Spatial distributions and environmental implications of diatom assemblages in surface sediments of Hulun Lake, China

Abstract

We examined the spatial distributions of diatom assemblages in surface sediments of Hulun Lake and explored the potential relationships between diatom distributions and environmental variables using multivariate analyses. These results may provide a basis for fossil record interpretation. Surface sediment samples were taken at 30 sites throughout the lake to analyse diatom assemblages, and environmental variables potentially influencing diatom distributions were taken concurrently. Principal components analysis (PCA) and redundancy analysis (RDA) were conducted to explore the spatial characteristics of diatom assemblages in the lake surface sediment and their relationship with the main environmental variables. Analyses showed remarkable spatial differentiation such that epiphytic and benthic diatoms dominated surface sediments in the eastern littoral region, while planktonic diatoms were dominant in the central and western profundal region. Additionally, in the southern part of the central and west profundal region, Stephanodiscus neoastraea was more abundant than Aulacoseira perglabra. RDA showed that the total nitrogen of surface sediments (TNs), which acts as a nitrogen source and stays balanced with lake water nitrogen levels, is the primary environmental variable influencing diatom assemblages in the surface sediments. S. neoastraea and A. perglabra in particular may be boosted by high nitrogen content in the sediment. Additionally, correlations of water depth with the distribution of sample sites and the ratio of planktonic to benthic diatoms indicated an inherent relationship between diatom distribution and water depth, where deep water drove a high planktonic/benthic ratio. This result further supports the use of the planktonic/benthic ratio in the fossil record to reconstruct historical change in lake depth.