Effects of moisture and salinity on soil dissolved organic matter and ecological risk of coastal wetland

Coastal wetland is the transitional area between land and ocean, which has a unique and sensitive ecosystem. In this study, the effects of moisture and salinity on dissolved organic matter (DOM) and adsorption of heavy metal ions (Cr(VI), Cd(II) and Pb(II)) by soil are investigated. Meanwhile, ecological risks for the potential release of N, P and heavy metals are also predicted. UV–Vis spectrophotometry and three-dimensional fluorescence spectroscopy are used to study the content and structural of DOM under different soil moisture and salinity. Soil adsorption of heavy metal ions is determined by inductively coupled plasma (ICP). The results show that soil moisture and salinity have significant effects on the basic physical and chemical properties of soil. DOM content is the highest in medium moisture and high salinity areas. In addition, the content of protein-like substances in DOM is the highest under all treatment conditions. The results also reveal that the increase of DOM promotes Cr(VI) adsorption and inhibits Cd(II) adsorption by soil. When Pb(II) concentration is high (150 mg/L), the increase of DOM inhibits Pb(II) adsorption by soil. The comprehensive ecological risk of heavy metals is the highest under high salinity. The potential release risk of N and P is the lowest at high moisture and low moisture, respectively. Base on above, effects of soil moisture and salinity on the surrounding ecological environment in coastal wetlands have been revealed, which provides a theoretical basis for the protection of coastal wetland ecological environment. •Moisture and salinity change the basic physical and chemical properties of soil.•DOM first rises and then decreases as moisture increase.•DOM increases with the increase of salinity.•DOM promotes the adsorption of Cr(VI), but inhibits Cd(II) adsorption by soil.•Comprehensive ecological risk is the highest in high moisture and salinity area.