November 29, 2012

New research has, for the first time, added the Great Lakes, the world’s largest group of freshwater lakes, to the list of marine ecosystems polluted by plastics. In recent years, seagoing vessels and scientific expeditions have encountered huge areas of floating plastic garbage in both the Atlantic and Pacific oceans. One area in particular, dubbed the Great Pacific Garbage Patch, extends over an area about the size of the state of Texas.

Scientists have raised the alarm about this plastic pollution, which is particularly worrisome because the material does not break down easily. Sea birds, turtles, seals, whales, and other marine animals can get tangled in plastic nets, bags, and packing material. These animals may also mistake plastic items for food and die of starvation if the plastic blocks their digestive system.

Scientists have found, however, that much, if not most, of the plastic pollution consists of tiny, even microsopic, pieces of plastic. In the oceans, plastics are gradually broken apart by sunlight and wave action, producing smaller and smaller pieces. Small marine animals, such as small fish, feed on the tiniest plastic pieces, which they mistake for tiny, drifting animals called plankton. As a result, toxic chemicals from the plastic become concentrated in their body tissue. These toxins are passed up the food chain, becoming more and more concentrated, as larger animals feed on smaller ones. This toxic food chain ultimately leads to human consumers of seafood.

The Great Lakes are Lakes Superior, Michigan, Huron, Erie, and Ontario. The lakes hold about 18 percent of the world's fresh surface water. (World Book map)

Similar microplastic was collected from three of the Great Lakes–Erie, Huron, and Superior–by scientists headed by environmental chemist Sherri Mason of the State University of New York at Fredonia. In an article published on the website Discovery.com, Mason speculated that most of the tiny pieces collected came from plastic bottle caps, chips from boats, and polyethelene microbeads. These plastic beads, which are added to many commercial facial cleansers, pass through water-treatment plants without being broken down.

Additional World Book articles:

• Conservation (Ocean conservation)
• Environmental pollution
• Lake Michigan
• Lake Ontario

March 23, 2012

The amount of ice covering the five Great Lakes in winter has decreased significantly, says a new report, and researchers warn that the loss could have a substantial impact on water quality and habitats in the region. The report, released by the American Meteorological Society (AMS), identifies an average decline of about 71 percent over the past 40 years. Measured losses vary from year to year and lake to lake. The Great Lakes are Lakes Erie, Huron, Michigan, Ontario, and Superior.

Researchers examined satellite photos and United States Coast Guard reports of ice coverage from 1979 to 2010. Lake Ontario, the smallest of the Great Lakes, showed the biggest decrease, with coverage falling by 88 percent. Coverage fell by 79 percent on Lake Superior, the largest of the lakes. The AMS also noted that only about 5 percent of the Great Lakes’ surface froze over this winter, though those data do not appear in the report. On average, the lakes have about 40 percent coverage in winter.

Together, the Great Lakes make up 18 percent of the world’s fresh surface water. Shrinking ice coverage on the lakes may speed up wintertime evaporation, leading to lower water levels and increased erosion along the shoreline. Lack of ice may also lead to an increase in algae blooms, which damage water quality.

The Great Lakes are the world's largest group of freshwater lakes. Declining levels of ice coverage may threaten the lakes and their surrounding habitats. (World Book map)

The report’s lead author, Jia Wang of the National Oceanic and Atmospheric Administration (NOAA) lab in Ann Arbor, Michigan, says the loss may be at least partly the result of climate change. Wang also noted that smaller climate patterns, such as El Nino and La Nina, may have played a role. “We are seeing the impact of global warming here in the Great Lakes,” says Wang, “but the natural variability is at least as large a factor.”

Additional World Book articles:

• Lessons from Lake Erie
• St. Lawrence Seaway
  
• Water (The water supply problem)