Tadesse Fetahi - Academia.edu (original) (raw)

Papers by Tadesse Fetahi

Research paper thumbnail of Greening a Tropical Abijata-Shala Lakes National Park, Ethiopia -A Review

The aim of this review is to assess and document the status of Abijata-Shala Lakes' National Park... more The aim of this review is to assess and document the status of Abijata-Shala Lakes' National Park (ASLNP), to investigate the possible causes for the water level reduction of Lake Abijata and to promote sustainable utilization of the Park. The Park was established to protect and conserve large number of water birds that use Lake Abijata as feeding and Lake Shala as nesting and breeding grounds. Actually, Lake Shala is the continent's most important breeding colony of great white pelicans. The Park also provides wintering ground and maintenance station for large number of birds including from Southern African, Sub-Saharan and Palaearctic species. Consequently, the Park was submitted to the Ramsar Convention on wetlands as an international important candidate site. However, this natural heritage is currently deteriorating due to human encroachment, grazing by cattle, uncontrolled water abstraction and other anthropogenic activities. Since the 1980s, the water level of Lake Abijata has significantly dropped, fishery has totally collapsed, and birds such as Lesser Flamingo (Phoeniconaias minor Geoffroy) and Great White Pelican (Pelecanus onocrotalus roseus) have been migrating to nearby lakes. Briefly, the lake is shrinking (so far greater than about 100 km 2) and facing imminent threat of collapse obliterating the existence of the Park. As a result, the Park is one of IBAs (Important Bird and Biodiversity Areas) in danger sites, which are priority sites for immediate action. To improve this deteriorating condition of the Park, I demonstrate resources use of the Park within the framework of green economy, which protects ecosystem services and utilizes natural resources sustainably. Lastly, a few recommendations for management measures are outlined as mechanisms to protect the ecosystems and the park.

Research paper thumbnail of Greening a Tropical Abijata-Shala Lakes National Park, Ethiopia - A Review

Journal of Ecosystem & Ecography, 2016

Research paper thumbnail of Plankton communities and ecology of tropical lakes Hayq and Awasa, Ethiopia

Research paper thumbnail of Evaluation of growth and biomass production of Arthrospira (Spirulina) fusiformis in laboratory cultures using waters from the Ethiopian soda lakes Chitu and Shala

Journal of Applied Phycology, 2014

The cost of nutrient media is the major challenge for biomass production of Spirulina. Although m... more The cost of nutrient media is the major challenge for biomass production of Spirulina. Although much effort has been made to use enriched seawater for the cultivation of this microalga, little attention has been given to the potential of water of soda lakes. In this study, growth (μ, day −1 ) and biomass production (B) of Arthrospira fusiformis cultivated using waters of the soda lakes Chitu and Shala with or without supplementation were evaluated. Comparable μ and B values were achieved in both Lake Chitu water-based media (CBM) and Lake Shala water-based media (SBM), with slightly higher values in the latter. Both CBM and SBM supplemented with the standard Spirulina medium (SM) by 25 % and 50 % supported considerably higher μ and B. The pH and salinity of the cultures showed significant variations (P<0.05) among the media and had considerable effect on μ and B. The observed higher μ and B were probably associated with the reduction in pH and salinity of the supplemented media due to addition of bicarbonate-carbonates and dilution, and provision of the limiting nutrient nitrogen. The higher μ and B in SBM may have resulted from some of their aggregate chemical parameters, which were closer to those in the SM, and abundant PO 4 -P. This seems to suggest that Lake Shala water is more conducive to Arthrospira. We contend that 25 % and 50 % supplemented Lake Shala water can be preferably used to produce Arthrospira biomass, thereby reducing the cost of nutrients by 75 % and 50 %, respectively.

