Yerubandi R. Rao

Transport and Mixing Between the Coastal and Offshore Waters in the Great Lakes: a Review

ABSTRACT The Laurentian Great Lakes of North America have horizontal scales of hundreds of kilometers and depth scales of hundreds of meters. In terms of coastal dynamics, they behave much like inland seas and exhibit physical processes characteristic of the coastal oceans. The lakes are dynamically similar to the coastal ocean in that their horizontal dimensions are larger than the vertical dimensions, and the principal source of mechanical energy is the wind. The major difference in dynamical processes is that the lakes are enclosed basins and are not connected to the deep ocean. This paper presents an overview of some of the significant aspects of physical processes in the coastal zones of the Great Lakes. The review is based on examples ranging from lake-wide experiments like the International Field Year on the Great Lakes (IFYGL) to several process-oriented coastal boundary layer experiments. The basic circulations in the nearshore zone and coastal boundary layer are summarized. The review concludes with suggestions for future work on the understanding of the physical processes that would have a bearing on lake management in the coastal zones of the Great Lakes.

Lake Erie hypoxia prompts Canada‐U.S. study

Because of its size and geometry, the central basin of Lake Erie, one of North Americas Great Lakes, is subject to periods in the late summer when dissolved oxygen concentrations are low (hypoxia). An apparent increase in the occurrence of these eutrophic conditions and ‘dead zones’ in recent years has led to increased public concern. The International Field Years for Lake Erie (IFYLE) project of the Great Lakes Environmental Research Laboratory (GLERL, a U.S. National Oceanic and Atmospheric Administration (NOAA) laboratory), was established in 2005 in response to this increase. This project is investigating the causes and consequences of hypoxia in the lake. As part of the effort, scientists from the United States and Canada conducted an extensive field study in 2005 to gather more information on the duration and extent of the hypoxic zone and its effects on the biota in the lake. This article gives a brief history and description of the problem and presents initial results from the field study.

The re-eutrophication of Lake Erie: Harmful algal blooms and hypoxia

Lake Erie supplies drinking water to more than 11 million consumers, processes millions of gallons of wastewater, provides important species habitat and supports a substantial industrial sector, with >

Modeling summer circulation and thermal structure of Lake Erie

50 billion annual income to tourism, recreational boating, shipping, fisheries, and other industries. These and other key ecosystem services are currently threatened by an excess supply of nutrients, manifested in particular by increases in the magnitude and extent of harmful planktonic and benthic algal blooms (HABs) and hypoxia. Widespread concern for this important international waterbody has been manifested in a strong focus of scientific and public material on the subject, and commitments for Canada-US remedial actions in recent agreements among Federal, Provincial and State agencies. This review provides a retrospective synthesis of past and current nutrient inputs, impairments by planktonic and benthic HABs and hypoxia, modelling and Best Management Practices in the Lake Erie basin. The results demonstrate that phosphorus reduction is of primary importance, but the effects of climate, nitrogen and other factors should also be considered in the context of adaptive management. Actions to reduce nutrient levels by targeted Best Management Practices will likely need to be tailored for soil types, topography, and farming practices.

Application of a numerical model for circulation, temperature and pollutant distribution in Hamilton Harbour

] Athree-dimensionalprimitiveequationnumericalmodelwasappliedtoLakeErieona2kmgridtostudyitssummercirculation andthermalstructure.Modelresultswerecomparedtolong-termobservationsofcurrentsandtemperaturemadein2005at severallocations,mostlyinitscentralbasin.IntheshallowandmostlyunstratifiedwesternbasincirculationisdrivenbyDetroitRiverinflow(modifiedtosomeextentbywind)andisfromwesttoeast. Inthecentralbasin(which isofintermediate depthandhasarelativelyflatbottom),themodeledcirculationisanticyclonic (clockwise),drivenbyanticyclonicvorticityinthesurfacewind,andthethermocline isbowl-shaped,inlinewithobservations.Inthedeeppartoftheeastern basin,the thermoclineisdome-shapedandcirculationiscyclonic (counter-clockwise),duetodensitygradients(aconfigurationtypicalforotherlargedeeplakes),whileshallower areasareoccupiedbyanticyclonic circulationdrivenbyanticyclonic windvorticity.Inthe centralbasin,modeledtemperatureandcirculationpatternsare quitesensitivetothespecificationofthe windfield.Anticyclonicwindvorticityleadstothinningofthehypolimnion inthecentralbasinandearlierdestratificationinthefall.

