Anna M. Michalak on the taming and invasion of Earth's largest fresh-water system.
Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC
The Great Lakes on the US–Canadian border are under intense pressure.
The Great Lakes that straddle the border of Canada and the United States hold one-fifth of Earth's surface fresh water, and cover almost 250,000 square kilometres — an area larger than the United Kingdom. They are home to 3,500 species of plant and animal, including more than 170 species of fish. Some 30 million people live in their watershed. Their scale and natural beauty are inspiring, yet for hundreds of years they have also been viewed as a resource to be conquered. Now, a perfect storm of invasive species, pollution, climate change and other pressures is playing out in the region.
In his engaging The Death and Life of the Great Lakes, journalist Dan Egan traces the lakes' history, from the arrival of the first Europeans, such as French explorer Jean Nicolet — who in 1634 set out on Lake Michigan in a birch-bark canoe, looking for a passage to Asia — to the present. Egan's focus is on invasive species that tagged along as humans re-plumbed the Great Lakes to serve their needs. Starting with the parasitic sea lamprey (Petromyzon marinus), which had spread across the Great Lakes by the 1930s, these have dramatically altered the lake system and devastated native populations. Egan tells a tale of human ambition, ingenuity and hubris. He also speaks of redemption and opportunity.
The Great Lakes had a central role in the industrialization of the continent, and have thus seen massive engineering projects with two primary goals: to open up the North American interior to shipping, and to dispose of its sewage. These, Egan shrewdly dubs the front and back doors.
The completion of the first canal and locks goes back to 1781, culminating in 1959 with the opening of the Saint Lawrence Seaway. As seagoing vessels made their way deeper into the Great Lakes, they brought with them freshwater species from around the world, especially in ballast waters used to stabilize ships. Along with the lampreys, the protagonists of Egan's story are alewives (a type of herring, Alosa pseudoharengus) and zebra and quagga mussels (Dreissena polymorpha and Dreissena bugensis), which have successively upended the food web and overtaken the ecosystem.
The management responses to these invasions parallel the broader history of environmental-restoration efforts. A selective poison was developed to control lampreys in the 1950s, after fisheries collapsed in Lake Michigan, Lake Huron and Lake Superior. Non-native coho and Chinook salmon (Oncorhynchus kisutch and Oncorhynchus tshawytscha, respectively) were introduced to tackle alewives, starting in the 1960s. The dual mussel infestation that began in the late 1980s continues but, in a fascinating twist, native whitefish (Coregonus clupeaformis) seem to be evolving to feed on the mussels and on another non-native fish, the mussel-eating round goby (Neogobius melanostomus). Biologists are now exploring other ways to take advantage of native predators to tackle invasives. This shift towards leveraging the strength and complexity of natural systems is a recurring theme in environmental restoration.
The construction of the “back door” that links the Great Lakes to the Mississippi watershed — which drains 40% of the continental United States — was completed in 1848. This safeguarded the water supply for Chicago, Illinois, by sending sewage down the Mississippi River rather than into Lake Michigan. With it, the Great Lakes have become vulnerable to yet more invasive species, most notably the Asian carp that have overrun the Mississippi watershed.
We are still far from a solution, as Egan shows. Record-shattering extremes have abounded over the past decade across the Great Lakes, ranging from record low water levels immediately followed by record high ice cover and rises in lake levels, to massive 'dead zones' of hypoxia — low oxygen — and harmful algal blooms. One bloom shut down the water supply in Toledo, Ohio, for two days in 2014.
Egan weaves solid quantitative scientific information into a narrative rich with tales of individuals who have spearheaded engineering projects, witnessed their consequences or studied their implications. This leaves the reader with a trove of knowledge, told like a great story rather than an academic lecture. I did wish for a few maps, pictures or diagrams to illustrate key ideas and to introduce the invasive protagonists. A deeper exploration of parallels with the expansion of non-native species in other parts of the world would also have been welcome, and links to water quality, fluctuating lake levels and climate change felt a bit tangential in places. Overall, however, the book is an impeccably researched portrayal of a fascinating story.
The path ahead is perhaps best illustrated by two quotes that Egan cites. In 1995, Ismail Serageldin, then World Bank vice-president, opined that “the wars of this century have been fought over oil, and the wars of the next century will be on water”. The US naturalist Aldo Leopold wrote in the 1940s that “a thing is right when it tends to preserve the integrity, stability and beauty of the biotic community”. This book is a reminder that human communities are part of the broader biotic community; it enjoins us to choose Leopold's vision, for the Great Lakes and beyond.