Study on the characteristics of soil nutrients and salinization of lake wetlands in semi-arid region: taking Daihai Lake as an example

Influenced by human activities and climate change, the salinization of shallow lake wetlands in semi-arid regions is becoming worse, which threatens the health of riparian ecosystems. Daihai Lake, a typical salinized lake, was selected to analyze the distribution of four nutrients such as organic matter (OM), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP) and available potassium (AK), as well as soil calcium ion (Ca²⁺), magnesium ion (Mg²⁺), exchangeable potassium ion (K⁺), exchangeable sodium ion (Na⁺), carbonate ion (CO₃ ²⁻), bicarbonate ion (HCO₃ ⁻), chloride ion (Cl⁻) and sulfate ion (SO₄ ²⁻) concentrations in three types of soil profile, including riparian grassland, shoal and saline-alkali land. By statistical methods such as principal component analysis (PCA) and redundancy analysis, the salinization characteristics and influencing factors were investigated. The results showed that the difference in the spatial distribution of salts in different types of soil profile in Daihai lakeside zone was large, and there was obvious salt accumulation in grassland and shoals, with the total salt average of 1.99 g/kg and 15.27 g/kg, respectively, on the soil surface; however, the total salt content was the highest at 10-20 cm in the saline-alkali soil, with a total salt content of 17.30 g/kg. pH in the lakeside zone soil was 8.24-8.86, which was higher in the deep soil of shoal and saline-alkali land, as well as the shallow soil of grassland. According to the classification of alkalization, saline-alkali land and shoal soil belonged to alkali soil, and the surface soil of grassland was mainly moderate alkali soil, with a decline of alkalization as the soil went deeper. The major salinization factors in the three land types of Daihai Lake were Cl⁻, Mg²⁺, SO₄ ²⁻, Na⁺, total salt, HCO₃ ⁻, pH, and CO₃ ²⁻. The concentrations of the four nutrients showed a trend of decline with the increase of depth in the 3 types of soil. Besides, the nutrients were the most abundant in the shoal. According to redundancy analysis, a strong correlation existed between most ions in the 3 types of soil. AP and Mg²⁺ were negatively correlated with pH, but other salts and nutrients showed a disparity in different types of soil.