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Global Analysis of Phosphorus Concentration and its Relationships with Environmental and Anthropogenic Factors Across Varied Climates

Vahab Ghalyaei, Sara | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58286 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Sheikholeslami, Razi
  7. Abstract:
  8. Phosphorus is a key nutrient in the Earth's biogeochemical cycle and plays a crucial role in agricultural productivity and global food security. It is primarily utilized in the manufacture of chemical fertilizers. At the global scale, phosphorus concentrations in surface waters are regulated by a complex interplay of environmental, climatic, and anthropogenic factors. Excessive phosphorus input into aquatic systems, particularly through agricultural runoff and industrial wastewater, can lead to eutrophication, water quality degradation, and serious ecological issues. Understanding the drivers of phosphorus concentration on a global level is therefore essential for sustainable water resource management. This study investigated the functional relationships between environmental, human, and climatic variables and total phosphorus concentration using data from 3,450 river monitoring stations across 520 major watersheds worldwide. The analysis spanned 2012 to 2021 and covered five distinct climatic zones. A comprehensive database was first constructed, integrating diverse predictor variables. Then, a Generalized Additive Model (GAM) was employed due to its strength in capturing nonlinear relationships and interpretability. The model revealed that dry (R² = 0.87) and tropical (R² = 0.834) zones exhibited the highest prediction accuracy, while the temperate zone showed the lowest (R² = 0.522). Variable sensitivity analysis using the Mean Decrease Accuracy (MDA) permutation method showed that in tropical and continental zones, land use, topography, and runoff were more influential. In contrast, in polar and temperate zones, climatic variables such as temperature and livestock played a more prominent role, respectively. Interestingly, phosphorus levels in soil and the human population emerged as strong predictors across all climate zones. In particular, human activity indicators such as population density and wastewater production were consistently identified as key determinants of phosphorus concentration on a global scale. Partial Dependence Plots (PDPs) were used to better understand interaction patterns. These visualizations illustrated that precipitation, runoff, and population had an increasing effect on phosphorus concentration across all climates, while forest cover had a generally decreasing effect. Overall, this study highlights the complexity and significance of interactions between human and natural systems in controlling phosphorus levels. Its findings can provide a scientific foundation for the development of climate-sensitive environmental policies and management strategies aimed at reducing phosphorus pollution, improving wastewater treatment systems, and promoting more sustainable agricultural practices
  9. Keywords:
  10. Water Quality ; Phosphorus Pollution ; Eutrophication ; Machine Learning ; Sensitivity Analysis ; Water Quality Control ; Water Resources Management ; Generalized Additive Model (GAM)

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