A multidisciplinary study of the Guadalquivir River assesses water quality along its entire course
The study of water quality, from its source to its mouth, combines physicochemical and biological parameters, indicating a gradual deterioration throughout the river, despite generally good quality
The Guadalquivir is the most important river in Andalusia. Stretching 657 kilometers, it forms the backbone of Andalusia, from its source in the Sierra de Cazorla mountains to its mouth in Sanlúcar de Barrameda. These facts, along with its name, of Arabic origin (Wadi al-Kabir), and its strategic role in the economy, agriculture, and tourism, are widely known. Few studies, however, have comprehensively assessed the quality of the "Great River" along its entire course.
To address this knowledge gap, the "Molecular Biology of Stress Response Mechanisms" and the "Waste Bioengineering: Green Engineering" groups at the University of Córdoba have joined forces to study the river's entire course. For the first time, they are carrying out a holistic, multidisciplinary analysis that considers not only the water's physicochemical variables, but also microbial factors to assess water quality and identify critical sections where it may be compromised. The Ecotoxicology, Ecophysiology, and Biodiversity of Aquatic Systems group at the Institute of Marine Sciences of Andalusia (ICMAN-CSIC) is also participating alongside them.
"To integrate the physicochemical parameters, we used the Water Quality Index, a standardized system used internationally that includes variables such as pH, dissolved oxygen concentration, water turbidity, and the presence of coliforms," explained researcher José Ángel Siles. Twenty-five different physicochemical variables were analyzed, and the nine most important were selected and applied to the water quality index, with weighted values (not all the variables are of the same importance). "This index showed us that the river's quality is generally good, although we did identify specific sections where, as in other river basins, the quality drops slightly."
For the first time, a biological analysis of the microbial community was added to this physicochemical one. "We characterized the microbiome along the entire river and calculated biological indices to determine water quality," explained Marina Barbudo, the lead researcher on this study, published in the Journal of Contaminant Hydrology. "We integrated the physicochemical parameters with biological ones and detected a gradual decline in quality along the river's course, though it always remained at adequate levels," added researcher José Alhama.
The groundbreaking aspect of this work is its combination of these two perspectives, as physicochemical analyses can fail to detect contaminants when they are present in very low concentrations; even in these cases, however, pollutants can interact with each other in complex ways, generating toxicity, an effect that will be reflected in the biological component. According to Carmen Michán, another participating researcher, "Biological characterization helps reveal what sometimes goes undetected by physicochemical analysis alone."
Results of the river's "X-ray"
"In the study, water samples were taken from 20 different points along the entire course of the river at the end of a dry season. This was important because weather conditions affect water quality, and this is usually when it’s at its worst," added researcher María Ángeles Martín.
The results showed "a gradual, though not concerning, deterioration along the Guadalquivir River, with poorer water quality in the middle-lower section of the river," which is common in all freshwater waterways, according to the team.
A striking finding for the team was that, in the middle-upper reaches of the river, while the water quality index (the physicochemical parameters) was good, there was a change detected in its microbiological parameters: in that section, there was a significant decrease in bacterial diversity, indicating ecological deterioration, along with a high prevalence of tolerant opportunistic microorganisms, particularly those in the Comamonadaceae family. While the team is still seeking an explanation for this microbiological change, it demonstrates how microbiological parameters reveal something that eludes physicochemical evaluation. "It's very difficult to detect chemically, but the biological changes show us that something is happening." Analyzing other tributaries that flow into the river, or the surrounding agricultural activity, where olive monoculture predominates, could be avenues of investigation to explain this discrepancy between parameters.
"This study demonstrates the suitability of this multidisciplinary and integrative method for analyzing water quality in freshwater waterways," added Arturo Chica, and the team recommends its use by the research community. It could serve as a model to create risk maps that pinpoint critical areas and uncover potential environmental threats not detected by more conventional methods.
Barbudo-Lunar M, Arjona GL, Trombini C, Pérez-González L, Chica AF, Martín MÁ, Blasco J, Michán C, Siles JÁ, Alhama J. A multidisciplinary approach to risk assessment enables the identification of deteriorated sections within a major waterway: The Guadalquivir River as a case study. J Contam Hydrol. 2026 Jun 6;282:105019. doi: 10.1016/j.jconhyd.2026.105019.
Journal
Journal of Contaminant Hydrology
Method of Research
Meta-analysis
Subject of Research
Not applicable
Article Title
A Multidisciplinary Study of the Guadalquivir River Assesses Water Quality Along its Entire Course
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