Tuesday

Severe weather patterns and pollution taking the toll

As the scramble for Lake Naivasha’s riparian lands intensifies, a major catastrophe is looming. The lake is crawling to its death bed.

Naivasha, one of the Rift Valley's four fresh water lakes, stretches across some 105 to 160 square kilometres depending on the season. However, severe weather patterns in the two years, and a myriad of human activities now threaten its very existence.

Most recently, experts have sounded warnings over the poisonous blue green alga, a species said to be capable of reducing the entire ecosystem to toxin.

The alga's presence means the breeding ground is a conducive and that its toxicity might kill everything living in the water.

The path to the pollution can be traced to the catchment area – about 32,000 square kilometres – which continues to be ruined.

"It should be understood that this is a shallow basin lake, meaning that it has no outflow level. It has thus depended on replenishment from the catchment areas surrounding it.

But recently even the rivers in the catchment area have been drying up," said Ms Sarah Higgins, secretary of the Lake Naivasha Riparian Owners Association, a conservationist.

For the past 20 years, encroachment on the lake has led to extreme damage and exploitation of the water sources.

Deforestation and farming on the shores have also exposed the water catchment areas to vulnerability.

The papyrus plants – which act as silt and nutrient filters around the lake and are capable of recycling excess nutrients within the water system – have been depleted. "Then there are all these small dips by animal owners settled here which release organic phosphates into the water and contaminate it some more," Ms Higgins explains.

The flow of the rivers Malewa and Gilgil, from which Lake Naivasha has been feeding, has been slightly diverted by a dam constructed on the Tarasha river to the north of the lake.

Because of the dam, water from the two rivers into Lake Naivasha is now limited. This makes the lake even more vulnerable.

The damage posed by human activities around the wetlands is what has aggravated the presence of the blue green alga in the lake.

In March, visiting scientists and experts from Britain's University of Leicester confirmed the alga's presence, predicting a possible increase in the poisonous species and posing grave danger to the lake.

According to zoologist /hydrobiologist Mbogo Kamau, a monitoring officer around the lake, multiplication by this alga species is inevitable for as long as encroachment continues.

Mr Kamau explains how the blue-green alga manifests itself in the water: "Its growth in the water system is supported by two main plant nutrients – phosphates and nitrates.

"The source of the nutrients could be within the system or outside. Generation of nutrients in a system occurs through an inherent process whereby dead plant and animal material decompose and disintegrate into the water column to be used by the alga."

From outside, nutrients are transported into the system via river discharge, surface water runoff during rain and, to a certain extent, a sub-surface flow where the water aquifer is shallow.

The outside-the-system nutrients include domestic waste (sewage), animal waste, industrial/urban waste and the phosphate and nitrate fertilisers commonly used for agriculture. The implications of a dying Lake Naivasha are dire. Mr Kamau explains: "It results in a decline of biodiversity. It starts with submerged plants, aquatic invertebrates, then fish, birds and other animals dependent on the water. At this point, the water is of no use to man."

Lake Naivasha is now moderately eutrophic, meaning that the amount of nutrients in the water is moderately high and can be maintained or, better still, improved with proper management.

During the survey, Dr David Harper of the University of Leicester team, noted that the major threat to the lake is the increasing nutrient level as the water demand increases.

Dr Harper and his team have found that the nutrient increase is to be attributed to destruction of the buffer vegetation on the lake's fringes, which has reduced from 48km squares in 1960 to only 10km squares today.

This is the main reason why the Lake Naivasha Riparian Association (LNRA) and other expert stakeholders are concerned about the deteriorating state of the lake and its environs.

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