麻豆传媒

Editorial: Biodiversity trumps 鈥榥ature鈥� in the Gulf

The bays and bayous of coastal Louisiana were in trouble even before the Deepwater Horizon disaster. How far should we go to return them to their former glory?

STANDING knee-deep in the waters of Bay Jimmy in south-eastern Louisiana, Daniel Deocampo pours a bucket of clay mixed with seawater into the marsh. Oil swirls around our legs and the air reeks of burnt petroleum. With oil from BP鈥檚 Deepwater Horizon spill sitting in the bay, the burning question is 鈥� remove the oil or wait for nature to take its course?

R. Eugene Turner, a coastal ecologist at Louisiana State University (LSU) in Baton Rouge, says that interfering with nature could backfire. Even just wiping oil off leaves, he says, spreads the toxic residue around. But Deocampo, a sedimentary geochemist at , Atlanta, and his colleague Kuk-Jeong Chin say leaving the oil will doom the marsh, and are testing ways to give oil-munching bacteria a turboboost. 鈥淚f we do nothing, all the plants will die,鈥� Chin says. 鈥淣ature will take too long.鈥�

鈥淟eaving the oil will doom the marshes, if we do nothing the plants will die. Nature will take too long鈥�

The disagreement underscores a debate that has been raging over marsh restoration for decades. Even before the spill, the marshes were disappearing at an alarming rate 鈥� the consequence of the dams, levees and canals built to provide shipping channels and protect New Orleans from flooding. Without intervention Louisiana鈥檚 bayous could become open water within 50 years.

As a result, support has been growing for a suite of projects to resurrect the marshes (see map). At one end of the spectrum are those who advocate minimal intervention and letting nature take its course. At the other, the call is for yet more engineering: new, hardier breeds of grasses, seeding from the air and artificial reefs to shore up the sinking sediment.

Ultimately, the marshes are vanishing because sediment is in short supply. Wind and waves constantly erode the shoreline, and dams and levees hold back sediment flowing down the Mississippi. What鈥檚 more, a network of canals dredged by the oil and gas industry carry saltwater inland, killing freshwater marshes. Add to all this rising sea levels and the largest oil spill in US history and the situation is desperate. Without its marshes, Louisiana鈥檚 thriving seafood industry would crumble and the state鈥檚 coast would lose its natural defences against the powerful storms that blow in from the Gulf of Mexico.

Turner advocates small-scale intervention: filling in thousands of kilometres of abandoned canals with the dredged sediment that is still piled up alongside them. He also favours helping sediment flow to the marshes. Historically, when the Mississippi鈥檚 waters ran high, 鈥渃revasses鈥� appeared in the river banks and carried sediment into the deltas. Dams and levees now prevent this, so Turner suggests punching holes in the river鈥檚 embankment to spur the process. 鈥淪o many marsh restoration ideas assume we can do better than nature,鈥� says Turner. 鈥淚 think that鈥檚 pretty arrogant.鈥�

Others say we need to think big. 鈥淥ver the years, we鈥檝e done all kinds of patchwork projects,鈥� says Harry Roberts, a retired sedimentary geologist at LSU. 鈥淭hey鈥檙e not long-term solutions.鈥� Roberts has calculated that 18 to 24 billion tonnes of sediment will be needed to maintain the delta as the sea level rises in the next century (Nature Geoscience, ). Small crevasses can never meet that demand, he says.

For researchers like Roberts the question has become not how to restore Louisiana鈥檚 lost Eden but how to create a new, improved one. As part of that, in April, a to pipe mud more than 6 kilometres from Cote Blanche Bay to Vermilion Bay鈥檚 Marsh Island Wildlife Refuge. The aim is to recreate 160 hectares of marsh.

Once the soil is in place, you need grasses 鈥� and not just any grasses. Two decades ago, Michael Materne, a wetland plant specialist at , collected varieties of the native smooth cord grass (Spartina alterniflora) from across the US, searching for the hardiest ones. Today, Materne鈥檚 Vermilion variety, named after the Louisiana parish it originated in, is the only one used in re-vegetation projects. To increase genetic diversity in the restored ecosystems, it will be joined next year by up to six more varieties that he has cross-bred.

Materne鈥檚 grasses may be the hardiest available, but they suffer from one flaw. Like wild varieties, what little seed they produce is fragile and slow to germinate. They must be planted by hand, a slow process during which grasses can be trampled and wrecked.

Materne鈥檚 colleague Herry Utomo may have the solution. He has cross-bred seeds from 126 cord grasses to produce 15 varieties with hardy seeds. Early next year, he will shower them over Marsh Island from a plane.

Further inland, AgCenter researchers are testing ways of restoring freshwater marshes. Artificial floating platforms are being planted with freshwater maidencane (Panicum hemitomon) to mimic the thick floating mats of vegetation that used to cover the area.

And beneath the water鈥檚 surface, more changes are afoot. Compacting, sinking sea floors mean that natural reefs made of dead oyster shells 鈥� which would normally lie just beneath the surface 鈥� have effectively drowned. Steven Hall and his colleagues have devised building blocks for artificial reefs made of cement, limestone rock and oyster shells. These raise the bed of the estuary in chosen locations and offer a new home for oysters to colonise. Each doughnut-shaped block is 1.5 metres across and is stripped of the sand grains that would normally fill pores in the building material. This allows water to move through the reef as it would in nature.

Hall鈥檚 patented Oysterbreak is being tested in estuaries as a way of creating new habitats and reducing wave energy. When he tested it in a wave tank in 2007, it reduced wave energy by 70 per cent 鈥� enough to protect marshes and coastal regions from strong waves during storms. He has now been awarded a $3.8 million federal grant to test an artificial reef, several kilometres long, in the wild, alongside the Rockefeller Wildlife Refuge. Work should begin by spring of next year.

鈥淥ysterbreaks create homes for oysters and protect marshes from high waves during storms鈥�

In Bay Jimmy, Deocampo and Chin hope to find gentler ways to help nature recover from disastrous oil spills. They are replicating a Spanish experiment from the 2002 Prestige oil spill, in which researchers collected contaminated soil samples and added clay to half of them. After three years, 90 per cent of the oil in the clay samples had broken down compared to just 30 per cent in the control samples. They think the electrostatic charge of the clay may bind both the oil and the microbes, bringing them together.

Even if their experiments are successful, the clay fix is unlikely to be deployed on a large scale in Louisiana. Throughout the clean-up, the US Environmental Protection Agency鈥檚 policy has been to let nature do its thing. By the time the results come in, it will be too late to change this. But the pair hope they can prove that engineering solutions can work without harming ecosystems. If they succeed, it could change policies for the next big spill. From coastal restoration to oil remediation, Louisiana鈥檚 bayous have become a testing ground to figure out who knows best 鈥� science or nature.

Update, 7 October 2010: Louisiana state has . Dredging for the initial 56-kilometre berms continues.