CANADA-ONTARIO AGREEMENT RESPECTING
THE GREAT LAKES BASIN ECOSYSTEM
Lake Erie is the comeback kid. Over-fertilized with human waste, farm
chemicals and phosphate detergents, the lake almost choked to death on
masses of decaying algae back in the 1970s. Only concerted action by the
governments of Canada and the United States, the Great Lakes states, the
Province of Ontario and municipal governments, through the Canada-U.S.
Great Lakes Water Quality Agreement and the Canada-Ontario Agreement Respecting
the Great Lakes Basin Ecosystem (coa), pulled Lake Erie back from the
brink.
By the mid-1980s,nutrientlevels
had dropped back to acceptable, sustainable levels. The blooming algae
were under control, and within 10 years, the waters were clear again.
Fish populations were restored, resuscitating a dormant fishing industry
and attracting a new fleet of charter boats. It looked like clear trolling
into the new millennium.
But Lake Erie is a lake in flux, a lake at the crossroads … again.
In recent years, researchers have tracked some disturbing trends. Nutrient
concentrations in inshore areas of the lake are beginning to creep back
up, while productivity may be dropping in deeper waters. And some fish
stocks, the hallmark of a healthy ecosystem, are declining once again.
The experts can point to a host of possible contributing factors. There
is the influence of growing urban centres, the polluted run-off from area
farms, on-going chemical contamination, loss of critical wetlands and
other habitat, the invasion of non-native species, even the demands of
an invigorated fishing fleet.
Under the Canada-U.S. Lake Erie Millennium Plan, scientists are working
to more fully understand the complex interplay of the forces at work,
and what can be done to safeguard the progress made so far. “The
Millennium Plan is an attempt to draw together Canadian and American researchers
– federal, provincial, municipal, non-governmental and academic –
from all over the basin,” says Environment Canada’s Murray Charlton,one
of four directors of the Millennium Plan. Identifying Lake Erie’s
most pressing environmental problems is part of implementing Lake Erie’s
action-oriented Lakewide Management Plan or LaMP.
When nutrient loadings are optimal, Lake Erie supports
a richfoodchain with lots of game fish at the top.
Three lakes in one
Lake Erie is actually three lakes in one, three distinct basins linked
together along an east-west axis and separated by shoals and reefs. The
Western Basin, which stretches from Toledo in the United States at the
western tip of the lake to Point Pelee in Ontario, is the shallowest with
an average depth of around seven metres. That drops to 18 metres in the
large Central Basin, and down again to 25 metres in the Eastern Basin,
hitting a maximum of 64 metres in the deepest holes. Because the whole
lake is relatively shallow, the water warms quickly in the spring and
cools again as quickly in the fall.
The smallest of the Great Lakes by volume, Lake Erie is still the most
productive and the most biologically diverse of the five. Some 143 different
species of fish have been identified in its watershed. The annual catch
of the commercial fishery in Lake Erie is greater than the catch in the
other four Great Lakes combined, making it the most valuable freshwater
fishery in the world.
The topographic features that make Lake Erie a fishing paradise also
place it in environmental jeopardy. “A shallow lake recycles nutrients
better than a deep lake,” says Charlton. “Every unit of nutrient
put into the lake generates a higher level of biological production.”
When nutrient loadings are optimal, Lake Erie supports a rich foodchain
with lots of game fish at the top. Add too much of the nutrient phosphorous
and you get more algae. Eventually those massive algal blooms die and
drift to the bottom where they are decomposed by a very active bottom-dwelling
community of micro-organisms. This process is called eutrophication and
it can strip the water of oxygen making the lake very inhospitable. On
the other hand, push nutrient levels too low and productivity drops. Again,
the food chain collapses because there is not enough algae.
Invasion of the zebra mussel
“By the mid 1980s,we had achieved the targeted nutrient loading
goals set under COA,” says Charlton. “We had managed to cut
nutrient levels in half in the Western Basin where the (algal) problem
was the worst.” Then the zebra mussel arrived in the ballast tanks
of some overseas freighter and quickly spread through the lake, feeding
on the rich phyto-plankton and upsetting the delicate nutrient/algae balance.
