Widespread deoxygenation of temperate lakes

Area of Science:

• Environmental Science
• Limnology
• Climate Change Research

Background:

• Dissolved oxygen (DO) is crucial for aquatic ecosystems, regulating biodiversity, nutrient cycling, and water quality.
• Long-term DO declines in oceans are linked to climate warming, but lake DO trends remain poorly understood.
• Lake DO is complex, influenced by temperature, stratification, decomposition, and primary production.

Purpose of the Study:

• To investigate long-term trends in dissolved oxygen concentrations across numerous temperate lakes.
• To identify the primary drivers of observed changes in lake DO, differentiating between surface and deep waters.
• To assess the impact of climate change and water clarity on lake DO and ecosystem services.

Main Methods:

• Analysis of 45,148 dissolved oxygen and temperature profiles from 393 temperate lakes.
• Calculation of long-term trends for DO and temperature from 1941 to 2017.
• Statistical analysis to correlate DO changes with factors like water temperature, stratification, and water clarity.

Main Results:

• A widespread decline in dissolved oxygen was observed in both surface and deep waters of the studied lakes.
• Surface DO decline is mainly due to reduced solubility from warming, except in highly productive lakes where it increased due to phytoplankton.
• Deepwater DO decline is linked to increased thermal stratification and reduced water clarity, not gas solubility changes.

Conclusions:

• Climate change and declining water clarity are significantly altering the physical and chemical conditions of lakes.
• Freshwater DO declines in lakes are substantially greater (2.75–9.3 times) than in oceans.
• Observed DO trends pose a significant threat to essential lake ecosystem services and biodiversity.