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Dark lakes change how microbes eat land carbon

In a dark Ontario lake, more aromatic terrestrial organic matter lowered bacterial production and slightly raised CO2.

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Which two lakes were used?

Clear Swan Lake and dark Lake Laurentian near Sudbury, Ontario.

How did the authors label the lakes?

Swan as the clear lake and Laurentian as the dark lake.

How much more light reached Swan sediments?

More than four times higher light at the sediment surface.

What t-OM quantities were mixed into sediments?

0%, 5%, 25%, 35%, and 50% terrestrial organic matter.

How were quantity × quality treatments replicated?

Each of 5 quantities × 3 qualities was replicated three times per lake.

What does SUVA indicate?

The average aromatic fraction of DOM per unit DOC.

How did aromatic DOM change bacterial production?

Higher SUVA lowered BP; 25% more aromaticity cut mean BP by 14.5%.

What happened to CO2 in the dark lake as BP fell?

A small increase in CO2 production, suggesting a higher respiratory cost.

Why was BP lower in the clearer lake despite less aromatic DOM?

Nutrient limitation: 13.6% less N and 15.0% less P relative to C.

What genetic evidence did they use?

Metagenomics of sediment bacterial functional genes for hydrolytic and oxidative enzymes.

What lake-specific futures do they predict?

Dark lakes may bury more t-OM; clear lakes may feedback via extra CO2 and algae.