Simulation of Recent and Projected Total Phosphorus Trends in Lake Ontario

Recent trends (1965 through 1978) of total phosphorus were analyzed with a time-variable, nutrient budget model of Lake Ontario. Future conditions were also simulated to estimate the effect of anticipated control measures on the lake's water quality.The analysis suggests that recent improvements in Lake Ontario's total phosphorus concentration are attributable to point source reductions due to detergent limitations and waste treatment by the Province of Ontario and the State of New York. Projections show that present point source controls will maintain the lake at the upper level of mesotrophy (15-20 μgP/L) to the year 2000, whereas the absence of controls would result in eutrophy (～30 μgP/L). Further indications are that some diffuse source reduction may be required if oligotrophy (<10 μgP/L) is the ultimate goal and that Lake Ontario's fate is closely related to that of Lake Erie.An attempt is made to assess the effect of model uncertainty and phosphorus availability on the projections. In general, the inclusion of uncertainty indicates that more stringent load reductions will be needed to meet water quality objectives with greater than 50% certainty. Inclusion of availability tends to improve prospects for lake restoration and to enhance point as opposed to diffuse source controls.     

Mass Exchange Between Hamilton Harbour and Lake Ontario

The mass exchange between Hamilton Harbour and Lake Ontario waters through the Burlington Canal is important for estimating the dissolved oxygen budget of the harbour. Lake-harbour exchange is caused by either the oscillatory flow in the canal during isothermal conditions or the densimetric flow during thermal stratification. During the study period (September 1975), the canal water was found to be quasi-isothermal; consequently oscillatory flow existed. A computational method was developed to estimate the exchange based on excursion distance travelled for each limnological episode, and the final flow in each direction was checked with dissolved solids budget. An average of 2.04 × 10⁶ m³.d^?1 (24 m³.s^?l) of harbour water is estimated to flow into the lake, while 0.73 × 10⁶ m³.d^?1 (8 m³.s^?1) of lake water flowed toward the harbour during September 1975. This accounts for the total and net daily exchange of 0.98% and 0.48% of harbour volume, with net exchange being toward the lake. The total and net exchanges were respectively 8 and 4 times the natural drainage during the study period. On a monthly average, more water leaves than enters the harbour. The lake-harbour exchange is considered important for maintaining and even improving the existing harbour water quality. The harbour dilution factor was estimated as 0.0019 per day for the present study.     

Isotopic Variations in Hamilton Harbour Water as an Indicator of Lake Ontario Exchange Flow

In September, 1993, and May, 1994, surface water samples were collected from Hamilton Harbour at the western end of Lake Ontario to determine if hydrogen and oxygen isotopes could be used to estimate the volume of lake water entering the harbor through the Burlington Canal, a shipping canal at the harbor's eastern end. In addition, the survey sought to determine if the isotopic variations were significantly different to allow mapping of the lake water plume present within the harbor. The results of this preliminary survey show a west to east enrichment in stable oxygen and hydrogen ratios. This distribution results from mixing via the Burlington Canal of lake water at the eastern end of the harbor that is enriched in ¹⁸O and ²H, with harbor water that is depleted in ¹⁸O and ²H relative to lake water. The results suggest that variations in the isotopic signature between Lake Ontario and Hamilton Harbour waters differ significantly to allow the use of oxygen and hydrogen isotopes to examine lake water-harbor water mixing relationships. A more detailed sampling will allow the amount of exchange across the Burlington Canal to be calculated, and the extent of the harbor's lake water plume to be determined.     

