Study on non-point source pollution characteristics under different spatial scales: a case study of Hanjiang River...

Area of Science:

• Environmental Science
• Hydrology
• Water Quality Management

Background:

• Non-point source (NPS) pollution research often focuses on large scales, with limited studies integrating small watershed and runoff plot analyses.
• Understanding NPS pollution mechanisms across different spatial scales is crucial for effective watershed management.

Purpose of the Study:

• To investigate the characteristics and mechanisms of NPS pollution at multiple spatial scales (runoff plot, small watershed, basin).
• To evaluate the applicability of the MIKE model for simulating NPS pollution in the Hanjiang River Basin.
• To identify critical source areas and propose pollution control scenarios.

Main Methods:

• Combined natural rainfall monitoring with the MIKE model (hydrology, hydrodynamics, pollution load coupling).
• Analyzed runoff, sediment yield, total phosphorus, and total nitrogen at runoff plot and small watershed scales.
• Utilized the MIKE model to simulate pollution scenarios and identify critical source areas.

Main Results:

• Strong correlation observed between rainfall and runoff/sediment yield.
• Runoff and sediment yield per unit area followed the order: woodland > forested and grassy land > arable land.
• Total nitrogen pollution was significant (avg. 3.8 mg/L), primarily as nitrate nitrogen (63.06%).
• Small watershed scale showed similar initial scour effects as runoff plots but with a lag in pollutant concentration increase.
• The MIKE model demonstrated strong applicability for basin-scale NPS pollution simulation.
• Critical source areas were identified, with centralized livestock and poultry farming showing the best pollution reduction effect in scenario modeling.

Conclusions:

• NPS pollution characteristics vary significantly across different spatial scales.
• Integrated modeling and monitoring approaches are effective for understanding and managing NPS pollution.
• Targeted interventions, such as controlling centralized livestock and poultry farming, can effectively mitigate NPS pollution.