Microbiological analysis of the waters of lake Victoria in relation to the invasion of the water hyacinth, Eichhornia crassipes (Mart.) solms: a case study of the lake Shores of Mwanza Municipality.

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University of Dar es Salaam
Physico-chemical properties of sediment and water were analyzed from six stations in Mwanza municipality along the shores of Lake Victoria. Parameters which were analyzed included pH, dissolved oxygen, temperature, surface light intensity, conductivity and Secchi depths. All samples were analyzed for phosphate-phosphorus (P04 P), nitrate-nitrogen (N03-N), dissolved trace metals and ions. The mouth of Mirongo River and water hyacinth-infested stations were observed to be the most polluted, as indicated by higher concentrations of phosphate-phosphorus (P04-P), nitrate-nitrogen (N03-N) and trace metals as compared to offshore open water areas. The least polluted station was the control station. Major sources of pollution included municipal sewage, floodwater containing agro-chemicals especially fertilizers, agroindustrial wastewaters and manure from intensive livestock farming contributed significantly to the pollution load in Lake Victoria. Low dissolved oxygen (DO) levels were observed in the water column under the water hyacinth plants which caused precipitation of metals which then settled in the sediments. The recorded values of the physico-chemical parameters and limits set for surface waters for domestic and recreational purposes by international water quality bodies suggest that the shores of Lake Victoria along the study area are polluted. It should be noted that the study was carried out in an extremely complex ecosystem, where indeed there could be many factors affecting the parameters studied. The presence or absence of the water hyacinth may be one of the variables in addition to others which could have varied as well. The biotic characteristics of the nearshore waters of Lake Victoria are also described. The objective was to evaluate biomass of aerobic and anaerobic bacteria, phytoplankton (algae), moulds and yeasts in the water column of Lake Victoria in Mwanza as biological indicators of water quality. High algal biomass (Chl. a), dissolved oxygen (DO) content and aerobic bacteria counts were observed in clear and open waters. These sampling stations were also characterized with less numbers of moulds, yeasts and lower values of total suspended solids (TSS) and volatile solids (VS).Stations infested by the water hyacinth weed were characterized with less DO and phytoplankton biomass (Chl. a), high content of TSS and VS, high anaerobic bacteria, moulds and yeasts counts. The mouth of Mirongo River station had the highest content of TSS and TSS and VS, Chl. a and counts of r moulds and yeasts. Water hyacinth-infested shores and the mouth of Mirongo River were observed to be more eutrophic than the offshore open waters. The water hyacinth root swab (HY) was observed to have the highest density of pathogenic bacteria indicators and pathogens (total coliforms, faecal coliforms, faecal streptococci, Clostridium perfringens, Salmonella species, and Vibrio species) and the lowest MPNs wete observed in the water column at the control station (NY). Identification of isolates indicated that the water hycinth root swabs contained more bacterial species than the other samples tested, followed by water column from the mouth of Mirongo River station. These results suggested that there is an input of bacteriologically contaminated wastewater into the lake especially through riverine and municipal discharge. Faecal coliforms/ faecal streptococci ration (FC/FS) showed that there was faecal contamination of human origin as indicated by high values of the tested samples. The results also showed that the water hyacinth weed has a negative effect on the bacteriological quality of water as it immobilises pathogenic bacteria around its roots, which then live longer on the roots than in water, and therefore acts as a reservoir for pathogenic bacteria. These observations have health implications to those whose livelihood depends directly upon the lake's waters. The distribution of populations of sulphate-reducing bacteria (SRB) in sediments from various stations in Lake Victoria shores of Mwanza municipality was studied. Lactate-utilizing SRB were observed to be the dominant species in sediments covered by the water hyacinth weed (S2) and at mouth of Mirongo River station (S3) while acetate-utilizing SRB dominated the offshore open water sediments. Sediments from the offshore and open water station (SI) were observed to have the lowest most probable numbers (MPNs) for all the SRB species investigated. Lactate-utilizing SRB were almost absent in sediments from the offshore and open water. A positive correlation between the total populations of SRB and sulphate (SO) in sediments was observed. The cause of the foul smell at the lake shores resulted from gaseous form of HS produced by SRB activity. Most probable numbers (MPNs) of methanogens in various freshwater sediments were also determined using an anaerobic culture medium supplemented with either acetate or formate. Average MPNs for acetate-utilizing methanogens dominated at all the stations studied. Sediments from the mouth of Mirongo River station (S3) were recorded to have the highest average MPN of (7.2 ± 4.0) x 106 g-1of dry weight sediment for acetate-utilizing methanogens while those from the offshore and open water station (S1) had the lowest average acetate-utilizing methanogenic population of (1.2 0.4) x g' of dry weight sediment. A maximum population of (4.4± 1.7) x 105 MPN g-1 dry weight sediment of formate-utilizing methanogens was recorded at the mouth of Mirongo River station (S3) while sediments from the water hyacinthinfested station (S2) and the offshore and open water station (S 1) had average populations of (5.1 ± 8.7) x 105 and (3.9 ± 2.0) x 104 g-1 dry weight sediment, respectively. A new methanogen, strain TM, was isolated from sediments of Lake Victoria in Mwanza in a minimal medium containing trimethylamine as the sole carbon and energy source. The goal of the study was to isolate and identify the methanogenic archaea from eutrophic freshwater sediments of Lake Victoria, which up to now had not been investigated. Strain TM consisted of coccoid-like irregular cells occurring in clusters and were non-motile. The clusters consisted of cells mostly in twos and fours. The cells fluoresced weakly under ultraviolet light. The diameter of the individual cells ranged from 0.5 to 1.2 um. In agar, strain TM formed white ovallike colonies which reached a diameter of 1.0 to 1.5 mm in 6 weeks. Strain TM was analyzed phylogenetically and a phylogenetic tree was constructed. On basis of its high level of homology with the most closely related methanogen, Methanomethylovorans hollandica(97.0%), its position on the phylogenetic tree, its morphology (which is different from that of members of the genera Methanomethylovorans hollandica), it was proposed that strain TM is a member of the novel genus Methanomethylovorans, This isolate was named Methanomethylovorans victoriae since its origin is Lake Victoria. The GenBank/EMBL nucleotide accession number for the sequence of the 16S rRNA gene of strain TM is AJ276437.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF QK495.P783M89)
Water hyacinth, Eichhornia crassipes, Lake Victoria, Mwanza
Muyodi, F. J. (2000). Microbiological analysis of the waters of lake Victoria in relation to the invasion of the water hyacinth, Eichhornia crassipes (Mart.) solms: a case study of the lake Shores of Mwanza Municipality. Doctoral dissertation, University of Dar es Salaam.