Managing phosphorus input pressures for improving water quality at the catchment scale

Area of Science:

• Environmental Science
• Water Quality Management
• Nutrient Cycling

Background:

• Freshwater phosphorus (P) pollution poses a significant threat to water quality and aquatic biodiversity.
• Agriculture and wastewater are the primary contributors to freshwater P pollution.

Purpose of the Study:

• To quantify and differentiate phosphorus input pressures from agriculture and wastewater sectors.
• To link these P input pressures to pollution threats in the River Stour catchment.
• To assess the effectiveness of mitigation strategies for improving water quality.

Main Methods:

• Substance Flow Analysis (SFA) was employed to calculate P input pressures from agriculture and wastewater.
• Physiographic regions of the River Stour catchment were analyzed.
• Riverine P flux was correlated with Net Anthropogenic P Inputs (NAPI).
• River P concentration (C) and flow discharge (Q) data were used to distinguish diffuse P sources.

Main Results:

• Agricultural P inputs were linked to livestock feed imports and manure, while human P inputs were driven by food imports and population density.
• Total P input pressures (NAPI) strongly correlated with riverine P flux (r² 0.8–0.9).
• Estimated agricultural P fluxes varied up to 0.92 kg ha⁻¹ yr⁻¹, dependent on land P surplus.
• Reducing agricultural P surplus by 7 kg ha⁻¹ yr⁻¹ could lower river SRP concentrations by one-third, yet remain above eutrophication targets.

Conclusions:

• A combined approach of enhanced wastewater P removal and reduced agricultural P inputs is necessary for water quality improvement.
• The methodology of linking SFA outputs with riverine P data offers a valuable tool for setting effective mitigation targets.
• Further testing of this approach in other catchments is recommended for international relevance.