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Lake Apopka is the third largest lake in the U.S. state of Florida. It is located northwest of Orlando, mostly within the bounds of Orange County, although the western part is in Lake County. Fed by a natural spring, rainfall and stormwater runoff, water from Lake Apopka flows through the Apopka-Beauclair Canal and into Lakes Beauclair and Dora. From Lake Dora, water flows into Lake Eustis, then into Lake Griffin and then northward into the Ocklawaha River, which flows into the St. Johns River. ==History== Through the 1940s, Lake Apopka was one of Central Florida’s main attractions. Anglers traveled from throughout the United States to fish for trophy-sized bass in Lake Apopka, and 21 fish camps lined the lake’s shoreline. Lake Apopka has a history of more than 100 years of human alteration, beginning with construction of the Apopka-Beauclair Canal in 1888. In 1941, a levee was built along the north shore to drain 20,000 acres (80 km²) of shallow marsh for farming. The discharge of water, rich in nutrients from agricultural and other sources, produced conditions that created a chronic algal bloom and resulted in loss of the lake’s recreational value and game fish populations. In July 1980, Tower Chemical Company (TCC), a local pesticide manufacturer, improperly disposed of significant amounts of DDE, a known endocrine disruptor, along with other toxic chemicals. As a result, these chemicals spilled into Lake Apopka, and the US Environmental Protection Agency was alerted. TCC shut down their operations in December 1980. In 1981, an EPA investigation began and the site was decommissioned and designated as a Superfund clean-up site. Despite their efforts, some of the chemicals seeped into the Florida aquifer and have proliferated into some of Central Florida's interconnected lakes and waterways. This chemical has caused health problems in much of the lake's wildlife population, and has caused infertility and other sexual disorders in several species, including alligators. In 1991, a coalition of real estate interests from the West Orange Community organized the Friends of Lake Apopka (FOLA) with the goal of reclaiming the lake from the agricultural interests who were discharging phosphorus laden water into the lake basin. Water from the lake was used to flood the farm fields during the hot summer months to restrict erosion and then discharged back to the lake before the growing season. A series of canals and high capacity pumps allowed the water to be introduced for irrigation and flooding or to discharge it when necessary. The phosphate laden water created a hypereutrophic condition resulting in algal blooms, robbing the lake water of oxygen and sunlight necessary to sustain plant life on the lake bottom. Over the decades, this condition caused the sandy bottom lake to be covered by a deep layer of muck. In 1996, Governor Lawton Chiles signed the Lake Apopka Restoration Act that provided funding to purchase the farmland responsible for the discharges. The shuttering of the farms allowed for the St. Johns River Water Management District (SJRWMD) to begin plans to convert the fields back to the marsh area it had once been. A survey was taken of the site that identified the hot spots that contained chemical contamination and clean up was initiated. ===North Shore Enhancement Area (NSEA)=== Historically, more than 85 percent of the phosphorus going into Lake Apopka was from farms on the lake’s north shore. To combat this problem, the District and the U.S. Department of Agriculture (USDA) purchased almost all of the farms for restoration between 1988 and 2001. This contributed to reducing discharges of excessive nutrients from farms to the lake. The 1996 Lake Apopka Improvement and Management Act authorized the District to set a phosphorus concentration target. Subsequently, the District established a restoration phosphorus-loading target for Lake Apopka of 15.9 metric tons of phosphorus per year. This represents a 75 percent reduction from 1989–1994 farming discharges. The target was later adopted as a total maximum daily load (TMDL) for the lake, which has a goal of attaining an in-lake total phosphorus concentration of 55 parts per billion (ppb). Restoration of wetlands on the NSEA can reduce stormwater discharges to Lake Apopka and related nutrient loading, accelerating the enhancement of the lake. The innovative restoration and remediation plan for the NSEA focuses on infrastructure requirements, soil inversion and soil amendment work needed to prepare the system for wetland restoration. The soil inversion process was developed as a remediation method to address the high levels of organochlorine pesticides (OCPs) found in organic surface soils (the top 30 centimeters (cm) of soil). The pesticides remain in the organic soils from years of farm pesticide applications. The inversion process used modified farm equipment to plow up to one meter deep and essentially flip the soil, bringing up uncontaminated soil to the surface and covering the contaminated surface layer of soil. The work was completed in May 2009 and it helped ensure that OCPs were unable to enter the food chain. The inversion process reduced contaminants in the biologically active soil layer to safe levels on about 1,600 hectares (4,000 acres) in the NSEA. Soils in the NSEA also contained excess nutrients such as phosphorus due to many years of agricultural production. Applying a “soil amendment,” which is a drinking water treatment residual, helps to trap excess phosphorus in soils. This helps mitigate the release of phosphorus from the soil to overlying water when the area is reflooded. The soil amendment was applied to about 2,800 hectares (7,000 acres) in the NSRA and was mostly complete in 2009. As infrastructure construction is completed for each phase, a biological assessment is prepared for review and submitted to the U.S. Fish and Wildlife Service (USFWS). With USFWS concurrence, saturation and restoration flooding begins. The infrastructure is designed to help establish full wetland habitat with a wide range of water levels. The infrastructure also allows water transfer among different areas within the NSEA to minimize the need to discharge waters to the lake. As each new phase is flooded and naturally populated with wildlife, fish samples are routinely collected and analyzed to ensure that pesticide levels in their tissues are below established safe levels for fish-eating birds. Newly flooded phases are carefully monitored for at least one year to ensure that any accumulation of pesticides through the aquatic food web do not present a risk to water birds. In addition, weekly bird surveys are conducted to monitor usage and to ensure that problems are detected quickly. As of January 2011 nearly 4,000 hectares (9,870 acres) are in various stages of reflooding. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lake Apopka」の詳細全文を読む スポンサード リンク
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