Response of geochemistry and bacterial communities to water-level rise in the soil and sediment of the coastal zone in Qinghai Lake

Abstract:

[Objective] To investigate the response of geochemistry and bacterial communities to water-level rise in the soil and sediment of the coastal zone of Qinghai Lake. [Methods] Surface samples were collected from the onshore soil (soil: S1, S2), littoral zone (transition: E0, E6, E17) and deep sediment (sediment: D1, D2) along the direction perpendicular to the shoreline near the Bird Island of Qinghai Lake. The water depth of the soil and sediment samples (soil water depths were expressed as negative numbers) was employed to characterize the transformation of shoreline soil into sediment caused by inundation. Geochemical analysis and 16S rRNA gene high-throughput sequencing were employed to explore the geochemical characteristics and microbial community composition in the collected soil and sediment samples. [Results] (1) The water level rise of Qinghai Lake significantly affects the geochemical characteristics, nutrient levels, and organic carbon types in the soils and sediments of the coastal zone. Specifically, the pH and mineral associated organic carbon contents of the soil and sediment in the shore zone increased significantly while the C/N value and the contents of dissolved organic carbon (DOC) and particulate organic carbon decreased significantly with the increase of water level; (2) The water level rise of Qinghai Lake will reduce the diversity of bacterial communities and change their community structure in the coastal soils and sediments. These changes in bacterial communities are closely related to changes in environmental factors caused by water level rise. Specifically, after the onshore soil was inundated by water level rise, the bacterial communities inhabiting it exhibited a decrease in the number of operational taxonomic unit (OTU) and Shannon diversity index; the changes of bacterial community diversity was closely related to the content of organic carbon bound with active metal; the important environmental factors that affect bacterial community structure included physicochemical properties (pH), nutrient level (total organic carbon content), and organic carbon quality (C/N value, organic carbon pool II, and mineral associated organic carbon content). Physicochemical properties, nutrient level, and organic carbon quality contributed equally to the differences in bacterial community structure. [Conclusion] The water level rise of Qinghai Lake has significantly affected the physiochemical characteristics, nutrient levels, and organic carbon quality of coastal soil and sediment, and reshaped the bacterial community structure. This implies that the regional carbon cycle homeostasis of the Qinghai-Tibetan lakes will change in the context of the extensive expansion of lakes on the Qinghai-Tibet Plateau. This study provides a data base and theoretical support for the evolution of soil and sediment microbial communities and the evaluation of ecosystem carbon stability in response to lake expansion.