Dynamics of Phytoplankton and Physicochemical Features of the Ethiopian Soda Lakes Chitu and Shala, and Evaluation of the Potential of their Waters for the Production of Arthrospira (Spirulina) Fusiformis (Cyanophyceae) in Laboratory Cultures
| dc.contributor.advisor | Kifle, Demeke (PhD) | |
| dc.contributor.author | Ogato, Tadesse | |
| dc.date.accessioned | 2018-07-23T13:27:53Z | |
| dc.date.accessioned | 2023-11-09T04:20:34Z | |
| dc.date.available | 2018-07-23T13:27:53Z | |
| dc.date.available | 2023-11-09T04:20:34Z | |
| dc.date.issued | 2015-06 | |
| dc.description.abstract | Soda lakes provide great opportunity for the study and understanding of aquatic ecosystems, owing to their unique biotic assemblage of great ecological and economic values and high sensitivity to environmental changes. In addition, Arthrospira (Spirulina), an alga of high ecological values to soda lakes ecosystems and produced commercially using high-cost chemical medium as a nutritional supplement to humans, grows naturally in some of the soda lakes. In this study, physicochemical features and phytoplankton community of the soda lakes Chitu and Shala, morphology of Arthrospira fusiformis in its natural habitat and its production using waters of the soda lakes were investigated. Measured parameters of underwater light climate of both lakes depicted light-limited conditions, which were associated with the accumulation of Arthrospira in Lake Chitu and non-biological turbidity in Lake Shala. The water column of Lake Chitu exhibited superficial thermal stratification with weak vertical mixing and considerable variability of dissolved oxygen (DO). Lake Shala showed superficial thermal stratification, but with turbulently mixing and well-oxygenated water column. Inorganic nitrogen sources in the euphotic zone of both lakes were often very low or undetectable while phosphorus sources were considerably high, possibly due to their phosphatic mineral-rich rock basins. NH3 and soluble reactive phosphate (SRP) showed dramatic increase with depth in Lake Chitu due to internal loading. SiO2 was remarkably low in both lakes, which was probably associated with biological uptake, some chemical processes within the lakes and organic matter accumulation. The phytoplankton community of Lake Chitu, which was constituted by a few (15) species belonging to the algal classes Bacillariophyceae (60%), Cyanophyceae (26.7%) and Cryptophyceae (2.3%), was dominated by A. fusiformis throughout the annual cycle, accounting for up to 98% of total phytoplankton abundance. The observed high mean phytoplankton biomass (chlorophyll-a, 150 μg chl-a L-1 and dry weight, 0.26 g L-1) in Lake Chitu showed significant seasonality (P < 0.05) with higher levels occurring during the rainy season. The algal biomass and abundance were correlated strongly and positively with rainfall and negatively with alkalinity-salinity, probably suggesting that hydrological control of the salinity of the lake is the major driving force for algal dynamics in Lake Chitu. Phytoplankton community of Lake Shala, which was of relatively higher diversity (23 spp. belonging to Bacillariophyceae, Cryptophyceae, iv Cyanophyceae and Dinophyceae), was persistently dominated by Bacillariophyceae and Cryptophyceae, respectively, accounting for about 57% and 22% of the total number of species, and 28% and 69% of total phytoplankton abundance. Cryptomonas spp. were the most abundant, contributing about 59 to 95% of total phytoplankton abundance of Lake Shala, while Thalassiosira sp. was the second most abundant (1–35%). Although seasonality was not large, the observed variations in the abundance of the dominant species in this lake were associated with water transparency, SiO2, rainfall and its effects on salinity and pH. Mean algal biomass, which was generally low (17 μg chl-a L-1), also showed small seasonal variations in Lake Shala, with strong but inverse relationship with water transparency. In general, the notable variations in phytoplankton and physicochemical parameters in Lake Chitu, probably suggest its sensitiveness to environmental perturbations and that any environmental changes including increased salinization may greatly affect the key alga (A. fusiformis) and the flamingos, with eventual impairment of its ecosystem services. On the other hand, the observed small variations in the physicochemical and phytoplankton variables in Lake Shala seem to suggest the lake‟s resilience to the current level of environmental perturbations, owing to its presumably high stress absorbing capacity associated with its large size and great depth. Three distinct morphotypes of A. fusiformis, tightly coiled (H-type), spiral or loosely coiled (S-type) and intermediately coiled (C-type) were observed in Lake Chitu, with the H-type (50%) and S-type (40%) being the first and second most dominant morphotypes. The dominance of H-type and tightening of its helix pitch were strongly associated with NO3- and HCO3- deficiencies, and high levels of photosynthetically active radiation (PAR) and temperature of the lake, while the abundance of S-type was more strongly but negatively correlated with the high salinity of the lake. The variability in morphology seems to suggest that A. fusiformis undergoes morphological changes in response to environmental stresses in its natural habitat, resulting in the occurrence of various morphotypes of the same species. Comparable growth rate (μ) and biomass (B) of A. fusiformis were observed 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) (25% and 50%) supported considerably higher μ and B, which were probably associated with the reduction in pH and salinity, and provision of the limiting nutrient nitrogen in the supplemented media. The higher μ and B in SBM, probably due to some of their aggregate chemical parameters that were closer to those in the SM, and abundant SRP, 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, thereby reducing the cost of nutrients by 75% and 50%, respectivel | en_US |
| dc.identifier.uri | http://etd.aau.edu.et/handle/123456789/9862 | |
| dc.language.iso | en | en_US |
| dc.publisher | Addis Ababa University | en_US |
| dc.subject | Dynamics of Phytoplankton and Physicochemical | en_US |
| dc.subject | Features of the Ethiopian Soda Lakes | en_US |
| dc.title | Dynamics of Phytoplankton and Physicochemical Features of the Ethiopian Soda Lakes Chitu and Shala, and Evaluation of the Potential of their Waters for the Production of Arthrospira (Spirulina) Fusiformis (Cyanophyceae) in Laboratory Cultures | en_US |
| dc.type | Thesis | en_US |