环境与分析毒理学

Physicochemical Parameters and Planktonic Species as Indicators to Assess Water Quality of River Basin and Winam (Nyanza) Gulf of Lake Victoria Catchment, Kisumu County, Kenya (East Africa)

Abstract

Manohar S

Presence (+) or absence (-) of planktonic species is the direct indication of differences in physicochemical characteristics of water because all living microorganisms appear, survive, develop and multiply in suitable specific habitats within an aquatic ecosystem. Planktonic species as indicators with relation to physicochemical parameters were studied to assess water quality of ten selected (S1-S10) sampling stations along Nyalenda swamp (S1), River Kisat (S2-S5) and part of Winam (Nyanza) Gulf (S6-S10) within Lake Victoria Catchment in Kisumu County, Kenya (East Africa). There are 14 genera (Amphora, Aulacoseira, Closterium, Cyclotella, Cymbella, Diatoma, Fragillaria, Gomphocymbella, Navicula, Nitzschia, Pinnularia, Stephomodiscus, Surillela and Synedra) composed of 28 planktonic species. During the field study, Genus Nitzschia is represented by its five species but only four species N. lucastris; N. palea; N. recta and N. sub-acicularis together with other three genus and four species which are Cymbella cistula; Cymbella sp; Diatoma hiemiale; Navicula granatum are present with 100% frequency in all the ten sampling stations (S1-S10) and very well adapted within wide range of pH, dissolved oxygen, conductivity, turbidity, alkalinity, total nitrogen and phosphorus levels. Six species belong to five genera: Aulacoseira ambigua; Aulacoseira nyassensis; Cyclotella kutzinghiana; Diatoma elongatum; Navicula sp; and Surilella ovalis appeared with 80% frequency. There are six genera: Amphora, Cyclotella, Cymbella, Fragillaria, Navicula and Synedra represented by two species each, while other five genera including Closterium, Gomphocymbella, Pinnularia, Stephomodiscus and Surillela are represented with one single species each. There are two species of genus Amphora but only one Amphora sp appeared with 70% frequency. Three planktonic species: Nitzschia dessipata, Synedra cunningtonii, and Synedra ulna are with 60% frequency; three species: Amphora ovalis; Fragilaria aethiopica; and Stephomodiscus astraca appear with 50% frequency; two species: Aulacoseira schroidera and Cyclotella ocellata are with 30% frequency; and three species: Closterium aciculare, Diatoma valgare, and Pinnularia viridis appeared with 20% frequency and lastly, other two remaining species: Fragillaria longissimi and Gomphocymbella beccari are present only in sampling station (S5) with 10% frequency. Each planktonic species is an indicator species of its own low or high levels of physicochemical parameters. Study revealed that mean monthly values of physicochemical levels of pH, dissolved oxygen, alkalinity and silicate show significant difference (p=0.001 ≤ 0.05) but electrical conductivity (381.25 μS/cm to 839.65 μS/cm), turbidity (32.37 NTU to 134.98 NTU), total nitrogen (388.56 μg/l to 908.88 μg/l), phosphorus (329.21 μg/l to 1246.38 μg/l) levels are higher than permissible standards of WHO, EU, KEBS and NEMA. Based on these results, these water bodies are polluted and not good source for drinking water. It is recommended that planktonic species should be used in the field as quick bio-indicator(s) to assess the water quality of any global aquatic ecosystem(s).