Volume Visualization of Temperature in Hamilton Harbour,Lake Ontario

The inner structures of lakes can be revealed using volume visualization algorithms since lakes are three-dimensional objects that are explored by taking samples at various stations and at different depths. These algorithms did not exist 20 years ago, they could only be run on supercomputers 10 years ago, on workstations 3 years ago, and now they can be run on personal computers. Using computer graphics it is now possible to combine data, their three-dimensional location, and lake topography to create images of water quality patterns which supersede conventional surface, two-dimensional, graphics. Through solid modeling, temperature data collected on 28 May 1990 and 8 August 1990 in Hamilton Harbour, Lake Ontario, are mapped into voxels and projected onto two-dimensional screens. Various three-dimensional representations of temperature data are displayed including water masses with temperatures of less than 12°C, 13 to 14°C, 16°C to 17°C, and greater than 23°C. The calculation of the 3D representations allows the computation of volumetric properties, e.g., masses, since each voxel has water quality values associated with it and these values can be summed or elaborated numerically as needs arise. For example the harbor has a volume of 254 × 10⁶ m³, and the water mass on 28 May 1990 at 12–13°C had a complex three-dimensional shape with a volume of 61 × 10⁶ m³. A third benefit of visualization is that the data can be viewed interactively from different viewpoints thus increasing the interaction between scientist and the data. These methods should also be able to be used in other limnological applications such as visualization of sediments, algal blooms, and other biological and chemical data.     

Tributary and Point Source Total Phosphorus Loading to Lake Erie

Total phosphorus data from tributaries, municipal and industrial sources, connecting channels, and atmospheric deposition have been evaluated to estimate the loading of phosphorus to Lake Erie. The annual total load from these sources has declined over the study period from a high of 27,944 tonnes in 1968 to a low of 10,452 tonnes in 1981. Of all sources the Detroit River represented the single largest component of the total load. Reductions in the Detroit River annual load, which is a complement of both U.S. and Canadian loads, from 17,822 tonnes to 3,541 tonnes was principally responsible for the overall total phosphorus loading decrease. These decreases were attributed principally to the phosphorus abatement program on municipal sources and the restriction of phosphate concentrations in detergents. In 1978 the contribution to the total load from tributary sources for the first time exceeded the load of phosphorus from the Detroit River, with U.S. tributary sources representing approximately 47 percent of the total lake load.     

Predicting Variability in a Lake Ontario Phosphorus Model

The prediction of a model always has a degree of uncertainty. Because the level of uncertainty is inversely related to the value of information contained in the prediction, there is a need to quantify the uncertainty. One approach to estimate prediction uncertainty is first-order error analysis. In this method, the error in a characteristic (variable or parameter) is defined by its first nonzero moment (the variance). Errors are propagated through the model using first-order terms in the Taylor series, and the variances are then combined to yield the total prediction uncertainty. An alternative approach to model prediction error analysis is Monte Carlo simulation. In this technique, probability density functions are assigned to each characteristic (variable or parameter), reflecting the uncertainty in that characteristic. Then, values are randomly selected from the distribution for each term and inserted into the model, to calculate a prediction. Repeating this process a number of times produces a distribution of predicted values, which reflects the combined uncertainties. These two approaches (first-order error analysis and Monte Carlo simulation) are applied to Lake Ontario data using a steady state mass balance phosphorus model. Comparisons are made which suggest guidelines for the use of each.     

Changes in Lake Ontario Total Phosphorus Concentrations 1976–1978

An apparent decrease in total phosphorus concentrations of approximately 4.l μgP/L has been reported recently for the spring values of 1977 and 1978 in Lake Ontario. Investigation of the loading reduction for this period independent of sedimentation factors can account for only 10% of the change. The results indicate that changes in the sedimentation rate of total phosphorus during this period offer an explanation for the majority of the change in concentration.     

Trends in Lake Ontario Surveillance Parameters, 1974-1980

Data from 66 cruises on Lake Ontario, sampling some 95 stations, were subjected to trend analysis. The data were reduced to monthly means and statistically significant (P≥0.01) decreases in total phosphorus (TP), chlorophyll a, and paniculate organic carbon (POC) were observed between 1974 and 1980. Seasonally corrected trend-in-time equations were formulated for the 17 zones established by the International Joint Commission for five commonly measured surveillance parameters (temperature, TP, chlorophyll a, POC, and chloride). In general, offshore areas produced seasonally corrected trend-in-time equations with higher coefficients than did nearshore areas, indicating that the offshore areas have been more stable during the historical period studied.     

