Data from: Promoting success in thin layer sediment placement: effects of sediment grain size and amendments on salt marsh plant growth and greenhouse gas exchange

Thin layer sediment placement (TLP) is a method to mitigate factors
resulting in loss of elevation and severe alteration of hydrology, such as
sea level rise and anthropogenic modifications, and prolong the lifespan
of drowning salt marshes. However, TLP success may vary due to plant
stress associated with reductions in nutrient availability and hydrologic
flushing or through the creation of acid sulfate soils. This study
examined the influence of sediment grain size and soil amendments on plant
growth, soil and porewater characteristics, and greenhouse gas exchange
for three key US salt marsh plants: Spartina alterniflora, Spartina
patens, and Salicornia pacifica. We found that bioavailable nitrogen
concentrations (measured as extractable NH4+-N) and porewater pH and
salinity were found to have an inverse relationship with grain size, while
soil redox was more reducing in finer sediments. This suggests that
utilizing finer sediments in TLP projects will result in a more reduced
environment with higher nutrient availability, while larger grain-sized
sediments will be better flushed and oxidized. We further found that grain
size had a significant effect on vegetation biomass allocation and rates
of gas exchange, although these effects were species-specific. We found
that soil amendments (biochar and compost) did not subsidize plant growth
but were associated with increases in soil respiration and methane
emissions. Biochar amendments were additionally ineffective in
ameliorating acid sulfate conditions. This study uncovers complex
interactions between sediment type and vegetation, emphasizing limitations
of soil amendments. The findings aid restoration project managers in
making informed decisions regarding sediment type, target vegetation, and
soil amendments for successful TLP projects.