Integrated coastal management of Mumbai metropolitan region

ABSTRACT The restoration of Hamilton Harbour, from an environmental standpoint, is a current concern for the agencies involved with remediation efforts in the harbour. Estimates of circulation and mixing are needed to assess the fate and transport of water quality constituents in the harbour. A three-dimensional hydrodynamic modeling system (ELCOM) is used to study the circulation and thermal structure in the harbour. The model results were compared with profiles of temperature at several moorings and currents and water levels in the harbour. The model showed considerable skill in reproducing the thermal structure, surface currents and water levels. Mean summer circulation in the harbour showed two counter-rotating gyres occupying the harbour. The model produced harbour-lake exchange characteristics are in agreement with previous studies. Simulations using passive tracers qualitatively agreed with chemical tracer studies conducted near a sewage treatment plant outfall. The accuracy of these simulations suggests that the model is capable of describing flow and transport of material required for detailed water quality simulations.

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

Mumbai Metropolitan Region (MMR) is the largest coastal city in India. The region experienced tremendous growth over the years due to rapid industrialization and urbanization. MMR is also the major center of economic activity in India. As a result there is a continuous and constant influx of population from the rest of the country. The high population density and uneven growth rate have resulted in serious environmental problems in the MMR coastal region. This paper discusses several aspects of the MMR coastal region that suffer from a wide variety of environmental as well as socio-economic problems due to unplanned and non-integrated sectoral developmental activities over the years. These problems need to be addressed in developing an Integrated Coastal Management plan for the MMR coastal region.

On Recent Trends in Atmospheric and Limnological Variables in Lake Ontario

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.

Sediment resuspension mechanisms and their contributions to high‐turbidity events in a large lake

Thesurface air andwater temperatures increased at allseasonalandannualtime scales duringthe last40 yr in Lake Ontario. The annual mean air and surface water temperatures have increased by 1.43 86 0.398 and 1.26 86 0.328C, respectively, over 1970‐2009. The air temperature increased at a faster rate than the surface water temperature in winter and autumn, whereas in spring and summer the surface water temperature warmed faster than the air temperature. The length of summer stratified season has increased by 12 6 2 days since the early 1970s due to the increase in water temperature. The decline of surface wind speed over Lake Ontario resulted in a shallower surface mixed layer and enhanced the summer thermal stratification, which increased the summer surface water temperature more rapidly than the air temperature.

Integration of best management practices in the Bay of Quinte watershed with the phosphorus dynamics in the receiving waterbody: What do the models predict?

High-resolution field data, collected during April to October of 2008–2009, were analyzed to investigate the quantitative contribution of sediment resuspension to high-turbidity events in central Lake Erie. Resuspension events were distinguished within high-turbidity events according to turbidity, fluorescence and acoustic backscatter timeseries, as well as satellite images. We observed 16 high-turbidity events, causing a total duration of ∼20 d (out of 344 d) with elevated nearbed turbidity (> 10 NTU). Of these events, 64% were correlated with algal biomass, with the remaining 18%, 5%, and 4% being attributed to sediment resuspension by surface waves, storm-generated currents and enhanced nearbed turbulence induced by high-frequency internal waves, respectively. This is the first time that resuspension by enhanced nearbed turbulence from high-frequency linear internal wave degeneration has been observed in a large lake. Resuspension was parameterized as a function of the instantaneous critical bottom velocity, bottom shear stress and the Shields parameter. From the in situ measurements, we suggest an extended Shields diagram for silty bed material that can be used to predict resuspension in other aquatic systems with similar sediment composition (∼20% cohesive sediment).