Potential for Fisheries Rehabilitation in the Hamilton Harbour-Cootes Paradise Ecosystem of Lake Ontario

Present and historical information on the status of the Hamilton Harbour-Cootes Paradise ecosystem is synthesized to evaluate the potential for fisheries rehabilitation. Although the Hamilton ecosystem is seriously degraded, it is the largest and most important warmwater fish habitat in western Lake Ontario. Habitat losses, hypolimnetic anoxia, contaminated sediments, nutrients, and sediment inputs are impediments to rehabilitation. Rehabilitation should focus on the warmwater fish assemblage as restoration of the historic coldwater fishery appears unlikely in the foreseeable future. Carroll's Point has the best potential for rehabilitation, the south shore does not have any potential, and the remaining areas fall in between these extremes. Cootes Paradise, which has moderate potential, is adversely affected by sediment inputs from Spencer Creek, nutrients from the Dundas sewage treatment plant, and a large carp population.     

Phosphorus Inputs to Lake Simcoe from 1990 to 2003: Declines in Tributary Loads and Observations on Lake Water Quality

Total phosphorus (TP) inputs to Lake Simcoe have led to hypolimnetic dissolved oxygen (DO) depletion and loss of cold water fish habitat. Since 1990, efforts have been made to reduce the total TP input to the lake below a defined target of 75 t/year, which was predicted to lead to reductions in spring TP concentration and improvements in end-of-summer hypolimnetic DO concentrations. The total TP load to the lake during the most recent period of record (1998/99-2003/04) ranged from 53 to 76 t/yr and averaged 67 t/yr, compared to an average of 114 t/yr estimated between 1990/91 and 1997/98 (range 85-157 t/yr). Reductions in TP loads from the catchment via tributary discharge (∼26 t) accounted for the majority of the decrease in total load between the two time periods. Total P concentrations decreased significantly in four out of six long-term monitored tributaries; however, concentrations in all six tributaries remain above the level recommended to avoid nuisance plant growth (30 μg/L). Although TP loads to the lake are currently below the target 75 t/yr, excessive growths of filamentous algae and macrophytes continue to be a problem in the nearshore zone. End-of-summer minimum hypolimnetic DO concentrations (average 4.3 mg/L, 1998/99-2003/04) remain substantially below the level (7 mg/L) that is considered protective of lake trout. Efforts to reduce TP loads to the lake therefore need to continue.     

Organochlorine Contaminant Levels in Waterbird Species from Hamilton Harbour,Lake Ontario: an IJC Area of Concern

The levels of organochlorine (OC) contaminants in eggs and tissues of waterbird species nesting in Hamilton Harbour, Ontario, an International Joint Commission Area of Concern, were monitored between 1981 and 1992. PCBs, DDE, and mirex were present at the highest concentrations of the 29 organochlorines and one trace metal measured. Most contaminants in the various species tested showed a declining temporal pattern during that period. Double-crested cormorant eggs generally had higher concentrations of contaminants than those in herring gull eggs which in turn were higher than those in eggs of black-crowned night-herons, Caspian terns and common terns. The levels of contaminants in the eggs reflect the dietary preferences of the species with the fish-eating birds containing consistently higher accumulations of contaminants when compared to the herbivorous Canada goose for which the levels were consistently much lower for all compounds. The concentrations of contaminants detected are among some of the highest in the Great Lakes but when compared to other sites on Lake Ontario, the levels in Hamilton Harbour are generally equal or lower. Elevated levels of contaminants such as PCBs, mirex, and DDE were also detected in liver and muscle tissues of migrant waterfowl species from the harbor. Despite habitat degradation and continued presence of contaminants, the harbor supports a large number and wide variety of waterbird species. Except for black-crowned night-herons, the nesting populations of colonial waterbirds have increased between 21 and 1061 % since the last survey in 1987.     

Theoretical Model of the Littoral Drift System in the Toronto Waterfront Area,Lake Ontario

A computer model is described which simulates the interaction between shoreline geometry and shoaling waves in the Toronto waterfront area on the north shore of Lake Ontario, between Highland Creek in the east and the Credit River in the west, and establishes potential littoral drift patterns. Thirteen wave conditions, defined by height, period and direction of approach, characterising the annual hindcast spectrum for Toronto, are used in the determination of the shore-parallel components of wave energy flux. To identify the long term net effects of the distribution of wave energy flux which produce the dominant littoral drift pattern, a simple summation procedure is used whereby the individual effect of any wave condition at a shoreline point is weighted according to its frequency of occurrence. The long term average pattern of potential littoral drift based on zones of potential erosion (increasing alongshore wave energy flux), transport (constant alongshore wave energy flux) and deposition (decreasing alongshore wave energy flux) is established. Identification of nodal points (zero alongshore wave energy flux) and drift cells allows a test of the ‘geomorphological sense’ of the model by comparison with observed drift patterns.     