Research paper thumbnail of Trophic analysis of Lake Awassa using mass-balance Ecopath model

Research paper thumbnail of Trophic Interactions in Lake Tana, a Large Turbid Highland Lake in Ethiopia

Developments in Environmental Modelling, 2012

Research paper thumbnail of Key drivers for phytoplankton composition and biomass in an Ethiopian highland lake

Limnologica - Ecology and Management of Inland Waters, 2014

We studied the temporal phytoplankton community pattern of the deep crater Lake Hayq in the highl... more We studied the temporal phytoplankton community pattern of the deep crater Lake Hayq in the highlands of Ethiopia from October 2007 to October 2008. Earlier sporadic surveys indicated that the phytoplankton community was predominantly characterized by heavy diatoms, which characteristically suffer from rapid sedimentation. The trophic status of Lake Hayq was reported to have changed from oligotrophic to eutrophic in 1992. The present study addresses the potential reasons for the diatom dominance as well as causes of the trophic change. Net and integrated water samples were used for determination of physico-chemical parameters and phytoplankton biovolumes. Our results revealed that diatoms and chlorophytes dominated during most of the study period in Lake Hayq and seem to be favored by the mixing regime of the water body, which can be described as partial atelomixis with daily mixing of the epilimnion maintaining the algae within the euphotic depth via regular re-suspension. However, the epilimnion may be decoupled from the hypolimnion by a seasonal chemocline. Nutrients were not limiting in the lake with an overall mean concentration of soluble reactive phosphorus of 22 g L −1 and total phosphorus of 58 g L −1 and of dissolved inorganic nitrogen of 305 g L −1 , with ammonium being the primary form. In the 1940s only diatoms were reported, but since the 1990s other phytoplankton groups and taxa have become relevant. Canonical correspondence analysis showed that chlorophytes were mainly associated with nutrients and rainfall, euglenophytes with elevated alkalinity and the diatoms with silica and zooplankton. Chlorophyll a as measure of total phytoplankton biomass was significantly influenced by seasonality and underwater light supply, reflecting the significant role of atelomixis in persistent occurrence of heavy taxa in the epilimnion. The lake is still categorized as a eutrophic system, demonstrating that the trophic change reported in 1992 was not short-lived. In addition to changes in the catchment the eutrophication process was probably primarily triggered by a previous introduction of Tilapia in the lake, causing a cascading effect in the food-web interactions. This implied that the phytoplankton composition and biomass of this tropical deep tropical lake can be controlled through biomanipulation, as has been demonstrated for temperate lakes.

Research paper thumbnail of Zooplankton community structure and ecology of the tropical-highland Lake Hayq, Ethiopia

Limnologica - Ecology and Management of Inland Waters, 2011

Lake Hayq, a highland lake in Ethiopia, was stocked with Tilapia fish (Oreochromis niloticus) in ... more Lake Hayq, a highland lake in Ethiopia, was stocked with Tilapia fish (Oreochromis niloticus) in late 1970s, offering an opportunity to study the effect of fish predation in a natural lake. Since 1930s, some limnological surveys have been done sporadically documenting a change in zooplankton composition including the disappearance of cladocerans, hypothesizing the stocked planktivorous fish could be a cause. Nevertheless, no detailed research was conducted to identify potential effects of fish stocking predominantly due to its remote location. The article presents data about zooplankton composition, abundance and biomass done between October 2007 and January 2009 on short-time intervals including the underlying limnological variables. The zooplankton community was depauperate comprising two copepods, three cladocerans, and six rotifers taxa, as typical for tropical lakes. Total mean standing biomass of all crustacean zooplankton was 237 mg dry mass m −3 , which gave Lake Hayq an intermediate position when compared with other tropical lakes. Of copepods, Thermocyclops ethiopiensis was almost an exclusive species, and its temporal variation was influenced by food supply and water temperature. We refute the hypothesis that Tilapia was the cause for the seasonal disappearance of cladocerans, and attribute it to the adverse effect of episodic mixing. Nevertheless, the planktivorous fish probably plays a key role in structuring the cladocerans in particular the large-sized Daphnia magna. In January 2008, we observed a massive planktivorous fish mortality that triggered high algal biomass, which was later grazed by large-sized D. magna demonstrating the trophic cascade hypothesis in a natural ecosystem.

