To read Part I of this series on the Great Lakes and learn about their importance, click here.
The Great Lakes are vital to our livelihood and economy, but they face a myriad of threats ranging from dead zones caused by pollution to a huge and ravenous fish species.There are many individual threats to the Great Lakes and their ecosystems. Let’s explore them by category:
1. Invasive species. An invasive species is a plant or animal introduced into a habitat that, without predators and with ample food sources, breeds unchecked. In the case of the Great Lakes, most invasive species were introduced through ballast water carried in via ships. Currently over 180 invasive fishes, plants, viruses and other organisms thrive in the Great Lakes basin, such as sea lamprey, zebra mussels and hydrilla. Each of these invaders bring their own unique problems to the Great Lakes ecosystems. Zebra mussels attach to and colonize inside water intake pipes, wells, and screen systems. The sheer numbers of mussels clog pipes and reduce the flow, which affects drinking water supply and industrial use. Since the prolific number of mussels filter water (each mussel, the size of a fingernail, can filter up to a liter of water per day), they’d seem like a helpful invader, but that’s not the case. That increased water clarity means sunlight goes deeper in the lake and helps more algae to grow. Too much algae chokes out other stuff trying to survive and can create a toxic bloom that hurts people, fish and wildlife. The invasive mussels feed on plankton, which is the base of the Great Lakes food chain. The Great Lakes suffer a double whammy from the mussel invaders.
The most recent invasive threat is the Asian Carp. Asian carp were imported by catfish farmers in the 1970’s to skim algae from aquaculture ponds, the fish escaped from their original home and migrated throughout the Mississippi River, massively depleting plankton and pushing out other species. They take over spawning areas, eat everything in their path and grow to huge sizes. Carp can also cause direct harm to humans. Silver carp are known to jump out of the water at high speeds, which can injure boaters and damage boating equipment. Like sci-fi aliens, the Asian carp are voracious eaters, prolific breeders and high jumpers–this fish will take over any water space it can enter. Recently a 19 pound Asian carp was caught six miles away from Lake Michigan in a landlocked lake, so the threat is getting nearer and nearer.
2. Toxic Chemicals. Untreated sewage and runoff dump bacteria into the Great Lakes, leading to swimming bans and illness for those who enter Great Lakes waters. A soup of chemicals washes in from storm sewers, farms, factories and other sources. Fecal coliform and E. coli bacteria from animal feces, dirty diapers, failing septic systems and sewer overflows lead to higher levels of bacteria. This pollution has been happening for decades and has never been cleaned up. PCBs and DDT were both banned in the 1970s, but they still linger in the sand, clay, silt and organic matter found at the bottom of the lakes.
Newer substances, such as mercury and PBDEs, are being dumped even today. Chemical pollution causes a chain reaction throughout the Great Lakes food system. Bottom feeders can absorb some of these chemicals into their bodies. Fish eat the bottom feeders – and the chemicals they contain. Next, waterfowl and even humans eat the fish, passing the chemical exposure higher up the food chain. This is a process called ‘biomagnification,” and it harms animals and humans.
Other toxic chemicals enter the Great Lakes from agricultural runoff, lawn chemicals and air pollution.
3. Water Levels.The Great Lakes are a one-time gift from glaciers that melted tens of thousands of years ago. Though these great expanses of water may appear to be a never-ending resource, each year only 1 percent of Great Lakes water gets replenished. Drought and increasing demands for water put the Great Lakes at risk. Over time, lake levels are falling, and local communities have seen their groundwater supplies diminish – which negatively impacts the streams and wetlands that are key parts of the Great Lakes ecosystem. Water levels in the Great Lakes have been below their long-term averages during the past 14 years, and this winter the water in Lakes Michigan and Huron, the hardest-hit lakes, dropped to record lows, according to the Army Corps of Engineers. Low water levels changes habitats, and human industry is affected as shipping channels and harbors become impassable.
4. Habitat Destruction. Waterfront property is a big seller and we’ve done a terrible job protecting the shorelines of the Great Lakes from human development. The diverse and fragile wetland areas in the Great Lakes basin keep our lakes and rivers clean, help prevent floods and provide important breeding grounds for fishes, waterfowl and animals. More than two-thirds of Great Lakes fish species spawn in wetlands, and many rely on near shore vegetation for food and shelter. Wetlands maintain water quality by filtering water before it drains into the Great Lakes. Wetlands aid in preventing erosion along exposed shorelines, too. We’ve destroyed 50 percent of fragile wetlands in the Great Lakes region, more than 90 percent in some areas. These valuable buffers have been permanently lost to human development–in the name of agriculture, industry and housing. Additional shoreline has been destroyed and replaced with concrete barriers, lawns, stone seawalls and parking lots.
5. Plastic. The Great Pacific Garbage Patch isn’t just an ocean phenomenon. Researchers collected samples from lakes Erie, Superior and Huron last summer and found the typical kinds of trash like shreds of plastic bags, plastic bottles and large quantities of round, plastic pellets–microbeads. Microbeads are those tiny plastic balls used in products like facial scrubs, body washes and toothpastes. They scrub away dead skin and are designed to wash down the drain. As you know if you regularly read this blog, flushing stuff down the drain doesn’t make it disappear–and microbeads are no exception. These plastics can–and do–bypass wastewater treatment processes. Microplastic is easily confused with natural food found in lakes. The microbeads and other tiny bits of plastic can remain in fish and be ingested by humans. Plastic in the Great Lakes will float to shore, drift out to the ocean or absorb chemicals from the water, which weigh the particles down and cause them to sink to the bottom of the lakes. Plastic will not biodegrade and its implications on fish, wildlife and humans is still unknown. You can learn more about this most recent threat to the Great Lakes in National Geographic.
Whew! Enviro Girl finds this list of threats to the Great Lakes exhausting–and depressing! Stay tuned to see if there is hope for the future of our Great Lakes in part III of this series.