The mussels were tremendously efficient in further reducing algal levels,
and their impact was felt all the way up the food chain. The number of
yellow perch, walleye and white perch declined across the lake, while
smelt populations dropped in the Eastern Basin. Conservative harvest strategies
have been adopted by the Lake Erie Committee of the Great Lakes Fisheries
Commission in order to permit the recovery of these species to their former
potential.
In addition to algae, the zebra mussels also filter out some of the suspended
solids from the water column. “We have 32 years of data and you can
see the water’s clearer, especially in the shallower Western Basin
and inshore areas of the lake,”says Charlton.
However, after years of rapid population growth, the spread of the zebra
mussel has slowed. They have already colonized all the suitable rocky
outcroppings and hard surfaces on the lakebed; all that is left is the
soft sediment where it is tougher (but not impossible) for the mussel
to establish a foothold.
At the same time, phosphorus concentrations in Lake Erie’s shallow
waters are beginning to rise again. “Phosphorus levels were decreasing
up till the mid-1990s,” s a y s Charlton, “but they’ve
been on the way back up since 1995.” It appears that zebra mussels
can no longer be relied upon to keep eutrophication under control.
Even as scientists strive to understand the lake, the biological community
continues to change. On average, another foreign species grabs a niche
in the lake’s ecosystem every 11 months. The invading zebra mussel,
the round goby, the white perch, and the spiny water flea are each taking
their best shot at grabbing a bigger share of the food web, upsetting
the delicate energy cycling mechanisms. This makes life more difficult
for native species.
The stress of urban and rural life
In the shallow
basins of Lake Erie, the volume of water is limited and environmental
stressors exert a proportionally larger impact. In the 1960s, the huge
urban and industrial complex centered around Detroit had a devastating
effect on the Western Basin. Municipal sewage fed an algal population
explosion every summer, while effluents loaded with toxic chemicals contaminated
the sediment and poisoned the food chain. Expensive sewage treatment plant
upgrades, supplemented by bans on high phosphate detergents helped cut
nutrient loadings.
Nutrient loadings from urban centres may be creeping back up. One-third
of the total population of the Great Lakes Basin – nearly 12 million
people – lives around Lake Erie. “You’ve got to keep doing
a better job, increasing the level of sewage treatment, just to keep even
with population growth,” explains Charlton. In addition, the lake
receives some 80 percent of its flow, and much of its nutrient load,
from the Detroit River. Remedial Action Plans (rap) for the Detroit River
and the St. Clair River are therefore critical links in efforts to clean
up Lake Erie.
Rural non-point source loadings are also cause for concern. The Lake
Erie watershed is one of the most intensively farmed landscapes in North
America. Nutrient, sediment and bacterial levels in the watershed tributaries
often exceed government guidelines. “If nutrient levels in rural
run-off could be better controlled,” says Charlton, “these rivers
and streams would provide better spawning grounds and fish populations
in the lake would likely increase.”
…Under the Millennium Plan, scientists throughout
the basin are trying to unravel Lake Erie’s perplexing ecosystem
…
Some good news and some bad
Dr. Jan Ciborowski, professor of biological sciences at the University
of Windsor, and the second of four Millennium Plan Directors, is interested
in what benthic organisms can tell us about the state of Lake Erie’s
health. Paradoxically, it appears that “things are getting both better
and worse,” says Dr. Ciborowski.
The burrowing mayfly, Hexagenia, is an excellent bio-indicator of the
lake’s environmental recovery. Forty years ago, eutrophication wiped
Hexagenia out of the polluted Western Basin. “The larvae need good
levels of oxygen to survive,” says Dr. Ciborowski. “Even 24
hours of conditions without oxygen can knock them out.” Today, you
can find Hexagenia throughout the Western Basin, all along the south shore
of the lake, and in the muddy reaches along the north shore.
