OTHER LARGE LAKE SYSTEMS, SECTORS AND DECISION MODELS .1 Climate change research in other selected large-lake systems

The preceding discussion demonstrates that considerable climate impacts related research is being conducted on the Laurentian Great Lakes, however, until recently, there has been little research relating to the responses of large deep lakes in the Canadian northern regime. As indicated from GCM simulations, the northern regime may be one of the most vulnerable areas to the impacts of climate warming, especially during the winter season. The importance of understanding the potential climate impacts in the northern regime is underscored by the realization that some of the largest lakes in the world are located in the northern Mackenzie Basin (Table l), (Schertzer, 1997). The Mackenzie River is the largest North American source of freshwater to the Arctic Ocean and changes in this vast hydrologic basin can have implications to the global climate system. The basin experiences wide climatic fluctuations, and recent research has shown that the Mackenzie Basin is experiencing a pronounced warming trend which is amongst the highest anywhere in the world (Stewart et al., 1998). Intensive research on the Mackenzie basin hydrology is currently being conducted as part of the Global Energy and Water Cycle Experiment (GEWEX-MAGS) as part of the World Climate Research Program (WCRP), (Rouse, 1997). While the main focus of the GEWEX-MAGS is on quantifying the heat and mass exchanges of the basin, part of the goal is to assess the potential impacts of climate change on the various surface types including large lakes. With respect to the large-lake component, initial collaborative research has focussed on Great Slave Lake (main-lake) to specify over-lake meteorology, hydrology, air-water interaction, heat budget, sea-state (waves) and thermal structure as well as hydrological budgets (Schertzer et al., 2000). Large lake responses, in this northern lake system, can be simulated using modifications to models developed from the Laurentian Great Lakes. Intensive data collected over the last decade are valuable for determining interannual variability of key physical components. An assessment of the potential climate change responses both for large lakes and a vast number of small lakes in this system is currently being conducted under the GEWEX-MAGS program (e.g., Schertzer, 2000; Rouse et al.

1997; Rouse et al., 1999). Climate change assessments are also planned for a range of other basin hydrological components.

It is interesting to note that preliminary research on possible changes in large deep lakes (including northern regions) due to climate warming was conducted by Meyer et al. (1994) by applying a GFDL GCM climate scenario to a hypothetical lake at different geographical zones over the world. The analysis suggested that the sensitivity of lake thermal stratification to changes in air temperature greatly increased in transition zones such as the subtropics (30°-45” N/S latitude) and the sub-polar zones (65”-80’ N/S latitude). Warmer atmospheric temperatures significantly affected turn-over characteristics in these zones where turnovers occurred earlier and the duration of well mixed layers in summer was enhanced. In the sub-polar and polar regions, ice cover was most sensitive to changes in air temperatures regardless of depth. Changes in the duration of summer thermal stratification and mixing characteristics were also determined from climate studies of the Laurentian Great Lakes.

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7.2 Climatic change concerns in other sectors related to large lakes

The preceding discussions strongly suggest that there is a strong linkage between the climate change impacts on the physical, bio-chemical regime of a large deep lake and other sectors large deep lakes. Potential ecosystem effects may include greater over-winter mortality of whitefish eggs, and thus potentially lower year class size and lower diatom production associated with the loss of the stable environment afforded by the formation of a continuous winter ice cover. Changes in the mixing characteristics of lakes, especially sensitive eutrophic lakes and embayments, has significant water quality implications such as the development of hypolimnetic anoxia (Lam & Schertzer, 1987; Lam et al., 1987a,b).

Increases in water temperature, changes in temperature cycles, and potential impacts on water quality in susceptible lakes and embayments/wetlands, has serious implications for fisheries which may see shifts in species composition (Meisener, et al. 1987; Coutant, 1990;

Magnuson et al. 1990; Regier et al. 1990). Water use and management is an important issue especially in basins expecting decreases in water supplies resulting from impacts of climate change and variability. A decrease in water supply has implications on urban and rural water usage, groundwater availability, assimilation of treated sewage, water level, and impacts on socio-economic sectors (recreation) (Brown et al., 1996 a,b; Krutzweizer, 1996; Lee et al., 1996; Mortsch & Mills, 1996). Adverse changes in climate are also expected to impact on coastal wetlands by affecting wetland area1 extent, quality, productivity and vegetation communities (Mortsch & Koshida, 1996). For large lakes associated with industrial communities, changes in thermal patterns and hydrodynamic characteristics can impact on the distribution of accidental chemical spills. As well, climate change may impact on the atmospheric distribution of and transport of pollutants and changes in water surface temperatures can be expected to affect the air-water exchange of volatile toxic chemicals (Booty, 1996).

