Spatial Distributions of Humic Substances and Evaluation of Sediment Organic Index on Lake Dalinouer, China

The aim of this study is to examine and interpret the spatial distribution of sedimentary humic substances in Lake Dalinouer. Humic substances in sediments were analyzed separately in different fractions: humins (HM), humic acid (HA), fulvic acid (FA), and different forms of organic carbon. The results showed that total organic carbon (TOC) contents varied from 7.25 to 65.54 g kg−1 with a mean of 36.37 ± 17.74 g kg−1. It was found that high TOC concentrations were at lake’s center and low TOC concentrations occurred at the estuary of inflows. Different redox conditions caused by water depth were of the most important factors which might influence TOC contents. Concentrations of HM, HA, and FA in sediments were detected in range of 6.40–58.16 g kg−1, 0.27–3.50 g kg−1, and 0.27–4.26 g kg−1, respectively. Of them, HM was the dominant form and accounted for 74–94% of TOC and 80–90% of humus. Organic Sediment Index (OSI) was used to assess the organics accumulation, and the value of OSI ranged from 0.001 to 0.30, which indicated that Lake Dalinouer was relatively clean. The relative high degree of humidification was found in the eastern of lake, where it should be taken into consideration seriously.