03 July 2008

World's great lakes under threat

A lake is the landscape's most beautiful and expressive feature. It is earth's eye; looking into which the beholder measures the depth of his own nature. ~Henry David Thoreau

Lakes are indeed expressive, and reflecting upon them -- listening to what they are telling us -- does not speak well of humanity's essence. Many of these great lakes are under threat; poisoned, dried-out shadows of their former selves. These lakes are vitally important for their local area, influencing the local weather and providing economic and physical resources for all the flora and fauna. Loss of these resources can prove disastrous (and indeed has...) for the region. The problem is global. And while the immediate sources of danger to the lakes are myriad, the impetus behind them all is the usual suspect, humankind. Our influence ubiquitous; the consequence of Our Way of Life.

On the border of Bolivia and Peru, Lake Titicaca is undeniably polluted, though no detailed studies of the water's state have been done. One apparent cause is 'enormous natural ponds filled with a toxic cocktail of sewage, organic pollution and industrial and mining waste'. The lack of sewage treatment is also a concern for many communities as well. This not only makes the water undrinkable, but the aquatic plants of the lake absorb much of the pollution. These plants are subsequently used as fertilizer or hay to feed livestock. The net result spreading the pollutants into the wider system, with unknown effect.

Out amongst the melting permafrost of Siberia lies Russia's Lake Baikal. The lake is warming rapidly, over 1 degree since the 1940s. This is related to a loss in the annual number of days with ice cover, 18 days fewer in the last 100 years. The changing conditions are posing a threat to the local flora and fauna:

...Baikal's seal, which raises its pups on the ice, could suffer because the animal has several onshore predators. If ice caves the pups are raised in melt, Asian crows could also eat the pups...

Changes in the food cycle have already been seen. Numbers of multicellular zooplankton, which normally live in warmer waters, have increased 335 percent since 1946, while numbers of chlorophyll have risen 300 percent since 1979...

North America's Great Lakes have been an ongoing concern since the 1960s and 70s when high levels of pollution were noted in Lake Erie. Some of these problems, while more under control, exist into the 21st century. Last year, Lake Superior saw record low water levels, a trend expected to continue as a result of the Great CO2 Enhancement Experiment. As with Lake Baikal, warmer temperatures and reduced ice cover result in enhanced evaporation and lower water levels.

The spread of invasive species also threatens the Great Lakes. The Diporeia, a small 'shrimp-like energy dense creature', is undergoing a 'population freefall'. This critter was/is a 'major food source for commercially important species like lake whitefish and many prey fish upon which salmon, trout and walleye rely.' The cause(s):

The spread of invasive zebra and quagga mussels - voracious filter feeders with an overlapping diet - largely coincides with Diporeia's decline and is widely believed to be at least partially responsible. But research cannot yet explain the link...

...[A]nother possible contributor to Diporeia's decline: water pollutants like pesticides, polychlorinated biphenyls (PCBs), flame retardants or others.

[...]Regardless of the reason, Diporeia's decline has already had some measurable negative effects on various fish species. Alewives...have declined in growth rates, condition...and caloric density since Diporeia populations began declining...

The Great Rift Valley of eastern Africa features its own set of 'Great Lakes'. A recently issued report Africa: Atlas of our Changing Environment details (with excellent satellite imagery) many of the ecological issues facing the region. Lake Victoria was invaded by water hyacinth in the 1990s. Pollution and fluctuating lake levels are also an issue. Many of the problems have their source in the rapid population growth around the lake. Further south, Lake Mawali is suffering from overfishing of the easily-accessible shallow waters. The nutrient-loading of the lake is also being change by fertilizer runoff

A particularly striking case of human-caused ecological disaster is Lake Chad, bordered by Chad, Cameroon, Niger, Central African Republic and Nigeria. The last part of the Sahel diary of UN Special Advisor Jan Egeland provides some insight:

Today we visited what was once Lake Chad in eastern Niger, which as recently as the 1960s covered a total 25,000 sq km, of which 4,000 sq km were inside Niger. Since the droughts that have been recurrent since the 1970s the lake has now has shrunk to nothing inside Niger.

This is a very dramatic environmental crisis, with enormous consequences for hundreds of thousands of people. For me the visit was epitomised by an old customs boat which is now stranded in the middle of the desert, a desert covered in sea shells...

The report noted above states that the Lake has decreased by 95% in the last 35 years or so, a result of climate variability and overuse. One of the many problems associated with the declining lake (from Egeland's diary):

...[T]here are already many conflicts between and among nomads and agricultural people in Niger, and between various ethnic groups, because of the scarcity of resources. Others have estimated that around Lake Chad there are as many as 30 or more named armed groups, and the potential for increased conflict is endless.

The various crises the world's great lakes face are all anthropogenic in origin. Climate change is a factor in many cases, but issues such as pollution, resource use and overpopulation are also paramount. This reinforces the notion that in tackling the environmental issues before us, we cannot focus on climate change to the exclusion of all else. The other issues facing us are important as well. These are difficult, perhaps intractable problems. And it may be too late to stop the damage; we just don't know. That cannot be an excuse for inaction. Doing nothing guarantees failure.

Is there reason for hope? After all, Lake Erie noted earlier recovered somewhat from its 1970s low point. And attempts to rescue the Aral Sea, ravaged by the Soviet Union, are apparently to be bearing some fruit, providing at least a glimmer of hope (but not much more than that, really...). Days are early, and there remains a long way to go. Ideally, we would leave these lakes alone and let them recover on their own. That tactic seems to work for some species in the Great Barrier Reef. However, this is not a feasible option; we (and the rest of the ecosystem...) need the water to survive. The key is effective use and management of the resources these lakes represent, with an eye towards preserving future needs.

Images: 1: Lake Baikal surrounded by hotspots and smoke, 18 May 08. EO Natural Hazards

2: Lake Chad in 1972 and 2007 (right). National Geographic News.

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