Hexagenia have made an incredible comeback, says Dr. Ciborowski. “Ten
years ago there were none. Now we are measuring 80 to 90 kilograms of
larvae per hectare,” he says. “That’s a lot of fish food
that hasn’t been there since the 1950s.” Those Hexagenia are
supporting a thriving walleye population through the winter and feeding
perch all summer long.
In the “battle of the benthos”, Hexagenia has gone head-to-head
against the zebra mussel in the the soft muddy sediment in the Western
Basin. So far, Hexagenia appears to be gaining the upper hand. The masses
of mayfly larvae stir up a lot of silt while grazing through the bottom
muck. Dr. Ciboorowski believes that this “microturbidity” might
clog the gills of the mussels, slowing their incursion into Hexagenia
turf.
While Hexagenia may be pinning its mussel to the mat, the little bottom-dwelling
crustacean Diporeia may be losing its’ bout. The shrimp-like macro-invertebrate
is very high in calories and an important part of the diet of smelt, whitefish
and young lake trout. As Diporeia disappears from the deep, cold waters
of the Eastern and Central Basins, the fish populations there are starting
to sag.
Along with competition from zebra mussels, there are other hypotheses
that explain why Diporeia are in decline. They may be at a low point in
their population cycle. Perhaps there is another non-native invader playing
a role. “We really don’t know,”Dr. Ciborowski admits. The
massive disruption caused by eutrophication may have masked other, more
complex problems in Lake Erie. “The issue of fish and insect reproduction
didn’t really matter when all the fish and insects were dead,”
he says.
Under the Millennium Plan, scientists throughout the basin are trying
to unravel Lake Erie’s perplexing ecosystem. There’s too much
work for any one individual or agency to handle. “If we are to get
anywhere, we have to coordinate our research and that research has to
address the questions relevant to the people managing the lakes.”
The answers they uncover will be crucial to protecting Lake Erie, a lake
at the crossroads again.
What is a LaMP?
It’s a Lakewide Management Plan, and LaMPs have been created
for lakes Erie, Ontario and Superior. Coordinated by the governments
of Canada and the United States, the Lake Erie LaMP brings together
the Province of Ontario, the Great Lakes states and a broad network
of stakeholders to describe the lake’s problems, identify the
source(s) of those problems, and envision the preferred future state
of the resource.
Established under the Canada-U.S. Great Lakes Water Quality Agreement,
the LaMP process was designed to address and eliminate bioaccumulative
toxic chemicals. The Lake Erie LaMP also covers habitat loss, nutrient
and sediment loadings, and the invasion of non-native species. The
Canada-Ontario Agreement Respecting the Great Lakes Basin (coa)
is one of the main mechanisms used to determine government of Canada
and Ontario contributions to the LaMP.
Canada and Ontario have identified three goals for lakewide management
over the next five years:
clearly understanding the environmental problems and causes
of ecological impairment;
having broad based support for priority actions; and, making
progress on habitat restoration and protection, and;
reducing the impact of harmful pollutants.
For more information on the Lake Erie LaMP, including tips on how
you can get involved, visit the Environment Canada website at www.on.ec.gc.ca/glimr/lakes/erie.
By the mid-1980s,nutrientlevels
had dropped back to acceptable, sustainable levels. The blooming algae
were under control, and within 10 years, the waters were clear again.
Fish populations were restored, resuscitating a dormant fishing industry
and attracting a new fleet of charter boats. It looked like clear trolling
into the new millennium. 
In the shallow
basins of Lake Erie, the volume of water is limited and environmental
stressors exert a proportionally larger impact. In the 1960s, the huge
urban and industrial complex centered around Detroit had a devastating
effect on the Western Basin. Municipal sewage fed an algal population
explosion every summer, while effluents loaded with toxic chemicals contaminated
the sediment and poisoned the food chain. Expensive sewage treatment plant
upgrades, supplemented by bans on high phosphate detergents helped cut
nutrient loadings.