Inputs of Phosphorus from Precipitation to Lake Michigan

Precipitation samples were collected at six locations around Lake Michigan and analyzed for the concentrations of the different forms of phosphorus present. The concentrations were found to be higher in the southern part of the lake. Precipitation-weighted concentrations of total phosphorus and dissolved reactive phosphates were found to be 0.023 mg/1 and 0.011 mg/1, both higher than the concentrations found in the open lake of 0.009 and 0.002 mg/1. Inputs of total phosphorus to the lake were calculated to be 1.0 × 10⁶& kg/yr or about 18% of the present phosphorus budget of the lake.More than 40% of the phosphorus in precipitation is in the form of dissolved reactive phosphates and it is estimated that about 0.6 × 10⁶& kg/yr of the phosphorus coming into the lake in precipitation becomes available to organisms in the lake.     

洞庭湖区高含铁地下水除铁试验研究

对高含铁地下水的除铁滤层及除铁机理进行了试验研究。结果表明 :对含铁量为 16～ 2 0mg/L的地下水 ,宜采用粒径为 1 6～ 2mm ,厚度为 1m的均粒石英砂滤层处理 ;在高含铁地下水除铁过程中 ,没有或很少有微生物作用     

Analysis of Polychlorinated Biphenyl (PCB) Loading Trends in Lake Michigan

PCB concentrations in coregonid fishes (bloater chubs) collected from Lake Michigan between 1972 and 1980 are used to infer an historical loading trend for polychlorinated biphenyls (PCBs). A mass balance model was developed to describe the dynamics of PCBs by assuming that historical fish concentrations are proportional to concurrent water column concentrations of PCB. The validity of this assumption is strengthened, since the data represent a single species of fish (a pelagic feeder), a specific age class of that species, and a single laboratory performing the collections and analysis of the data. The results of model analysis indicate that PCB loading to Lake Michigan during the period of observation can be described by a linearly decreasing trend. The calibrated model also forecasts the response of selected fish species to various loading scenarios. Forecast results indicate that a continuously decreasing load will result in compliance with U.S. and Canadian guideline value for human consumption by 1987. However, should PCB loadings not continue to decrease, compliance with the proposed U.S. and extant Canadian guideline of 2.0 mg/kg is doubtful. Forecast accuracy may be improved by the availability of precise measurements of water:fish distribution coefficients.     

Estimating the Extent of Reduction Needed to Statistically Demonstrate Reduced Non-Point Phosphorus Loading to Lake Erie

The need to reduce non-point phosphorus contributions to Lake Erie has led to extensive efforts to implement conservation tillage in the Lake Erie basin. Because annual loads are highly variable, statistical approaches will be required to document the success of conservation tillage and other best management practices in reducing loads. Important management issues are how large a reduction will be required, and how long it will take to achieve the needed reduction. In response to these issues, a method is presented for estimating the amount of change needed to establish a statistically significant reduction, based on the standard t-test. Analysis of data from the Sandusky River, a north-central Ohio tributary of Lake Erie, indicates that the necessary change is about 35% of the current loads. When the loads are adjusted for variations in discharge, the necessary change can be reduced to about 20%. Based on projections of the Army Corps of Engineers of adoption rates of conservation tillage, and the associated effects on phosphorus loads, a 35% change would take 25 years or more, but a 20% change would occur by the end of 8 years. The documentation of these changes will require high quality monitoring data, collected before and during the implementation period with the same sampling strategy.     

Physical Processes Controlling Taste and Odor Episodes in Lake Ontario Drinking Water

Circulation and thermal structure of the coastal waters were studied as a part of an interdisciplinary program to investigate the taste and odor problem in drinking water along the north and western shores of Lake Ontario. The currents and temperature variations were found to be strongly linked to winds, with winds from the west causing upwelling and eastward flowing currents, and winds from the east inducing downwelling and warm westward flowing currents. The downwelling along the north shore during late August and early September of 2000 was associated with a pulse in concentration of the taste and odor causing compound geosmin. This study indicates that during this episode the onshore directed mean currents and cross-shore fluxes in the surface layer transported geosmin to the coastal waters of the north shore.     

