Abstract
Lake Hawassa is currently impinged by the various human activities in its watershed. This could create favourable conditions for the invasive macrophytes like water hyacinth attacking Lake Tana and Koka. Hence, identification of the impacts of pollution on the macrophytes species diversity, distribution and coverage is very important. In doing so, rapid bioassessment method in five pollution entry points, where major socio-economic activities prevail around the lake is applied. Thirty six samples were taken, following three transect lines, approximately equidistant from each other, and from each sampling site, onshore, up to the end of the macrophytes spreading into the lake, using rake. A total of 120 samples were collected and speciation was done using standard identification keys and photographs. Macrophytes coverage were approximated and different biotic indices were calculated for comparison between the sampling sites. The maximum distance of the macrophytes is 200m and minimum is 30m. The minimum distance was recorded around Tikur Wuha (30-100m); the only river flowing into the lake and maximum is at Amora Gedel (80-200m); the fish market area. The five species of macrophytes covering 8% of the lake are Paspalidium germinatum, Nymphaea caerulea, Typha angustifolia, Potamogeton schweinfurthii, and Cyperus exaltatus. The highest diversity (H’=1.25) is observed around Dore Bafano site and lowest is at Tikur Wuha (H’= 0.53). The variation observed between these extreme Shannon diversity index values were ascribed to their relative species richness of Tikur Wuha and Dore Bafano (R=4 and 5 respectively) and evenness (E=0.38 and 0.78 respectively). There was greater organic pollution loads carried by the Tikur Wuha River when compared to other sample sites. One the other hand, all the sample sites have more than 75% Sorenson Similarity Index; indicating the impact of pollution between the sample sites is not that much different. Even though there are no invasive macrophytes species at this time, the disparity in diversity of the species supported at each specific site are one indication of the pollutants irregularly supporting the specific macrophytes. It is better to stop the pollutants prospectively than trying to abandon the invasive species after their existence.
Key Words: Pollutants, Macrophytes, Invasive Species, Community structure
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