It is well known that the large heat storage capacities of large lakes can affect the local climate. Changes in the lake climatology may also contribute to weather and heat related morbidity changes especially for the elderly during summer heat spells (Tavares, 1996) and an increase in debilitating diseases such as malaria (Duncan, 1996). Warmer water temperatures in the nearshore zones may lead to the increase of bacteria in water used for recreation resulting in an increase in beach closures and other impacts on tourism and recreation (Rissling, 1996). Changes in the rural hydrology can affect the stream discharge to the lakes and thus affect the nutrient budgets of lakes and water quality conditions (Schertzer

& Lam, 1996).

7.3 Management Strategies: Environmental Decision Support Systems

While more research is still required on studying climate change impacts in large lakes, there are significant results from preliminary studies that concern possible management and adaptation strategies. For example, research is being conducted at the National Water Research Institute, Environment Canada, to develop a decision support system (Lam, 1997) that includes some of the major climate change effects such as thermal stratification and hydrological runoffs, as part of the considerations for environmental management. The

thermal layer thicknesses and water temperature from several GCM scenarios are used to investigate possible impacts on nutrient and dissolved oxygen levels in Lake Erie, in conjunction with other considerations such as phosphorus abatement programs, agricultural non-point sources, and effects due to the arrival of zebra mussel and other exotic species. All these considerations are necessary for the development and implementation of the Lake Erie Lake-wide Management Plan. To utilize the knowledge on large lake hydrological processes, the system links together various models for lake thermal stratification, phosphorus dynamics, basin hydrology and non-point sources runoffs. Using long-term data from many sampling stations, the objective of this investigation is to establish the uncertainties of these models and the integrated results, to provide preliminary advice on management strategies and to identify research gaps.

7.4 Exploring hydrological “adaptive” measures : hypolimnetic anoxia

Possible adaptive / mitigative measures to “control” the water quality (hypolimnetic anoxia) response of Lake Erie were investigated (Lam et al. 1983). Long-term water quality simulations showed linkage between the occurrence of hypolimnetic anoxia (dissolved oxygen concentrations < 1.5 mg/L) and weather which resulted in the formation of shallow hypolimnia (< 4m thick) and with vertical diffusion across the thermocline (< 1 cm2/s), (Schertzer, 1987; Lam & Schertzer, 1987; Lam et al., 1987). It was suggested that moderating the hypolimnion thickness through clever timing of lake water levels may be a possible measure for alleviating extreme occurrences of hypolimnetic anoxia.

Figure 4 shows the mean hypolimnetic dissolved oxygen concentration based on 12-year simulation results in the central basin of Lake Erie for the days 150-260 in response to three cases of water level variation scenarios referenced to the datum. In general, the simulated results at the time before lake thermal overturn, support the plausibility of using water level to regulate the dissolved oxygen condition in the Lake Erie central basin. When water levels are high, for example under entrainment reversal conditions (simulation 3) or for simulations using constant high water levels (simulation 2), the hypolimnion dissolved oxygen levels remain above anoxic levels. However, simulations conducted using “shallow hypolimnion”

scenarios in response to climate forcing indicates that at the period before fall overturn, dissolved oxygen levels are near or below anoxic levels. This example is a simple demonstration of hypothesis testing and does not consider possible effects of water level increases on other parts of the ecosystem. Under climate warming with expected decreases in net basin supplies and consequent reductions in water levels, more complex scenario testing using environmental decision support methodologies will be required to provide options for lake management. Other examples of adaptive measures include the use of lake water for cooling systems in hydro-electric power generating plants, protection of fish habitats and wetland ecology, recreational use of beaches, adaptive farming practices during drought conditions, and so on. These are a sample of areas requiring further research on impact analysis under scenarios of potential changed climatic conditions.

8 SUMMARY

This report provides a synopsis of some of the ongoing research being conducted to assess the potential climate change effects on large deep lakes, surrounding basin hydrology and extended impacts which are affected by the integrity of the large lake system.

