ST. PAUL, Minn. (AP) — Nitrogen is a crucial part of all living things. But the millions of tons of nitrogen manufactured by humans every year are a two-edged sword.

Artificial nitrogen, applied as fertilizer, has greatly increased food supplies. But the escape of nitrogen into the environment causes serious air and water pollution, as well as human health problems.

So the Freshwater Society and University of Minnesota College of Biological Sciences are sponsoring a free public lecture Thursday by Otto Doering, a Purdue University agricultural economist who chaired an Environmental Protection Agency committee on nitrogen. Doering will discuss choices facing scientists and policy-makers as they seek to maintain the benefits human-created nitrogen provides while limiting its environmental damage.

The lecture is at 7 p.m. in the Student Center Theater on the St. Paul campus.

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Online:

Freshwater Society: http://www.freshwater.org

U of M College of Biological Sciences: http://www.cbs.umn.edu