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Hydrobiologia

, Volume 610, Issue 1, pp 193–209 | Cite as

Limnological and ecological characteristics of tropical highland reservoirs in Tigray, Northern Ethiopia

  • Tadesse Dejenie
  • Tsehaye Asmelash
  • Luc De Meester
  • Afework Mulugeta
  • Abreha Gebrekidan
  • Sarah Risch
  • Annemie Pals
  • Katleen Van der Gucht
  • Wim Vyverman
  • Jan Nyssen
  • Jozef Deckers
  • Steven Declerck
Primary research paper

Abstract

The semi-arid highlands of Northern Ethiopia (Tigray) have numerous small reservoirs that have been created by microdams in an attempt to provide water supply for irrigation and livestock drinking. Although the reservoirs have substantial added value to residents, their use as water resource is jeopardized by eutrophication and a high occurrence of blooms of toxic cyanobacteria. So far, there is no systematic information available on the limnological and aquatic ecological characteristics of these dams. We carried out a standardized survey of 32 reservoirs and assessed a wide set of morphometric, abiotic and biotic variables. The sampling was performed during two seasons, September–October 2004 (end of the wet season/start of the dry season) and April–May 2005 (towards the end of the dry season). Using multivariate analysis, we revealed dominating patterns of variable associations and compared the variability in these patterns among seasons. According to standardized PCA and RDA analyses, the most important axis of variation was mainly represented by a gradient in nutrients and altitude that was also positively associated with phytoplankton biomass, suspended matter and oxygen concentration, and negatively with water transparency. For most variables, correlations between the wet and dry season were weak, which suggests that individual reservoirs behaved rather differently in their response to seasonal changes. Nevertheless, a Mantel correlation (r = 0.32; P = 0.035) showed a weak but significant overall concordance in the variable association patterns among seasons. A number of reservoirs became very shallow or fell dry in the dry season, a process that was associated with an increase in suspended matter and conductivity and a decrease in transparency. These reservoirs contained lower amounts of fish and tended to be less eutrophic than the deeper, permanent systems, as they had lower levels of phosphorus and chlorophyll-a. With multiple regression analysis, we constructed most parsimonious models in an attempt to explain the variation in key biotic variables: phytoplankton and cyanobacteria biomass, cladoceran biomass, fish biomass and the abundance of submerged vegetation. Phytoplankton and fish biomass tended to be positively related with the concentration of total phosphorus, whereas cladoceran biomass was not associated with nutrient concentrations. The positive association of fish and phytoplankton with nutrient concentrations suggests a bottom-up control, whereas the absence of an association between zooplankton and nutrient concentrations may be indicative for top-down control. The biomass of cyanobacteria was negatively related to the biomass of cladocerans (Daphnia), which likely reflects a top-down effect. Most reservoirs were turbid. The occurrence and abundance of macrophytes tended to be positively related to water transparency and was negatively associated to TP and the amount of livestock frequenting the reservoirs. However, macrophytes were not limited to clear-water reservoirs.

Keywords

Cyanobacteria Daphnia Garra Reservoir Zooplankton Tigray Ethiopia Tropical highland 

Notes

Acknowledgements

This study is part of the “Aquatic Ecology” project of the VLIR IUC scientific cooperation program between several Flemish universities (Belgium) and Mekelle University (Ethiopia). We thank the Flemish government for the financial support of this program, and the many people who joined us in the field or contributed by solving logistic issues. Steven Declerck is a postdoctoral researcher with the National Fund for Scientific Research, Flanders.

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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • Tadesse Dejenie
    • 1
    • 2
  • Tsehaye Asmelash
    • 3
    • 4
  • Luc De Meester
    • 2
  • Afework Mulugeta
    • 5
  • Abreha Gebrekidan
    • 5
  • Sarah Risch
    • 2
  • Annemie Pals
    • 6
  • Katleen Van der Gucht
    • 4
  • Wim Vyverman
    • 4
  • Jan Nyssen
    • 7
    • 8
  • Jozef Deckers
    • 9
  • Steven Declerck
    • 2
  1. 1.Department of BiologyMekelle UniversityMekelleEthiopia
  2. 2.Laboratory of Aquatic Ecology and EvolutionKatholieke Universiteit LeuvenLeuvenBelgium
  3. 3.Department of MicrobiologyMekelle UniversityMekelleEthiopia
  4. 4.Laboratory of Aquatic Ecology and ProtistologyGhent UniversityGentBelgium
  5. 5.Department of ChemistryMekelle UniversityMekelleEthiopia
  6. 6.Laboratory of BotanyKatholieke Universiteit LeuvenHeverleeBelgium
  7. 7.Department of Land Resources Management and Environmental ProtectionMekelle UniversityMekelleEthiopia
  8. 8.Geography DepartmentGhent UniversityGentBelgium
  9. 9.Division Forest, Nature and LandscapeKatholieke Universiteit Leuven, Geo-instituutLeuvenBelgium

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