Restoration of wetlands may have toxic foundation

By Mike Taugher
CONTRA COSTA TIMES
Sunday, February 26, 2006

The push to restore wetlands around the Bay Area could unintentionally add to an already serious mercury pollution problem.

That is the dark reality underlying an otherwise hopeful drive in recent years to reverse the loss of wetlands in San Francisco Bay and the Delta.

Tens of thousands of acres are slated for restoration as a way to improve water quality and habitat for fish, birds and other wildlife.

But creating new wetlands can also boost the levels of a highly toxic mercury compound, raising concern among scientists and wetland restoration managers about how to best move forward.

Around the Bay and Delta, former wetlands have been dried for farming, salt ponds and development. Many have sunk. Restoration involves raising their elevations, cutting channels, contouring the ground and breaking levees to allow the tides to flow back in and out, among other things.

But restoration quickly gets complicated, and the threat that new wetlands could increase the mercury problem in the Bay and Delta makes it even more so.

"If we do this wrong, someone's going to be held accountable," said Sam Luoma, a senior scientist at the U.S. Geological Survey who has warned of the problem for years.

Wetlands restoration managers are trying to design projects that will not add to the mercury pollution, though the problem is not yet fully understood.

The issue involves two of the most serious environmental challenges in the Bay and Delta: the loss of wetlands and the drainage of mercury that began 150 years ago and continues today.

Between the Gold Rush and 1986, an estimated 95 percent of tidal wetlands in the Bay and Delta were lost, first to farms and salt ponds and later to roads and urban development.

That means there is less habitat available for fish to lay eggs and birds to feed. Wildlife, from the smallest fish to sea lions, lose out on places to eat, grow and rest.

Wetlands also act as filters, cleaning pollutants and sediments out of the water to improve water quality in the Bay and Delta.

Meanwhile, the pollutant that most worries San Francisco Bay water quality regulators is mercury, which was widely used during the Gold Rush and after, before the danger it posed was fully appreciated.

The remnants of the toxic metal have already rendered many of the fish in the Bay and Delta unsafe to eat, according to fish consumption warnings, and a Bay cleanup plan estimates it will be more than a century before the advisories can be lifted.

Mercury conversion

The problem facing wetlands restoration projects is that marshes, and particularly newly created marshes, can convert mercury from a diluted and comparatively harmless contaminant into a highly toxic form with a propensity to concentrate in the food chain.

In wetlands, certain kinds of bacteria convert mercury to methylmercury, which readily enters the food chain and concentrates in the tissue of fish. When bigger fish eat the smaller fish, the poison concentrates further so that fish, birds and people at the top of the food chain are exposed to the highest concentrations.

Mercury is particularly hazardous for fetuses and children and can impair mental development and coordination. In high doses it can be fatal. Mercury also causes developmental abnormalities in wildlife.

Researchers are still learning what conditions affect the conversion of mercury into the more toxic form. The amount of oxygen in the water, the chemistry of the soil, and the elevation and size of the wetlands are among the variables that can influence not only how much mercury is converted to methylmercury, but also how much methylmercury is converted back.

Projects increasing

Despite the unknowns, wetlands restoration is picking up steam.

"In a period of little more than a decade, we went from wetlands restoration projects that were 10 to 20 acres to 25,000 acres," said Will Travis, executive director of the Bay Conservation and Development Commission.

Today, there are tens of thousands of acres slated to become wetlands once again. The cost is estimated in the hundreds of millions of dollars.

More than 10,000 acres are being restored in a single project near the Napa River. Another 16,000 acres are in the early stages of restoration in the South Bay. Near Oakley and across Carquinez Strait near Rio Vista, restoration projects are in planning and implementation stages.

The Dutch Slough restoration project near Oakley is one example of how concerns about mercury are affecting wetlands restoration.

There, wetlands will be restored in 1,166 acres of former dairy and grazing land.

The project's designers are planning for large, medium and small marshes to be built at different elevations to compare how the wetting-and-drying cycles of wetlands might affect mercury.

Lower marshes, for example, are covered with water longer and do not dry out as thoroughly as higher marshes. There is some evidence that higher marshes might methalyze more mercury than the lower marshes.

Minimizing pollution

Regulators, scientists and wetlands restoration advocates have come to a consensus in the last few years that restoration should continue, but projects should be designed in a way that will allow researchers to better understand how wetlands affect the conversion to methylmercury and then design the wetlands to minimize it.

"Mercury methylation is definitely a worry, but we don't think as a community that it should bring to a halt the wetlands restoration," said Richard Looker, a water resources control engineer at the San Francisco Bay Regional Water Quality Control Board.

The uncertainties surrounding the mercury problem are outweighed by the known environmental benefits of wetland restoration.

"We don't know how long it's going to take to get answers on how you can control methylmercury, or even if it's possible," Looker added.

A historic problem

The mercury problem began with miners who used about 13,000 tons of it to chemically pull gold out of the rocks they blasted off Sierra Nevada mountainsides with powerful hoses, and much of that mercury found its way down streams and rivers and into the Bay. Abandoned mercury mines also continue to trickle mercury into creeks that empty into the Bay.

But only when mercury is converted to methylmercury does it become a widespread threat in the Bay and Delta, to both wildlife and the thousands of people who eat the fish.

"If it wasn't for methylation, we wouldn't care that much about mercury," said Larry Kolb, assistant executive officer for the San Francisco Bay Regional Water Quality Control Board.

Luoma said he is hopeful, but not convinced, that wetlands restoration will be done in a way that does not worsen a mercury problem that already has made it unsafe to eat many of the fish.

The new wave of wetlands restoration is in its early stages, he said, and it is too soon to say how it will go.

"There's no history of people doing a careful (wetlands restoration). So far, most of our restoration efforts have involved common sense" instead of careful science, Luoma said.

For example, despite plans to restore tens of thousands of acres to tidal wetlands, Luoma said he does not know of a single monitoring program that has been set up to adequately measure mercury and the more toxic form, methylmercury, at those restoration sites.

Without that kind of information, it will be difficult to determine later what the effects of new wetlands are once they are constructed.

"I don't believe there are any that have incorporated monitoring," he said, adding, "A lot of times, science is the last thing to get funded."

John Cain, a restoration ecologist at the Natural Heritage Institute, which is working on the Dutch Slough project, suggests broadening the investigation.

"We should set up large-scale restoration projects as learning labs," he said.

That kind of experimentation, however, can affect how much high-quality fish and wildlife habitat can be built, posing an interesting question for scientists and wetlands restoration managers.

"Is it more important to learn or achieve your goals?" Cain said.

"We have been told that we don't know enough about the process of mercury methylation to adequately design strategies to minimize mercury methylation," Cain said. "That (restoration projects that incorporate experiments) would inform the next generation of wetlands restoration."

Mike Taugher covers natural resources. Reach him at 925-943-8257 or mtaugher@cctimes.com.