One of the important functions of the wetland is the retention of
catchment nutrients and improving lacustrine water quality. This study analyzed
how much nutrients were retained in the Nyashishi wetland, southern part of
Lake Victoria, and went further to analyze the processes which were responsible
in the reduction of nutrients. Three major processes were analysed in this
study, namely nutrients uptake by three macrophyte species (Eichhornia crassipes, Cyperus papyrus and Typha domingensis) dominating the Nyashishi wetland, nitrification
and denitrification processes. The study demonstrated high nutrients retention
especially phosphorus nutrients of which up to 98% were retained. In some
occasions, particularly for nitrogen nutrients, there was 0% retention
especially during wet season. In some other instances, the inflow exceeded the
outflow meaning that, more nutrients were generated by the wetland itself. Among
the three processes analyzed, nutrients uptaken by macrophytes were more
efficient in reducing nutrients in wetland water. Biological nitrification and
denitrification which are believed to be the major pathway for ammonia removal
in both natural and constructed wetlands were less important in this study.
Among the macrophyte species, Eichhornia
crassipes demonstrated higher uptake rate than the other two species
possibly due to its high turnover rate. This ability can be exploited in
removing excess nutrients from runoff by frequent harvesting of the mature
plants.
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