New method for scaling nonpoint source pollution by integrating the SWAT model and IHA-based indicators

Area of Science:

• Environmental Hydrology
• Water Quality Management
• Geospatial Analysis

Background:

• Nonpoint source (NPS) pollution exhibits spatial scaling effects influenced by topography and river networks.
• Quantifying NPS pollution scaling effects is crucial for effective environmental management but lacks integrated methodologies.

Purpose of the Study:

• To develop and propose an integrated methodology for quantifying the spatial scaling effects of nonpoint source pollution.
• To provide a quantitative description of NPS pollution patterns at various spatial scales.

Main Methods:

• Delineation of nested catchments using the eight-direction algorithm.
• Simulation of interannual runoff, sediment, and total phosphorus (TP) using a semidistributed hydrological model.
• Quantitative description of NPS pollution patterns using average, extrema, and change rate indicators.

Main Results:

• Coefficients of variation for runoff and TP indicators ranged from 0.6-0.8; sediment indicators varied widely (0.4-1.6).
• NPS load indicators increased with drainage area, while load intensity indicators decreased, influenced by hydrological and topographic heterogeneity.
• A turning point of 825 km² was identified for scaling transformation based on the logarithmic variance of the change rate.

Conclusions:

• The proposed methodology effectively quantifies NPS pollution scaling effects.
• The findings provide insights into NPS pollution dynamics across different spatial scales.
• This approach can guide targeted monitoring and control strategies for NPS pollution in watersheds.