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

E Contreras; C Aguilar; M J Polo

doi:10.1016/j.scitotenv.2023.167261

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

Sci Total Environ. 2023 Dec 1:902:167261. doi: 10.1016/j.scitotenv.2023.167261. Epub 2023 Sep 28.

Authors

E Contreras¹, C Aguilar², M J Polo³

Affiliations

¹ Dynamics and Hydrology Research Group, Andalusian Institute for Earth System Research, University of Cordoba, 14071 Cordoba, Spain. Electronic address: econtreras@uco.es.
² Dynamics and Hydrology Research Group, Andalusian Institute for Earth System Research, University of Cordoba, 14071 Cordoba, Spain. Electronic address: caguilar@uco.es.
³ Dynamics and Hydrology Research Group, Andalusian Institute for Earth System Research, University of Cordoba, 14071 Cordoba, Spain. Electronic address: mjpolo@uco.es.

PMID: 37774889
DOI: 10.1016/j.scitotenv.2023.167261

Abstract

The characterization of non-point source pollution at the watershed scale difficult owing to its distributed nature combined with the lack of suitable measurements for validation. This study proposes the classification of land within a Mediterranean watershed according to its potential source of non-point pollution, considering interannual precipitation variability and dam regulation effects. For this purpose, the potential non-point pollution index (PNPI) developed by the Italian Environmental Protection Agency was modified to include annual local precipitation behavior, named local annual PNPI (APNPI). PNPI and APNPI were computed for the Guadalquivir River (Spain), which has a drainage surface of 57,500 km² and is highly regulated by >60 reservoirs. The results reflect the vulnerability along the Guadalquivir River in terms of the spatially variable non-point pollutant nature of its contributing watersheds. The annual average nitrate concentration values on the southern side exceeded the average value on the northern side by almost five times and showed a statistically significant power fit with the PNPI, with an R² of 0.65. Long-term available nitrate data (1981/82-2006/07) on a monthly scale at the outlets of some watersheds allowed us to rank priority pollutant source areas within the watershed. The power fits between the annual average nitrate loads and the APNPI (R² = 0.51-0.99) were statistically significant, which validated the utility of adding the variability of precipitation at an annual scale as a dynamic factor in the index. The APNPI can constitute a simple dynamic classification index for assessing the relative risk of non-point source pollution across a large area, especially in data-scarce situations.

Keywords: Guadalquivir River; Modeling; Non-point source pollution; Precipitation; Regulation; Water quality.