Phosphorus mitigation to control river eutrophication: murky waters, inconvenient truths, and "postnormal" science

Area of Science:

• Environmental Science
• Ecology
• Water Resource Management

Background:

• Phosphorus (P) mitigation is a primary strategy for managing eutrophication in rivers.
• Despite reduced P inputs, many rivers show insufficient recovery in water quality and algal growth.

Purpose of the Study:

• To investigate why P-based nutrient mitigation has failed to restore water quality in some rivers.
• To explore the challenges in eutrophication management and propose alternative strategies.

Main Methods:

• Analysis of P-based nutrient mitigation effectiveness.
• Examination of factors hindering river ecosystem recovery, including land-use legacies and ecological thresholds.
• Case study analysis from the Red River Basin.

Main Results:

• Past land-use management creates persistent P legacies.
• Algal growth responses to P loading can be decoupled in impaired rivers.
• River recovery may be nonlinear, involving thresholds and alternative stable states.

Conclusions:

• Current P-based nutrient criteria may be insufficient for restoring degraded river ecosystems.
• A holistic eutrophication management approach is necessary, integrating P controls with other nutrient management, pollutant reduction, and river restoration.
• Addressing uncertainties in 'postnormal' science is crucial for effective water quality and ecosystem management.