Article by: Rick Nordin (PhD) (posted by BCLSS in Fall Newsletter)
Also from BCLSS: Why is Collecting Dissolved Oxygen and Temperature Profiles in BC Lakes so Important?
In the past few years, it has become evident that many lakes in BC are changing in different ways. Shallow lakes seem to be responding to climate change particularly dramatically – they are sensitive as an early indicator of more changes to come – an aquatic ecosystem equivalent of the canary in the coal mine?
Shallow lakes in BC, and around the world, are responding to climate change by having:
- Increasing water temperatures
- More frequent algal blooms or increased aquatic plant growth
- Phase shifts – changes in dominance by planktonic algae to aquatic vascular plants or vice versa
- Changes in water levels – particular significant decreases
- Longer periods of thermal stratification when stratified – and more intense deep water oxygen depletion
- Changes in ecological structure – different dominant species or more suitable conditions for invasive species
What’s going on?
First of all, there doesn’t seem to be an accepted definition of what a “shallow” lake is. The key characteristic seems to be whether the lake stratifies thermally in the summer. Most lakes that are less than five meters deep are easily mixed by wind energy and do not normally stratify. Geography and weather patterns can have a significant effect. If a lake is well protected from wind – in a valley or in an area with low wind exposure, the lake may temporarily stratify even if it is very shallow. Some shallow lakes that normally stratify can have periodic mixing events due to hot weather during the summer, moving nutrients from bottom waters causing algal blooms. Fall overturn can also happen earlier than normal due to increased heating of the deeper waters. Lakes up to ten meters deep may be continuously mixed during the summer – if they are in an area with strong winds – or if they do not receive normal heating (thermal energy) from the sun or may under different conditions (low wind energy), display a strong thermal stratification. So, it is complicated (lakes are that way!). Lakes of particular concern are those with a depth of 5-10 meters – defined here as “shallow” lakes.
Many stratified shallow lakes are vulnerable to episodic mixing events caused by weather e.g. wind storms – or climate change that might change the heat input into the lake (and making stratification periods longer or shorter) and the amount / length of ice cover. Many lakes that had a history of ice cover 100 years ago no longer have ice cover. Other consequences can include “regime shifts” (changes from aquatic plant dominated system to dominance by algae) and making habitats more suitable for invasive species. Shallow lakes respond to climate change faster and more sensitively than deep lakes; they warm up and cool down more quickly, and the impact can be significant. In some low precipitation areas, shallow lakes may (and have) completely disappeared.
In British Columbia we have several examples of shallow lakes which seem to be particularly affected by recent changes in climate. Quamichan and Somenos Lakes are two urban / agricultural affected lakes of particular concern to local and provincial governments and local residents that are on Vancouver Island near the city of Duncan. As is often the case, the lakes are being affected by several factors, watershed land use and increased nutrient inputs, invasive species as well as changes in climate. The photo below shows the two lakes.
The acceleration of deterioration has become quite evident when looking at the data from a program (BC Lake Monitoring Network – BCLMN) of the provincial government comparing the water quality and productivity of 61 lakes across the province. Quamichan Lake stands out as having particularly high phosphorus and chlorophyll concentrations in comparison to other lakes. Figures below are from a report (Larratt 2020) compiling data from the monitoring network.
Another example of a shallow lake that has experienced very noticeable deterioration is Nulki Lake in the Nechako valley. The lake has a maximum depth of about 7.5 m so fits within the arbitrary definition of vulnerable shallow lakes stated above. It is a very productive lake resulting in excellent fish production and thus popular for recreational fishers. However because of climate change and other factors in recent years the lake has produced very dense aquatic plant coverage and spectacular algal blooms and risk of significant fish kill – due to low oxygenation at night (typically described as “summerkill”) and high temperature and potentially a thermal destratification.
With increased lake water temperatures, one of the important consequences is higher lake water evaporation and if more water evaporates from the surface – there can be up to a meter of water lost during the summer – and coupled with the evaporation losses from the watershed, there can be a major change in the water budget and a much longer (and less desirable) lake “flushing rate”.
These kinds of data to quantify changes are difficult to collect and it is only at looking the longer term trends that change can be documented. Lake stewardship groups play an important role in data acquisition – through stewardship group monitoring programs and projects like the ice-on / ice off observations collected by BCLSS members.
Shallow lakes are often not seen as “valuable” as the larger more conventional lakes but they are important – especially as indicators of change and a predictor of future trends in lake water quality.
Some references below for those who might have interest in what researchers from around the world are reporting.
References:
British Columbia Lake Monitoring Network:
https://www2.gov.bc.ca/gov/
Meerhoff, M., F. Teixeira-deMello, C. Kruk, C. A. González-Bergonzoni, J.P.Pacheco, G. Lacerot, M. Arim. M.Beklioğlu, S.Brucet, G.Goyenola,C. Iglesias,N. Mazzeo,S.Kosen, Erik Jeppesen. 2012. Environmental Warming in Shallow Lakes: A Review of Potential Changes in Community Structure as Evidenced from Space-for-Time Substitution Approaches. https://doi.org/10.1016/B978-
Larratt Aquatic Consulting. 2020. B.C. Lake Monitoring Network, Water Quality, Phytoplankton and Zooplankton Taxonomy. Summary Report for 2015-2020. Prepared for the BC Ministry of Environment and Climate Change Strategy. 108p
R Iestyn Woolway, Sapna Sharma, John P Smol. Lakes in Hot Water: The Impacts of a Changing Climate on Aquatic Ecosystems BioScience, Volume 72, Issue 11, November 2022, Pages 1050–1061, https://doi.org/10.1093/
Zingel, P., M. Boveri, H. Agasild and E. Jeppesen. 2025.Secrets of shallow lakes – insights from Research. 2025. Hydrobiologia 852:283-288.
About the author:
Rick Nordin, PhD was the BC Provincial Limnologist from 1974 to 2002. Rick was involved with projects in all areas of BC with particular emphasis on eutrophication and drinking water protection. He taught part time at the University of Victoria from 1989 to 2016 and had an appointment as an adjunct professor in the biology department teaching a number of courses, carried out research programs, and supervised graduate students. From 2002 to 2008, Rick worked as senior research scientist in the Environmental Management of Drinking Water Program at UVic. He has been a board member of BCLSS since it was formed (1997) and has also served on the board of directors for the North American Lake Management Society.