Effect of reclamation on C, N, and P stoichiometry in soil and soil aggregates of a coastal wetland in eastern China

Abstract

The elements carbon (C), nitrogen (N), and phosphorus (P) in soil are crucial to all biological processes. Reclamation in coastal wetlands would alter the balance of multiple chemical elements in soils and sediments. This study aimed to investigate the effect of reclamation on total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and C:N:P stoichiometry in bulk soil and soil aggregates of a coastal wetland in eastern China. The space-for-time substitution method was used to determine the impact of reclamation on soil properties. Field investigation and soil sampling were conducted in September 2012 and April 2014. Four experimental sites were reclaimed in 1951, 1974, 1982, and 2007. The tidal flat was regarded as the control. We sampled soils based on the random uniform grid method to ascertain the basic trends in soil physicochemical properties for the whole study area. After identifying two areas with significant differences, we mainly selected the seasonally typical land use/cover types to analyze the effects of land use/cover on TOC, TN, TP, and C:N:P stoichiometry in bulk soil and soil aggregates (macroaggregate, > 250 μm, microaggregate, 53–250 μm, and silt + clay fraction, < 53 μm). Soil TOC and TN content significantly increased, and EC and pH decreased after reclamation. C:N decreased from 19.997 to 9.527, while C:P and N:P increased from 4.441 to 8.101 and 0.222 to 0.850 respectively over the reclamation time. The main aggregate fractions were microaggregates in the natural wetland and macroaggregates after reclamation. TOC and TN were more likely to be reserved in macroaggregates, while TP was mainly stored in the silt + clay fraction. Compared with the sediments in the tidal flat, the effects of land use/cover types on TOC, TN, TP, and C:N:P stoichiometry in both bulk soil and soil aggregates after the 63-year reclamation were not significant. Long-term chronosequence reclamation could radically improve soil properties in coastal wetlands. Soil physicochemical properties tended to reach a steady state 32 years after reclamation. TOC and TN were mainly reserved in macroaggregates, and increasing the proportion of macroaggregates can contribute to increase TOC and TN content. Soil development owing to the long-term reclamation played a relatively more important role in the soil nutrient stoichiometry than land use/cover change.