Coastal wetlands are fragile ecosystems influenced by human activities. Vegetation-induced changes in wetland soil nutrient pools have significance at local, regional and global scales.
Seawalls have been widely used as mitigation for sea level rise and storm surges in coastal ecosystems and have the potential of changing coastal wetlands. Of great importance are the changes that occur in soil organic carbon (SOC) and total nitrogen (TN). But the spatial patterns of wetland soil SOC and TN changes after seawall reclamation is relatively unknown. The evaluation of spatial changes in these parameters requires a suitable spatial analysis method. Further it is necessary to understand these changes in the context of changing plant communities and soil salinity after seawall reclamation. Here, we use a spatial statistics method, Quadrat Variance Analysis, to quantify the spatial scaling of soil SOC and TN along a sea-land gradient in a 30 years seawall-reclaimed coastal wetland, compared with a natural wetland in the Yellow River Delta, China. Further, we related plant variables and soil salinity to the observed patterns of soil SOC and TN in both wetlands.
Results/Conclusions
The results showed significant spatial changes in soil SOC and TN in seawall-reclaimed wetlands. (1) There were two scale variances in soil SOC and TN in seawall-reclaimed wetland. The larger one (140m) reflected the influences of shrub on soil SOC and TN, while the smaller one (40m) reflected the influences of soil salinity on them. However, there was only one obvious scale variance (90m) in natural wetland, which reflected the influence of soil salinity on soil SOC and TN. (2) Soil SOC and TN in seawall-reclaimed wetland were closely related to the number and crown width of the shrub species Tamarix chinensis. In natural wetlands, however, soil SOC and TN had a higher correlation with soil salinity. The patterns of shrub and soil salinity may play different roles in determining the spatial patterns of soil SOC and TN in seawall-impacted and natural wetlands, respectively.