TO STUDY SEASONAL VARIATION AND THE EFFECT OF SOME CHEMICAL CONSTITUENTS ON SPECIES COMPOSITION OF ALGAL FLORA IN THE WATER SUPPLIES OF KARACHI CITY AND ITS SURROUNDINGS

The distribution identification and effect of physico-chemical factors on species composition of algae in the water supply system of Karachi city and its surroundings was carried out. Of a total number of 136 species of phytoplankton, including 6 genera and 16 species of Cyanophyta 1 species of Chrysophyta, 18 genera and 39 species of Bacillariophyta, 20 genera 77 species of Chlorophyta, 2 genera 3 species of dinophyta were recordedA seasonal variation both in quantity and quality of algal population during summer and winter was observed. Cyanophycean algae which flourished during the summer season included Merismopedia glauca, M. punctata. M. temuissima, Microcystis aeruginosa, M. flos-aquae, Oscillatoria curviceps, O. limosa and O. tenuis. During the winter season species of Bacillariophyta viz. Synedra ulna, S. ulna var. amphirhynchus, Cymbella ventricosa, Cymbella sp., Epithemia sorex, E. sorex var. gracilis, Navicula cryptocephala, N. radiosa and species of Chlorophyceae viz. Coelastrum microporum, Oedogonium inclusum, Claaophora glomerata, species of Spirogyra, Zygema and desmids were dominantIn the water supply systems (Sources), originating from Kalri lake, Haleji lake and Hub river is not directly utilized due to preponderance of algae. The presence of which produces fishy smell and unpleasant taste. The growth of algae in the water treatment plants is controlled by chlorination, which does not completely destroy the algae. Remainder algal population is eliminated by filtration through sand filter beds. At the water treatment plants 69 filter clogging algae were collected. Of these algae Microcystis aeruginosa, Coscinodiscus sp. Synedra ulna, S. ulna var. amphirhynchus Coccnneis placentula, Cymbella ventricosa, Epithemia sorex, Novicula cryptocephala N. radiosa dna Rhopalodia gibba were predominant. Of the algae which passed through sand filter beds viz., Microcystis aeruginosa, Coscinodiscus sp., Synedra ulna var. amphirhychus, Cymbella ventricosa, Epithemia sorex and Tetraedron minimum were detected in the clean water reservoirs. At the domestic water reservoirs 21 algae were commonly recorded including Merismopedia glauca, Microcystis aeruginosa, Synedra ulna, S. ulna var. amphirhynchus, Cymbella ventricosa, Epithemia sorex and Navicula cryptocephalaOf the physico-chemical factors a temperature of 29-34 C during summer was found favourable for the growth of the species of Merismopendia, Microcystis and Oscillatoria. Whereas during winter a temperature of 18-26 C was found suitable for the species of Synedra, Cymbella, Epithemia, Navicula and green algae Coelastrum microporum, oedogonium inclusum, Cladophora glomerata, and species of Spirogyra, Zyengma and desmids. The abundant growth of algae during winter on the one hand, decreases the total hardness by the precipitation of carbonates but on the other increases the pH value due to high activity of photosynthesis. The turbidity increased in summer due to organic or inorganic concentration, heavy blooms of blue-green algae and the organic detritus of the last season. High alkalinity, sodium and nitrogen was recorded in summer with the growth of blue-green algae. The lower concentration of K and PO4 in all seasons indicate that algae requires small amount of these elements for their growth, whereas, higher concentration of Ca and Mg show that these minerals are also necessary for algae. The physico-chemical results show that water supplied to the citizens of Karachi, is within the rangeof international standardsThe ground water mostly contained diatoms viz. Coscinodiscus sp., synedra ulna, S. ulana var., amphirhynchus, Cocconeis placentula, Cymbella ventricosa, Epithemia sorex, Gomphonema gracile var. aurita, Mastogloia recta and Navicula cryptocephala etc. The physico-chemical properties of ground water shows that such water is not good for domestic use because it contained high counts of cholera, polio, typhoid and gastro-intestinal diseases are caused due to consumption of contaminated water