Spatio-Temporal Variations in Phytoplankton Communities in Sediment and Surface Water as Reservoir Drawdown—A Case Study of Pengxi River in Three Gorges Reservoir, China

Wenjuan Ouyang,Zhe Li,Lunhui Lu,Jixiang Yang,Jinsong Guo

doi:10.3390/w13030340

Abstract

The resting stages of phytoplankton are usually regarded as the seed bank and source of harmful algal blooms because of the recruitment of phytoplankton from sediment to the water column under suitable environmental conditions. Information about resting stages of phytoplankton is abundant in shallow lakes and littoral sea; yet, studies on river–reservoir systems are rare. The river–reservoir continuum shows a unique structuring of longitudinal gradients of hydrological and hydrodynamic conditions. We hypothesized that the seed bank and algal blooms in reservoirs are influenced by the hydrodynamic conditions of each reservoir. We used Illumina Miseq sequencing to examine the spatio-temporal variation in the phytoplankton community in the sediment as reservoir drawdown and in surface water during algal blooms in Pengxi River, a tributary of China’s Three Gorges Reservoir. The results show that the cyanobacteria community in sediment is significantly influenced by temperature, total carbon, maximum flow velocity, and total phosphorous, the eukaryotic phytoplankton community in sediment is significantly influenced by total phosphorous, temperature, total carbon, maximum flow velocity, and total nitrogen. Additionally, the dominant species in sediment is significantly different from that in surface water during algal blooms. Our results suggest that the dominant species in surface water during algal blooms is more influenced by the environmental factors and hydrodynamic conditions in the water column than the seeds in the sediment. These findings are fundamental for further research on the influence of hydrodynamic conditions on algal blooms in artificially regulated river-reservoir systems.

Highlights

Introduction iationsThe increasingly frequent harmful algal blooms (HABs) are significantly degrading the water quality in both inland and coastal water bodies around the world [1,2], threatening the aquatic environment, freshwater and marine ecosystems, and human health [3,4].The resting stages of phytoplankton in sediment, which are regarded as the seed bank and source of HABs, have been extensively studied over the past decades [5,6]
We investigated the spatio-temporal variations in the phytoplankton community to examine the relationship between the resting stages of phytoplankton in sediment and the dynamic conditions of the reservoir, and the relationship between the phytoplankton community in surface water during algal blooms and the dynamic conditions of the reservoir
Previous studies showed that the area from Gaoyang Lake (PX3) to confluence is the area at high risk of algal blooms, but our result showed that the most abundant cyanobacteria in sediment were located in PX1 in the initial period of reservoir drawdown [47]

Summary

Introduction

The resting stages of phytoplankton in sediment, which are regarded as the seed bank and source of HABs, have been extensively studied over the past decades [5,6]. A resting strategy in sediment is adapted by many phytoplankton species to survive under stressful environmental conditions, such as cold temperatures, ice cover, and low irradiance [7,8,9]. It is widely accepted that the resting stages of phytoplankton played an important role in initiating blooms of marine dinoflagellates [10,11,12], in blooms of cyanobacteria [9,13,14], and dinoflagellates [13,15] in freshwater. The temporal and spatial characteristics of phytoplankton communities in sediment need to be studied

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Discussion

Conclusion