Description and Rationale of Project, Research Objectives, Methodology, Work Plan
We are conducting a 2 year project to identify and quantify the most recent natural (past 2000 years) and human-induced (past 100 years) physical, chemical and biological changes that have occurred in selected key lacustrine basins of the northern Great Plains of western Canada. These changes will be interpreted with respect to water level fluctuations and related to both extrinsic and intrinsic causal/driving mechanisms. Four representative lakes, chosen because of their location and distribution within the Canadian Great Plains, their recent record of water level fluctuation, and the impact of these water level and related ecological changes on the local economy, are: Manito Lake (located near Marsden in western Saskatchewan), Waldsea and Deadmoose lakes (near Humboldt in south-central Saskatchewan), and Antelope Lake (near Swift Current in southern Saskatchewan). On the basis of my previous reconnaissance work on these lakes, each of these basins offers tremendous potential for detailed, high resolution paleoenvironmental reconstruction because of their finely laminated deposits and suitable sediment composition and geochemistry. However, most importantly from the perspective of the SPG-SC, each basin has significant hydrologic and water level issues that are adversely affecting the local communities and public use of these lakes.
To formulate a definitive long-term record of water level and ecological history of these four basins, lake sediment cores will be collected and microbialite/biohermal structures sampled. Analyses will be carried out at the highest temporal resolution possible and over a period that captures a broad range of climatically-relevant conditions. The past 1500 to 2000 years is the most obvious target since this period is characterized by several prominent climatic episodes of hemispherical (and probably global) extent, the Medieval Warm Period and the subsequent Little Ice Age, as well as ongoing post-Little Ice Age warming. Sediment sequences covering this interval will be readily obtainable from each of the lakes. However, inherent chronological limitations due to varying sedimentation rates, radiometric dating errors and other factors will likely limit the resolution achievable to approximately decadal scale.
Strategic Project Objectives
During the past 2000 years many changes have occurred in our environment. Most of these changes have been brought about by climatic variations which have altered the hydrologic regime and the stability of vegetational cover on the land's surface. The lake basins of the northern Great Plains reflect these changes by variations in rate and nature of the sediment deposited. In recent times, humans have become involved in influencing the hydrology of the watersheds by such activities as plowing, cropping, construction, paving, and drainage diversion. Addition of contaminants and pollutants can also result as a direct consequence of these and other human activities. Furthermore, it is now well documented that the atmospheric concentration of CO2 and other greenhouse gases has increased exponentially since the mid-nineteenth century, in part due to anthropogenic deforestation and related land use changes, and to increased combustion of fossil fuels. It is clear that human activities are accelerating the rate of increase and that the continued exponential increase will likely lead to significant environmental degradation and global warming.
In the context of the northern Great Plains, it is evident from previous research that the complex dynamics of large open-drainage lakes (e.g., Lake Manitoba, Lake Winnipeg, Lake Winnipegosis) make them less desirable sites for paleoenvironmental analyses. In these large open systems with very large catchments, water levels are controlled by the complex interaction of tectonics, basin sedimentology, drainage basin changes, as well as climate. Similarly, playas and other episodically dry wetland basins, which comprise the greatest proportion of lacustrine environments in the Great Plains, present difficulties because high-discharge events as well as extended dry episodes can remove sedimentary records. These attributes make it difficult to establish a continuous and accurate chronology.
In contrast, the best sites for reconstructing the history of hydrologic and climatic change in the Canadian Great Plains are the relatively small but perennial closed-drainage lakes. These lakes are highly sensitive to changes in their water, sediment and nutrient balances and therefore their deposits are much more likely to provide an unambiguous record of past hydrologic and climatic fluctuation. The regional abundance of these closed-basin lakes in the Great Plains combined with the general scarcity of other paleoenvironmental indicators, such as tree rings, ice cores, etc., dictates that the lacustrine records in many parts of the region provide the only basis of both short term as well as long term climatic fluctuations. As shown in many other paleolimnological studies elsewhere (e.g., southwestern United States, Africa, China, Australia), investigation of both the physical and chemical components of the lacustrine deposits can lead to important conclusions regarding paleoenvironmental conditions of the basin.
The sediment in small closed-basin lakes of the northern Great Plains provides information about the pre-cultural water level, salinity, and natural environmental fluctuations. The deposits in these lakes also contain a detailed history of anthropogenic stress during post-settlement time. Even small changes in virtually any element of the hydrological budget of the salt lake basins are reflected rapidly and directly by physico-chemical, sedimentological and/or geobiological fluctuations. Indeed, the fact that these salt lakes are essentially closed hydrological entities and discrete ecosystems provides researchers with a unique opportunity to evaluate the complexity of various geological, hydrological, and geochemical interactions.
The main objective of this project is to formulate a comprehensive, scientifically sound ~2000-year record of the magnitude and frequency of water level changes and corresponding ecological fluctuations in four lacustrine basins in the Canadian Great Plains. This will be accomplished by analyzing the most appropriate physical, geochemical, and biological evidence contained in the sediments of these lakes.
The data and interpretations arising from this objective will provide a rigorous scientific basis for understanding the range of natural variability in these lakes, which will help place the dramatic changes currently evident in the basins into proper context. The results of this project are required to answer the following critical research questions:
Are the hydrological variations and resulting ecological changes in the study lakes witnessed during the past three to four decades within or beyond the range of natural variation observed during the past several millennia?
Does climatic variability play a significant role in determining natural variations of hydrological and ecological conditions in the basins?
