Biomass and net aboveground primary productivity of macrophytes in relation to physico-chemical factors in the littoral zone of Lake Ziway, Ethiopia

摘要

Biomass. and net aboveground primary productivity of the macrophyte community was assessed at seven sites near the shore of Lake Ziway between August 2010 and July 2011 with the Weigert and Evans method. Typha latifolia (813.3 +/- 27.8 g DW m(-2)) and Cyperus papyrus (795.1 +/- 189 g DW m(-2)) were dominant in terms of biomass although their distribution was restricted to only a few parts of the lake. The productivity of these macrophytes was also found to be higher (2394 and 2196 g DW m(-2) yr(-1), respectively) than other macrophytes in the lake. Although Arundo donax and Potamogeton schweinfurthii had higher relative density and frequency than other macrophytes in the lake, their biomass and productivity were found to be low. Redundancy analysis suggested that relatively high concentration of soluble reactive phosphate, nitrate, total phosphorus, and total Kjeldahl nitrogen concentration in the sediment were correlated with high biomass and production of the macrophytes. pH was inversely correlated with most of the macrophytes which suggested that high pH of the lake may negatively influence the productivity and biomass of the macrophytes. Even though macrophytes seem to contribute more production (carbon) to the system than phytoplankton in Lake Ziway, their biomass and productivity is still low compared to other freshwater systems. Low nutrient levels in the lake system may be limiting the productivity and biomass of the macrophytes in the lake.