Effect of Seawall Embankment Reclamation on the Distribution of Cr, Cu, Pb and Zn Pollution in Invasive Spartina alterniflora and Native Phragmites australis Coastal Saltmarshes of East China

Simple Summary Coastal reclamation is the process of converting sea area to land. It is a land use practice commonly associated with loss and damage to the environment, pollution, and affecting the subsistence of man, animals, and plant life. In China, seawalls are constructed along the coastlines to transform wetlands into additional productive land. However, the construction of these seawalls comes with some negative environmental impacts. This study examined the impact of seawalls on the distribution of trace metal (TM) pollution in reclaimed and unreclaimed wetlands. Plant and soil samples were collected from the affected wetlands and analyzed in the laboratory. Results show that the construction of the seawalls, coupled with factors such as plant organic matter, soil water, and salt content influenced the significant increase in TM pollution in the reclaimed wetlands compared to the unreclaimed wetlands. A comparison of the results with international standard quality guidelines shows that the soils from wetlands on the coastline of the study region were moderate to severely polluted by copper, zinc, and chromium. Overall, soils affected by reclamation posed a greater ecological risk than in unreclaimed wetlands. Stakeholders can use this scientific outcome to mitigate TM pollution caused by seawall construction in coastal ecosystems. Coastal reclamation by seawall embankments and the spread of invasive C-4 perennial grass Spartina alterniflora have recently become more prevalent in eastern China's coastal wetlands. While trace metals (TMs), carbon, and nitrogen dynamics concerning reclamation have extensively been explored across China's coastal wetlands, to date, the impact of reclamation by coastal embankment and exotic plant invasion on TMs' pollution dynamics in coastal marshes remains largely unexplored. We compared TMs Cr, Cu, Pb, and Zn cumulation in coastal embankment-reclaimed versus unreclaimed S. alterniflora and Phragmites australis saltmarshes in eastern China coastal wetlands. In both S. alterniflora and P. australis marshes, coastal embankment reclamation spurred an increase in Cr, Cu, Pb, and Zn concentrations by 31.66%, 53.85%, 32.14%, 33.96% and by 59.18%, 87.50%, 55.55%, 36.84%, respectively, in both marsh types. Reclamation also reduced plant biomass, soil moisture, and soil salinity in both plants' marshes. Our findings suggest that the impact of coastal embankment reclamation and replacement of native saltmarshes by invasive S. alterniflora had a synergistic effect on TM accumulation in the P. australis marshes, as corroborated by bioaccumulation and translocation factors. Reclamation by coastal embankments and invasive alien plants could significantly impair the physico-chemical properties of native plant saltmarsh and essentially weaken the accumulation of Cr, Cu, Pb, and Zn potential of the coastal saltmarshes. Our findings provide policymakers with an enhanced knowledge of the relationship between reclamation, plant invasiveness, and TM pollution dynamics in coastal wetlands, providing a baseline for attaining future goals and strategies related to the tradeoffs of various wetland reclamation types.

Automated summary

Coastal reclamation and the spread of invasive grass have led to an increase in trace metal pollution in coastal wetlands in eastern China. The construction of seawalls and invasive plant species have resulted in higher concentrations of trace metals in the reclaimed wetlands compared to unreclaimed wetlands, and have also impacted plant biomass and soil properties. This study provides valuable information for policymakers and stakeholders to mitigate trace metal pollution caused by reclamation and invasive species in coastal ecosystems.