Changes in carbon and nitrogen with particle size in bottom sediments in the Dan River, China

Understanding the composition and changes in nutrients in sediments and soil will enable a better description of sedimentation and environmental processes. In this study, soil from the source (Ss) of the Dan River and sediments along the river were sampled. The particle size distribution (PSD) of sediment and soil was analyzed, together with the total nitrogen (TN), total organic carbon (TOC) and the C/N ratio. The dominant particle size of Ss was < 0.05 mm, while the sediments showed no obvious dominant particles. Concentrations of TN and TOC in sediments were significantly lower than in Ss. The < 0.05 mm fraction of sediments manifested good ability to maintain TN and TOC, as indicated by average levels of 0.59 g N/kg and 13.85 g/kg, respectively. In the downstream portion of the Dan River, the TN contents decreased, while the TOC contents remained stable throughout the river. Cluster analysis indicated that TN division became simpler as the particle size decreased, while it became more complicated for TOC. There was no significant difference in the C/N ratio of Ss among particle sizes, and the ratio was below 25: 1 for all groups. Conversely, the C/N ratio of sediments increased obviously with decreasing distance to the Danjiangkou reservoir. The nitrogen levels in particles < 0.05 mm were preserved relatively well so that the C/N ratio of this fraction was relatively stable. The enrichment ratio of nutrients in sediments of the upstream portion of the river also showed that a finer fraction was associated with a greater capacity for holding nutrients, especially particles < 0.05 mm. Overall, comprehensive control of sediments in rivers should focus on large particle sediments. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.