By Nyang’au Araka
It is evening and the immensity of Lake Victoria stretches continuously, its calm waters glistening with the reflections of strewn clouds that float sluggishly above.
Fishermen in wooden boats move smoothly by, their silhouettes framed by the weakening sunlight, while distant hills rise around the shore.
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The air is filled with the comforting sound of rippling waves and the infrequent call of a bird as it swoops elegantly above the water.
The scene feels everlasting, as if the lake has witnessed centuries of stories unfold, and yet its beauty never grows old.
But this scenic beauty of the lake depends on where one is getting it from, for the lake now has a toxic bacteria that makes the water turn green.
Experts have equated it to the same green that one sees on stagnant ponds, and is caused by tiny organisms called cyanobacteria, according to an article published by The Conversation this week.
Joint research
The article is an outcome of joint research by Lauren Hart and Gregory Dick from the University of Michigan, and their Bowling Green State University (BGSU) counterparts; Kefa Otiso and George Bullerjahn.
Prof Otiso who is a Kenyan and his co-researchers have warned that “Lakeside communities that rely on the gulf for drinking water and domestic tasks are at risk of exposure to cyanoHAB toxins.”
“Cyanobacteria thrive in warm, sunny lakes and ponds that contain excess nitrogen and phosphorus nutrients derived from fertiliser, manure and sewage,” the article says.
When conditions are right, cyanobacteria multiply rapidly and form smelly green scums on the water’s surface.
Known to science as cyanoHABs (cyanobacterial harmful algal blooms), the scums are harmful to livestock, wildlife, pets, people and aquatic organisms like fish.
Toxins make untreated water unsafe to drink, swim in, or even touch. Sometimes they can become suspended in air and be inhaled.
“The cyanoHABs also harm ecosystems by depleting oxygen, killing off whatever lives in the water, and disrupting food webs and fisheries,” the researchers says.
CyanoHABs are a global threat and receive considerable scientific attention in North America and Europe, and blooms are becoming a bother worldwide.
This, according to the experts, is due to rising temperatures that promote cyanobacterial growth and more intense rainfall delivers nutrients from the landscape.
“Only effective management of nutrients can reverse this trend,” the article says, adding that the problem is understudied in Africa’s main lakes, including Lake Victoria.
Past research on cyanoHABs has mostly used microscopy to study the kinds found there, but microscopy cannot differentiate between toxic and non-toxic cyanobacterial cells.
The professors say that they identified which cyanobacteria were the most abundant in the gulf and which ones were producing the main toxin of concern.
Through the findings, local authorities can monitor for specific cyanobacteria and warn residents to stay away when blooms are present.
As well, cyanoHAB prevention practices (nutrient reduction, land-use practices) can target the cyanobacteria that cause the problem.
Greening of lakes
The research discloses that the lake receives large influxes of nutrients because of growing lakeside populations and land-use changes.
“Nutrients from agriculture, industry and urbanisation fuel the growth of cyanoHABs,” the article says.
CyanoHABs occur in many basins in Lake Victoria but are highly concentrated in Kenya’s shallow Winam/Nyanza Gulf.
Changing nutrient and temperature conditions can also alter which types of cyanobacteria dominate the gulf and the types and levels of toxins in the water.
Modern genome sequencing technologies can identify genes encoding the production of known and novel toxins and other molecules of interest, such as those with medicinal properties, according to the researchers.
“Our latest study adds to a growing number of recent studies our team has carried out in and around Lake Victoria,” the researchers write.
They visited over 31 sites to collect scientific samples and data, and the same were later analysed for DNA, the biological “instruction manual” inside every living thing.
Past reports identified Microcystis as the dominant cyanobacteria in the Winam Gulf.
However, the researchers found Dolichospermum was the most abundant type in major cyanoHAB events there.
“This finding might be due to recent environmental changes in the region,” the researchers who linked Microcystis to microcystin said.
Microcystis is liver-damaging toxin that can kill livestock, wildlife and humans, especially those whose immune system isn’t working well.
Microcystis occurs mainly in murkier river mouths where green scums are not visible, making scientific monitoring and public alerts even more important.
Local authorities can now monitor for cyanobacteria and warn residents to stay away when blooms are present, and know which cyanobacteria to target in prevention efforts like reducing the amount of phosphorus and other nutrients entering the gulf.
Future research
The study uncovered over 300 uncharacterised genes that may produce novel cyanobacterial molecules.
“These molecules could have toxic or therapeutic effects, and provide an opportunity for future investigators to explore,” the researchers said in the jointly published article.
They noted that rapid human population growth and settlement around lakes and their watersheds is leading to high levels nutrients in water masses around the world.
“This results in excessive growth of algae and aquatic plants, and the danger is likely to increase with global warming because warm temperatures promote algal blooms,” the researchers said.
They argued that their study provides a foundation for remedying the unfolding ecological scenario in Lake Victoria – and possibly discovering beneficial properties in cyanoHABs.
The greening of the lake reminds one the water hyacinth, which is largely considered a menace, although studies have lately found how it can be economically useful.
The weed, which covers parts of the lake from time to time often takes a toll on different stakeholders that depend on the water body for their livelihoods.
The bulk of this article was first published here: https://theconversation.com/lake-victoria-is-turning-green-the-deadly-bacteria-behind-it-249298?utm_medium=article_native_share&utm_source=theconversation.com
