Effects of freshwater input on trace element pollution in salt marsh soils of a typical coastal estuary, China

- Freshwater input led to higher levels of As, Cr, Pb and Cd in RW soils.
- The studied heavy metals had similar sources except for As in both wetlands.
- As and Cd had significant enrichment levels compared to other heavy metals.
- As and Ni exceeded ERLs and TELs and exhibited higher contributions to TUs.

SummaryFreshwater input is an important pathway for the restoration of degraded coastal wetlands, however, little information is available on the negative effects of freshwater inputs on salt marsh soils in restored wetlands. Soil profile samples to a depth of 70 cm were collected in both degraded wetland (DW) and freshwater restored wetland (RW) in the Yellow River Delta of China to analyze the trace element pollution effects of freshwater input on coastal wetland soils. Heavy metals (i.e. Cd, Cr, Cu, Ni, Pb and Zn) and arsenic (As) concentrations were determined using the inductively coupled plasma atomic absorption spectrometry to investigate their distributions, sources and ecotoxicity in marsh soils from both wetlands. Our results showed that these trace elements had moderate spatial variability in both DW and RW soils. The concentrations of As, Cr, Pb and Cd in all soil layers were generally higher in RW soils than those in DW soils (p < 0.05), whereas the concentrations of Zn and Cu were higher in DW soils. Heavy metals had similar source in both wetlands, however, As and Zn in DW or As, Zn and Ni in RW might have another similar origin. The enrichment factor (EF) values for Cu, Ni and Pb in both wetlands indicated minimal enrichment levels, whereas both As and Cd were significantly enriched with EF values 3 or 6 times greater than 1.5, implying a significant natural or anthropogenic origin. As and Ni exceeded the effect range low (ERL) and threshold effect level (TEL) in both wetlands, even As exceeded the probable effect level (PEL) in RW soils. Cr, Cu and Cd were grouped into TELs-PELs, moreover, Cr concentrations in RW soils exceeded the ERL. However, both Pb and Zn concentrations were below the TELs in both wetlands. Generally, The toxic unit in more than 85% of DW or RW soil samples showed low toxicity with higher contribution of As and Ni. It is necessary to monitor and control trace elements in the freshwater supplied to restored wetlands in coastal wetland restoration projects.