A highly endangered shoebill.
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Spreading disease. The effects of global warming caused by increased greenhouse gases read like descriptions of the Great Tribulation in The Bible. The first climate change conference was held in and with increasing urgency, scientists have been raising red flags ever since, warning us that because of unchecked consumption of fossil fuels, the human species is approaching a critical threshold where we will no longer be able to influence the warming climate.
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Environmental Impacts of Dams | International Rivers
Harlan Glenn, one of a handful of experts on man-made lakes and a consultant for the Lake Sherwood restoration. Lake Sherwood, which was completed in , was formed by a dam to hold irrigation water for the ranch that eventually became Westlake Village, Glenn said. Like swimming pools, man-made lakes require regular use of some chemicals, as well as periodic cleaning, said Glenn, who owns an Orange County-based consulting firm. But maintaining a lake is substantially more complex than keeping a backyard pool because its waters are home to competing varieties of fish, birds, plants and microorganisms.
Lakes and Reservoirs
As with many lakes, Lake Sherwood had been steadily deteriorating because of the growth of vegetation and the buildup of soil from surrounding hillsides. If a proposed project by the Murdock Development Co. Lake Sherwood will need air pumps, fish, water, chemicals and regular cleaning, much the same elements as those needed in an aquarium, Glenn said. An acre-foot is about , gallons. In a normal year, the lake level will drop about five feet from evaporation, Glenn said. Lake Sherwood normally reaches an average depth of 15 feet, Murdock representatives said.
The alteration of a river's flow and sediment transport downstream of a dam often causes the greatest sustained environmental impacts.
Life in and around a river evolves and is conditioned on the timing and quantities of river flow. Disrupted and altered water flows can be as severe as completely de-watering river reaches and the life they contain. Yet even subtle changes in the quantity and timing of water flows impact aquatic and riparian life, which can unravel the ecological web of a river system. A dam also holds back sediments that would naturally replenish downstream ecosystems. When a river is deprived of its sediment load, it seeks to recapture it by eroding the downstream river bed and banks which can undermine bridges and other riverbank structures, as well as riverside woodlands.
Riverbeds downstream of dams are typically eroded by several meters within the decade of first closing a dam; the damage can extend for tens or even hundreds of kilometers below a dam. Riverbed deepening or "incising" will also lower groundwater tables along a river, lowering the water table accessible to plant roots and to human communities drawing water from wells.
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Altering the riverbed also reduces habitat for fish that spawn in river bottoms, and for invertebrates.