The Great Lakes – Superior, Michigan, Huron, Erie, and Ontario –
contain about twenty per cent of the world’s surface fresh water.
Shared by Canada and the United States, the lakes not only supply water
to the communities nearby, but they are also vital to commercial
shipping and tourism, not to mention the fish, reptiles, and waterfowl
that call them home.
Because the lakes are so large, the water they contain seems
inexhaustible. However, ninety-nine per cent of the water was
left behind when the glaciers that gouged the lakes out of rock
receded. That means that only one per cent of the lakes’ water is
renewable in the form of ground run-off or precipitation.
When water levels dropped steadily between 1997 and 2003, leaving docks
high and dry and large ships unable to navigate the lakes, scientists,
environmentalists, businessmen, recreational boaters, and cottagers
alike became very concerned. Changes in water levels are part of
the normal cycle of the lakes. However, given the size of the
drop and the importance of the water system, it seemed prudent to
investigate the causes of the decline and ascertain how much is
attributable to mismanagement by man. Lees discusses three of
those causes in some detail.
Groundwater pumping is one drain on the water system that is covered in
agreements between the Canadian provinces and American states bordering
the lakes. There is evidence that groundwater that was once
thought to come from the Mississippi watershed and ends up being pumped
back into the Mississippi River, in fact comes from the Great
Lakes. While, comparatively speaking, this is not a great drain
on the lakes, the re-drawing of groundwater boundaries needs to be
addressed.
Dredging in the St. Clair River has permanently lowered the lake level
by 27 centimetres. As part of the St. Lawrence Seaway, the level
of the river is governed by agreement between Canada and the United
States, but was recently found to be far deeper than allowed by the
agreement. Dredging of the river has gone on for nearly a century
and, while it must be maintained to keep the Seaway open, some effort
needs to be made to ensure that over-dredging does not occur.
Global climate changes and weather also affect the level of the
lakes. As an example, Lees describes how the exceptionally-warm
winter of 1997-98 drastically reduced ice cover on Lakes Superior and
Michigan, resulting in increased evaporation. Scientists cannot
agree on what effect global warming will have on the lakes: while
some believe that warmer weather will result in more evaporation and
lower water levels, others expect more clouds and rain, and therefore
higher levels.
Everyone can, however, agree that it is important to find out whether
the change in lake levels is normal fluctuation or a man-made problem
requiring international co-operation and action. If the latter,
all are also agreed that action must come sooner rather than later.