Aquatic ecosystems are highly sensitive to climate change. Warming temperatures and precipitation variability can have far reaching implications to water supply, water quality, and the aquatic food web that will affect us all—from ranchers to anglers. As the amount, seasonality, intensity, and distribution of precipitation changes, we can expect more drought and lower lake levels in some Montana watersheds as well as higher localized precipitation and flooding in others.
The discharge regimes of mountain streams and rivers that supply water to many Montana lakes will become more variable. In Montana, we are likely to experience earlier peak flows in spring and lower summer flows that will affect the transport rate of sediments and nutrients downstream. Warmer stream temperatures will also stress native fish species and give a competitive edge to more warm-water-tolerant introduced species.
A changing climate will mean that Montana lakes could experience a shift in their heat balance, temperature profiles and vertical mixing regimes. Warming atmospheric and stream temperatures will increase lake surface temperatures and decrease ice-cover, affect nutrient fluxes, alter the productivity and composition of lake plankton, and decrease dissolved oxygen levels for all aquatic life.
It will take the active partnerships of government agencies, universities, NGOs, and private citizens to protect our Montana water resources in a changing climate and to create resilience strategies for the future.
Lake Ice
The maximum density of water is 39.2 Fahrenheit at sea level. Any water that is warmer or cooler than the temperature of maximum density will float on top. In early winter as surface water temperatures reach the freezing point, ice will begin to form on top of the lake. The onset of ice formation can depend on the size and depth of the lake, along with local meteorological conditions. Lakes with larger volumes take longer to lose their heat and oftentimes have longer fetch distances than smaller lakes. Fetch is the unimpeded wind flowing over the lake that causes waves that can break up thin ice that initially forms around the edges of the lake. Ice forms most efficiently during very cold and windless conditions.
The photo below shows Whitefish Lake in early winter as lake surface temperatures cool. Very cold temperatures coupled with calm conditions drive ice formation.
Whitefish Lake cooling down. Photo courtesy gravityshots.com
“Ice Breakup on Whitefish Lake.” Photo courtesy gravityshots.com