Elevated temperature and browning increase dietary methylmercury, but decrease essential fatty acids at the base of...

Area of Science:

• Environmental Science
• Ecotoxicology
• Aquatic Ecology

Background:

• Climate change scenarios predict rising temperatures and increased terrestrial organic matter supply to aquatic ecosystems.
• These changes can alter nutrient and contaminant transfer within aquatic food webs.
• The impact of these changes on essential nutrients like polyunsaturated fatty acids (PUFA) and contaminants like methylmercury (MeHg) at the food web base is not fully understood.

Purpose of the Study:

• To investigate how increased water temperature and terrestrially-derived dissolved organic matter (tDOM) supply, and their interaction, affect MeHg and PUFA levels in subalpine lake seston.
• To assess the implications for the base of aquatic food webs under projected climate change conditions.

Main Methods:

• An outdoor mesocosm study was conducted in subalpine lake ecosystems.
• Manipulated water temperature and tDOM supply to simulate climate change impacts.
• Analyzed MeHg and PUFA concentrations in seston (small plankton) and microplankton.

Main Results:

• The interaction of higher temperature and tDOM significantly increased MeHg burden in seston and microplankton.
• Polyunsaturated fatty acid (PUFA) levels decreased in seston but increased in microplankton (filamentous algae).
• The bioavailability of PUFA to zooplankton decreased due to the shift towards less edible algal forms.

Conclusions:

• Experimental evidence shows elevated dietary exposure to MeHg and reduced dietary access to essential PUFA for aquatic consumers.
• Climate change scenarios, characterized by increased temperature and tDOM, degrade the food quality at the base of aquatic food webs.
• This deterioration impacts higher trophic levels by increasing toxicant exposure and lowering nutrient availability.