Phytoplankton as Bio-Indicator to Assess Pollution Status of Yardantsi Reservoir, Gusau, Nigeria

Abstract

Background: Phytoplankton are hydrophytes with photosynthetic ability, they play a vital role in the aquatic food chain; the herbivorous zooplankton feed on them and in turn serve as an energy source to animals in higher trophic levels, fishes inclusive.. Yardantsi Reservoir is the main source of water for Gusau populace; it receives both organic and inorganic waste through runoffs from the catchment area. Objectives: The study aimed to determine the status / water quality and productivity of Yardantsi Reservoir, Gusau using phytoplankton as a bio-indicator. Methods: The samples were collected between May, 2015 and April, 2017 using standard methods. Four (4) groups of phytoplankton (viz; Bacillariophyta, Chlorophyta, Cyanophyta and Dinophyta) comprising eleven (11) various species were observed. Results: Bacillariophyta, Chlorophyta, Cynophyta and Dinophyta account for 27.25%, 39.29%, 11.50% and 21.96% respectively. Similarly; Bacillariophyta, Chlorophyta, Cynophyta and Dinophyta recorded 25.51%, 35.17%, 12.84% and 26.48% for the dry season and 28.36%, 41.90%, 10.65% and 19.10% for the rainy season respectively. The first two PCA components accounted for 89.6% and 9.3% respectively, making a total of 98.9% of the total percentage variance observed. Phytoplankton exhibited a positive correlation with temperature, NO₃-N, pH and dissolved oxygen; highly positive correlation with sulphur and PO₄-P; negative correlation existed with hardness, alkalinity, total dissolved solids, transparency, chloride and electrical conductivity.  Conclusions: The study revealed that the reservoir is slightly polluted. Effective management strategies such as restricting cultivation on steep slopes should be employed to improve water quality.

Keywords: Bio-indicator, Phytoplankton, Pollution, Reservoir