“Shrimp and crabs in Ben Tre are always better than shrimp and crabs elsewhere, because the saltwater percentage is the best, so the meat tastes better,” he said.
But Nguyen Van A also knows the percentage at which they begin to die.
Last year, when the delta was devastated by the worst drought in recorded history, the amount of salt in Ben Tre’s water hit that target, and kept shooting up. The province's rice crops were the first to die, followed by hardier fruit trees and coconut palms. But eventually, even his salt water shrimp were all lost.
The policy achieved these goals, but in the process the fertile delta soil has been depleted. At the same time, rising seas are causing saline intrusion that kills the relatively delicate crop.
Wyatt, of the IUCN, argues that a paradigm shift is needed in how saltwater is seen.
Since the reunification of the north and south in 1976, the government has pursued an aggressive water management policy designed to support its rice cultivation targets. This has led to the construction of more and more sluice gates, dams, and dykes to keep freshwater in and saltwater out.
But Wyatt says this is unsustainable. The infrastructure is increasingly ineffective against rising seas, even as the Vietnamese government is taking on more and more debt to build and reinforce it. Opening sluice gates also flushes agrochemicals into coastal areas.
Instead of treating salinity as an enemy, Wyatt says, residents of the Mekong Delta need to learn to embrace it. Counter-intuitively, giving up the fight and letting in the rising seas can even have environmental benefits.
“We also need to keep these ecosystems open instead of sluicing off these rivers,” he said. “Then we have better biodiversity outcomes.”
Farmers are increasingly recognising this: in some areas, they are even demanding that sluice gates be opened and salty water be allowed to flow in so they can begin growing shrimp. But official policy has lagged behind.
Ca Mau, the province at the southernmost tip of Vietnam, is surrounded by ocean on three sides, making it especially vulnerable to rising seas and typhoons. The location also makes it a particularly good place to start a shrimp farm. But shrimp farming could destroy many of the same mangrove forests the province depends on for protection.
Those working on the Mangroves and Markets project hope to change that by switching to shrimp-mangrove systems. “Before the project, around 10 years ago, the trend was for the shrimp to expand and the forest to dwindle,” Wyatt said.
In contrast to large, boxy industrial shrimp farms, shrimp-mangrove systems are long and thin, with brackish pools of water alternating with strips of mangrove trees. In addition to providing a more sustainable way to protect the coast than concrete seawalls, shrimp-mangrove farms actually raise the level of the earth by trapping sediment. In some cases they can accumulate as much as 25 centimetres of earth annually, which is greater than sea level rise and subsidence combined.
Unlike intensive shrimp farms or shrimp grown in rice paddy fields, they also cool themselves, which requires less groundwater pumping and makes them more resilient. During last year’s drought, many mangrove-shrimp systems escaped unscathed even as shrimp on other types of farms died in droves, according to Wyatt.
Mangroves and Markets has been so successful that it is now working with thousands of additional shrimp farmers Ben Tre and Tra Vinh, where mangroves are also under threat and erosion is a major problem – up to 60 metres of shoreline per year are lost in some areas.
This will be good news for farmers along the coast like Nguyen Bin A, who says he knows mangroves are ecologically important, but isn’t quite clear on why.
But there’s one thing he’s sure of: “In the future, if the sea levels rise, it doesn’t matter if you build a dam higher. It will destroy your farm.”
Source: IRIN | 23 May 2017