Reducing Nitrogen Inputs Can Rapidly Reverse Eutrophication in Shallow Phosphorus-Rich Lakes.

Area of Science:

• Environmental Science
• Limnology
• Ecology

Background:

• Lake eutrophication is a global issue, historically managed by focusing on phosphorus (P) reduction.
• Shallow, P-rich lakes often exhibit complex responses to nutrient inputs.
• Nitrogen (N) enrichment, particularly in excess of balanced ratios, can exacerbate eutrophication.

Purpose of the Study:

• To investigate the impact of nitrogen (N) and phosphorus (P) stoichiometry on lake eutrophication.
• To assess the effectiveness of reducing N inputs in shallow, P-rich lakes.
• To determine the contribution of excess N to eutrophication in U.S. lakes.

Main Methods:

• A long-term field mesocosm experiment manipulating N and P inputs.
• Comparing lake productivity under low N:P versus high N:P input scenarios.
• Analyzing the effects of eliminating N fertilization while maintaining P fertilization.

Main Results:

• Nitrogen enrichment above balanced N:P ratios (20-50 molar) significantly increased phytoplankton biomass.
• Reducing N inputs, while maintaining P inputs, led to a 57 ± 3.1% decrease in phytoplankton biomass.
• Excess N contributes to eutrophication in an estimated 40% of U.S. lakes.

Conclusions:

• Reducing nitrogen inputs is a viable strategy for managing eutrophication in shallow, P-rich lakes.
• Nitrogen management can be as crucial as phosphorus management for lake ecosystem health.
• This approach offers a potential pathway to mitigate harmful eutrophication effects.