Prowling the waters of Lake Superior last month, the 87-foot research vessel Blue Heron was closing in on its quarry: dozens of souped-up thermometers that scientists had thrown into the frigid lake 12 months before. Capt. Mike King, one eye on his Global Positioning System (GPS), nosed the boat toward a point where one string of gauges was supposed to be hanging on a submerged cable. Figuring they were within range, a technician leaned over and lowered an acoustic transmitter into the water. The transmitter sent a signal that freed the cable, which shot to the surface on a steel float. Along for the ride: four yellow aluminum tubes containing thermometers that oceanographer Elise Ralph of the University of Minnesota at Duluth had placed in the lake last year.
The devices had been taking the lake's temperature every 15 minutes. As soon as the crew hauled the dangling tubes on deck, Ralph opened them, exposing a modem jack and circuit boards. She plugged a phone line into the jack, downloaded all the data in four minutes--and could hardly believe what the computer screen displayed. Last summer surface temps were in the 70s--20 degrees above normal. Even 100 feet down the water was 15 degrees hotter than usual. "That was the warmest Superior has ever been," says Ralph. "And it's going to be another warm one this year, too."
Good news for swimmers--who in the past had to have polar-bear genes to enjoy the water--may be bad news for the lake. The rising water temps threaten to roll out the welcome mat for alien species and decimate the cold-water plankton on which the lake life depends. But running a fever is not the Great Lakes' only problem. Today's pollutants include toxic chemicals that ride in on the winds from distant countries. And urban sprawl threatens to alter the lakes' ecosystem irrevocably. Which prompts a question: have we saved the lakes... only to lose them?
By any measure, the Great Lakes were indeed saved, in one of environmentalism's most dramatic successes. Only 30 years ago Lake Erie was dead, with garbage and rotting fish regularly washing onto beaches and runoff of fertilizer and raw sewage causing massive algae blooms that starved fish of oxygen. The Cuyahoga River, which feeds Erie, was so polluted with oil, logs, sewage and every other kind of garbage that it caught fire on June 22, 1969. The walleye in Erie contained so much toxic mercury that the government banned its consumption. Cormorants were born horribly deformed by pesticides, local populations of peregrine falcons had been driven toward extinction by DDT, and lake trout in Michigan and Huron were wiped out by overfishing and by sea lampreys that had invaded the lakes through a canal from the Atlantic.
But thanks to the Clean Water Act and the Great Lakes Water Quality Agreement of 1972, overflows from most municipal sewage systems are almost history and factories no longer treat the lakes as their own private cesspools. Erie today is a world-class fishery (you can even eat the walleye). Ontario is home to hundreds of healthy double-crested cormorants (so many that nine men, including several fishing guides frustrated by birds' gorging on smallmouth bass, shot more than 800 of the federally protected creatures on Lake Ontario last summer). Michigan is teeming with prized steelhead, salmon and brown trout. Lake trout in lower Huron and Superior are thriving.
Are the lakes back from the brink for keeps? Only if someone can figure out how to beat back the new generation of threats:
Sprawl destroys habitat and unleashes runoffs of pesticides and fertilizer from lawns. It covers shoreline with cement, preventing rainwater from replenishing the lakes. Sprawl, say scientists, has surpassed industrial pollution as the leading threat to the Great Lakes today. "Unless sprawl is brought under control," says Michael J. Donahue, executive director of the Great Lakes Commission, "the tremendous successes we've seen over the last 30 years may be in jeopardy."
Air currents from as far as Mexico and Russia bring toxic chemicals such as the banned pesticide DDT and PCBs, once used in electronics manufacture. Enough mercury, from coal-fired power plants, continues to fall in the lakes that it sank a plan to deplete the lakes of sea lampreys by selling the predatory fish to Portugal. The lamprey's mercury load exceeded the European Union's safety limit.
Global warming is still more a hypothetical threat than an actual one. But what it lacks in immediacy it makes up for in destructive potential. Cold temperatures have kept aliens like zebra mussels and round gobies (a fish) mostly out of Superior, for instance. "There are lots of exotic species queued up to invade the Great Lakes," says biologist Joseph Koonce of Case Western Reserve University. "If the temperatures rise, then we're looking at a terrible series of invasions" that could wipe out native flora and fauna and upend the ecosystem that supports $4 billion a year in sport fishing. Biological effects of the warmer waters are already here. Elise Ralph's catch from the Blue Heron shows that Superior is running a temperature. Plankton, the base of the food chain, have already descended this year from 50 feet down, their usual hang zone, to 75, where the cooler water they need to survive has now sunk. Since less light penetrates the depths, the plankton grow more slowly, producing less food for fish and other creatures up the food chain. If something suddenly made the plankton population crash, says Ralph, "the whole food chain could start to collapse."
Warming could make the Great Lakes only Middling: in a warmer world, more water evaporates. Computer models developed by hydrologist Frank Quinn of the National Oceanic and Atmospheric Administration predict that, by 2050, global warming could drop water levels in Lake Erie by four feet and Huron and Michigan by six feet. Already lake levels are at their lowest in three decades; Michigan and Huron have fallen two feet in the last year. "It is very clear that we will have a pronounced lowering over the next 50 years," says Donahue. "That will have profound effects not only on the environment but also on the economy." Less water in the lakes means less water surging through hydropower stations. Freighters will run closer to the bottom, disturbing contaminated sediments and sending PCBs and dioxins back into the food chain. Erie and Michigan might not "turn over" in the spring and fall as they should: cold water plunging down from the surface carries oxygen, so without this delivery "there may not be enough oxygen for things to live at the depths," says NOAA's Quinn. Less ice cover in winter means that natives such as whitefish, which depend on ice to protect their spawning areas from destructive waves, could face a population crash.
The industrialized world has taken a few baby steps toward capping emissions of the gases (from the burning of coal, oil and natural gas) that trap heat in the atmosphere and thus warm the planet. But even if everyone plays by the rules, megatons of "greenhouse gases" will continue to waft into the stratosphere for decades to come. Like sprawl, global warming has no easy solution. In comparison, cleaning a flammable river and reviving a dead lake seem almost simple.