Abstract
Salinity alterations will likely change the plant and environmental characteristics in coastal marshes thereby influencing soil carbon accumulation rates. Coastal Louisiana marshes have been historically classified as fresh, intermediate, brackish, or saline based on resident plant community and position along a salinity gradient. Short-term total carbon accumulation rates were assessed by collecting 10-cm deep soil cores at 24 sites located in marshes spanning the salinity gradient. Bulk density, total carbon content, and the short-term accretion rates obtained with feldspar horizon markers were measured to determine total carbon accumulation rates. Despite some significant differences in soil properties among marsh types, the mean total carbon accumulation rates among marsh types were not significantly different (mean ± std. err. of 190 ± 27 g TC m−2 year−1). However, regression analysis indicated that mean annual surface salinity had a significant negative relationship with total carbon accumulation rates. Based on both analyses, the coastal Louisiana total marsh area (1,433,700 ha) accumulates about 2.7 to 3.3 Tg C year−1. Changing salinities due to increasing relative sea level or resulting from restoration activities may alter carbon accumulation rates in the short term and significantly influence the global carbon cycle.
Highlights
Wetlands significantly impact the global carbon cycle because they contain 20–25% of the world’s soil organic carbon pool (Roulet 2000; Mitra et al 2005)
We addressed the following questions: 1) how do short-term total organic carbon accumulation rates differ among marsh types in coastal wetlands, and 2) how do the environmental conditions influence the total organic carbon accumulation rates in these marsh types?
Significant declines in short-term carbon accumulation with increasing salinity were found when rates were regressed against mean annual salinity of surface waters; categorical analysis of short-term carbon accumulation rates showed no significant differences among marsh types, reflecting the high variability of short-term total carbon accumulation within marsh types
Summary
Wetlands significantly impact the global carbon cycle because they contain 20–25% of the world’s soil organic carbon pool (Roulet 2000; Mitra et al 2005). Carbon accumulation in marsh soils is an important ecosystem process that contributes to the burial of carbon, known as Bblue carbon^ (Chmura et al 2003; Mitra et al 2005; Hopkinson et al 2012). These carbon accumulation dynamics in marsh soils will likely be altered in response to future environmental conditions driven by climate change and coastal restoration activities. Large-scale restoration projects could introduce more fresh water to some estuaries, resulting in fresher marsh types (Morris et al 2013)
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