Five Decades of Wetland Soil Development of a Constructed Tidal Salt Marsh, North Carolina, USA

We periodically measured soil properties (bulk density, organic carbon, total nitrogen, and total phosphorus) in a tidal salt marsh constructed in 1970 over the past five decades (1984, 1995, 1998, 2017) to identify trajectories of soil formation over time. Bulk density was greater in surface (0–10 cm) than subsurface (10–30 cm) soils and decreased with time at a similar rate in both depths. Percent organic carbon (C), nitrogen (N), and total phosphorus (P) increased with time, with concentrations in surface soils increasing three times faster than subsurface soils. Surface C and N pools (g/m2, 0–10 cm) exhibited asymptotic trajectories with time, with rapid accumulation in the first two decades that began to equilibrate after 25 years, while subsurface pools of C and N continued to increase in a linear manner. Soil P pools did not exhibit a significant trend related to marsh age. Soil N:P increased in both depths over time, suggesting gradual relaxation of N-limitation of these systems. Our findings can help restoration ecologists identify soil properties, including bulk density, C, N, and C:N suitable for gauging restoration success and better estimate the time frame necessary for recovery of soil-based ecosystem services.