Arsenic sinks to new depths

More than a century of groundwater over-exploitation in Vietnam has drawn the water table down and, with it, arsenic. It may only be a matter of time before the toxic element also permeates deep aquifers in other Asian countries that follow the same practice, such as those around the Bengal Basin.

These conclusions, published today in the Proceedings of the National Academy of Sciences1, point to high future costs in terms of both health and water-purification processes. Some 100 million people throughout Asia are currently at risk from unsafe levels of arsenic in their water supplies. The element can trigger conditions ranging from anaemia to skin cancer. With deeper aquifers so far thought to be arsenic-free, some municipal authorities in Bangladesh, and many in Vietnam, are drilling into lower sediments.

In Vietnam, a nation that began overusing its deep aquifers under French occupation more than 110 years ago, the effect is already pronounced. In the region surrounding the densely populated city of Hanoi — with nearly 2,000 people per square kilometre — it is difficult to escape arsenic-contaminated water, no matter how deeply you drill.

The researchers analysed 512 private tubewells reaching to depths ranging from 10 metres to more than 50 metres throughout the country's Red River Delta. Their findings revealed that 27% of the wells contained levels of arsenic in excess of the World Health Organization's standard of 10 micrograms per litre, says Michael Berg, a senior scientist at the Swiss Federal Institute of Aquatic Science and Technology in Dübendorf and a co-author on the study1. This puts some 3 million people at risk.

The survey, carried out in cooperation with the Hanoi University of Science and Technology, also found harmful levels of other elements — about 7 million people in the Red River Delta are exposed to unsafe levels of at least one element. After arsenic, the most important of these is manganese, which exceeded World Health Organization guidelines in 44% of the wells. Elevated levels of this element can affect neurological development in children.
Mapping the depths

From the survey data, Berg's team created the first three-dimensional groundwater map, using statistical modelling to show levels that are relatively arsenic-free. "It is now clear where water is safe and where it is unsafe. That is one of the most important findings for the public," says Berg.

The map makes it difficult for officials to ignore the arsenic problem, says Dieke Postma, a senior researcher at the Geological Survey of Denmark and Greenland, who has been working in the region since 2004 and is unconnected with the new study. "It's important for the Vietnamese authorities because they haven't had an overview of how big the problem is," he says.
Postma says he hopes that an international scientific conference on the issue, to be held in Hanoi in November, will draw further official attention to arsenic contamination in the region.

The implications of the finding could be serious for countries around the Bengal Basin in South Asia. In Bangladesh, where some 70 million people2 are exposed, the use of deep aquifers is a more recent phenomenon. Decades ago, aid agencies introduced tube wells as a reliable and clean water source, only to find that the top-most sediment layers, formed in the 12,000 years since the start of the current Holocene epoch, contain naturally occurring arsenic that leaches into the groundwater.

To avoid contamination, wells in the Bengal Basin can be drilled into deep layers that were oxidized during the last ice age, in which the water is free of arsenic, Berg says. These aquifers were created during the Pleistocene epoch, between 12,000 and 2.5 million years ago, and lack the organic carbon that is needed for arsenic to leach into water.
Leaching lower

But if people in the Bengal Basin continue to exploit their water supplies at the current rates, arsenic-laden water from the upper layers may find its way into Pleistocene aquifers, the study suggests.

Berg's team is in contact with scientists in Dhaka to evaluate arsenic migration into deeper sediments.
The group is the first to give real-life evidence that arsenic in deeper layers can get into groundwater. Other lab-based studies2,3 have suggested that sediments in deeper aquifers tend to keep arsenic out of the water, says William Burgess, a hydrogeologist at the Department of Earth Sciences at University College London. On the basis of the new study, he thinks that such sequestration may not always happen and probably depends on the composition of sediments and the complexity of water flow underground.

