Variation Characteristics of Ammonium Nitrogen Load and Analysis of Landscape Driving Factors in Water Source Reservoir

[Objective] Identifying the key landscape pattern factors that affect water quality is of great significance for integrated watershed water quality management. [Methods] Based on the water quality data from January 2014 to August 2024, redundancy analysis (RDA) and Pearson correlation analysis were applied to investigate the relationship between landscape pattern indices and ammonium nitrogen concentration in the Gaoguan Reservoir Basin during the wet and non-flood periods. RDA was used to identify the key landscape pattern indices,and Pearson correlation analysis was used to quantify the intensity and significance of correlation coefficients between ammonium nitrogen concentration and landscape pattern indices. [Results] The results were as follows: (1) In the Gaoguan Reservoir Basin,the area of forest land was the largest,accounting for more than 84.9% of the whole area and significantly contributing to the improvement of water quality. (2) The absolute values of correlation coefficients between landscape pattern indices and ammonium nitrogen concentration in the non-flood period were always higher than those in the wet period,and the same trend was observed for landscape composition and land-use areas. (3) In the wet and non-flood periods,with the increase of landscape diversity,splitting degree,and degree of fragmentation,the risk of surface runoff carrying pollutants into water bodies increased and aggravated the ammonium nitrogen pollution. Largest Patch Index (LPI) presented a negative correlation with ammonia nitrogen content in wet period, but a positive correlation in level period. Conversely, Contagion (CONTAG) exhibited a opposite relationship with ammonia nitrogen content, and a significant positive correlation in the non-flood period; in other words,the better integrity of the landscape and the lower degree of fragmentation can reduce the output of ammonium nitrogen during the flood period. During the non-flood period,the closer the pollution-source landscape type was to the water body,the more severe the impact on water quality due to its proximity. [Conclusion] Overall,forest land exhibits a more pronounced effect on water quality improvement in the Gaoguan Reservoir watershed compared with other land-use types.During the non-flood period,landscape pattern indices demonstrate a more significant capacity to regulate and influence water quality relative to the wet period. However,in general,water quality in the reservoir is primarily governed by landscape integrity during the wet period,whereas during the non-flood period,it is mainly controlled by pollution-source patches located closer to the water body.The results will be of great significance for the integrated watershed management and water quality improvement of the Gaoguan Reservoir in the future.