Geochemical conditions of natural wetland and paddy fields in the Poyang Lake area, China

Evgeniya Soldatova,Irina Gromyak,Andrey Toropov,Zhanxue Sun,Irina Ivanova,Yihui Dong,Denis Dogadkin,Jiale Li

doi:10.1007/s42452-020-04060-8

Abstract

During the last several decades, wetlands are losing their ecological functions due to increasing anthropogenic loads. One of these functions is the ability to bind elements forming geochemical barriers. The research aimed to study the geochemical conditions of natural wetlands and flooded paddy fields (artificial wetlands) in the Ganjiang River basin to trace geochemical barriers. The research approach was based on a comprehensive analysis of water and aqueous extracts from bottom sediments and paddy soils, including chemical and mineral composition. The samples were collected in November 2019, during the dry season at the end of harvesting. Chemical analysis was performed using standard methods for natural substances: titrimetry, photometry, ionic chromatography, high-temperature oxidation, ICP-MS, and ICP-AES. The mineral composition of the soils and sediments was determined by XRD. It was found that the main physicochemical characteristics (TDS, pH, main component concentrations) of the natural wetland water correspond to the surface water of the study area, whereas the irrigation water is similar to shallow groundwater. The content of trace elements in the irrigation water is higher than in the natural wetland water. Generally, the trace element composition of the natural wetland water corresponds to the geochemical background of the study area. Analysis of the mineral and chemical composition of the paddy soils and sediments indicates the geochemical barriers that accumulate a wide range of elements. In the natural wetland, the geochemical barrier is likely associated with a decrease in oxygen content and advective transport rate in the sediments, whereas in the paddy fields, the precipitation of clay minerals in the soil profile forms the geochemical barrier related to a decrease in filtration properties and advection–diffusion transport.Graphic abstract

Highlights

The buffering function of wetlands and their ability to regulate climate, at least at a regional level, explains the growth of scientific interest in wetland geochemistry and the factors controlling their evolution
According to the value of total dissolved solids (TDS), the water of natural wetland is ultrafresh (TDS value is up to 100 mg/L), which corresponds to the values of TDS determined for the water of Ganjiang and Xiushui Rivers and Poyang Lake (Table 1, [27])
The low pH values of the natural wetland water corresponding to the pH of atmospheric precipitation (Table 1) indicate a significant role of natural processes in its chemical composition formation, it is confirmed by the low content of trace elements in comparison with the river, lake, and irrigation waters

Summary

Introduction

The buffering function of wetlands and their ability to regulate climate, at least at a regional level, explains the growth of scientific interest in wetland geochemistry and the factors controlling their evolution. During the last several decades, as a result of the dramatic increase of anthropogenic load, wetlands are losing their most important ecological functions, such as the role of a buffer zone for regulating natural disasters and the ability to self-purification [1] This provokes further hydrological regime changes, sediment transport, nutrients dynamics, water quality, and disturbance of aquatic biota migration routes and habitat [2]. We consider the chemical composition of water and aqueous extracts from natural wetland sediments and paddy soils combined with their mineral composition Such a comprehensive approach allows studying the geochemical conditions, migration, and accumulation of chemical elements in the water–rock system.

Methods

Results

Conclusion