Not All Wetlands Are Created Equal
24 January 2012/ by Rachel Nuwer/ Green Blog
To many, it’s a familiar scenario: a strip mall suddenly pops up in what was once a desolate quagmire or boggy boondock.
But people are coming to realize that these seemingly wasted plots where land meets water provide a valuable ecological service. In addition to nurturing biodiversity, wetlands purify water, produce fish, store carbon dioxide that would otherwise contribute to global warming, and protect shorelines from floods, storm surges and erosion.
Since the early 20th century, development has claimed over half the wetlands in North America, Europe, Australia and China. To repair the damage from those construction binges and regain the benefits of wetlands, restoration has become a booming business.
Yet new research calls into question whether manmade versions can ever compensate for wetlands buried beneath parking lots and subdivisions. In an article published on Tuesday in PLoS Biology, scientists write that restoration efforts often fall short of returning wetlands to their former biological complexity and functioning.
“In traditional restoration, people repair hydrology, put in some plants, and after a few years say the wetlands are good,” said David Moreno-Mateos, a wetland ecologist at the Jasper Ridge Biological Preserve at Stanford University and the lead author of the paper. “But if you look at what’s really going on down there, you see the processes are not recovering.”
“One of the results from this study is that we need to undertake more specific restoration measures focused on recovering processes, not just nice, beautiful wetlands with ducks,” said Dr. Moreno-Mateos, who conducted the research at the University of California, Berkleley.
Before the 1960s, many people perceived wetlands as dank places to be drained or avoided, Dr. Moreno-Mateos said. But in the last 20 years, the governments of the United States Canada, and Mexico have poured over $70 billion into restoring more than seven million acres of wetlands.
Some developers deploy the strategy of promising to create or restore wetlands in one location in exchange for getting permission to bulldoze wetlands in another location. In theory, this sounds fair, but the results fall short, Dr. Moreno-Mateos said.
To quantify the success of restoration projects, the researchers performed a meta-analysis of 621 restored and created wetland sites around the world. Most of the sites were in the United States, and some restoration plots dated back around 100 years. They compared the sites with 556 natural wetlands that served as reference points.
The researchers found that hydrology seemed to recover immediately after restoration, but results varied in areas like the recovery of animals, plants and nutrients. Even after 100 years of restoration, the wetlands recovered only 77 percent of their original flora and fauna, on average.
Within five years animals like birds and bats returned, as did flying insects like midges. Other macroinvertebrates like water fleas took a bit longer, around 5 to 10 years, and these communities usually did not reach their original levels of richness or abundance.
Plants were even slower to recover. On average, they took 30 years to return but still remained less biodiverse and abundant up to 100 years after restoration.
The plant lag may be related to recovering carbon, nitrogen and phosphorus storage. After 50 years, carbon levels were still below reference levels, and it took at least 30 years for nitrogen to return to normal. All in all, restored wetlands regained an average of 74 percent of their biogeochemical components by comparison with the reference sites.
“When we lose wetlands we’re losing something we won’t recover for years,” Dr. Moreno-Mateos said. “When people develop that huge shopping mall, it will take centuries to restore the functions we had before.”
Some wetlands did recover faster than others, depending on hydrology, size and climate. The more water flowing through a site, the more quickly it bounces back to reference values. Larger sites also fared better than smaller plots, and the warmer the temperature, the more rapid the recovery. “In some warm climates, things go fast, but cold climates take forever,” Dr. Moreno-Mateos said.
On average, however, the researchers describe current restoration practices as “slow and incomplete.” Dr. Moreno-Mateos plans to investigate the connection between the slow recovery of carbon storage and plants, and to seek a specific method that will expedite their restoration.
Although the results are not surprising for scientists, he said, this is the first time a study has placed the problem into a global context.
“Developers are kind of powerful people,” he said, “but carbon is really important for global warming, so I think it’s going to be controversial.”