Why is Collecting Dissolved Oxygen and Temperature Profiles in BC Lakes so Important?
BCLSS Project Coordinator, Amy Baxter collecting a dissolved oxygen and temperature profile on Lillian Lake
With dynamic environments such as lakes, groups often wonder where to start when it comes to monitoring and protecting BC waterbodies. Designing a lake monitoring program can be intimidating, especially considering how intricate and interconnected lake environments are with their surroundings and the countless number of influences on water quality there can be on any given lake.
There are so many physical, chemical, and biological parameters that can be researched, monitored or sampled, at levels including the lake itself, incoming tributaries, or even the entire watershed. Determining the most important parameters to monitor depends on the specific lake and objectives of the program, however, consistent dissolved oxygen and temperature profiling can offer extremely valuable information for the majority of lakes throughout the province.
Temperature and dissolved oxygen (DO) strongly influence physical, chemical and biological processes in lakes. Annual temperature and oxygen patterns vary depending on local climate, lake shape, prevailing wind direction and lake depth (BCLSS, 2022).
Water is most dense (heaviest) at 4°C which is the driving force behind lake stratification and turnover. During the summer, lakes that stratify experience a layering effect, with the warmer, less dense water sitting on top of the cooler and heavier water, separated by a thermocline. See Figure 1.
Figure 1 – Layers of Summer Stratification in Lakes (BCLSS, 2022)
Stratification prevents mixing between the bottom cool water and top warmer water which traps nutrients released from bottom sediments until the layers mix in the fall. This mixing is also called lake overturn and typically occurs twice per year. However, mixing regimes vary depending on local climatic conditions. During the mixing process, the bottom waters get recharged with oxygen, and nutrients are brought up to the surface. To learn more about the different stratification schemes found in BC check out our LakeKeepers Manual!
Figure 2 – Typical Summer Thermal Stratification in a Lake (BCLSS, 2022)
Stratification and turnover in lakes have intense impacts on many lake parameters and conditions (See Figure 2). For example, under aerobic (oxygenated) conditions, much of the phosphorus in a lake is bound to iron, manganese and/or calcium contained in lake bottom sediments (BCLSS, 2022). When bottom waters become anoxic, chemical changes occur in the sediments that result in phosphorus being released into the water column. When the lake begins to turnover, the phosphorus is mixed into the photic zone where algae and plants can utilize it, sometimes resulting in blooms. This phenomenon is known as internal loading. Iron, manganese, and hydrogen sulphide (H2S) can also be released into the water during these anoxic periods (BCLSS, 2022). Because of impacts such as this, obtaining dissolved oxygen profiles can give us information about internal nutrient loading, and some insight into phosphorus and algal dynamics in many lakes.
Another key reason for obtaining dissolved oxygen and temperature profiles is because both of these parameters are arguably some of the most important limiting factors for aquatic life. Many fish species, especially salmonids, show signs of stress at temperatures greater than 18ºC and DO concentrations less than 4 mg/L (Truelson,1997). Woolway et al., (2020) discusses how climate change is already leading to warmer surface water temperatures, reduced oxygen concentrations, earlier onset of stratification, and well as longer periods of stratification in many northern hemisphere lakes. As these impacts become more apparent in lakes across the province, sensitive fish species such as salmonids may become “squeezed out” of their ideal habitat range as temperatures in the epilimnion become greater than 18 ºC, while dissolved oxygen levels in the hypolimnion fall bellow 4 mg/L. To read more about the predicted impacts of climate change on BC Lakes check out this article written by BCLSS Director Dr. Ken Ashley.
By taking dissolved oxygen and temperature profiles of a lake, it may be possible to detect and track changes to the depth of the thermocline, the degree of warming, or in the time or length of stratification. Due to the variation in sensitivity of lake ecosystems to climate change, it is important that proactive measures be taken in order to better predict how lakes throughout BC will respond. The more lakes that provide temperature and DO profiles, the more data points there are for different regions and lake characteristics so that steps can be taken to mitigate impacts or provide information in advance of an extreme shift.
The best way to measure DO and temperature in a water column is to use a DO meter which measures the amount of dissolved oxygen in an aqueous solution and has a built-in thermistor so that temperature can be recorded with every DO reading. We typically recommend probes such as the YSI ProSolo, and profiles should be collected at regular intervals, every 1 or 2 weeks during ice-free periods.
Are you interested in obtaining an instrument to collect dissolved oxygen and temperature profiles on your favorite lake? If so, send us an email to info@bclss.org! The BCLSS offers our members recommendations on equipment, letters of support for obtaining funding to purchase the instrument, and training on how to use and care for your new equipment. For groups looking to do and learn more, we also offer extended in-person training workshops or certification courses that will expand your knowledge on lake ecology and monitoring, climate and human impacts to watersheds, and so much more! This knowledge increases the ability of citizens to steward their lakes, collect scientifically credible data, and make meaningful changes in their watershed. We are here to help you every step of the way! Let’s work together to preserve and protect our beautiful BC lakes for generations to come.
References
Ashley, K. 2024,. Predicted impacts of climate change on BC Lakes. BCLSS. https://www.bclss.org/environmental-issues/predicted-impacts-of-climate-change-on-bc-lakes
BC Lake Stewardship Society (BCLSS) 2022. LakeKeepers Manual. A Guide to Lake Stewardship and Ecology in British Columbia. https://www.bclss.org/programs#lake-keepers-manual
Truelson, R.L. 1997. Water quality criteria for dissolved oxygen. Prepared for British Columbia’s Ministry of Environment, Lands and Parks, Water Management Branch, Victoria
Woolway, R.I., M. Kraemer, J.D. Lenters, C. J. Merchant, C. M. O’Reilly and S. Sharma. 2020. Global lake responses to climate change. Nature Reviews Earth & Environment volume 1, p388–403.
