Phytoplankton responses to changes in macrophyte density in a tropical artificial pond in Zaria, Nigeria

The response of phytoplankton population dynamics to changes in densities of Nymphaea lotus L. and Polygonum limbatum Meisn. was studied in an artificial pond in Zaria, Nigeria, from June to November 2007. Antagonistic effects of these macrophytes on Netrium sp., Staurastrum sp., Ulothrix sp., Marssionella sp. and Closterium sp. were collinear and clearly separated from other environmental effects. Dermatophyton sp., Cyanoderma sp. and Pernia sp. were sensitive to high densities of both macrophytes, and were closely positively associated with DO and pH. Qualitative analysis confirmed the presence of glycosides, anthraquinone, saponins, steroids, triterpenes, flavonoids and alkaloids in N. lotus and P. limbatum. Fourier transform infra-red analysis peaks were recorded, confirming the presence of these allelochemical groups in both species. The observed variations in phytoplankton community structure and dynamics were closely linked to the presence of these macrophytes as well as to environmental conditions in the pond.