Identifying the influence factors at multiple scales on river water chemistry in the Tiaoxi Basin, China

The catchment environment and landscape is widely used as a predictor of stream-ecosystem condition, and the extent of its influence is closely linked to spatial scale. The aim of this study was to identify the influence factors on river water chemistry at multiple scales in a basin, namely the catchment, riparian corridor, and river reach scales. Information about the catchment and riparian corridor landscapes, reach-scale river properties, and catchment environments and river water chemistry data were collected monthly from 31 streams across the Tiaoxi Basin from July 2011 to June 2012. We used redundancy analysis to identify the relative influences of multi-scale variables on nine water quality indexes over both the whole study period and three sub-periods (before, during, and after rainy seasons). Results showed that all the selected factors helped to explain variations in water chemistry, although the relative effects of these factors changed considerably with variation in the spatial and temporal scales. Stream water chemistry across the entire study period was more sensitive to physiography and landscape variable at the catchment scale than at the reach and riparian corridor scales. From dry seasons to the rainy season, the influence of physiography and landscape variable at the catchment scale decreased slightly, while the effects of variables at the reach and riparian corridor scales increased noticeably. Besides, the influence of variables at the catchment scale was relatively strong and stable while the impacts of variables at the local scale were relatively weak and fluctuated widely with seasons. The findings from this study may improve our understanding of the main drivers of variations in stream water chemistry in different spatial and temporal scales, and will help managers protect and restore stream water environments using a basin-scale perspective.