Variation of Diatoms and Silicon in a Tributary of the Three Gorges Reservoir: Evidence of Interaction

Wei Xiao,Yonghong Bi,Hongyan Wu,Wujuan Mi,Yubo Huang

doi:10.3390/w11071369

Wei Xiao, Yonghong Bi + Show 3 more

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https://doi.org/10.3390/w11071369

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Abstract

To gain insight into the variation of diatoms and silicon and their interaction in a tributary of the Three Gorges Reservoir (TGR), the Xiangxi River was chosen as a representative tributary, and dissolved silicon (DSi) and biogenic silicon (BSi) were investigated monthly from February 2015 to December 2016, accompanied by diatom species composition and cell density analyses. The results showed that the diatom population and its relationship with silicon concentration were significantly different between the lacustrine zone and riverine zone (P < 0.05). The cell density in the lacustrine zone (6.20 × 105 ~ 9.97 × 107 cells/L) was significantly higher than that in the riverine zone (7.90 × 104 ~ 1.81 × 107 cells/L) (P < 0.01). Water velocity was a key factor in determining the diatom species composition. Centric diatoms were the dominant species in the lacustrine zone, and pennate diatoms were the primary species in the riverine zone, which indicated that centric diatoms outcompete pennate diatoms under the influence of the TGR’s operation. BSi showed a significant linear relationship with the cell density. DSi had a significant negative relationship with the cell density in the lacustrine zone, while no significant relationship was found in the riverine zone. This meant that the main contributor to BSi was diatoms, but DSi was primarily affected by water discharge, not diatom uptake. It could be deduced that the spatiotemporal heterogeneity of diatom communities was influenced by the TGR’s operation. Silicon cycling in the tributary was significantly affected by diatoms, and the current concentration of DSi was sufficient for diatom growth and showed no significant effects on the diatom community.

Highlights

Silicon originates from rock weathering and is transported from land to the ocean mainly by rivers
While centric diatoms were the dominant species in the lacustrine zone, a high proportion of pennate diatoms were found in the riverine zone in the summer and autumn seasons (Figure 7)
Our results showed that dissolved silicon (DSi) was negatively correlated with the diatom cell density in the lacustrine zone (Table 2)

Summary

Introduction

Silicon originates from rock weathering and is transported from land to the ocean mainly by rivers. DSi and biogenic silicon (BSi) are considered bioavailable silicon in natural waters. The recycling of BSi provides the major source of soluble reactive silicon required for diatom proliferation [2]. Silicon is a key nutrient for diatom growth because it is a kind of necessary element to form the diatom’s rigid cell wall [3]. BSi is generated when diatoms, plants and other organisms uptake DSi during photosynthesis, and it is an important source of DSi due to its typically amorphous form; it plays an important role in the earth’s Si cycle. DSi mainly originates from weathering, and anthropogenic activities can scarcely compensate for the loss of DSi from this

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