Accounting for the annual variability when assessing non-point source pollution potential in Mediterranean regulated...

Area of Science:

• Environmental Science
• Hydrology
• Water Quality Management

Background:

• Characterizing non-point source pollution at watershed scales is challenging due to its diffuse nature and limited validation data.
• Mediterranean watersheds face complex pollution dynamics influenced by precipitation variability and reservoir operations.

Purpose of the Study:

• To develop and validate a dynamic index for classifying land according to non-point source pollution potential.
• To assess the spatial variability of non-point pollution risk in the Guadalquivir River watershed.
• To incorporate interannual precipitation variability and dam regulation effects into pollution assessment.

Main Methods:

• Modified the Potential Non-point Pollution Index (PNPI) to create the Annual PNPI (APNPI), including local precipitation patterns.
• Computed PNPI and APNPI for the Guadalquivir River watershed (57,500 km²).
• Analyzed long-term nitrate concentration and load data (1981/82-2006/07) against PNPI and APNPI values.

Main Results:

• Significant spatial variations in non-point pollutant vulnerability were identified across the Guadalquivir River watershed.
• Annual average nitrate concentrations on the southern side were nearly five times higher than on the northern side, correlating with PNPI (R²=0.65).
• Annual average nitrate loads showed statistically significant power fits with APNPI (R²=0.51-0.99), validating the inclusion of precipitation variability.

Conclusions:

• The APNPI is a valuable, simple dynamic index for assessing relative non-point source pollution risk in large, data-scarce areas.
• The study highlights the southern Guadalquivir River watershed as a priority area for non-point pollution management.
• Incorporating precipitation variability enhances the accuracy of non-point pollution risk assessment.