965 resultados para Yangtze lakes
Resumo:
Vancouver Lake, located adjacent to the Columbia River and just north of the Vancouver-Portland metropolitan area, is a "dying" lake. Although all lakes die naturally in geologic time through the process of eutrophication,* Vancouver Lake is dying more rapidly due to man's activities and due to the resultant increased accumulation of sediment, chemicals, and wastes. Natural eutrophication takes thousands of years, whereas man-made modifications can cause the death of a lake in decades. Vancouver Lake does, however, have the potential of becoming a valuable water resource asset for the area, due particularly to its location near the Columbia River which can be used as a source of "flushing" water to improve the quality of Vancouver Lake. (Document pdf contains 59 pages) Community interest in Vancouver Lake has waxed and waned. Prior to World War II, there were relatively few plans for discussions about the Lake and its surrounding land area. A plan to drain the Lake for farming was prohibited by the city council and county commissioners. Interest increased in 1945 when the federal government considered developing the Lake as a berthing harbor for deactivated ships at which time a preliminary proposal was prepared by the City. The only surface water connection between Vancouver Lake and the Columbia River, except during floods, is Lake River. The Lake now serves as a receiving body of water for Lake River tidal flow and surface flow from creeks and nearby land areas. Seasonally, these flows are heavily laden with sediment, septic tank drainage, fertilizers and drainage from cattle yards. Construction and gravel pit operations increase the sediment loads entering the Lake from Burnt Bridge Creek and Salmon Creek (via Lake River by tidal action). The tidal flats at the north end of Vancouver Lake are evidence of this accumulation. Since 1945, the buildup of sediment and nutrients created by man's activities has accelerated the growth of the large water plants and algae which contribute to the degeneration of the Lake. Flooding from the Columbia River, as in 1968, has added to the deposition in Vancouver Lake. The combined effect of these human and natural activities has changed Vancouver Lake into a relatively useless body of shallow water supporting some wildlife, rough fish, and shallow draft boats. It is still pleasant to view from the hills to the east. Because precipitation and streamflow are the lowest during the summer and early fall, water quantity and quality conditions are at their worst when the potential of the Lake for water-based recreation is the highest. Increased pollution of the Lake has caused a larger segment of the community to become concerned. Land use and planning studies were undertaken on the Columbia River lowlands and a wide variety of ideas were proposed for improving the quality of the water-land environment in order to enhance the usefulness of the area. In 1966, the College of Engineering Research Division at Washington State University (WSU0 in Pullman, Washington, was contacted by the Port of Vancouver to determine possible alternatives for restoring Vancouver Lake. Various proposals were prepared between 1966 and 1969. During the summer and fall of 1967, a study was made by WSU on the existing water quality in the Lake. In 1969, the current studies were funded to establish a data base for considering a broad range of alternative solutions for improving the quantity and quality of Vancouver Lake. Until these studies were undertaken, practically no data on a continuous nature were available on Vancouver Lake, Lake River, or their tributaries. (Document pdf contains 59 pages)
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The Sarasota-Manatee area is a water-short area and the study was undertaken in 1963 in order to determine the storage capability and discharge rates of the Myakka water shed. It was found that many of the streams of the water shed were virtually dry during part of every year. However, the basins of the Myakka lakes, through which the river flows offer some storage potential, that if properly developed would provide a continuance drift of about seven million gallons of water per day of good quality water that would be high in color and temperature upon occasion. With reasonable treatment some of this water could be used to meet the present needs of the rapidly expanding coastal areas. (PDF contains 40 pages.)
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Thousands of hectares of native plants and shallow open water habitat have been displaced in Lake Okeechobee’s marsh by the invasive exotic species torpedograss ( Panicum repens L.). The rate of torpedograss expansion, it’s areal distribution and the efficacy of herbicide treatments used to control torpedograss in the lake’s marsh were quantified using aerial color infra red (IR) photography.(PDF has 6 pages.)