Research paper thumbnail of Trophic analysis of Lake Awassa (Ethiopia) using mass-balance Ecopath model

Ecological Modelling, 2007

A user-friendly software model, Ecopath with Ecosim, version 5.0 Beta, was used to construct ener... more A user-friendly software model, Ecopath with Ecosim, version 5.0 Beta, was used to construct energy flow and mixed trophic impact (MTI) for the Lake Awassa ecosystem (Ethiopia). We used data from the literature and also several parameters were estimated from the present study done from November 2003-August 2004. Thirteen functional groups including two ontogeny ones were used in the present analysis, which assessed the trophic relationship, energy flow and interactions between them. The producers particularly phytoplankton and detritus are under exploited; hence energy transfer from lower trophic levels is low. On the contrary, all consumers have ecotrophic efficiency (EE) close to 1 indicating that consumers are heavily exploited in the system. Flow from detritus was as important as flow from phytoplankton. Flow from both herbivorous and carnivorous zooplankton to consumers was high. MTI analyses indicate that phytoplankton and detritus have positive impact on most other groups while zoobenthos has negative impact on some groups. Lake Awassa has low ecological efficiency with a value of 0.00144 for the gross efficiency of the fisheries. The system primary production/respiration (P/R) ratio of Lake Awassa is 5.834 showing that the lake is at developmental stage, with high autotrophy, and some attention should be given to human impacts. This trophic model analysis also enabled us to confirm/refute previous studies and pinpoint critical gaps in the present knowledge about Lake Awassa.

Research paper thumbnail of Food web structure and trophic interactions of the tropical highland lake Hayq, Ethiopia

Ecological Modelling, 2011

We generated a mass-balance model to figure out the food web structure and trophic interactions o... more We generated a mass-balance model to figure out the food web structure and trophic interactions of the major functional groups of the Ethiopian highland Lake Hayq. Moreover, the study lay down a baseline data for future ecosystem-based investigations and management activities. Extensive data collection has been taken place between October 2007 and May 2009. Ecotrophic efficiency (EE) of several functional groups including phytoplankton (0.8) and detritus (0.85) was high indicating the utilization of the groups within the system. However, the EE of Mesocyclops (0.03) and Thermocyclops (0.30) was very low implying these resources were rather a 'sink' in the trophic hierarchy. Flows based on aggregated trophic level sensu Lindeman revealed the importance of both phytoplankton and detritus to higher trophic levels.

Research paper thumbnail of Greening a Tropical Abijata-Shala Lakes National Park, Ethiopia -A Review

The aim of this review is to assess and document the status of Abijata-Shala Lakes' National Park... more The aim of this review is to assess and document the status of Abijata-Shala Lakes' National Park (ASLNP), to investigate the possible causes for the water level reduction of Lake Abijata and to promote sustainable utilization of the Park. The Park was established to protect and conserve large number of water birds that use Lake Abijata as feeding and Lake Shala as nesting and breeding grounds. Actually, Lake Shala is the continent's most important breeding colony of great white pelicans. The Park also provides wintering ground and maintenance station for large number of birds including from Southern African, Sub-Saharan and Palaearctic species. Consequently, the Park was submitted to the Ramsar Convention on wetlands as an international important candidate site. However, this natural heritage is currently deteriorating due to human encroachment, grazing by cattle, uncontrolled water abstraction and other anthropogenic activities. Since the 1980s, the water level of Lake Abijata has significantly dropped, fishery has totally collapsed, and birds such as Lesser Flamingo (Phoeniconaias minor Geoffroy) and Great White Pelican (Pelecanus onocrotalus roseus) have been migrating to nearby lakes. Briefly, the lake is shrinking (so far greater than about 100 km 2) and facing imminent threat of collapse obliterating the existence of the Park. As a result, the Park is one of IBAs (Important Bird and Biodiversity Areas) in danger sites, which are priority sites for immediate action. To improve this deteriorating condition of the Park, I demonstrate resources use of the Park within the framework of green economy, which protects ecosystem services and utilizes natural resources sustainably. Lastly, a few recommendations for management measures are outlined as mechanisms to protect the ecosystems and the park.

