Impacts of landscape reconstruction caused by combined disturbances of geological disasters and human activities on river water quality

Abstract

[Objective] To clarify the quantitative impact mechanism of landscape pattern reconstruction on river water quality under the compound influence of geological disasters and intensive human activities in dry-hot valley basins, thereby providing a scientific basis for the coordinated management of soil and water resources in ecologically fragile areas of Southwest China. [Methods] Taking the Xiaojiang River Basin in the lower reaches of the Jinsha River as the study area, a synchronous monitoring network for water, sediment, and water quality was integrated. Landscape patterns were quantitatively analyzed using Fragstats 4.2 software. Redundancy analysis was applied to systematically investigate the impact of landscape reconstruction on river water quality under the combined action of human activities and geological disasters. [Results] The results showed that:(1) the average values of key water quality indicators such as total phosphorus, total nitrogen, ammonia nitrogen, and COD during the flood season were 2.00, 1.88, 3.21 and 4.43 times higher than those of the non-flood season, respectively.(2) The average concentrations of total nitrogen and COD were 2.28 mg/L and 27.36 mg/L in the disaster-affected areas, 2.03 mg/L and 9.23 mg/L in the residential areas, and 2.00 mg/L and 6.60 mg/L in the cultivated land.(3) Under rainstorm events, the pre-rain fluxes of total phosphorus, total nitrogen, ammonia nitrogen, and COD were 1.95, 2.41, 2.34, and 4.74 times higher than the post-rain fluxes, with the most pronounced increase observed in the disaster-affected areas.(4) At different buffer zone scales, the selected landscape indices explained over 94.00% of the water quality variation during the flood season. The indices with the highest explanation rate were the aggregation index of disaster-affected areas(43.10%), the dispersion and adjacency index of residential areas(40.70%), and the division index of cultivated land(16.80%). [Conclusion] Water quality indicators in the Xiaojiang River Basin exhibit significant seasonal variations. Spatially, pollutant concentration gradient follows the pattern: disaster-affected areas > residential areas > cultivated land. These spatial disparities are further amplified under the influence of rainstorm. Landscape pattern reconstruction caused by landslides and debris flows—similar to that driven by urbanization and agricultural expansion—may cause further deterioration of river water quality. The findings provide scientific guidance for soil and water conservation, aquatic environment protection, and disaster mitigation in the dry-hot valleys of Southwest China.

Keywords

dry-hot valleys / land use / landscape pattern / disaster-affected areas / river water quality / human activities / spatiotemporal distribution / ecologically fragile areas