Evaluation of spatio-temporal patterns of nutrient-related water quality parameters: A case study in Greater Houston Area, Texas.

This study analyzed spatial and temporal patterns of surface water quality, specifically focusing on nutrient-related parameters in the Greater Houston Area (GHA), Texas. It addressed two key questions: (1) How have population growth and changes in land use over the past four decades influenced water quality over time and across space? (2) Have ongoing pollution control efforts effectively maintained water quality over the past 40 years? We analyzed water quality data from 20 stations in GHA, focusing on total nitrogen, total phosphorus, dissolved oxygen, total solids, fecal coliform, and pH levels. The Mann–Kendall test and Sen’s slope estimator were utilized to detect long-term trends. The results show that nutrient pollution is increasingly becoming a significant issue in the GHA. Our spatial analysis reveals that water quality is inversely correlated with population density and the percentage of impervious land cover. This suggests areas with higher population density are more prone to water quality degradation. Mann–Kendall trend analysis indicates a strong increasing trend in fecal coliform, total nitrogen, and total phosphorus at stations situated in heavily urbanized counties. In contrast, these parameters remain stable in less populated counties, despite rapid population growth. The results demonstrate that the ongoing pollution control efforts have not been equally effective across the study area. These findings highlight the challenges in densely populated counties and underscore the necessity of sustained water pollution control and long-term monitoring efforts.