The Degradation of the Abo-Kebena River in Addis Ababa, Etiiiopia
No Thumbnail Available
Date
1988-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
1\ study of bi 0 I (I'li c(ll an(! ciwmi ea I ch,) ract'.'ri st i CS IWS con<luctf'o on tht'
Aho-Keb~na River, a tropicJI, high altitude m'luntain river, in th~ vicinity
of the city of !\ddis I\bab~, EthitJpia. Ttl<' study WilS carried out over a one
year pr:rioo - ,July 198(j to August 19B5. Observittions wen·, made dt 20
statiuns which had similar features (If depth, substrat~ and velocity. The
20 statiuns covered the stream aver its course from one side of the city to
the other. Though the mountain riv',r \'IdS free 1)1' pollution and thc: upper
part reasonabl'y clean, l'lat"r quality "f the bVlCr part of the river
dc:t"riorated significantly, particularly during the dry season.
llrterioration of watl,r quality caus"d by organic pollution from rloillestic
dnd municipal I'/03St'~5 \'IdS eXilc'~rbat"d by low f11MS and lu\'l dilution during
the dry SG'ason. The biological determination of ~Iatl'r qual ity was marl,~
using macroinvertebrates ,'s indicators. Throughout the study period,
18,934 organisms of 52 tilXil 1'lerL' collect(;<i. The chirl)llornids \'Iere very
important const itu'~nts compri si ng !i4X of th(~ benthi c macroi nvertebrate
community. They uccurred ilt all 5t,ltions throughout the study. The sludy
demonstrilt"d the df,?cts of urgilnic IJOllutants upun str:'am communities.
Plecoptera, Ephemerupteril, Trichoptera, and Colc()pteril \'Iere restricted to
the clean upper part of thi2 river and suppressed in the lower pilrt by water
qual ity conditiJns. Oth(c~r taxa which dominated the pullut('d part of the
river l'll're the Diptera; Ctlironomidae and the Oliguchaet,); Tubifcx spp.
Limnodrilus spp. and Nais spp. 1~lung the ephemernpterans, 8iletis hArrisoni
i'ldS -ubiC]uituus througTi0i"lt the drainage. Simulium spp. \'Ier(' also abundant
in both the cleiln and tilE! polluted part 0(111(, riv,~r. Although represented
by small numbers, Limnnphora lclrvae l'I('r(, found to r'?sist heilvy organic
p')llution in the Abo-Kebena River. There was signific,)nt seasonal
variation (Students t-test) in abundance of macroinvertebrat.,s. Almost ill I
of the benthic fauna \'I(lS found to be ilffected by flol'ls. Thei r nurnl1(,rs
dcclined during the \'let season. The Orthnclild1nac, ~ricotupus spp. I'Icre an
',~xception to this. Th8Y \'Ier.? very abuntlant and <lominated th" faunil during
the ~/fJt season.Nitrilte - nitrogen, orthophosphate ilnd BOOS incrp.asr!d
progressively rlo~lIlstrearn indicating enrichment of the river. A clear
se(lsonal variation in the nutrient level of thl.? rivc:r was al so noted.
Higher cnnwntrations of nutrients \'l<?r0 recQrded during thl.' dry seilson th~n
the wet seHson. The effects of I'rganic pollution 0n the river wcrp much
more severe during the ciry seilson \'Ihen the stream flow I~as low. Possible
sites of pollution have. bl't'n identifireci. The! prl'sl'nt condition uf AboKebena
River is compared with other rlegrad(~d streams and rivers in Ilfrica.
It is fl)und thJt organic p')llution has much the Silr.1,' dfects in Ethiopia as
in other cvuntri es. Recomml'ndat ions ha ve il"en mildr~ based on the pres(,nt
data.
Description
Keywords
Biology