摘要:

During the past century, the historical hydrology and nutrient regimes of the Everglades, a 700,000 hectare freshwater wetland in southern Florida, have been altered by agricultural and urban development. Changes in plant community composition (e.g. encroachment of cattail (Typha domingensisPers.) into sawgrass (Cladium jamaicenseCrsntz) and slough communities) have been observed in areas receiving nutrient and water loadings from agricultural activities. The distribution of210Pb and pollen in depth increments of peat was measured at a nutrient-enriched site and an unenriched site in Water Conservation Area 2A (WCA 2A) to describe how nutrient enrichment and water management might have altered the historical plant species composition of the Everglades. Species composition of the plant communities has changed during the past 20 to 50 years at both enriched and unenriched sites. At the unenriched location, there has been a general shift in community composition since 1950 as slough species (arrowhead (Sagittaria spp.), water lily (Nymphaea spp.)) have decreased and terrestrial plants (pigweed (Amaranthaceae), ragweed (Ambrosia spp.), andEupatorium spp.) have increased. The nutrient-enriched site also has seen an increase in terrestrial plant species since about 1950. In addition, since 1970, the sawgrass and slough communities at the enriched site have been replaced by a cattail-dominated community. The increase in terrestrial vegetation at both sites since 1950 could be due to drainage activities (construction of canals and levees) along the eastern perimeter of the Everglades and in the Everglades Agricultural Area (EAA) during the 1950s. The increase in cattail and concurrent decline in slough species at the nutrient-enriched site since 1970 probably is the result of the massive inputs of water (459,000,000 m3yr−1) and nutrients (1814 MT Nyr−1, 60 MT Pyr−1) from the EAA since WCA 2A was impounded in 1961.

ISSN:1040-2381    

DOI:10.1080/07438149609354273

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Many lakes in the Sudbury region of Ontario have been affected by acidic and metal inputs as a result of local smelting operations. Several initiatives are now underway to restore some of these systems. Long-term limnological data are rarely available, therefore lake managers must use proxy methods to set reasonable targets for lakes undergoing mitigation. Daisy Lake is presently an acidic (pH 4.7), metal-contaminated lake (Ni=370 μg L−1; Al=350 μg L−1), that has been selected for mitigation efforts. We used fossil pollen analysis to reconstruct past changes in terrestrial vegetation, and paleolimnological techniques (primarily diatoms and chrysophytes) to identify pre-disturbance conditions and to reconstruct past changes in water quality variables in Daisy Lake. Our data indicate that, if Daisy Lake and its watershed are limed to restore the lake to a state that approximates the pre-disturbance natural pH, the lake water pH has to be about 1.5 pH units higher than its present level.

ISSN:1040-2381    

DOI:10.1080/07438149609354274

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A two-phased Monte Carlo procedure is presented for estimating the probability distribution of annual phosphorus load to a lake and the response of the lake to the load. A watershed-level nutrient loading and lake response model, EUTROMOD, and a geographic information system (GIS) were used. The uncertainty in loading and lake response due to natural variability and parameter uncertainty were propagated separately throughout the analysis. The methodology was applied to Wister Lake in Oklahoma with the lake and its trophic state as the endpoint for total maximum daily load (TMDL) analysis. The watershed contributing to Wister Lake covers approximately 260,000 ha and contains a variety of point and nonpoint sources of pollution contributing to the degradation of the lake. Model results compared well with measured water quality data. EUTROMOD simulations indicated that the lake is eutrophic under current land use and management conditions. Nonpoint source (NPS) pollution was estimated to contribute nearly 90 percent of the annual phosphorus load with the remainder attributed to point sources. The majority of this NPS load was attributed to agriculture. Alternative management evaluations indicated that an average reduction of agricultural NPS loads by 25 and 35 percent would be needed to meet our water quality goal with and without point source controls, respectively. Due to uncertainties inherent in the evaluation procedure, the required reductions had large confidence intervals which must be taken into consideration in the decision making process.

ISSN:1040-2381    

DOI:10.1080/07438149609354275

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Stormwater detention ponds are one of the management options designed to reduce pollution of the receiving water bodies by urban runoff. Many such structures are operated in the Greater Toronto Area. A seasonal survey of four stormwater detention ponds was conducted to estimate the inventories of heavy metals and phosphorus in bottom and suspended sediments. The concentrations of heavy metals in suspended and bottom sediments suggest that land use has the most profound impact on the quality of suspended and deposited sediments, with the pond in an industrial/commercial catchment having the highest metals concentrations, followed by ponds located in the residential catchments. The suspended and bottom sediments data suggest that the removal of heavy metals in these reservoirs may not be adequate. Apart from land use, the magnitude of runoff and seasonal conditions impacted the sediment and water quality in these ponds. The deleterious effects of restricted water circulation during the dry summer conditions and under the winter ice cover are apparent from the elevated levels of ammonia-N, sometimes reaching or exceeding the levels recommended by the Canadian Water Quality Guidelines (CCREM 1987) for the protection of aquatic life.