Are the natural (and anthropogenic) fluctuations in lacustrine conditions synchronous across this large region or, as other research in the northern Great Plains and elsewhere in North America has demonstrated, are the changes more locally controlled or perhaps time-transgressive?
Using this enhanced understanding of climate-lake hydrology relationships, what is the prognosis for these basins (and other lakes in the Great Plains) under future climatic conditions for the Canadian Prairies as predicted by GCM simulations?
The specific objectives of this research project during the two years of support are to:
Retrieve sediment cores from the offshore basinal areas of Manito, Antelope, Waldsea, and Deadmoose lakes;
Acquire samples from carbonate microbialites, bioherms, and tufas from Manito Lake;
Establish a recent sediment chronology for the core and microbilite/tufa samples that allows differentiation of pre-settlement from post-settlement deposits;
Delineate and map any geomorphological and shoreline indicators of high water stands in each basin;
Evaluate long-term (1500‑2000 years) fluctuations in texture, petrography, bedding and sedimentary structures, mineralogy, organic content, and sediment and pore water geochemistry, and interpret these changes with respect to hydrologic and limnological fluctuations in the basins;
Examine the periodicity of stratigraphic and geomorphic/shoreline changes and relate any changes to causal mechanisms, such as climatic variation or changes in drainage basin characteristics;
Assess any recent, short‑term (~100 years) changes in the sedimentary and geochemical parameters and attempt to relate these to changing land use characteristics and/or specific human events;
Together with data and results from other paleolimnological investigations in the region, examine any regional pattern in the changes in these sediment histories, and relate these changes to either natural factors, such as climate, hydrology or geology, or to anthropogenic environmental modifications.
Benefits and Broader Impacts of this Research
The findings of this project will do much to increase general awareness about the sensitivity of lakes in western Canada and water resources of the northern Great Plains to climate change and the necessity of understanding impacts of paleoclimate change. Investigation of the sensitivity of climate-hydrology linkages and corroboration of past lake level changes as a result of climatic change
is a new and exciting field of applied Quaternary and geolimnological/paleolimnological research in Canada. This research will heighten societal interest in climate change. Most importantly, the results of the project will contribute additional perspective and confidence for advice on policy or decision-making by government programs on climate and hydrologic change in the Great Plains, a situation that is clearly in need of improvement as, for example, reviewed by Schindler (2005) and Schindler and Donahue (2006).
Important insight into long-term lake response under changed postglacial Prairie climates has already been obtained by several large multidisciplinary, multi-organizational projects such as the Geological Survey of Canada’s Palliser Triangle Integrated Research and Monitoring Area (Lemmen et al., 1993; Lemmen and Vance, 1999; Lemmen et al., 1997; Vance and Last, 1994 and related contributions) and the Lake Winnipeg Project (Lewis et al., 2001; Todd et al., 1996; Todd et al., 1998). However, few research programs have specifically targeted recent (past several millennia) lake level fluctuations in Prairie basins (e.g., Beaudoin, 2002; Campbell et al., 2000b; Laird et al., 2003; Lieffers and Shay, 1983; Michels et al., 2007; Sack and Last, 1994). Indeed, Recent and late Holocene paleolimnological research in the Canadian Great Plains region has lagged behind other areas of North American, Europe, and Australasia (Last and Ginn, 2005; Last, 2002c; see also Vélez, 2004). At present, assessment of future lake level variability in the Canadian prairies is still largely based on extrapolation of historically-recorded climate-hydrologic variation. Water level and associated lacustrine ecosystem changes in the Canadian Plains are already seriously compromising societal interests by limiting commercial and recreational use of the lakes, adversely affecting shore infrastructure and nearshore habitat, and, in several cases, drinking water supply and quality. Thus, by better quantifying inferred high-amplitude paleoclimate changes, and modeling the hydrological response to them, the sensitivity of water levels to climate change can be more accurately reconstructed.
Finally, the results of this project will contribute to enhanced evaluation of regional climate simulation models. Increases in atmospheric greenhouse gases will undoubtedly change the climate and hydrology of the Canadian Prairies (Lemmen and Warren, 2004; Sauchyn et al., 2003; Sauchyn et al., 2002). It is generally assumed that temperatures will rise in the Prairie region, although there is much less agreement about the changes in other factors such as precipitation, runoff, and evapotranspiration (Barrow, 2002; Warren, 2004a, b; Wittrock et al., 2005). Most general circulation models and the higher resolution RCMs (Regional Climate Models) predict greater overall precipitation for the northern Great Plains (e.g., Barrow, 2004; Plummer et al., 2006; Shepherd and McGinn, 2003). Whether this will offset the moisture stress resulting from the increased temperatures is contentious. For example, in the Prairies of north-central United States (North and South Dakota and eastern Montana) climate change due to a doubling of CO2 levels is predicted to result in a reduction of wetlands by over 50% (Poiani and Johnson, 1991; Sorenson et al., 1998). In contrast, Clair et al. (1998) maintain that few wetlands and sloughs in the Canadian Prairies would be adversely affected under this scenario. Similarly, McGinn et al. (2001) predict an overall increase in soil moisture for most of the Canadian Prairies region under 2xCO2 GMC simulations. At best, it is evident that the climate simulation models demonstrate a high amount of variability in predicted future changes for both mean temperature and total precipitation (Töyrä et al., 2005). More paleodata are clearly needed to test and better constrain the evolving GCM and RCM simulations (PARC, 2003).