Temporal changes of sediment dynamics within the Nairobi River sub-basins between 1998-2006 time scale, Kenya

Abstract

Temporal changes of sediment dynamics within the Nairobi River sub-basins between 1998-2006 time scale, Kenya The city of Nairobi is the heart of both industrial production and the economic hub in Kenya and the Eastern Africa region. The city of Nairobi and its environs are drained by three streams, namely: Nairobi, Mathare and Ngong rivers. These streams drain areas of diverse land use activities. The land use changes in a spatial manner from the rich agricultural system through residential cum urban to industrial. The significance of these various land use systems to pollutants generation, pollution, sediment generation and hence water pollution and quality degradation is quite enormous and worth investigation. The land use changes in a spatial manner making the basin ideal for a temporal variation of sediments yields along the river profile and their impacts on the water quality status. This paper examines the results of study carried out within the basins in the years 1998-2006. The method of study involved water sampling and laboratory analysis to reveal the trends in sediment load increases downstream the investigated streams. Soil samples were also investigated to determine their relationship to soil erosion rates and sediment fluxes. The study attempts further to find the best sediment management strategies in reversing their increasing trends and restoring water quality within the basin.

A comprehensive biogeochemical record and annual flux estimates for the Sabaki River (Kenya)

“…On a seasonal basis, CH 4 concentrations tended to rise and fall with discharge (Fig. 7a), opposite to observations in the Oubangui and Côte d'Ivoire rivers where highest concentrations are observed during low-flow periods and decrease as discharge increases (Koné et al, 2010;Bouillon et al, 2012), and are likely linked to the increased supply of organic waste primed for decomposition from Nairobi. On the other hand, the highest peaks (1857-2838 nmol CH 4 L −1 ; 85 171-135 111 % saturation) were observed over the dry JJAS dry seasons of 2012 and 2013, their timing coinciding with the peaks in POC, PN and NH 4 + previously discussed and attributed to large mammalian inputs, and we suggest these short-lived dry season CH 4 peaks likely represent the decomposition of these mammalian-mediated terrestrial subsidies.…”

“…10 in Marwick et al, 2014a), and reflects the range of δ 15 N signatures of NH 4 + (+7 to +12 ‰ ; Sebilo et al, 2006) and NO 3 − (+8 to +22 ‰ ; Aravena et al, 1993;Widory et al, 2005) sourced from raw waste discharge. As highlighted earlier, around 50 % of Nairobi's population of 3 million live in slums with inadequate waste management facilities which leads to increasing water quality issues (Dafe, 2009;Kithiia and Wambua, 2010), providing an evident explanation for the POC-loaded sediment flux from the A-G-S Basin in comparison to other African river basins.…”

Dynamic seasonal nitrogen cycling in response to anthropogenic N-loading in a tropical catchment, Athi–Galana–Sabaki River, Kenya

“…Numerous informal settlements are located within the riparian fringe of the Athi River headwaters (Kithiia, 2012). Poor waste disposal and management strategies have led to increasing water quality degradation (Kithiia and Wambua, 2010), where, for example, the total quantity of water passing through the A-G-S headwater streams (36.7 × 10 6 m 3 yr −1 ) and into the main channel equates to less than the combined domestic and industrial waste discharge for the region (Kithiia, 2012).…”

bg-2017-296 - Author responses

“…The combination of high-frequency sampling and long-term monitoring of dissolved CH 4 and N 2 O concentrations in the rivers of Africa remain scarce (Borges et al, 2015a). The average and median concentrations of CH 4 in the Sabaki River (483 ± 530 nmol CH 4 L −1 and 311 nmol CH 4 L −1 respectively; n = 50) often exceeded observations in other rivers of Africa, including the mid-and lower Tana River (54-387 nmol CH 4 L −1 ; Bouillon et al, 2009), the Comoé, Bia and Tanoé rivers of Côte d'Ivoire (48-870 nmol CH 4 L −1 ; Koné et al, 2010) and the Oubangui River of Central African Republic (74-280 nmol CH 4 L −1 ; Bouillon et al, 2012). On a seasonal basis, CH 4 concentrations tended to rise and fall with discharge ( Fig.…”