They are deadly for aquatic life and take years of pollution to develop, yet dead zones can be created in a flash by bubbling nitrogen through a lake.
Now some scientists say this technique could deter the Asian carp from using the Chicago Sanitary and Ship Canal to enter the Great Lakes. Researchers fear invasion by the voracious fish would cause untold environmental and economic disasters.
They envision blocking them with a zone of such low oxygen that fish and most plants can’t survive by flushing nitrogen in the waterway that connects Lake Michigan to the Mississippi River.
“The gas bubbles attract and dissipate oxygen from the water,” said Dave Chesney, lead researcher and a chemistry professor at Michigan Technological University. “It’s a safer method, leaves no long-term residues and it’s unlikely to violate the Clean Water Act.”
Another approach that would induce similar effects is by injecting oxygen-guzzling micro-organisms from partially treated food factory waste water into parts of the Chicago Sanitary Canal. It is unpopular with some government officials and researchers because it would violate pollution laws or require changes to them.
This doesn’t have to be with the nitrogen approach.
The bubbles merely flush through the water without any chemical reactions and wouldn’t lead to an algae bloom often associated with low oxygen areas that are also called hypoxic zones, said Tom Rozich, a retired fish biologist with the Michigan Department of Natural Resources.
It’s a process of the intermingling of gases to maintain equilibrium.
The researchers say this would be a novel and large-scale application of that process. But removal of oxygen by bubbling nitrogen is an established and accepted method of treating ballast water in ocean-going ships. It’s also used to seal food packages.
As each gas bubble rises, oxygen molecules in the water sense the lack of oxygen in it, prompting them to cross from the water into the bubble where they are rapidly transported and dispersed into the air.
Rozich attempted to discuss this idea with colleagues at the Michigan Department of Natural Resources hoping to get support to do further studies. Nothing came of it. He even sent the same idea to President Obama last year and all he got was a thank you note, he said.
But the idea is worth exploring, said Chesney, who carried out preliminary studies of the approach.
Electric barrier is not sufficient and time is running out
Nine eDNA samples of the Asian Carp were recently found by the U.S. Army Corps of Engineers on the Lake Michigan side of an electrical barrier used to prevent the carp invasion.
“Clearly the electric barrier is not working as effective as it should,” said Steve Yencich, president of the Michigan Lodging and Tourism Association, a lobby organization concerned that the invasion of the Asian Carp in the Great Lakes will drive away tourists interested in fishing.
Though it is not clear whether those samples suggest the presence of live or dead fish, Yencich suggests a cautious approach.
“It’s best to assume those samples come from live fish, he said.”
Permanent barrier elusive
Although researchers and the government differ on interim measures, most agree that a permanent separation of the basins is the only sure way to deter the carp.
But that’s not going to happen, said Chesney.
“Politically it’s going to be impossible,” he said. “It’s costly, involves a lot of considerations and the state of Illinois doesn’t want it.”
A complementary barrier is urgently needed because the electrical measure alone will not suffice, said Marcelo Garcia, a lead researcher with an Asian Carp Study group at the University of Illinois at Urbana-Champaign.
Some researchers say that the opportunity to control non-native species is slipping away. They want the government to act before the Asian carp and other alien species establish and disrupt the multi-billion fishery and tourism industries in the Great Lakes.
“I don’t think we have time for research studies,” Chesney said. “It’s time for the government to just roll the dice and go with their best shot.”
Would it lead to fish kill?
A narrow hypoxic zone for such a distinct purpose need not cause a fish massacre.
“At some point, even the damn fish will say, ‘wait a moment, I am not getting enough oxygen here’ and they will turn around away from this zone,” Chesney said.
The biggest concern for Chesney and Rozich is determining the oxygen-tolerance level for the Asian Carp.
Barely any studies have established this level, according to Chesney. Garcia and his team are working on it.
“Right now we believe a 0.3 mg of oxygen per liter of water would be effective,” Chesney said. “We believe they may not go for long without oxygen because of their high activity levels.”
The researchers estimate the cost of running the nitrogen barrier would be $30 million annually. The price of constructing the facility could range from $15 million to $45 million.
It’s a steep cost but nothing compared to the long-term cost of the impact of the species on the fishing and tourism industry, Rozich said.
Chesney regularly uses nitrogen to remove oxygen during lab experiments but on a larger scale. A trough constructed in the sanitary canal could be used to evaluate the process, he said.
“Such a setup would allow evaluation of the tolerance of the Asian carp to low oxygen levels and ultimately the effectiveness of the proposed barrier,” he said.