Research paper thumbnail of Greening a Tropical Abijata-Shala Lakes National Park, Ethiopia - A Review

Journal of Ecosystem & Ecography, 2016

Research paper thumbnail of Plankton communities and ecology of tropical lakes Hayq and Awasa, Ethiopia

Research paper thumbnail of Evaluation of growth and biomass production of Arthrospira (Spirulina) fusiformis in laboratory cultures using waters from the Ethiopian soda lakes Chitu and Shala

Journal of Applied Phycology, 2014

The cost of nutrient media is the major challenge for biomass production of Spirulina. Although m... more The cost of nutrient media is the major challenge for biomass production of Spirulina. Although much effort has been made to use enriched seawater for the cultivation of this microalga, little attention has been given to the potential of water of soda lakes. In this study, growth (μ, day −1 ) and biomass production (B) of Arthrospira fusiformis cultivated using waters of the soda lakes Chitu and Shala with or without supplementation were evaluated. Comparable μ and B values were achieved in both Lake Chitu water-based media (CBM) and Lake Shala water-based media (SBM), with slightly higher values in the latter. Both CBM and SBM supplemented with the standard Spirulina medium (SM) by 25 % and 50 % supported considerably higher μ and B. The pH and salinity of the cultures showed significant variations (P<0.05) among the media and had considerable effect on μ and B. The observed higher μ and B were probably associated with the reduction in pH and salinity of the supplemented media due to addition of bicarbonate-carbonates and dilution, and provision of the limiting nutrient nitrogen. The higher μ and B in SBM may have resulted from some of their aggregate chemical parameters, which were closer to those in the SM, and abundant PO 4 -P. This seems to suggest that Lake Shala water is more conducive to Arthrospira. We contend that 25 % and 50 % supplemented Lake Shala water can be preferably used to produce Arthrospira biomass, thereby reducing the cost of nutrients by 75 % and 50 %, respectively.

Research paper thumbnail of Trophic analysis of Lake Awassa using mass-balance Ecopath model

Research paper thumbnail of Trophic Interactions in Lake Tana, a Large Turbid Highland Lake in Ethiopia

Developments in Environmental Modelling, 2012

Research paper thumbnail of Key drivers for phytoplankton composition and biomass in an Ethiopian highland lake

Limnologica - Ecology and Management of Inland Waters, 2014

We studied the temporal phytoplankton community pattern of the deep crater Lake Hayq in the highl... more We studied the temporal phytoplankton community pattern of the deep crater Lake Hayq in the highlands of Ethiopia from October 2007 to October 2008. Earlier sporadic surveys indicated that the phytoplankton community was predominantly characterized by heavy diatoms, which characteristically suffer from rapid sedimentation. The trophic status of Lake Hayq was reported to have changed from oligotrophic to eutrophic in 1992. The present study addresses the potential reasons for the diatom dominance as well as causes of the trophic change. Net and integrated water samples were used for determination of physico-chemical parameters and phytoplankton biovolumes. Our results revealed that diatoms and chlorophytes dominated during most of the study period in Lake Hayq and seem to be favored by the mixing regime of the water body, which can be described as partial atelomixis with daily mixing of the epilimnion maintaining the algae within the euphotic depth via regular re-suspension. However, the epilimnion may be decoupled from the hypolimnion by a seasonal chemocline. Nutrients were not limiting in the lake with an overall mean concentration of soluble reactive phosphorus of 22 g L −1 and total phosphorus of 58 g L −1 and of dissolved inorganic nitrogen of 305 g L −1 , with ammonium being the primary form. In the 1940s only diatoms were reported, but since the 1990s other phytoplankton groups and taxa have become relevant. Canonical correspondence analysis showed that chlorophytes were mainly associated with nutrients and rainfall, euglenophytes with elevated alkalinity and the diatoms with silica and zooplankton. Chlorophyll a as measure of total phytoplankton biomass was significantly influenced by seasonality and underwater light supply, reflecting the significant role of atelomixis in persistent occurrence of heavy taxa in the epilimnion. The lake is still categorized as a eutrophic system, demonstrating that the trophic change reported in 1992 was not short-lived. In addition to changes in the catchment the eutrophication process was probably primarily triggered by a previous introduction of Tilapia in the lake, causing a cascading effect in the food-web interactions. This implied that the phytoplankton composition and biomass of this tropical deep tropical lake can be controlled through biomanipulation, as has been demonstrated for temperate lakes.

