LAUSR

Abstract Between October 2014 to September 2016 we investigated the distribution of macrophyte assemblages in relation to water quality in the south western littoral zone of Lake Tana. in situ measurements of physicochemical parameters (DO, pH, EC, TDS, temperature and Secchi depth) were accompanied by nutrient analyses for NO3-N, soluble reactive phosphate (SRP) and total phosphorus (TP). Macrophytes were collected manually using a belt transect method. Thirty macrophyte species belonging to fifteen families were identified. Emergent and amphibious plants had the maximum percentage composition at 53 % and 30 %, respectively and attained the highest relative frequency and density, followed by floating species and other forms. Redundancy analysis (RDA) indicated that the density of Azolla pinnata subsp. africana, Ceratophyllum demersum, Cyperus alopecuroides, Digitaria milanjiana, Pycreus macrostachyos, Pycnostachys coerulea and Scirpus pallidus was positively and strongly associated with pH, Secchi depth, SRP and TP whereas that of Amaranthus hypochondriacus, Cyperus papyrus, Echinochloa stagnina, Ipomoea aquatic, Panicum maximum, Sacciolepis Africana and Stuckenia pectinata was negatively and strongly associated with these variables but positively with NO3-N. The density of Brachiaria sp., Vossia cuspidate and Leersia hexandra was negatively and strongly associated with pH, SRP and TP whereas the density of Typha latifolia was positively and strongly associated with TDS and EC. The highest diversity index (H′ = 2.63) was recorded in Zegie Yiganda sampling site, which was better protected from anthropogenic impacts. In conclusion, Lake Tana is experiencing changes in physico-chemical parameters, which has favored a shift in species composition of macrophytes towards turbidity-tolerant emergent and amphibious species.