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Food webs of boreal lakes worldwide have been receiving no nitrogen deposition since ancient times. Now, these are expected to get an increased availability of inorganic nitrogen.

Simultaneously, certain factors are leading to an increase in the dissolving of terrestrial organic carbon loads into the aquatic systems.  

The current study was conducted by Umeå University in northern Sweden to demonstrate the consequence of this on food web structure and productivity in natural boreal lakes.

It was found that nitrate addition significantly increased phytoplankton production and biomass in all the lakes experimented. This triggering effect of nitrogen reduced with increased organic carbon in lakes.

Further, the response of phytoplankton consumers (i.e., zooplankton) to nitrogen addition varied on the basis of the organic carbon content of individual lakes.

In clear lakes with low organic carbon content, the nitrogen enriched phytoplankton became poor quality foods for zooplankton. This reduced the growth of zooplankton which resulted in a low energy transfer up the food chain.

In browner organic carbon rich lakes, the food web was unaffected by nitrogen addition.

These findings will aid in better equipping ourselves to manage future global changes, says the author Anne Deininger.

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