Resumo:
Whole-lake techniques are increasingly being used to selectively remove exotic plants, including Eurasian watermilfoil ( Myriophyllum spicatum L.). Fluridone (1-methyl-3-phenyl- 5-[3-(trifluoromethyl)phenyl]-4(1 H )-pyridinone), a systemic whole-lake herbicide, is selective for Eurasian watermilfoil within a narrow low concentration range. Because fluridone applications have the potential for large effects on plant assemblages and lake food webs, they should be evaluated at the whole-lake scale. We examined effects of low-dose (5 to 8 ppb) fluridone applications by comparing submersed plant assemblages, water quality and largemouth bass ( Micropterus salmoides ) growth rates and diets between three reference lakes and three treatment lakes one- and two-years post treatment. In the treatment lakes, fluridone reduced Eurasian watermilfoil cover without reducing native plant cover, although the duration of Eurasian watermilfoil reduction varied among treatment lakes. (PDF has 11 pages.)
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In response to nuisance growths of algae and vascular plants, such as dioecious hydrilla ( Hydrilla verticillata L.f. Royle), copper formulations have been applied in lakes and reservoirs for a number of years. Concerns have arisen regarding the long-term consequences of copper applications and those concerns have appropriately focused on sediment residues. In this study, we evaluated the toxicity of sediments from treated (for a decade) and untreated areas in Lake Murray, South Carolina and estimated the capacity of those sediments to bind additional copper. Two sentinel aquatic invertebrates, Hyalella azteca Saussure and Ceriodaphnia dubia Richard, were used to measure residual toxicity of treated and untreated sediments from the field and after laboratory amendments. (PDF has 5 pages.)
Resumo:
Variable watermilfoil (Myriophyllum heterophyllum Michx.) has recently become a problem in Bashan Lake, East Haddam, CT, USA. By 1998, approximately 4 ha of the 110 ha lake was covered with variable watermilfoil. In 1999, the milfoil was spot treated with Aquacide®, an 18% active ingredient of the sodium salt of 2,4-D [(2,4-dichlorophenoxy) acetic acid], applied at a rate of 114 kg/ha. Aquacide® was used because labeling regarding domestic water intakes and irrigation limitations prevented the use of Navigate® or AquaKleen®, a 19% active ingredient of the butoxyethyl ester of 2,4-D. Variable watermilfoil was partially controlled in shallow protected coves but little control occurred in deeper more exposed locations. 2,4-D levels in the treatment sites were lower than desired and offsite dilution was rapid. In 2000, the United States Environmental Protection Agency (USEPA) issued a special local need (SLN) registration to allow the use of Navigate ® or AquaKleen® in lakes with potable and irrigation water intakes. Navigate® was applied at a rate of 227 kg/ha to the same areas as treated in 1999. An additional 2 ha of variable watermilfoil was treated with Navigate® in 2001, and 0.4 ha was treated in mid-September. Dilution of the 2,4-D ester formulation to untreated areas was slower than with the salt formulation. Concentrations of 2,4-D exceeded 1000 μg/ L in several lake water samples in 2000 but not 2001. Nearly all of the treated variable watermilfoil was controlled in both years. The mid-September treatment appeared as effective as the spring and early summer treatments. Testing of homeowner wells in all 3 years found no detectable levels of 2,4-D.(PDF contains 8 pages.)
Resumo:
Angler creel surveys and economic impact models were used to evaluate potential expansion of aquatic vegetation in Lakes Murray and Moultrie, South Carolina. (PDF contains 4 pages.)
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Water chestnut (Trapa natans L.,sensu lato) is an annual, floating-leaved aquatic plant of temperate and tropical freshwater wetlands, rivers, lakes, ponds, and estuaries. Native to Eurasia and Africa, water chestnut has been widely gathered for its large nutritious seed since the Neolithic and is cultivated for food in Asia. Water chestnut is now a species of conservation concern in Europe and Russia. Introduced to the northeastern United States in the mid-1800s, the spread of water chestnut as a nuisance weed was apparently favored by cultural eutrophication. Water chestnut is considered a pest in the U.S. because it forms extensive, dense beds in lakes, rivers, and freshwater-tidal habitats.
