摘要:

Statistical relationships between 1) flushing-corrected total phosphorus (TP) loading rate and lake water TP concentration, 2) lake water TP and chlorophyll concentrations and 3) chlorophyll and temperature-corrected dissolved oxygen (DO) depletion rate have permitted the estimation of annual phosphorus loading rates of 89, 73, or 58 metric tons · yr−1required to achieve end-of-summer volume weighted average DO concentrations of 4, 5, or 6 mg · L−1in the 18-m to bottom zone of Lake Simcoe. These results are in good agreement with an independently developed deterministic model which showed that end-of-summer DO concentrations of 4, 5, or 6 mg · L−1could be achieved by reductions in phosphorus loading to 89, 72, or 55 metric tons · yr−1. These models also hindcast a pre-settlement (circa 1800 AD) end-of-summer DO concentration of about 8 mg · L−1in the zone of primary lake trout habitat. Present-day concentrations are in the 3 to 3.5 mg · L−1range and apparently declined in response to an increase in TP loading from about 32 metric T · yr−1in 1800 to about 100 metric T · yr−1in the early 1990s. The proposed TP loading target of 75 metric T · yr−1is predicted to generate a lake volume-weighted springtime (mixed water column) TP concentration of 9 to 10 μg P · L−1(presently at about 12.7 μg P · L−1). As a water quality objective, this concentration is consistent with the guideline presently advocated by the Ontario Ministry of Environment and Energy which states ‘…a high level of protection against aesthetic deterioration will be provided by a total phosphorus concentration for the ice-free period of 10 μg · L−1or less.’

ISSN:1040-2381    

DOI:10.1080/07438149709354310

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Eutrophication, increased fishing pressure, habitat destruction and invasion of non-native plants and animals have transformed Lake Simcoe and its assemblage of fishes over the past 150 years. Notable changes include die extirpation of lake sturgeon (Acipenser fulvescens), decline of muskellunge (Esox masquinongy), and failure of recruitment of lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis). Many species, including lake trout, lake whitefish, lake herring (Coregonus artedi), and yellow perch (Perca flacescens), have undergone major fluctuations in abundance. Fisheries management actions have evolved with changes in the lake ecosystem and changes in scientific knowledge. Early regulations substantially restricted the commercial fishery and imposed many of the existing controls on the sport fishery. Along period of adjustment and addition to these regulations along with reliance on supplemental stocking (i.e., stocking of a species where a self-reproducing population of that species exists) of native fish as well as introduction of non-native fish followed. In the last 3 decades, a scientific approach and ample monitoring have been established as basic requirements for making sound management decisions. Supplemental stocking of native species and stocking of non-native species have been largely replaced by stocking of native species for rehabilitation. Successful fisheries management in the future will need to address the uncertainty about the state of complex aquatic ecosystems, and identify the possible states of the system and the probable consequences of specific management actions.

ISSN:1040-2381    

DOI:10.1080/07438149709354311

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Average annual total phosphorus loads to Lake Simcoe are estimated at 100 metric tons. Urban sources of phosphorus such as water pollution control facilities and urban stormwater runoff account for approximately 30% of the total loading. Rural sources such as runoff from agricultural lands, leachate from septic systems, atmospheric deposition and soil erosion contribute the remaining 70%. A target load of 75 metric tons per year has been proposed to ensure an end-of-summer deep water dissolved oxygen concentration of 5.0 mg/L. To achieve the target load, it is necessary to reduce the export of phosphorus from the major controllable sources by 25 metric tons per year. Remedial measures and phosphorus control options to reduce point and non-point sources include controlling agricultural runoff, and erosion and urban stormwater runoff. Several management strategies have been evaluated using a GIS-assisted computer model called HYDROSIM which predicts changes in phosphorus loading in response to implementation of remedial measures within the Lake Simcoe watershed. Management scenarios examined the effectiveness of remedial options based on present and future conditions to ensure that the target load is achievable and sustainable. Modelling results indicate that the most substantial loading reductions can be achieved by controlling urban stormwater runoff and cropland soil erosion. Based on the implementation of an aggressive management program, the target load of 75 metric tons per year is considered to be achievable and can be maintained into the future.

ISSN:1040-2381    

DOI:10.1080/07438149709354312

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The Lake Simcoe drainage basin is located in Southern Ontario, approximately 25 km north of Metropolitan Toronto. It occupies 3592 km2with the land portion representing approximately 80% of the total area. The largest portion of the drainage basin is located to the south of Lake Simcoe in an area where streams flow north into the lake through a landscape highly modified by agricultural and urban activity. The entire basin is located in a transitional portion of the Southern Ontario landscape. In the southerly two thirds, deep fertile soils were deposited by glacial activity on top of limestone and shale bedrock. In the northerly third, thin soils are sparsely spread over a limestone, shale and granitic bedrock that has been exposed and eroded in many places by glacial action. The transitional nature of the basin, a varied geological past and over 200 years of intensive exploitation by European immigrants have created a complex ecological tapestry. The paper briefly explores the fundamental biophysical features and attributes of the basin.

