Composition, seasonal variation, and salinization characteristics of soil salinity in the Chenier Island of the Yellow River Delta

Abstract

Coastal wetlands, which are fragile and intricate ecosystems with continuously changing salinity and moisture, are especially sensitive to climate changes and anthropogenic activities. As a typical coastal wetland in North China, the Chenier Island of the Yellow River Delta served as the study area to demonstrate the composition, seasonal variations, and salinization characteristics of soil salinity in different seasons. A total of 144 soil samples from 0 cm to 60 cm depth in the coastal zone were comprehensively studied during pre−, among and post−monsoon seasons of 2015. Soil salt contents, anions and cations in the beach, seaward side, dune crest, and landside were quantitatively analyzed through field sampling and experimental determination, and the ion composition, seasonal dynamics, and salinization characteristics of soil salinity in different microtopography types were explored. Physicochemical data revealed that soil salinity changed with the seasons and ranged from 0.76 g·kg−1 to 13.57 g·kg−1 during the sampling period. Soil salinity exhibited distinct spatial heterogeneity and was high in landside and low in dune crest and seaward side along the Chenier Island of the Yellow River Delta. Considering the soil texture, the soil salinity of coastal saline soils was higher than that of shell sandy soils. Salt migration demonstrated seasonality, and soil salinity presented a downward trend in the rainy season, thereby showing a bottom accumulation pattern. Soil salinity tended to move upwards with capillary action in the absence of rain interference in the dry season, which reveals a surface accumulation pattern. The relationship among soil salt content and Na+, Mg2+, Cl−, and SO42− showed an extremely significant positive correlation at the 0.01 level, and that relationship between soil salt content and K+ showed a significant positive correlation at the 0.05 level. However, the correlation with Ca2+ was insignificant at the 0.05 level. Despite the high content of Ca2+, the ions of Na+, Cl−, and SO42− dominated salinity. Additionally, the present study indicated that soil salinity demonstrated seasonality in the order of spring > autumn > summer, and summer was selected as the optimal desalination time. The salinization situation among different microtopographies exhibited some differences, the soil was seriously salinized in the landside and beach, but only non-salinization or mild salinization was found in the seaward side and dune crest. Furthermore, shell sand in the Chenier Island of the Yellow River Delta could provide a favorable soil habitat for plant settlement and create advantageous conditions for the increase in biodiversity, which would provide a scientific basis for soil management and ecological restoration.