Daily suspended sediment concentrations and load variability in karst watersheds

Abstract

A better understanding of sediment dynamics and variability may provide helpful insights for improving the efficiency of community-based monitoring strategies, enhancing sediment yield estimation, and optimizing soil conservation practices. However, this issue is rarely studied in karst areas, which are experiencing severe soil erosion, and sediment concentrations and load are highly variable. The objectives of this study were to characterize the daily suspended sediment concentrations (SSC) and sediment load (SL) variability, and to test whether the watershed scale and lithology exerted substantial influence on this variability in 40 karst watersheds (420–3.4 × 105 km2) in southwest China. Several indicators of variability were used for daily SSC and SL including standard deviation, coefficient of deviation, inhomogeneity coefficient, the percentage of annual SL exported in 2% of the time (Ms2%), and the percentage of time necessary to transport 50% of the annual SL (Ts50%). Results indicated that the daily SSC and SL had high temporal variability, and the SL demonstrated stronger variability than the SSC. On average, half of the annual sediment load was discharged in<2.3% of the time in the period 2009–2012, implying that a few erosive events dominated the annual sediment load. The temporal variability of daily SSC and SL were scale dependent, and a larger watershed generally had a lower temporal variability. The Ms2% and Ts50% were relatively stable when the area of the watershed was greater than 0.15 million km2. However, no significant relationship was detected between karst coverage and Ms2% or Ts50% since karst coverage might not completely represent the characteristics of the 3-D hydrogeological structure in karst regions. The results from this study can help improve river flow management and control soil loss in karst watersheds.