Evaluation of

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10 , i- E 8-

Lake Erie Central Basin : Before Over-turn

-0.5 0 0.5 1.0 1.5 210 2.5 3.0 Mean Annual Water Level Above Datum (173.31 m)

Figure 4. Estimated Lake Erie Central Basin hypolimnion dissolved oxygen concentration for the period before over-turn, based on simulations from the NWIU g-box water quality model (Lam et al. 1987, a,b) in response to water level change scenarios, (1) a twelve year simulation, (2) a shallow hypolimnion type of thermal structure, and (3) and entrainment reversal type of thermal structure. The circles indicate dynamic data observed in the years shown by numbers.

such a system of impacts to climate is complex. The current research applies a range of methodologies to assess probable responses. Where available, long time-series of observations can be used to analyse the characteristics of the current climatology in an effort

‘to determine the presence of significant trends and or shifts in the key variables. Alternate techniques include the use of climate analogs, application of GCM steady-state or transient scenarios and climate transpositions. Research is currently underway to develop additional tools for the assessment / forecasting of environmental change which include such techniques as Bayesian belief systems and neural networks. Development of environmental decision support systems is a new technology which can integrate lake and basin complexities for scenario testing and formulating options for managing the water resource under climate changes. It is recognized that application of a range of assessment techniques is useful for minimizing uncertainties of impact predictions and testing the convergence/divergence of differing scenarios. .

Many of the world’s largest and deepest freshwater lakes are located in North America.

Historical measurements, especially on the Laurentian Great Lakes, have been invaluable for establishing baseline climatology and for development and verification of complex models of basin and lake hydrology, lake physics (thermodynamics, hydrodynamics), water quality and socio-economic interrelationships. These models all contain meteorological elements that can be affected by climate changes. The results included in this report are only a part of the important research which is being conducted to assess climatic impacts on the large lake system. Never-the-less, the report has shown that there are large-scale efforts underway to understand the effects of the climate processes on large lakes and basins. Selection of a particular climate scenario has a definite impact on the magnitude and direction of change.

For example, climate transposition scenarios applied to both basin and lake hydrology, shows enhancements of impacts compared to steady-state or transient scenarios, but they have an

advantage of incorporating natural variability within the existing climate which is not possible from either steady-state or transient GCM scenarios. Assessments of impacts on lake physics is progressing though application of a range of GCM scenarios to existing regional models. Long-term records are available for such components as surface temperature and ice cover and duration for evaluation of trends. However, modeling of the thermodynamical, hydrodynamical and air-water interaction processes is heavily dependent on assumptions and generally inadequate GCM model predictions from the current coarse grid resolutions which do not include water surfaces. It is encouraging to see that experts in these fields are very aware of the limitations of current models for climate change impacts analysis. Similar modeling efforts to that being conducted on the Laurentian Great Lakes hydrology and lake physics are currently underway in other large lake systems associated with GEWEX and other continental-scale investigations which will allow comparison of impacts results from a range of climatic conditions at different latitudes. Advances in modeling the lake physics is continuing as are developments in GCMs to refine land surface schemes to incorporate water surfaces in the prediction schemes.

The importance of understanding potential impacts on large lake systems is underscored by the increase in research efforts in sectors that are closely dependent on the integrity of the water resource. Water quality considerations are amongst the most important in the heavily populated areas of the Laurentian Great Lakes. Assessment of the climate change impacts on water quality components is difficult since the nutrients, contaminants etc. transported to and within the lake is dependent on accuracies of predictions on the hydrology, thermal and hydrodynamic changes in the lake system. Potential impacts of climate change on various water quality processes (nutrient and volatile toxic contaminants) has been derived based on probable changes in the physical - hydrological environment and there is a large body of research which is concerned with climatic impacts on wetlands and lake fish populations.

This report provided a brief discussion on climate change research being conducted in other sectors which are related to lake-basin systems. These included potential changes in basin (urban and rural) water supplies, groundwater resources, socio-economic factors (recreation, human health, power generation).

Advances in computing power will likely result in progressive improvements in GCM and regional climate scenarios as algorithms include more realistic physics. It is also expected that basin hydrology, lake physics, water quality and associated socio-economic models will continue development. With the continued investment in new technologies to integrate interactions between components of the system, assessments of climate impacts on the large lake systems is expected to improve progressively.

9 ACKNOWLEDGEMENTS

The authors are grateful to Dr. Fred Wrona, who encouraged the compilation of this work and Dr. William Booty who provided useful comments. We have included summaries of contributions from colleagues at the National Water Research Institute, the Great Lakes Environmental Research Laboratory and several other Institutes and Universities who participated in a state-of-the-art review sponsored by the Water Resources Engineering Division of the American Society of Civil Engineers (ASCE), edited by the authors.

Research support has been received from many agencies over the years. In particular, we acknowledge support provided from the U.S. E,nvironmental Protection Agency, Environment Canada’s Great Lakes 2000 Climate Program, the International Joint Commission and the Global Energy and Water Cycle Experiment (GEWEX-MAGS).

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