Improving the identification of pollution source areas with catchment-resolution sensitivity analysis.

Area of Science:

• Environmental Science
• Hydrology
• Ecology

Background:

• Riverine ecosystems are significantly impacted by total nitrogen (TN) and total phosphorus (TP).
• Identifying primary nutrient source areas in watersheds is crucial for effective management.
• Understanding the interplay between watershed characteristics and nutrient export is essential.

Purpose of the Study:

• To investigate the influence of terrain and land use on mean monthly TN (TNM) and TP (TPM) export.
• To analyze these influences across varying catchment resolutions in the Qiantang River Watershed.
• To identify optimal catchment scales for pinpointing critical nutrient pollution sources.

Main Methods:

• Correlation analysis between topographic factors (slope, SPI, TWI) and nutrient concentrations.
• Assessment of land use impacts (impervious surfaces, grassland, forest) on nutrient levels.
• Evaluation of varying catchment resolutions to determine the most effective scale for analysis.

Main Results:

• Topography significantly influences nutrient dynamics; land slope and SPI negatively correlate with TNM/TPM, while TWI positively correlates.
• Impervious surfaces correlate positively with nutrient concentrations; grasslands and forests show negative correlations.
• Catchment resolution critically affects the observed relationships, with a 700 km² scale proving most effective for identifying pollution hotspots.

Conclusions:

• Topographic and land use factors are critical drivers of riverine nutrient concentrations.
• Selecting an appropriate catchment resolution is imperative for accurately assessing watershed impacts on water quality.
• Identifying critical pollution source areas at an optimal scale (e.g., 700 km²) is vital for guiding effective nutrient pollution reduction strategies and enhancing watershed ecological integrity.