Water Pollution in Protected Groundwater-dependent Shallow Lakes: A Multi-Pollutant Assessment Approach

Abstract

This study uses a multidimensional approach to assess water pollution and soil degradation in two groundwater-dependent shallow lakes designated as Freshwater Protected Areas (FPAs). Sampling was conducted within and outside the FPAs to ensure representative data collection. Nutrients, pesticides, and bacteriological indicators in water, along with soil properties, were analyzed. Nitrateconcentrations in lakes, streams, and groundwater ranged from 8.0 to 107.0 mg/L in Los Padres andfrom 12.0 to 52.0 mg/L in La Brava watersheds, with several sites exceeding the drinking water standard of 45.0 mg/L NO3−. Phosphate values reached up to 28.6 mg/L in Los Padres and 24.0 mg/L in La Brava, substantially above recommended limits. Pesticides were consistently detected, with organophosphates dominating over pyrethroids and 2,4-D; chlorpyrifos was the most frequent compound, detected in over 40% of samples, with concentrations up to 0.22 μg/L in Los Padres and 0.11 μg/L in La Brava. All lake sampling sites contained Escherichia coli, with maximum values of 294 MPN/100 mL. The Nutrient Pollution Index ranged from 1.21 to 6.61 in Los Padres and 1.13 to 5.84 in La Brava, classifying waters overall as “moderately” to “very highly” polluted, with clear links to land use intensity. Soils in agroecosys tems exhibited significant declines in organic matter, nutrient content, structural stability, and porosity compared to natural soils, enhancing nutrient and pesticide fluxes into adjacent aquatic ecosystems. These findings highlight the need for targeted nutrient-load reduction and pesticide management strategies to preserve the ecological integrity of groundwater-dependent shallow lakes within protected areas.