Evaluation of impacts of environmental factors and land use on seasonal surface water quality in arid and humid regions using structural equation models

Understanding of the buffer scale effect on water quality changes analysis in arid and humid regions is of great significance for exploring the best scale for water quality pollution and scientific planning of land use. The objective of this study is to determine the optimal buffer scales (500, 1000, 1500, 2000, 2500 and 3000 m) of land use that affect ammonia nitrogen (NH3-N) and total phosphorus (TP) in the Jing-Bortala River Watershed (JBRW) (arid region) and the Liyang Region (LR) (humid region) under a site buffer. PLS-SEM was used to fit the pathway relationships between the influencing factors and water quality to investigate the driving factors of NH3-N and TP in different seasons. The results showed that: (1) seasonal fluctuations in NH3-N and TP con-centrations were found in both the arid and humid regions, with the arid region having higher values than humid region; the coefficient of variation (CV) of NH3-N and TP was higher in arid and humid region, and the CV of NH3-N and TP were higher in spring and autumn in arid region than that in spring and autumn in humid region; (2) the 2500 m (0.262 <= R2 <= 0.633) buffer is the optimal scale for studying NH3-N and TP in arid region, whereas the 2000 m (0.262 <= R2 <= 0.686) scale works well in humid region; and (3) farmland (NDVI) was the largest influencing factor for NH3-N and TP changes in arid region, accounting for 28.95 % of the average percent total impacts. Furthermore, water area (NDWI) was the predominant influencing factor in humid region, occupying 33.93 % of the average percent total impacts. The influence of land use type (indices) on surface water quality is greater than that of environmental factors. Thus, these new insights into an appropriate buffer scale can be used as a guide for water pollution management in arid and humid environments.