WES WEEK SEVEN: 22-26 October 2001

• Floor of Atlantic Ocean to slip under the North American continent -- According to research conducted at the University of Minnesota and at the Swiss Institute of Technology in Zurich, the plates of the earth's crust are expected to slip under one another in such a manner that the ocean bottom in the middle of the Atlantic Ocean should drive westward toward North American and then slip under the continental plate, forming a trench within the next 3 to 10 million years.  [EurekAlert!]
• Carbon credits could adversely affect the oceans -- An MIT professor and colleagues elsewhere recently warned that the use of "carbon credits" without certain restrictions by nations as proposed by the Kyoto Protocol on Climate Change as a means to reduce global warming could actually be detrimental to the oceans.  One means where industrialized countries could earn credits is to use a technique called "ocean fertilization" that would increase the number of maritime phytoplankton, which would reduce the atmospheric carbon dioxide.  However, this technique, if not regulated, could cause too much nutrient enrichment of the ocean water.  [EurekAlert!]
• Mountain cloud forests affected by land use below -- A team of scientists studying the effects of deforestation of the lands below the famous Monteverde cloud forests of Costa Rica report that the loss of the lowland forests could result in fewer clouds that are needed to maintain the cloud forests. As a result, many of the animal and plant species that inhabit these cloud forests could be endangered. [EurekAlert!]
• A good salmon run in the Northwest -- More salmon and steelhead have returned to the Columbia River and other rivers in the Pacific Northwest than any other year in the last 63 years.  Apparently a string of recent rainy winters has increased the number of fish that have survived.  Unfortunately, this year's drought could spell fewer fish in the annual runs within two to three years.   [ENN]
• Earth diary - A summary of the week's major environmental events on Planet Earth. [CNN]

Concept of the Week: Dams and Ecological Integrity

Dams disrupt the natural seasonal fluctuations in the flow of rivers and streams with potentially serious consequences for the integrity of aquatic ecosystems. For one, dams interfere with the upstream and downstream migration of fish. Storage of water in reservoirs behind dams reduces the downstream discharge of water, sediment, and nutrients. These and other alterations of fluvial habitats threaten or endanger more than 20% of all freshwater species.

The ecological impact of dams is extensive because these structures affect so much runoff. Worldwide, almost 3000 dams have a reservoir storage capacity exceeding 25 billion gallons-a combined volume of water roughly equivalent to that in Lakes Michigan and Ontario. The more than 70,000 dams in the U.S. can store half of the annual flow of all the nation's rivers and streams.

The continuity of the global water cycle implies that disruption of river and stream flow by dams can also impact marine and lacustrine (lake) ecosystems. In the Pacific Northwest, for example, only about 5% of juvenile salmon survive passage through dams and reservoirs on the Columbia and Snake rivers. Salmon are anadromous, that is, they spawn in freshwater streams, but spend most of their adult life in the ocean. After hatching, young salmon (smolts) swim downstream to the Pacific Ocean, where they mature and then return to the same streams to spawn. But the 56 major dams in the Columbia River watershed are formidable obstacles to salmon migration. Largely ineffective are fish ladders designed to help the salmon move upstream and other structures that guide them downstream around hydroelectric turbines. (These turbines have been likened to giant food processors for smolt attempting to swim through.) Furthermore, smolts on their downstream passage are held up in reservoirs where they are exposed to predators, pathogens (disease-producing organisms), and water that is too warm. Atlantic salmon have a similar fate. More than 900 dams on New England and European rivers prevent most Atlantic salmon from reaching their freshwater spawning grounds. Consequently, their population has declined to less than 1% of historical levels.

Traditionally, dam operators regulate stream and river flow for flood control and to supply water for electric power generation and irrigation. But recently, in response to the adverse impacts of dams on aquatic ecosystems, has come a growing interest in operating dams in ways that recreate the river's natural seasonal flow pattern and habitats. For example, this type of management is employed on the Flaming Gorge Dam on the Green River in Utah to protect sensitive habitats for endangered species including chubs and squawfish. The dam operator simulates spring floods of the pre-dam era by releasing a surge of water in May that facilitates the spawning of fish.

Concept of the Week: Questions

1. Alteration of aquatic habitats by dams [(is)(is not)] a reason why some fish species become threatened or endangered.
2. Anadromous species of fish spawn in [(the ocean)(freshwater rivers and streams)].

• 22 October 1987...Yakutat, AK surpassed their previous all-time yearly precipitation total of 190 inches. Monthly records were set in June with 17 inches, in September with 70 inches, and in October with more than 40 inches. (Sandra and TI Richard Sanders - 1987)
• 22 October 1988...A "nor'easter" swept across the coast of New England. Winds gusted to 75 mph, and large waves and high tides caused extensive shoreline flooding. A heavy wet snow blanketed much of eastern New York State, with a foot of snow reported in Lewis County. (The National Weather Summary) (Storm Data)
• 24 October 1785...A four-day rain swelled the Merrimack River in New Hampshire and Massachusetts to the greatest height of record causing extensive damage to bridges and mills. (David Ludlum)
• 25-26 October 1980...The combination of unusually high tides and southeasterly winds gusting to 75 mph generated waves with heights to 25 feet, resulting in serious flooding, beach erosion an sea wall damage along the Maine coast. Wind damage was considerable and as many as 100,000 homes were without power for up to 40 hours. (Accord Weather Calendar)
• 26 October 1998... Hurricane Mitch, a category 5 hurricane (on the Saffir-Simpson Scale) for 33 hours, finally dissipated after becoming the strongest October hurricane on record in the Atlantic Basin. Estimated rainfall totals of up to 75 inches caused devastating flooding and mudslides in Honduras and Nicaragua for days. Estimated death toll from this hurricane was more than 11,000, the worst since 1780. (Accord Weather Calendar)

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Prepared by AMS WES Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2001, The American Meteorological Society.