Research paper thumbnail of Zooplankton community structure and ecology of the tropical-highland Lake Hayq, Ethiopia

Limnologica - Ecology and Management of Inland Waters, 2011

Lake Hayq, a highland lake in Ethiopia, was stocked with Tilapia fish (Oreochromis niloticus) in ... more Lake Hayq, a highland lake in Ethiopia, was stocked with Tilapia fish (Oreochromis niloticus) in late 1970s, offering an opportunity to study the effect of fish predation in a natural lake. Since 1930s, some limnological surveys have been done sporadically documenting a change in zooplankton composition including the disappearance of cladocerans, hypothesizing the stocked planktivorous fish could be a cause. Nevertheless, no detailed research was conducted to identify potential effects of fish stocking predominantly due to its remote location. The article presents data about zooplankton composition, abundance and biomass done between October 2007 and January 2009 on short-time intervals including the underlying limnological variables. The zooplankton community was depauperate comprising two copepods, three cladocerans, and six rotifers taxa, as typical for tropical lakes. Total mean standing biomass of all crustacean zooplankton was 237 mg dry mass m −3 , which gave Lake Hayq an intermediate position when compared with other tropical lakes. Of copepods, Thermocyclops ethiopiensis was almost an exclusive species, and its temporal variation was influenced by food supply and water temperature. We refute the hypothesis that Tilapia was the cause for the seasonal disappearance of cladocerans, and attribute it to the adverse effect of episodic mixing. Nevertheless, the planktivorous fish probably plays a key role in structuring the cladocerans in particular the large-sized Daphnia magna. In January 2008, we observed a massive planktivorous fish mortality that triggered high algal biomass, which was later grazed by large-sized D. magna demonstrating the trophic cascade hypothesis in a natural ecosystem.

Research paper thumbnail of Trophic analysis of Lake Awassa (Ethiopia) using mass-balance Ecopath model

Ecological Modelling, 2007

A user-friendly software model, Ecopath with Ecosim, version 5.0 Beta, was used to construct ener... more A user-friendly software model, Ecopath with Ecosim, version 5.0 Beta, was used to construct energy flow and mixed trophic impact (MTI) for the Lake Awassa ecosystem (Ethiopia). We used data from the literature and also several parameters were estimated from the present study done from November 2003-August 2004. Thirteen functional groups including two ontogeny ones were used in the present analysis, which assessed the trophic relationship, energy flow and interactions between them. The producers particularly phytoplankton and detritus are under exploited; hence energy transfer from lower trophic levels is low. On the contrary, all consumers have ecotrophic efficiency (EE) close to 1 indicating that consumers are heavily exploited in the system. Flow from detritus was as important as flow from phytoplankton. Flow from both herbivorous and carnivorous zooplankton to consumers was high. MTI analyses indicate that phytoplankton and detritus have positive impact on most other groups while zoobenthos has negative impact on some groups. Lake Awassa has low ecological efficiency with a value of 0.00144 for the gross efficiency of the fisheries. The system primary production/respiration (P/R) ratio of Lake Awassa is 5.834 showing that the lake is at developmental stage, with high autotrophy, and some attention should be given to human impacts. This trophic model analysis also enabled us to confirm/refute previous studies and pinpoint critical gaps in the present knowledge about Lake Awassa.

Research paper thumbnail of Food web structure and trophic interactions of the tropical highland lake Hayq, Ethiopia

Ecological Modelling, 2011

We generated a mass-balance model to figure out the food web structure and trophic interactions o... more We generated a mass-balance model to figure out the food web structure and trophic interactions of the major functional groups of the Ethiopian highland Lake Hayq. Moreover, the study lay down a baseline data for future ecosystem-based investigations and management activities. Extensive data collection has been taken place between October 2007 and May 2009. Ecotrophic efficiency (EE) of several functional groups including phytoplankton (0.8) and detritus (0.85) was high indicating the utilization of the groups within the system. However, the EE of Mesocyclops (0.03) and Thermocyclops (0.30) was very low implying these resources were rather a 'sink' in the trophic hierarchy. Flows based on aggregated trophic level sensu Lindeman revealed the importance of both phytoplankton and detritus to higher trophic levels.