Soil properties and distribution in the riparian zone: the effects of fluctuations in water and anthropogenic disturbances

China's Three Gorges Dam has generated a large riparian zone around the reservoir that has changed the natural fluctuation in water level (FWL) and intensity of anthropogenic disturbance (AD, i.e. human activities triggering pollutant input). Knowledge about how riparian soil properties respond to such changes remains limited. The aims of this study were to identify the distribution of soil properties in the riparian zone and to determine which types of factors, local‐scale FWL or regional‐scale AD, have a larger effect on the soil properties. A total of 144 composite soil samples, collected from two riparian areas in four sampling surveys, were investigated. Multivariate regression tree analysis indicated that the variation in soil properties was mainly controlled by FWL (40.1%) compared with the minor role of AD (2.1%). Soil total carbon, total nitrogen and organic matter were mainly affected by AD, whereas FWL had a major influence on soil pH, ammonium and nitrate. Along the elevation gradient (150–175 m), the soil properties were determined mainly by the sampling elevation, accounting for 67.6% of the variation, followed by short‐term (5.6%) and long‐term flooding (3.3%). The 167.5‐m elevation was proposed to be the threshold that divides the riparian zone into two different response zones. Soil below 167.5 m was mainly affected by local‐scale FWL, whereas that above 167.5 m was largely affected by regional‐scale AD. This proposed threshold suggests that riparian soil management around the Three Gorges Reservoir should consider both local‐ and regional‐scale factors and that different approaches and strategies for ecological restoration need to be applied along an elevation gradient. Highlights We studied how soil properties respond to fluctuation in water level (FWL) and anthropogenic disturbance (AD). The relative importance of local‐scale FWL and regional‐scale AD was evaluated quantitatively. The 167.5‐m elevation divides the riparian zone into two areas that respond differently to local and regional factors. The variation in riparian soil properties was mainly controlled by local FWL (40.1%) rather than regional AD (2.1%).