Characterising phosphorus and nitrate inputs to a rural river using high-frequency concentration-flow relationships.

Area of Science:

• Environmental Science
• Hydrology
• Water Quality Management

Background:

• Nutrient pollution from anthropogenic sources poses a significant threat to riverine ecosystems.
• Understanding nutrient dynamics and sources is crucial for effective water quality management.
• High-frequency monitoring provides detailed insights into short-term variations in nutrient concentrations.

Purpose of the Study:

• To investigate the sources and dynamics of total reactive phosphorus (TRP) and nitrate in the River Enborne.
• To analyze the relationship between nutrient concentrations and river flow using hysteresis patterns.
• To differentiate between various nutrient inputs, including sewage treatment works (STW) and agricultural runoff.

Main Methods:

• Hourly monitoring of TRP and nitrate concentrations from January 2010 to December 2011.
• Analysis of concentration-flow relationships to identify nutrient sources and dynamics.
• Study of hysteresis patterns during storm events to infer input pathways.

Main Results:

• TRP concentrations showed dilution with increasing flow and clockwise hysteresis, indicating dominant inputs from STW and in-channel remobilization.
• Agricultural diffuse TRP inputs were observed only during May storms.
• Nitrate concentrations exhibited dilution curves, with major inputs from groundwater and STW, and significant agricultural inputs during early winter storms.

Conclusions:

• STW are a primary source of phosphorus pollution in the River Enborne, necessitating improvements to STW operations.
• Groundwater and STW are significant contributors to nitrate levels, with agricultural runoff playing a role during specific periods.
• The combined analysis of high-frequency data, concentration-flow relationships, and hysteresis offers a valuable approach for understanding nutrient dynamics in river systems.