Rising Temperatures, Falling Water? (excerpt)
ONTARIO’S WASAGA BEACH is one of the finest swimming destinations in all of North America. Nestled into the southeast corner of Lake Huron’s expansive Georgian Bay, Wasaga boasts nine miles of white sand that slants out into Lake Huron’s azure waters at such a gradual slope that a hundred yards from shore the water barely reaches a swimmer’s waistline. A provincial park since 1962, Wasaga is just eighty miles from cosmopolitan Toronto, which helps explain why it is one of the most popular day-use tourist destinations in Canada. They come for the fun, and the sun, and to frolic in one of the most bountiful freshwater ecosystems on earth. “On a busy weekend we can have 60,000 to 120,000 people,” says park superintendent Mark Shoreman. “We claim it’s the world’s longest freshwater beach.”
But Wasaga is also an ideal place to witness the remarkable natural fluctuations that occur in Great Lakes water levels. Thanks to the faint tilt in the sand at Wasaga Beach, when Lake Huron’s water level falls by one vertical foot, it can actually change the Wasaga Beach waterline by dozens of feet. In 1986, during historic high water levels on the Great Lakes, Wasaga’s visitors only needed to amble a few yards from the tree line to reach the water’s edge. But in 2000, when water levels approached historic lows, beachgoers were forced to walk 150 yards to the water, often dodging the large thickets of sedges and coastal meadow that had sprouted in the sand where water once stood.
Tourists find these widely varying lake levelsto be alarming— something must be wrong, they assume. Nothing could be further from the truth. Vacillating lake levels are what experts refer to as “natural variability,” and that variability plays a key role in the complex Great Lakes ecosystem. “Natural variability is an absolute necessity,” says Douglas Wilcox, a wetlands expert with the U.S. Geological Survey’s Great Lakes Science Center in Ann Arbor, Michigan. “The [Great Lakes] plant and animal communities are not only adapted to that variability, but they absolutely require that variability to provide habitat and food, and nesting/spawning [areas] to maintain their populations.”
The interface between land and water is a rich and ecologically productive venue, and different creatures benefit at different waterlevel stages. During low water, long beaches and broad expanses of mudflats are created at the lakes’ edges. These flats are actually seed banks that have been harboring the progeny of rare water-leveldependent plants for decades. When the waters recede, these areas are exposed to the air and the unique plants embark on a robust growth binge, creating all sorts of food, cover, and other habitat for a variety of important wetland species. In essence, these beaches and mudflats imitate a desert after a cloudburst—they bloom. That’s precisely what happened in 2000, when lake levels dropped after a long period of high water. “It was incredible. It was just absolutely incredible,” says Mr. Wilcox. “These sediments were exposed and just came back like gangbusters [with] the most diverse vegetation you can imagine.” This is a cycle that has repeated itself for thousands of years in the Great Lakes Basin.
The extent of these lake-level fluctuations is impressive. It’s not unusual for water levels in the Great Lakes to change by more than a foot from one year to the next. And the difference between the historic high and historic low water levels on some Great Lakes is more than 6 vertical feet.1 Since water-level monitoring began in the mid-nineteenth century, record-keeping suggests that the lakes may operate roughly on a thirty-year cycle from high point to high point, with a dip falling approximately every fifteen years in between. Water fluctuations like that may be invigorating to the ecosystem, but they can cause headaches for humans who relish lake-level consistency. Docks can stand awkwardly high and dry one year, and then be under water a decade later.
What kind of effect will climate change have on these natural water-level fluctuations? That is one of the most intriguing and complex questions facing Great Lakes scientists and policymakers today...