"Pumping from the Pleistocene aquifer has certainly had an adverse effect in terms of drawing down arsenic at significantly high concentrations over about 100 years," says Burgess. "These deep wells weren't being monitored 10, 20, 30 years ago, so we don't know how quickly arsenic got down there, but it got there sometime in the past 100 years."
For more info- http://www.nature.com/news/2011/110117/full/news.2011.20.html

Cholera and Cooperation Play Into Haiti Reforestation

From the passenger seat of a truck rumbling along a rough and dusty road in rural Haiti, Drew Kutschenreuter points out trees planted to feed the country’s charcoal habit, patches of millet, and irrigation canals cut along the sides of rolling brown hills.

An agronomist from Wisconsin, Kutschenreuter has been working in Haiti for more than two decades, most recently on soil conservation and hillside terracing projects run by the International Organization for Migration. Kutschenreuter’s goals: to create jobs and reverse the country’s downward spiral into ecological degradation and extreme poverty—problems exacerbated by last year’s earthquake and the island’s history of hurricane damage.

With only a fraction of its forest cover remaining, Haiti has become increasingly vulnerable to flash floods and mudslides. Without underground tree roots, only a quarter of the water that should permeates the soil. Storms often damage what water systems do exist, crippling access to clean drinking water supplies. The United Nations (UN) estimates some 36 million tons of rich topsoil are carried away each year by wind and rain, much ending up in rivers and lakes that become lifeless mudscapes during the rainy season. With the loss of soil fertility, crop yields drop, and farmers have increasingly turned to cutting trees for firewood and charcoal as a source of revenue.

With the recent outbreak of cholera in camps crowded with earthquake victims, and in mountainous rural areas where people take their drinking water from the river or underground wells, there may be an added stress on forest resources. According to Wesler Lambert of Partners in Health, when citizens are asked to boil water as a protection measure against cholera or other water-borne diseases, they use charcoal, leading to more deforestation and therefore more flooding.

Rebuilding Hillsides, Futures

Kutschenreuter works in an area of northern Haiti called Gonaîves, which did not see earthquake devastation, overseeing planting and hillside terracing projects to slow down the flow of water and protect topsoil. While the project area is only a small patch of Haiti, it offers a glimpse of how an environmentally rehabilitated landscape could look.

Mending Haiti’s environment is the ambitious end game of a new program called the Haiti Regeneration Initiative, spearheaded by Columbia University’s Earth Institute and the UN Environmental Programme (UNEP). The effort started in 2008 with the ecological restoration of one of the country’s several dozen watersheds. Now, having secured $8 million in funding, the project’s leaders are expanding its scope along Haiti’s southern coast, and will couple environmental restoration with development efforts, such as building infrastructure for drinking water and sanitation, and efforts to improve the livelihoods of local Haitians.

Until now, much of the work has been focused on planning: using soil quality surveys, and satellite data that accounts for topography and water patterns, to create a map that determines which hillsides can support which crops. They’ve also installed an automated rain gauge, which communicates wind speed and precipitation data in real-time via satellite back to New York, and could be developed into a flood risk early warning system.

The program builds on practices the UN has developed in African villages. "Haiti's are among the lowest crop yields in the world,” said Marc Levy, a Columbia University professor and Earth Institute program director. “By using fertilizer feeds and best management practices, they could double or triple their yields very quickly.” Fruit-bearing trees like banana and mango could be planted along hillsides, and walls built to shore them up against erosion. By focusing on more efficient use of “good” land, like plateaus, farmers might be able abandon some of the steeper grades altogether. Reforestation programs could provide alternative jobs to cutting trees for firewood and charcoal production.

But the idea that choosing not to farm a particular slope because of its value for flood protection and water quality—an individual sacrifice for a collective benefit—challenges the coping strategies that poor farmers have relied on for centuries, said Levy. He argues that it will take a significant change, like the one the Haiti Regeneration Initiative promotes, to reverse the country’s ecological decline.
For more info- http://news.nationalgeographic.com/news/2011/01/110113-haiti-cholera-reforestation-water-floods-hurricane-earthquake/