Regional Water Balance Variability on the Boreal Plain of Alberta: A Component of the Sustainable Forest Management Network of Centres of Excellence
Collaborators: Dr. Terry Prowse (NHRC), Dr. Ellie Prepas and others (University of Alberta)
This study examines the hydrology and hydrologic controls on ecosystem processes in lakes of the boreal plain of Alberta. The research is motivated by the need to improve the understanding of observed ecosystem variability in undisturbed, burnt and cut watersheds. The main processes being examined include: watershed runoff to lakes, lake residence times, lake outflows, and associated nutrient concentrations/fluxes, which are known to be altered by disturbances.
The hydrology of the boreal lakes of Alberta is not well known. Traditional field approaches for measuring individual components of the water cycle (inflow, outflow, evaporation, water level changes) using precision field instrumentation can be time-consuming and prohibitively expensive, especially for use in large-scale inventories. Traditional modelling approaches have also proven ineffective in complex, low-relief wetland-rich watersheds typical of the Canadian boreal forest. As such, we have adopted an environmental isotope technique which has been developed for use in complex terrain.The isotope method can be readily applied to any lake, and requires only collection of 30 ml (1 oz.) samples of water which are subsequently analysed in the laboratory. We will apply isotope balance principles as a tracer of the water balance and its variability, and to categorize lakes by their water balance properties, thus allowing disturbances to be evaluated in lakes with similar hydrologic regimes. The isotope method is thus being developed and tested as a versitile field-based sustainable forest management tool with considerable potential for identification of lakes with delicate hydrologic-nutrient balances. Such applications of the isotopic tech nique were discussed in an international workshop ISOBALANCE hosted by NHRI and co-sponsored by SFM-NCE in July 1997. A selection of papers presented at the meeting will be published as a special journal issue in late 1998. Historical water balance information can also be obtained from the isotopic record preserved in organic lake sediments obtained from lake cores. This technique will be exploited for the first time to study the impact of fires on lake hydrology and lake ecoystems.
Progress to date: Isotopic data were collected from 70 Alberta lak es during 1996 and 1997 (3 times per year for most lakes). The isotopic composition of precipitation was estimated for each lake-site along with relevant physical paramters (temperature, humidity, precipiation amount) by spatial interpolation of availabl e data from climate stations in the Mackenzie Basin. As shown in the figure below, average isotopic composition of the lakes is enriched relative to the isotopic composition of precipitation at each site due to the effect of open-water evaporation. Differences in the isotopic separation between lakes and precipitation are systematic when various lakes and lake groups are compared. For example, isotopic enrichment in the TROLS group is higher than the other goups, suggesting that they are relatively high evaporation-low outflow systems (i.e. closed basins). Good agree ment is obtained for water balance parameters estimated from the two independant tracers (oxygen and hydrogen) and the results are consistent with anticipated latitudinal trends.
Stable isotopic composition of lakes (measured) and annual precipitation (estimated) for 70 boreal lakes in northern Alberta. Isotopic separation between precipitation and lakewater is a function of the throughflow rate, residence time, and effective drainage area of the lakes.