Resumo:
A limnological and fish survey program was developed on 112 lakes and reservoirs of Argentina during the summers of 1984 to 1987. Bathymetric surveys with a SIMRAD Skipper 411 model echosounder and line and lead were conducted on more than 40 lakes. This report presents bathymetric maps for seventeen lakes and reservoirs situated in Patagonian Andes Region and Patagonian Plateau betweem 38°53'S and 45°30'S. The bathymetric maps for two reservoirs were made from topographic maps before impoundment. Hypsographic and depth-area curves, and some morphometric parameters are presented for twenty one Patagonian lakes. Mean depth ranged from 2.0 to 111 m. The deepest lakes are situated in Patagonian Andes Region. Colhue Huapi Lake on Patagonian Plateau, is very shallow, having a mean depth of 2.0 m and being 810 km. in surface area.
Resumo:
A limnological and fish survey program was developed on 110 lakes and reservoirs of Argentina during the summers of 1984 to 1987. Here we exclude lakes without fish. Lakes and reservoirs were visited once each, except for six situated in Chubut Province that were studied seasonally over the course of two years. Here we present raw data used to evaluate the potential fish yield of Argentinian lakes and reservoirs. (Document contains 56 pages.)
Evaluación del rendimiento pesquero potencial de la República Argentina: II. Evaluación por regiones
Resumo:
A limnological and fish survey program was developed in 110 lakes and reservoirs of Argentina during the summers of 1984 to 1987. Lakes and reservoirs were visited once, except for six situated in the Chubut Province that were studied seasonally over the course of two years. The sampling surveys were performed by the "Instituto Nacional de Investigación y Desarrollo Pesquero" and the "Provincia de Chubut". Here we present preliminary results of potential fish yield assessment on a regional basis, using empirical models. (Document contains 11 pages.)
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Age and growth of populations of three fish species from sixteen lakes and reservoirs situated in the Patagonian Andean and the Patagonian Plateau Region (Argentina) were studied. They included two native species, the Patagonian smallmouth perch. (Percichthys trucha) and the Patagonian silverside (Patagonina hatcheri) and the introduced rainbow trout (Oncorhynchus mykiss). For the three species backcalculated lenght at age was obtained from scale readings. Von Bertalanffy growth curves were usually adjusted to data. For the three species, faster growth was related with lake productivity. (Document contains 38 pages.)
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The introductions of salmonids in Argentina can be considered as successfull. The have become established as reproducing populations in southern and middle-western lakes and reservoirs. An extensive sampling programme on 112 lakes and reservoirs was carried out during the summers of 1984 to 1987. Environmental features that determine their present distribution were analyzed. The hypothesis, which we used as starting-point, is that it has been attempted to introduce at least once and least one species of salmonids in all lakes and reservoirs of Argentina.
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Cambodia is one of the poorest countries in the world; much of its population live in rural areas and many live below the local poverty line. The management of common property aquatic resources is of over-riding importance to food security and sustainable rural development in Cambodia. The key groups of poor people who use aquatic resources as part of their diverse livelihoods portfolios are subsistence fishers, small-scale aquaculture practitioners and aquatic resources collectors. Subsistence fishers access mainly the rivers, lakes and inundated forests in Tonle Sap provinces, the lower Mekong and Bassac regions and the upper part of the Mekong. Small-scale aquaculture and/or the collection of aquatic resources are most important in provinces that are not rich in fisheries resources including Kompong Speu, Ratnakiri, Mondulkiri, Preah Vihear and Ortdar Meanchey. Freshwater capture fisheries probably contribute more to national food security and the national economy in Cambodia than in any other country in the world. (19 p.)
Resumo:
Many Central Florida lakes, particularly those in the Kissimmee River watershed, are maintained 0.5 to 1.0 m lower than historic (pre-1960) levels during the summer hurricane season for flood control purposes. These lower water levels have allowed proliferation and formation of dense monotypic populations of pickerelweed ( Pontederia cordata L.) and other broadleaf species that out compete more desirable native grasses (Hulon, pers. comm., 2002). Due to the limited availability of data on the effects of metsulfuron methyl on wetland plants, particularly in Florida, the present study was carried out with the objective of testing its phytotoxicity on six wetland species, to determine the feasibility of its use for primary pickerelweed control.