New study highlights expense of battling invasive species Ecosystem
A new study of a tiny organism that has infiltrated nearly two dozen Wisconsin lakes is the latest example of the expensive fight Great Lakes states are facing with the spread of aquatic invasive species.
A University of Wisconsin-Madison study concludes that the estimated cost of controlling a single invasive species, the spiny waterflea, in just one lake could range from $86.5 million to $163 million over 20 years.
The research focused on the spiny waterflea in Lake Mendota and highlights the challenge that the zooplankton poses for other pollution fighting efforts in the basin.
The study's results, say the researchers, show that scientists and policy-makers should take into account a broader measure of the costs in controlling aquatic invaders.
More than 180 invasive species inhabit the Great Lakes.
In 2008, a Cornell University researcher estimated in congressional testimony that municipalities and power companies in 23 states spent $1 billion to $1.5 billion from 1989 to 2007 to keep their water intake pipes from plugging up with invasive mussels.
A separate study in 2012 at the University of Notre Dame placed the ecological costs for damage to fishing and other recreational uses in the Great Lakes at $138 million to $800 million annually.
But a secondary effect is the migration of species to inland waters of the state — transported, often unwittingly, via the hulls of boats, bilge tanks and bait buckets.
"In addition to what is happening in the Great Lakes, we wanted to stress the effect on inland lakes," said Jake R. Walsh, a limnologist who is completing his doctorate at UW-Madison and will begin post-doctorate work there this fall.
His collaborators were Stephen R. Carpenter and M. Jake Vander Zanden, both UW limnologists.
There are 37 types of invasive species in inland lakes, according to the state Department of Natural Resources.
Some Wisconsin lakes have been untouched, while others are riddled with foreign species that can upend the ecosystem of a lake.
Eurasian water milfoil is well entrenched in the state. It forms dense mats, and that can prevent light from penetrating to native plants.
There also are more recent arrivals. Starry stonewort was found for the first time in Wisconsin in Little Muskego Lake in Waukesha County in 2014. It also grows in dense clusters, crowding out native plants and habitat of young fish.
The number of new invasive species has leveled off in the recent years, according to Bob Wakeman, aquatic invasive species coordinator at the DNR.
The agency spends about $4 million annually on inland lakes for various efforts to control the spread of invasives, including public education and grants to lake management districts.
The DNR helped fund the UW study because officials want to learn more about the spiny waterflea and its potential to harm native fish populations, Wakeman said.
The spiny waterflea inhabits at least 22 Wisconsin waterways.
It arrived in Lake Michigan in 1986 and turned up in the Madison lakes of Mendota and Waubesa in 2009. (There is no sign it has been found in metropolitan Milwaukee lakes.)
Like many other invading organisms, the spiny waterflea, whose native territory ranges from England to the Caspian Sea, is believed to have entered the Great Lakes in ballast tanks of freighters from European ports, especially St. Petersburg, Russia.
Measuring about 1 centimeter, the crustacean feeds on a native zooplankton, known as daphnia. Daphnia play an important role in a lake's food web because small fish consume them. Previous research has shown that perch populations don't grow as quickly when the spiny waterflea is present.
But another major benefit of daphnia is its ability to help clean up a lake by consuming large quantities of algae. Declining numbers of daphnia can, in effect, lead to more algae blooms.
The UW researchers turned their attention to the spiny waterflea for a study published this month in the Proceedings of the National Academy of Sciences.
They did not have to go far.
UW's Center for Limnology lies on the shore of Lake Mendota, which is considered one of the most studied lakes in the world.
Using information from previous research, including a study of Dane County residents' attitudes toward clean water, the scientists evaluated the costs of a seldom-measured variable — the "public benefit" of natural resources, such as sport fishing and the value of water clarity.
Lake Mendota has long been bedeviled by algae, which are fed by phosphorus from residential and agricultural fertilizer, manure from farm fields and other nutrient-rich runoff.
Since the arrival of the spiny waterflea, a combination of excess phosphorus and a decline in daphnia has degraded water clarity by about 3 feet.
Scientists don't have a magic bullet to eliminate the spiny waterflea from a lake.
"We don't have one, so how else can we improve water quality?" Walsh said.
One approach would veer away from invasive species entirely and instead target phosphorus runoff by using better farming practices or more street sweeping.
Using computer modeling, Walsh and the other researchers determined it would take a 71% reduction in phosphorus coming into the lake to restore about 3 feet of lost water clarity.
That computes to a cost of $86.5 million to $163 million over two decades, based on other research conducted by Strand Associates, a consulting firm, for the Clean Lakes Alliance, a nonprofit organization that is working on ways to improve water quality in Dane County.
While costly, Dane County residents might be willing to pay for it.
A 2001 study by UW agriculture economists — and updated in the latest UW study to account for inflation and population growth — found Madison-area residents were willing to pay $645 per household for 3 feet of improved water clarity. That computes to a price tag of $140 million.
According to UW's paper, the shorelines of inland lakes collectively in states bordering the Great Lakes have 36 times more lake frontage than do the Great Lakes themselves.
Said Walsh: "We did think that having a better representation of the costs on inland lakes was a better way to think about the threat invasive species pose on lakes in general."