Bottom Sediment Chemistry, Nutrient Balance, and Water Birds in Small High Altitude Tropical Reservoirs in the Rift Valley, Kenya

Abstract

Water bird characteristics, nutrient loadings, and the levels of bottom sediment silicon oxide (SiO₂), aluminium oxide (Al2O3), ferric oxide (Fe₂O₃), calcium oxide (CaO), copper (Cu), phosphorus (P) and organic carbon (C) was studied in eight high altitude (2040-2640m) small shallow (0.065-0.249 km2; 0.9-3.1 m) reservoirs in the central rift valley of Kenya. The general aim was to assess the nature of the bottom sediments in relation to nutrient balance in the water bodies and their birdlife from a geographic perspective of spatial comparative analysis. The findings showed positive correlation between the levels of SiO₂, CaO and P with the levels of total-N and total-P. In addition, there was an inverse correlation between C, Al₂O₃, Cu and Fe₂O₃ in the bottom sediment and two nutrients. A total of six water bird counts across the eight sites recorded 49 species for all the reservoirs and an overall average of 60 individuals per reservoir. The counts of nine water bird species were established to increase significantly with increase in the levels of total-N and total-P. The results indicated a correlation with the levels of SiO₂, C, P, Fe₂O₃, and CaO in the bottom sediment for 12 water bird species, namely, African Fish Eagle, African Jacana, Black-headed Heron, Brack Crake, Common Teal, Great Egret, Great White Pelican, Grey Crowned Crane, Knob-billed Duck, Purple Gallinule, Ringed Plover, and Yellow-billed. The most sensitive species were the African Fish Eagle, Brack Crake, Common Teal, Great White Pelican, and Purple Gallinule. The actual impact of sediment chemistry on the utilization of reservoirs by water birds was not established and should, therefore, be an important subject for further investigation.

Keywords: Bottom Sediments; Total-N; Total-P; Tropical Reservoir; Waterbirds