The ecological condition of Lake Tinishu Abaya was assessed using benthic macroinvertebrates as well. The results from this aspect of the study showed that a total of 5735 benthic macroinvertebrate specimens comprising of 23 taxa were collected from all the study sites. There was spatial effect on the number and distribution of benthic individuals (p <0.05). It was high at Dacha riverside (n=2089) followed by Bobodo riverside (n=1145), Reference site (n= 963), Badober riverside (n= 859), and Maingate side (n=679). The abundance of benthic communities significantly varied between the study seasons (p<0.05). Higher individuals were observed during the wet season (n=3583) than in the dry season (n=2152). The Hemiptera family were the predominant macroinvertebrates that contributed the largest number (n=2546) of the total samples followed by Diptera (n=878), Coleoptera (n=835, 14.56%) and Gastropoda (n=631). The Ephemeroptera (n=172), Hirudinae (n=335) and Oligochates (n=116) were represented by low number of animals. The majority (about 70%) of the benthic communities of Lake Tinishu Abaya are composed of pollution tolerant species as compared to the presence of pollution sensitive ones (<30%) in most of the sampling sites. This indicated that the existence of organic pollution and thus Lake Tinishu Abaya is undergoing environmental stresses. This obviously calls for participatory and interdisciplinary actions of watershed management and wise use of aquatic resources with compliance to commonly set agenda of sustainable use of natural resources.

The present study was undertaken to investigate the photosynthetic productivity and biomass of phytoplankton for Lake Tinishu Abaya to observe the potentiality of the lake water for fish production. The study was carried out from January to December 2016. For the analysis of various physicochemical parameters, water samples collection was taken from two predefined sampling stations (open-water and nearshore). Biomass of phytoplankton was measured as concentration of chlorophyll a. Primary productivity of phytoplankton was measured at the open station within the Euphotic depth using lightdark bottle technique. It was observed from the results that the light-saturated rate of photosynthesis (Amax), ranged from 0.62 g C m-3 h-1 to 2.02 g C m-3 h-1 and biomass-specific rate of photosynthetic productivity at light saturation (Pmax) ranged 0.02 g C (mg Chl a)-1 h-1) to 0.106 g C (mg Chl a)-1 h-1). The hourly integral photosynthetic production (∑A), varied between 0.247 g C m-2 h-1 and 1.022 g C m-2 h-1, whereas the calculated pattern of variation for the daily integral rates of photosynthesis (ΣΣA) was ranged 5.43 g C m-2 d-1 to 9.194 g C m-2 d-1. The concentration of phytoplankton biomass (chlorophylla) was varied from 18.97mg/L to 65.05 mg/L. Based on the results of the study on various physicochemical factors, photosynthetic productivity and biomass of phytoplankton, it was concluded that the water of Lake Tinishu Abaya was chemically and biologically productive which supports most aquatic lives, production of fish, and other related multidimensional uses.

The ultimate objective of this study was, to explore community structure and biomass of zooplankton in relation to key environmental drivers to bear out the productivity of Lake Tinishu Abaya. Zooplankton samples collection was carried out for a year from January to December 2016 from two sampling sites (open and shore) using 30 µm mesh size net within the euphotic depth. Biomass of zooplankton was anticipated using length-weight regressions adjusted for the representative microcrustacean and biovolume of Rotifera from linear dimensions applied to simple geometric formula appropriate to body shape. In parallel, in-situ and laboratory measurements of the various physicochemical factors were performed using the standardized method. The results of the present study are given strongly generalized that Rotifera had the highest number of species (11 species) followed by Cladocera (5 species) and Copepods (2 species). Diversity parameter, the Shannon diversity index was higher for Rotifera (2.45) than cladocerans (2.395) and copepods (2.384). The mean total biomass of copepods, cladocerans, and Rotifera were 174.4, 46.76 and 13.67 µg/L at open site and 101.8, 51.35 and 10.9 µg/L at shore site, respectively. Physicochemical factors responsible for the observed variations in the biological features of the lake generalized that the lake water was fresh, well oxygenated, slightly warm, alkaline, very turbid, and with relatively high inorganic nutrients. The presence of fairly high diversity, abundance, and biomass of zooplankton in the study shows that the ecosystem of Lake Tinishu Abaya is chemically, physically and biologically productive which supports most of the aquatic life.

The present study was undertaken to investigate the photosynthetic productivity and biomass of phytoplankton with respect to changes in various physicochemical factors for Lake Tinishu Abaya (Ethiopia) to observe the potentiality of the lake water for fish production and other multiple designated water uses. The study was carried out for a year from January to December 2016. For the analysis of various physicochemical parameters, water samples collection was taken from two pre defined sampling stations (open-water and near shore). Biomass of phytoplankton was measured as concentration of chlorophyll a. Primary productivity of phytoplankton was measured at the open station in the euphotic depth using light-dark bottle technique with measuring O 2 concentration and its value was converted to carbon contents. It was observed from the results that the light-saturated rate of photosynthesis (A max), ranged from 0.62 g C m-3 h-1 to 2.02 g C m-3 h-1 and Biomassspecific rate of photosynthetic productivity at light saturation (P max) ranged from 0.02 g C (mg Chl a)-1 h-1) to 0.106 g C (mg Chl a)-1 h-1). The hourly integral photosynthetic production (∑A), varied between 0.247 g C m-2 h-1 and 1.022 g C m-2 h-1 , whereas the calculated pattern of variation for the daily integral rates of photosynthesis (ΣΣA) values was ranged from a minimum of 5.43 g C m-2 d-1 to a maximum of 9.194 g C m-2 d-1. The concentration of phytoplankton biomass (chlorophyll-a) was varied from a minimum of 18.97mg/L to a maximum of 65.05 mg/L. The various physicochemical factors responsible for the observed temporal variations in the physical, chemical and biological features of the lake are discussed and generalized that the lake water was well oxygenated, slightly warm, alkaline, contained more TSS, and EC, very turbid and low transparency. The lake water was fresh based on TDS value. Most of the inorganic nutrients were relatively higher and supports most aquatic lives. Based on the results of the study on various physicochemical factors, photosynthetic productivity and biomass of phytoplankton, it was concluded that the water of Lake Tinishu Abaya was a productive which supports the life of most aquatic lives, production of fish, and other related multidimensional uses.

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