Modelling phosphorus inputs and dynamics in a large tropical semiarid basin

Area of Science:

• Environmental Science
• Hydrology
• Water Quality Management

Background:

• Tropical semiarid regions face unique water resource challenges.
• The Castanhão dam reservoir is crucial for water supply in Brazil.
• Understanding total phosphorus (TP) dynamics is vital for managing water quality.

Purpose of the Study:

• To develop and validate a process-based model for predicting TP inputs and dynamics.
• To analyze the contributions of point sources (PS) and non-point sources (NPS) to TP loads.
• To assess the effectiveness of TP reduction strategies and the impact of climate change.

Main Methods:

• A monthly process-based model was developed for water balance and TP dynamics.
• The model incorporated complete mixing, steady-state flow, and piston-type transport with first-order decay.
• Model validation used primary and secondary data, achieving deviations of approximately 20%.

Main Results:

• Non-point sources (NPS) were the dominant TP contributors, ranging from 61% to 99% of the total load.
• TP concentration increased with river flow rate, and a consistent decay was observed along the river system.
• All simulated TP values exceeded the mandatory limit of 0.05 mg/L, with climate change exacerbating the issue.

Conclusions:

• Non-point source (NPS) reduction is the most effective remediation strategy for total phosphorus (TP) control.
• The model is applicable to diverse hydroclimatic conditions and land uses.
• Management strategies must consider climate change impacts on TP loads and water quality.