Spatial variation of soil phosphorus in the water level fluctuation zone of the Three Gorges Reservoir: Coupling effects of elevation and artificial restoration

Changes of riparian soil-plant system phosphorus responding to hydrological alternations of Three Gorges Reservoir

The anti-seasonal hydrological alternation in the Three Gorges Reservoir (TGR) significantly impacts the release of phosphorus (P) from the riparian soil-plant system, posing a threat to the aquatic environment. To investigate this issue, riparian soils and plants in three tributaries of the central TGR were sampled at three distinct stages: early exposure, final exposure, and soon after inundation receded. Soil properties, P forms, and plant P content were analyzed. A significant decrease in exchangeable P and organic P during exposure, and a decrease in aluminum/iron-bound P during inundation were observed. These changes were linked to the mineralization of organic matter and the reduction of iron oxides. Compared to bioavailable inorganic P, bioavailable organic P contributed more to the total soil P release during the exposure-inundation cycle. Plant P uptake accounted for 76.08% of the bioavailable P released by the soil during exposure. During inundation, plant P release significantly exceeded soil P release. Therefore, the soil-plant system could act as a P "sink" during exposure and a P "source" during inundation. The hydrological alternation of the TGR was the primary driver of this "source-sink" transformation. To mitigate P release in riparian zones, recycling plant materials and establishing monitoring sites are recommended.

Differential insights into the distribution characteristics of bacterial communities and their response to typical pollutants in the sediment and soil of large drinking water reservoir

In this study, a large drinking water reservoir (Fengshuba Reservoir) was chosen as a representative case, and the bacterial communities in the sediments and soils of Water-level fluctuating zone (WLFZ) as well as their responses to heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) were systematically investigated. The results indicated that the abundance and diversity of the bacterial community obviously changed with seasonal hydrological variations in sediments, and the absolute abundance and composition of bacteria community differed significantly between the sediment phase and soil phase. Bacteria with the ability to degrade pollutants rapidly proliferate and gain ascendancy in the soil phase, with Burkholderia-Caballeronia-Paraburkholderia (B-C-P) and Bradyrhizobium forming the core of the largest community. Furthermore, Co-occurrence network analysis indicated that a more stable bacterial community composition in the sediment phase. The community assembly pattern of bacteria in sediments exhibit a higher degree of stochasticity than that observed in soils of the WLFZ. Furthermore, the Spearman correlations found that the interaction between physicochemical factors, HMs, and PAHs with bacteria community was stronger in the soils of WLFZ. In total, the structural equation models indicated that PAHs were the main driver in altering the deterministic process of bacterial community in the sediment, while HMs and physicochemical factors had a greater effect on the bacteria community in the WLFZ. This study systematically revealed the differential characteristics of bacterial community and their response to typical pollutants between the sediments and soils of large drinking water reservoir.

Spatial and temporal evolution and factors influencing soil aggregate stability in the riparian zone during exposure: A case study of the water-level fluctuation zone of the Three Gorges Reservoir, China

The water-level fluctuation zone (WLFZ) is a unique riparian region that forms in response to the operation of the reservoir. The periodic submersion-exposure conditions severely affect the properties of soil and vegetation, thus also change the spatial and temporal development of soil aggregate stability. Nonetheless, the changes in both space and time concerning soil aggregate stability and the factors influencing it during the exposure period in the WLFZ are still unclear. Consequently, the WLFZ within the Three Gorges Reservoir area (TGRA) was taken as the research object, soil and plant samples were obtained from various elevations along the slope at different times to capture the spatial and temporal changes in soil and plant characteristics throughout the exposure period. Moreover, the wet sieving method was utilized to measure the aggregate size distribution and stability of soil aggregates. To further analyze the effects of both individual and mutual variables on the spatial and temporal changes in aggregate stability, methods such as Pearson's correlation analysis, redundancy analysis (RDA), variation partitioning analysis (VPA), and partial least squares path modeling (PLS-PM) were employed. The findings revealed that aggregate stability increased with increasing elevation until peaking and then decreased spatially, whereas the passage of time contributed to enhanced aggregate stability. The spatial variation in aggregate stability was greater than temporal variation. RDA revealed that soil properties (bulk density, soil water content in mass, clay, silt, sand, pH and soil organic matter), environmental factors (elevation, water level, submersion duration and exposure duration) and plant characteristics (shoot and root biomass) contributed 53.6 %, 45.4 % and 0.9 %, respectively, to the spatiotemporal variability in aggregate stability. VPA and PLS-PM analysis further revealed that the main factors controlling the aggregate stability were soil chemical properties. These results provide a basis for further studies on the soil and water conservation in the WLFZ.

Phosphorus adsorption characteristics and release risk in saline soils: a case study of Songnen Plain, China

Introduction

The Songnen Plain is one of the three major saline-alkali areas in China, covering a vast area, where drought and overgrazing have exacerbated the salinization trend, and will have great potential for development if utilized rationally. Phosphorus, as one of important soil nutrients, plays a crucial role in plant growth. How to minimize its loss and migration has become a current research hotspot. The objective of the present study was to elucidate the adsorption properties of phosphorus in soils affected by salinization and to establish the correlation between the potential for phosphorus release and soil properties.

Methods

A batch treatment test was conducted in this study using three soils with the various salinization degrees to examine the impact of environmental factors on the adsorption properties and potential release of phosphorus.

Results and discussion

It was found that the maximum phosphorus adsorption by the three salinization soils in 0-360 minutes accounted for 86.8%-90.5% of the total adsorption capacity; the equilibrium adsorption capacity was: HS> MS> LS. In cases where the phosphorus level in the surrounding liquid is low, the three levels of salinized soils exhibited varying levels of phosphorus discharge, with the adsorbent acting as the origin of contaminants. The Pseudo-second-order model kinetics and Langmuir equation can well describe the adsorption process, and the adsorption process is spontaneous heat absorption with entropy increase. Increasing the pH led to an increase in the adsorption of phosphorus from the three salinized soils. Additionally, the adsorption was enhanced by introducing varying concentrations of Na+, Ca2+, and Al3+ to the background solution. The phosphorus eutrophication release risk (ERI) demonstrated a gradual decline as temperature increased. Correlation analysis revealed a noteworthy positive correlation between TN, TP, and ERI, as well as a significant negative correlation between CEC, K+, and ERI. Furthermore, there was a highly significant negative correlation between coarse silt and fine silt. Considering local climatic and environmental factors is crucial for controlling the adsorption capacity of phosphorus in various salinized soils, as it can unveil the mechanism of phosphorus adsorption and impact its migration and release risk.