Successful reduction of diffuse nitrogen emissions at catchment scale: example from the pilot River Odense, Denmark

Area of Science:

• Environmental Science
• Ecology
• Water Resource Management

Background:

• Danish coastal waters have seen reduced nitrogen (N) loadings since 2000 through general and targeted mitigation.
• Wetland restoration aims to increase catchment-specific N retention, a strategy extensively applied in the River Odense catchment.

Purpose of the Study:

• To quantify the impact of intensive wetland restoration on nitrogen (N) loads in the River Odense catchment.
• To compare N load trends in a catchment with extensive wetland restoration to a control catchment with less intensive restoration.

Main Methods:

• Comparative analysis of N concentration and loss data from a gauging station in the River Odense catchment and a control catchment.
• Monitoring data from two restored wetlands within the River Odense catchment.

Main Results:

• An excess downward trend in N loss of 124 tons N per year was observed in the River Odense catchment, attributed to wetland restoration.
• Total N load reduction in the River Odense catchment reached 377 tons N per year (39%) since 2000.
• Monitoring data from restored wetlands supported the observed downward N trend.

Conclusions:

• Intensive wetland restoration is a highly effective measure for reducing nitrogen (N) loads in coastal waters.
• The River Odense catchment's experience demonstrates a successful large-scale application of wetland restoration for N mitigation.
• Wetland restoration contributes significantly to achieving water quality improvement goals.