ISSN:1040-2381    

DOI:10.1080/07438149609354276

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Farming practices and other anthropogenic influences have affected the water quality and shifted trophic state of Lake Trichonis, western Greece, from oligotrophic to oligo-mesotrophic. This change has been accompanied by an expansion of dense reed beds ofPhragmites australisin places where limited growth existed in the past. This study measured the seasonal changes in nutrients and heavy metals in the reed beds of Lake Trichonis, and assessed the applicability of reed harvesting on maintaining or improving the water quality of the lake. The results have illustrated three types of accumulation dynamics of nutrients and heavy metals in the reeds of Lake Trichonis. The first type shows maximum accumulation occurring early in the growing season and gradually declining throughout the year. P, K, Cl and NO3follow this type of accumulation. The second pattern followed by fluoride, showed constant accumulation throughout die year. The third accumulation pattern, followed by Na, Zn, Cd, Co, Mn, Fe, Mg, Ca, Cu, Al, Ni, Cr, and SO4, showed increases in accumulation throught the growing season, reaching a maximum in August and September and then declined steadily. The reeds beds are a significant sink for nutrients in the early growing season and a potentially significant source of nutrients later in the season. The results indicate that removal of the reeds in the early spring would remove a large reservoir of potentially mineralizable P from the lake. To properly control the flow of nutrients and heavy metals in a lake through reed harvesting, the dynamic cycling of P and die seasonal changes in accumulation should be considered.

ISSN:1040-2381    

DOI:10.1080/07438149609354277

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Lake Okeechobee, Florida, is managed for multiple uses, including drinking water supply, recreation, wildlife habitat, and flood control. Because much of the drainage basin is in agricultural production, maintenance of water quality conditions is a major management consideration for the lake. An evaluation of water quality data collected over a 20-year period indicated that Lake Okeechobee and its major inflows generally comply with applicable numerical criteria, and that parameters that exceeded criteria at inflows have not impaired die designated uses of the lake. Of 59,781 water quality measurements, 6,409 (10.7 percent) exceeded the applicable criteria. For most monitored parameters, values that exceeded criteria generally represented less than 25 percent of die measurements at specific locations. Exceptions included dissolved oxygen (DO) andiron. Low DO values (>5.0 mg·L−1) represented 9 to 100 percent of measurements at inflow stations, although fewer than one percent of the observations at any in-lake station were below die criterion. Iron values were commonly higher than die applicable criteria at many inflow and in-lake stations. However, most of die high iron values were greater than the secondary drinking water standard, and very few were greater than the criterion for protection of aquatic biota. Trace metals (including mercury) and organic contaminants were rarely greater than die criteria in the lake and its inflows, in spite of die predominance of agriculture in die basin. Pesticide application methods, degradation processes and dilution appear to be responsible for the generally low concentrations of pesticides and herbicides in Lake Okeechobee and its inflows. Many of the criteria that were exceeded are drinking water standards that do not relate to protection of aquatic biota. Because of water treatment processes, they do not appear to have affected die suitability of the lake as a potable water supply. Additional monitoring of biological conditions, in conjunction with continued monitoring of selected water quality parameters, is recommended to document whether die lake and its inflows meet their designated uses.

ISSN:1040-2381    

DOI:10.1080/07438149609354278

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A phosphorus budget and mass balance model were developed for Lake Champlain in order to identify load reductions necessary to attain interim in-lake total phosphorus concentration criteria established in a water quality agreement between New York, Quebec, and Vermont Total phosphorus loadings were measured from 31 tributaries, 88 wastewater discharges, and direct precipitation. Mean annual tributary loadings were estimated using the FLUX program (Walker 1987). The total base year phosphorus loading rate of 647 mt·yr−1included 29% from point sources, 47% from cultural nonpoint sources, and 24% from natural sources. A mass balance model for 13 lake segments was developed and calibrated to the data using the BATHTUB program (Walker 1987). Exchange flows between lake segments were evaluated using a mass balance for chloride. The BATHTUB program error analysis procedure was used to evaluate model prediction uncertainty, based on variance estimates for all input data terms. The modeling results were used with a minimum-cost optimization procedure to determine that an overall phosphorus load reduction of 192 mt·yr−1distributed among specifically targeted lake segment watersheds will be needed to attain the in-lake phosphorus criteria.

ISSN:1040-2381    

DOI:10.1080/07438149609354279

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Municipal wastewater effluent was removed in 1992 from a cove (Cedar Cove) of Kings Bay in an attempt to reduce the bay's ambient total phosphorus (TP) and total nitrogen (TN) concentrations. Many citizens and professionals viewed nutrient removal as the solution to reducing the bay's nuisance growths of aquatic macrophytes and filamentous algae. Wastewater removal reduced average TP from 105 μg·L−1to 27 μg·L−1and average TN from 620 μg·L−1to 220 μg·L−1in Cedar Cove. TP (24 μg·L−1to 28 μg·L−1) and TN (300 μg·L−1to 260 μg·L−1), however, were not significantly reduced in southern Kings Bay. There were no significant changes in mean frequency of occurrence of vallisneria in Cedar Cove (0% to 1%) or southern Kings Bay (19% to 22%). Average hydrilla occurrence decreased significantly after wastewater removal in Cedar Cove (54% to 36%) and southern Kings Bay (61% to 35%). Eurasian watermilfoil occurrence significantly increased in Cedar Cove (6% to 24%) and southern Kings Bay (11 % to 32%). Filamentous algal occurrence in Cedar Cove averaged 34% prior to and 40% after wastewater removal. In southern Kings Bay, the frequencies of occurrence averaged 5% and 2%, respectively. If removal of Crystal River's wastewater discharge was responsible for the differences detected in plant abundances, die same reductions/increases in species abundance should not occur in Cedar Cove as in southern Kings Bay. Significant changes in plant occurrence were attributed to the March 13, 1993 “Storm of die Century,” not to die removal of wastewater. Further nutrient control is not recommended as an option for reducing nuisance growths of submersed aquatic vegetation in Kings Bay-Crystal River, Florida.

ISSN:1040-2381    

DOI:10.1080/07438149609354280

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor