved phosphorus, and nitrate were significantly elevated in hippo pools relative to non hippo pools (P<0.01). Ammonia, and dissolved organic carbon were not statistically significant between hippo and non hippo pools but their absolute levels were slightly higher in hippo pools. Physical parameters of the GRR were also assessed including measures of dissolved oxygen (DO), pH, conductivity, temperature, and chromophoric dissolved organic matter (CDOM). Dissolved oxygen, pH, and conductivity were significantly higher in the hippo pools compared to non hippo pools (P<0.001). Temperature and CDOM did not vary with hippo density (P>0.05). Stable isotopes of carbon (13C) and nitrogen (15N) were also assessed during the study to examine whether this technique could help us identify use of hippo delivered nutrients by river consumers such as fish. Carbon and nitrogen stable isotopes were not significantly different for the fish sampled in hippo and non hippo pools. This lack of difference may derive from saturation of C4 plant derived 13C in the GRR ecosystem. This study provides for the first time more insight into the influence of hippo vectored organic material in aquatic ecosystem dynamics in the GRR.


Master Thesis


Hippopotamus amphibious, Vectored subsidies, Ecology of aquatic ecosystem, Ecosystem, Aquatic ecosystem