Spatial ecology of reintroduced walleye (Sander vitreus) in Hamilton Harbour of Lake Ontario

Many coastal embayments in the Laurentian Great Lakes have been subjected to extensive human physical modification and pollution that has led to the loss of freshwater biodiversity. For example, Hamilton Harbour is a large coastal embayment situated at the western end of Lake Ontario, with a long history of industrial and urban development that has resulted in the loss and degradation of aquatic habitat and the extirpation of several fish species. To restore the fish community in Hamilton Harbour, several attempts have been made to increase apex predator biodiversity by reintroducing native walleye (Sander vitreus). To assess how reintroduced (i.e., stocked) walleye use Hamilton Harbour, we used acoustic telemetry to characterize the residency of individuals within the boundaries of the harbour as well as their seasonal space use, with a focused interest on the spring spawning period. During the 1?yr tracking period tagged walleye spent an average of 357?days (range 135–365?days) within the harbour. Most individuals (12/15) remained within the harbour during the entire spring spawning period, and over half of the tagged fish departed (n?=?7) at the end of summer and beginning of fall. Core use areas appeared to gradually shift more easterly as the seasons progressed from winter to summer. Results from this study indicate that stocked fish are resident within Hamilton Harbour for most of the year, including the reproductive period, which suggests that stocking efforts to re-establish walleye populations may be an effective restoration strategy if recruitment is successful.     

Regression and Weighted Averaging Models Relating Surficial Sedimentary Diatom Assemblages to Water Depth in Lake Ontario

Diatom assemblages in surface sediment samples in depth profiles from Lake Ontario and from East Lake, a shoreline lake, were analyzed for the purpose of describing the relationship between species distribution and water depth. At both sites species composition varied markedly with sample depth. In East Lake a multiple regression of four habitat groups: benthic, epiphytic, tychoplanktonic, and euplanktonic, against water depth (30 cm–8 m) produced a relationship with a standard error (SE) of 1.5 m. An analysis of the ratio of euplanktonic diatoms to periphytic diatoms over a transect from 3 m to 150 m in Lake Ontario produced a multiple regression with an SE of 11.8 m. In another approach, water depth optima for 91 diatom taxa were developed using a weighted averaging (WA) technique. A good correlation (r² > 0.9) was found between measured and inferred water depth over the range 3 m to 30 m using a unimodal WA regression model. The transfer functions offer the possibility of inferring Holocene water level changes in Lake Ontario from fossil diatom assemblages in sediment cores.     

Stream nutrient and agricultural land-use trends from 1971 to 2010 in Lake Ontario tributaries

Urbanization is generally recognized as the most widespread form of landuse/landcover change (LULC) within populated regions, including southern Ontario, and is often at the expense of surrounding agricultural land. However, changes in agricultural LULC within these peripheral regions should be considered when interpreting water quality changes in watersheds containing mixed LULC. The objectives of this study were to first, quantify changes in LULC within twelve Lake Ontario tributaries between 1971 and 2010, and secondly, to determine whether these changes co-occurred with changes in total phosphorus (TP) and nitrate‑nitrogen (NO₃-N) concentrations in streams. Water quality data were obtained from the Ontario Provincial Water Quality Monitoring Network while historical land use was reconstructed from agricultural census reports, historical land cover maps, and modern remotely sensed datasets. Urban cover increased, although percent increases in urban cover were small in the most agriculturally dominated watersheds (3–8%). The area of agriculture declined across all watersheds, yet the proportion of agricultural land dedicated to crop (corn, soybean, and wheat) production increased, including in the most urbanized watersheds (e.g. Mimico 89% urban; 2009–11). Total P concentrations in streams were highest at the urbanized watersheds, particularly in the 1970s, before declining in recent decades. In contrast, NO₃-N concentrations were highest (>1.5 mg/L; 2000–10) within the most agricultural watersheds (e.g. Gages 71% agriculture) and have increased over the same period of row crop expansion. Further research is needed to determine the mechanisms behind the potential relationship between expanding row crop cover and stream NO₃-N concentrations in southern Ontario.