WHY IS THE ROBERT LAKE ECOSYSTEM AT RISK?
In B.C., saline-alkaline lakes are a rare landscape feature, mostly restricted to the Cariboo and Thompson-Okanagan regions. They primarily form in evaporative basins. An evaporative basin is one where there is no outflow stream. Over the years, seasonal waters bring in salts (mineral ions) from the surrounding soils and then the water evaporates over the summer, thus concentrating the salts. In the absence of human activity, it is not unusual for these lakes to completely dry up for years at a time, and in other years they may not dry up at all, all depending on changes in the local weather patterns. Although two or three of these lakes might occur in small clusters on the landscape, the clusters themselves tend to be geographically isolated from each other. This makes it difficult for many of the salt adapted species to disperse from one lake to another because of the inhospitable habitat between. This lack of connectivity among saline habitats can magnify the effects of human disturbance of a single lake.
It is most likely that Robert Lake is an example of a saline lake that established in, at least one, evaporative basin. In his status report to the Central Okanagan Land Trust, Roland Gebauer has indicated that the area was a meadow in the earlier part of the 20th century. He reports that the meadow basin filled with water due to agricultural activity, and then became saline due to the Kelowna landfill displacing water from Alki Lake (the evaporative basin in which the landfill is now located) which flowed downhill into the Robert Lake basin. While this may be true, it should also be considered that the ‘meadow’ represented a dry period during the life of the Robert Lake evaporative basin and that the soils here were alkaline. So, when hydrological conditions caused the basin to fill with fresh water, the salts in the soil were drawn into solution to make the water salty.
Click on the button below to read Roland Gerbauer's full report.
Shallow saline lakes like Robert Lake exhibit strong seasonal cycles when their basins fill with water and then subsequently the water evaporates, thus diluting and then concentrating the salts. Continued concentration of the ions in the water, at some point, results in them precipitating out as solids into the soils, and then inputs of fresh water cause dissolution of the salts from the solid state back into a dissolved state. If water is removed from the lake (as was done in Robert Lake by the City of Kelowna) then salts are removed as well, and incoming fresher water causes further dissolution from the sediments. Continued pumping causes removal of these salts, and the water body becomes increasingly fresh.
Resident biota have mechanisms to survive seasonal dilution and concentration of salts, but long term changes put them in peril.
Measurements of specific conductance (a function of salt concentration) indicate that a dilution effect occurred in 2018 and 2019 due to the City of Kelowna pumping water out of the lake to effect a lowering of high water levels that were encroaching on private lands. Specific conductance values obtained in June 2001, 2002 and 2016 show a magnitude of about 17 mS/cm (equivalent to about 10.2 ppt [1]) whereas in June 2018 and 2019, readings of 7.9-10 mS/cm were recorded (about 4 ppt), and these low salinities remained throughout the summer and autumn. The city did not pump water out of the lake in 2021, but is willing to do so again if water levels threaten to flood onto surrounding properties.
The Robert Lake ecosystem and its surrounding meadows are at-risk due to:
human development of the surrounding hillsides;
road construction;
the Kelowna Landfill;
increased inputs of water from up slope entering the basin causing lake levels to rise and thus prompting the City of Kelowna to pump water out of the lake to effect a lowering of water levels;
intensive irrigation of surrounding fields, and
climate change.
[1] Note that standard seawater is 35ppt. Robert Lake went up to 52ppt in August 2002.