Enes Özgenç
Water quality assessment in agriculturally dominated basins requires approaches that capture seasonal pressure pathways rather than isolated optical signals. The Meriç-Ergene Basin in Türkiye was selected because cropland covered 70.49% of the basin in 2025 and because limited surface water extent, seasonal hydroclimatic variability, and land use pressure create suitable conditions for pressure-based water quality assessment. This study developed a monthly Google Earth Engine-Python-ArcMap framework to model organic pressure, inorganic-sediment pressure, and total water quality pressure during 2019-2025 using Sentinel-2, Sentinel-1, CHIRPS, ERA5-Land, land use/land cover (LULC), terrain, drainage, and long-term surface water indicators. Unlike concentration retrieval studies, the framework produced relative pressure scores based on satellite and environmental proxies. Organic pressure showed the strongest seasonal contrast, with a seasonal mean range of 0.181, and was highest during spring-summer conditions. Inorganic-sediment pressure exhibited a distinct seasonal pattern, with higher values during autumn-winter and the largest spatial range among the pressure components (0.410). Total water quality pressure was more compressed seasonally, with a seasonal mean range of 0.062. High sediment pressure conditions were episodic: high inorganic-sediment pressure score (ISPS) records accounted for only 0.49% of valid monthly observations, and maximum hotspot persistence reached 0.036. Interannual fitted changes were small for all pressure scores, indicating limited basin-scale directional change during 2019-2025. The framework provides a reproducible screening tool for identifying seasonal pressure windows and prioritizing field monitoring in data-limited basins.