ISSN:1040-2381    

DOI:10.1080/07438149709354313

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Agriculture represents 31 percent of the land use within the Lake Simcoe basin and contributes approximately 45 metric tons of phosphorus to the lake annually. Agricultural sources of phosphorus include livestock operations and soil erosion from cultivated land, fallow land and pasture. Rapid urbanization of the basin has been largely responsible for the decline of the number of farms and for some reluctance of the farming community to invest in larger capital remediation projects. Since the late 1980s, cost-share programs have been in place to reduce agricultural loadings to the lake. Over 300 remediation projects have reduced phosphorus loadings by an estimated 7.5 metric tons per year. With the increased costs of farming and rapid urbanization in the southern half of the basin, targeted programs and innovative low cost solutions, such as vegetative filter strips and flocculaters to treat milkhouse washwater systems, were developed to deal with agricultural pollution concerns.

ISSN:1040-2381    

DOI:10.1080/07438149709354314

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The long range aim of the programme described in this paper is to raise public awareness of water environmental issues to a point where meaningful and informed public participation in environmental decisions is possible. The approach to achieving this goal is as follows:

ISSN:1040-2381    

DOI:10.1080/07438149709354315

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Algal growth causing taste and odor problems in surface drinking water supplies can be costly to treat. A study was conducted to determine the relationship of lake water quality to algal growth in Lake Manatee, Florida, a nitrogen (N)-limited water body. Chlorophylla(chla) concentration was used as the indicator of algal density. A number of water quality parameters measured from monthly water samples collected during 1990–1992 were evaluated to determine whether a relationship with algal density existed. Using sensitivity analyses to determine which parameters were most influential, a prediction equation was developed using water temperature, nitrate concentration, nitrite concentration, total N/total phosphorus (P) ratio, and electrical conductivity as the most important independent variables. Existing equations used to predict Chlaconcentration, developed from previous research, were also tested for applicability in Lake Manatee's situation (using independent data collected in 1993) and were found to be inadequate. The equation developed from this study (p < 0.01, r2= 0.41) was verified using the same independent data collected in 1993. We conclude that algal density changes resulting in blooms which cause water quality degradation may be predicted based on timely sampling and analysis of key water quality parameters.

ISSN:1040-2381    

DOI:10.1080/07438149709354316

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Test plantings of native aquatic plant species were made in two Texas reservoirs. Founder populations of three native submersed or floating-leaved species were established within small (2- × 2-m) exclosures utilizing actively growing transplants. Herbivory and excessive sedimentation proved to be deterrents to plant survival and expansion. Nine small founder populations ofVallisneria americana wereestablished within North Lake, a small reservoir with limited water level fluctuations and a developing community of native pioneer aquatic plants. Plants within all nine exclosures successfully established and began vegetative growth. In intact exclosures, the plants rapidly covered the sediment surface within the exclosures. Expansion beyond the exclosures was variable and occurred primarily during the cooler portions of the year when herbivory was assumed to be low. During the spring of the second growing season, herbivores cropped most of the previous expansion leaving only a narrow fringe of plants surrounding the exclosures. At Lewisville Lake, a large, turbid reservoir with significant seasonal water level fluctuations and no existing aquatic macrophytes, two native pioneer species (Potamogeton nodosusandHeteranthera dubia) were planted within exclosures. Good survival and growth occurred within undamaged exclosures, although no expansion ever occurred outside the fenced areas. Plantings ofH. dubiain undamaged exclosures also showed excellent survival except for those planted in areas subject to very high turbidity and sedimentation rates. Again, herbivory prevented any expansion outside the protective exclosures.

ISSN:1040-2381    

DOI:10.1080/07438149709354317

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Experimental mesocosm studies revealed that the presence of benthivorous smallmouth buffalo (Ictiobus bubalus) significantly enhanced turbidity, phytoplankton biomass, ammonium (NH4+), and total nitrogen (N) and phosphorus (P) concentrations in a shallow, aerobic, hypereutrophic oxbow lake. The effects ofIctiobusonwater quality are similar to the results of experiments performed on other benthivorous fish species. Prior studies have suggested that enhanced phytoplankton biomass in the presence of benthivorous fishes is a result of P excretion by fish and physical relocation of sediment P to the water column. However, our results revealed that enhanced microbial NH4+regeneration and subsequent uptake by phytoplankton may also be an important factor causing increased phytoplankton biomass levels in the presence of benthivorous fishes. Net sediment plus water column particle NH4+fluxes were over six times higher in the presence ofIctiobus, relative to the control. Increased biological demand for phosphate, as well as adsorption to resuspended sediments, resulted in a significant increase in water column particle phosphate demand in the presence ofIctiobus, relative to the control. Furthermore, we estimated that approximately 60% of the increase in water column total N in the presence ofIctiobus, relative to the control, was attributed to increases in phytoplankton and bacterial biomass, while 77% of the P increase could be explained by physical resuspension of sediment P.

ISSN:1040-2381    

DOI:10.1080/07438149709354318

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor