Trophic analysis of Lake Awassa using massbalance Ecopath model
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Date
2005-01
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Addis Ababa University
Abstract
Comparatively Lake Awassa is one of the most thoroughly studied lakes in
Ethiopia. However no attempt was made to bring the available information
together in order to see the foodweb relationship in the ecosystem. Perhaps one
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of the plausible reasons for not modeling lakes till now is lack of comprehensive
and easy-to-use model. A friendly software model, Ecopath with Ecosim (EwE),
was constructed for Lake Awassa using different published and unpublished data
that were originally studied in the lake. Several parameters were also estimated
from the present study such as primary productivity, phytoplankton biomass,
Tilapia biomass and zoobenthos. The study was conducted between November
2003-August 2004. Thirteen functional groups including two ontogenic groups
were used in the present analysis to see the trophic relationship and energy flow.
The results of the model give an overview of the resources found in the lake
simultaneously and reveal the degree of interactions. The consumers are heavily
exploited in the system as shown by high ecotrophic efficiency while the
producers including detritus are under exploited. Hence energy transfer from
lower trophic level seems very low. Flows from detritus were as important as
flows from phytoplankton, designating the importance of both detritus and
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grazing food chain in the system. Mixed Trophic Impact (MTI) analyses indicate
that phytoplankton and detritus have positive impact on most other groups. On
the other hand, herbivore zooplankton and tilapia had negative impact on
phytoplankton, the former being stronger. Lake Awassa has a low ecological
efficiency with a value of 0.001. System primary production! respiration (P!R)
ratio of Lake Awassa is 9.844 showing the lake is at developmental stage or a
young ecosystem, warning that extra care should be given to human
interventions. However, since production is high the lake can contribute in the
food self-sufficiency program of the country. This trophic model analysis also
enables us to confirm the previous works and pinpoint the critical research gaps.
Production, biomass, mortality, feeding, reproduction etc for zoobenthos, Garra sp., Labeobarbus amphigrama and Ap/ocheilichtyes sp. are open to research.
The biomass, mortality etc of Labeobarbus intermidius should also be studied.
Key words: Lake Awassa, Ecopath with Ecosim, modeling, trophic
interaction, aquatic ecosystems
Description
Keywords
Lake Awassa, Ecopath with Ecosim, modeling, trophic interaction, aquatic ecosystems