Mengistu, Seyoum(Professor)Kassa, Yezbie2018-07-242023-11-092018-07-242023-11-092016-06http://etd.aau.edu.et/handle/123456789/9903Nutrient dynamics plays an important role in establishment and proliferation of macrophytes in freshwater bodies. Recently Lake Tana has experienced some undesirable ecological changes due to decrease in water level, increasing trend of sedimentation and silt load(with loading rate of 8.96-14.84 million tons of soil per year) and invasion by the exotic weed, Eichhornia crassipes(Water hyacinth).With a view to come up with scientific information usable in the protection of aquatic resources,this study was carried out between 2011 to 2014 to assess the macrophyte species composition, biomass and diversity in Lake Tana in relation to abiotic factors and the nutrient uptake and storage dynamics of some species in constructed wetlands and their overall water quality improvement in a natural Yitamot wetland near Bahir Dar. Macrophytes were collected manually using a belt transect method and physicochemical parameters were measured in situ using a YSI 556 multi-probe system. Selected nutrients (SRP, TP. Nitrate) and metals (K, Na, Ca, Mg, Mn, Fe, Cu, Zn, Al, Cd, As, Cr) were analyzed using standard methods from water, sediment and plant tissue. In Lake Tana, a total of 30 species of macrophytes which belonged to 15 families were identified in the south western littoral zone and 41 species that belonged to 20families in the north eastern littoral zone of the lake. The emergent vegetation had the highest percentage composition (83 %) and attained the highest relative frequency and density, followed by floating and other forms in the south western littoral zone whereas in the north eastern zone,Eichhornia crassipes(Water hyacinth)was the dominant macrophyte. Tissue TN and TP content varied significantly between species and plant parts (paired sample T-test, P< 0.01) and leaves of all macrophyte species stored more nutrients than the stems. Results of RDA indicated that Nitrate, SRP, TP, pH and Secchi depth were among the factors that had significant impact on the diversity, distribution, biomass and plant tissue nutrient contents of the macrophytes in the lake. Azolla africana,Cyperus alopecuroides, Ceratophyllum demersum, Cyperus macrostachyos and Digitaria milanjiana,were almost restricted to sites where there was higher SRP and TP and Echinochloa stagnina, Brachiaria sp. and Phragmites karkato sites where there was higher nitrate concentration and Ceratophyllum demersum was mainly restricted to sites with high Secchi depth reading. Studies done in the natural wetland of Yitamot indicated that water quality was improved as the levels of DO (1.54 to 5.01 mg/l) and pH (5.70 to 7.61) significantly increased (p < 0.05 ANOVA) and TSS (0.41to 0.04), Turbidity (276.40 to 10.80 NTU) and COD (207.00 to 5.25 mg/l) significantly decreased (p < 0.05 ANOVA) to optimal levels at the outlet due to uptake by macrophytes. Nutrients were removed from the natural wetland via assimilation by vegetation, sediment adsorption or pore water retention. The higher concentration of nitrogen and phosphorus of aboveground tissue of almost all macrophyte species studied in Yitamot natural wetland (% TN ranged from 3.70 to 12.13 % N g DWand %TP ranged from 0.26 -to 1.69 % g DW) was higher than the value for emergent and floating-leaved plants in natural wetlands, which suggests that these macrophytes have a higher nitrogen and phosphorus retention capacity and can contribute to overall water quality improvement. However, in the influent water (S1), most of the parameters except temperature, EC and TDS were beyond the Ethiopian effluent allowable discharge limits into water courses, despite high rates of nutrient retention (for nitrogen species; 99.85% for NO2-N, 99.29% for TN, for phosphorus species: 89.21% for SRP, 95.27% for TP) in the wetland. The heavy metals such as As, Cr, Cu and Fe were not removed in the wetland and were also higher than the maximum allowable concentration ranges for fisheries and aquatic life. This indicated that heavy metals could cause adverse health effect to end users unless removed by additional treatment processes before they entered the wetland Further study in experimental treatment beds in HSSFCWshowed that the progressive increase in the plant density, shoot length and stem diameter was positively correlated with the nutrient removal efficiency of the two macrophyte species, which had maximum removal efficiency of 58% for nitrate and 84% for phosphate.Pollutant removal efficiency differences were statistically significant (p < 0.05) between planted and unplanted treatment beds for PO43-. In conclusion, the in-situand experimental data obtained indicate that the dynamics of nutrients has great impact on composition, biomass anddiversity of the macrophyte species in Lake Tana, and the high nutrient uptake and storage capacity of some macrophytes can potentially contribute to the overall water quality improvement in natural and constructed wetland systems. The increasing trend inconcentration of nutrients and reduction in transparency and water level could favor the dominance of turbidity-tolerant floating and emergent macrophytes in Lake Tana.Macrophyte EcologyNutrient Dynamics and Water Quality of the Littoral Zoneand Yitamot WetlandLake TanaEthiopiaThesis