Seawall effects in a coastal wetland landscape: spatial changes in soil carbon and nitrogen pools

Seawalls are common features in coastal landscapes. They can alter ecological processes in coastal wetland ecosystems at multiple scales. Evaluation those ecological effects requires consideration of spatial characteristics of variables. We used a scaling method, quadrat variance analysis, to quantify the patterns and scale characteristics of soil organic carbon (SOC) and total nitrogen (TN) in a wetland reclaimed by a 30-year-old seawall and a natural wetland in the Yellow River Delta, China, and then analyzed their spatial relationships with different plant and soil variables. The results revealed that spatial variances in SOC and TN in the seawall-reclaimed wetland had two scales. The smaller scale (40 m) was the distance between soil salinity patches, reflecting the influences of soil salinity on SOC and TN. The larger one (130 m) was the distance between shrub communities and the grass patches beneath them, reflecting the influences of shrubs on SOC and TN. However, in the natural wetland, both SOC and TN had only one scale of variance (90 m), which reflected the influences of soil salinity. Soil salinity determined the spatial patterns of dominant grass patches, and thus SOC and TN. Seawall altered plant distributions and shrub-grass interactions, thereby affected the patterns of SOC and TN. Scaling method can help us to efficiently evaluate the landscape impacts of seawalls on coastal wetlands.