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Water Lentils on the Offensive |
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By Yensi Rivero*
A weed species is posing a major threat to Venezuela's Lake Maracaibo, the biggest lake in South America. With rakes and poles, fisherfolk are fighting to eliminate this "intruder" that is a danger to many types of fish.
CARACAS - A rebellious green stain has spread kilometers and kilometers since March over Venezuela's Lake Maracaibo. It is a rapidly reproducing freshwater weed, known as 'lemna' in Spanish, or water lentil, because of its similarity to edible lentils.
It looks like the green lentil, "but its branches are intricately interlaced to form a fine but resistant layer" over the lake surface," biologist Gonzalo Godoy, of the environmental group Procuencas, told Tierramérica.
Experts say the new aquatic weed, also known as duckweed, contributes to the contamination of the already polluted lake, and could significantly alter the habitat of various fish species because it exhausts their oxygen supply and cuts off light from the lake's depths.
"It is the first time that this has happened to the lake, and that is why it is so worrisome. The great quantity of nutrients in the water, as well as the high temperatures and recent rains favor this weed," Godoy explained.
Duckweed, of the Lemnaceae family, is in its element in Maracaibo's water, with its low level of salinity. This is not normally the case for this lake, which covers 12,000 square km and holds 245 billion cubic meters of water, the salinity of which has increased a great deal in the past few decades due to oil industry activity.
The lake, the biggest in South America, is connected to the Caribbean Sea by a natural bay that opens to the Gulf of Venezuela, which has been dredged since the 1950s to allow the big tanker ships to get through. And with those ships, more saltwater entered Maracaibo.
In the first half of the 20th century, the lake's salinity was 1.0 to 1.5 grams per liter, but reached nearly five grams per liter at the water's surface, and as much as 15 grams in the lake's depths during dry season.
"But the freshwater from the torrential rains that have fallen in recent days has reduced the salinity, from 12 to 13 milligrams per liter to four milligrams, favoring the emergence of duckweed," Carlos Rivero, environmental manager for the state-run oil giant PDVSA told Tierramérica.
Furthermore, the sewage from the cities on the shore, "particularly from Maracaibo (population 1.5 million), Cabimas (250,000) and Ciudad Ojeda (150,000), as well as the farmers' use of pesticides and other chemical agents in the Catatumbo River valley have contributed to its contamination," said Rivero.
The pollution does not yet threaten the population of edible fish species, like the armadillo (Dasypus novemcinctus), bocachico (Prochilodus magdalenae), doncella (Coris julis), lisa (familia Mugílidos) and the pampano (Stromateus maculatus).
But the water lentils could alter the habitat of these fish "by blocking the photosynthesis process, and they could hurt the fishing industry, because the weed adheres to their boats, affects the cooling systems and obstructs travel," the PDVSA official added.
While environmental authorities and experts are debating how to eliminate the weed, fisherfolk are organizing in groups to take out the duckweed with rakes and poles.
The lakebed and the shores of Maracaibo were the largest South American oil field throughout most of the 20th century, and the area continues to produce more than a million barrels a day of crude, some of which is shipped from Maracaibo ports.
Over the lake stands a sort of forest of hundreds of oil drilling towers, many of which are inactive or have been abandoned, and thousands of kilometers of pipeline runs under the surface of its waters. Small leaks and accidents over the decades have left a big environmental debt.
The new problem of water lentils is added to the seasonal difficulties afflicting life in the lake, such as prolonged drought or early rains. The intense precipitation in early May left more than 100 people homeless along the southern Maracaibo, and several mayors declared a state of emergency.
The rainy season could stretch to November, and it is an unknown factor whose effect is to "irrigate" the duckweed, Angel Graterol, spokesman for the Air Force Meteorology Department, told Tierramérica.
* Yensi Rivero is a Tierramérica contributor.
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