Soil organic carbon variability in Australian temperate freshwater wetlands

Abstract

Globally, there is little information on freshwater (non‐tidal) wetland below ground soil organic carbon (SOC) stocks, sequestration rates and, in particular, their within‐wetland variation. This basic information is critical for designing programs to sample SOC stocks and identifying areas that sequester large amounts of carbon so that they can be managed to prevent degradation and carbon loss. Here, focusing on temperate seasonally inundated freshwater wetlands in south‐eastern Australia, we compared SOC stocks and sequestration rates (via radiometric dating) among wetlands, within wetland locations (High water mark, Edge and Middle), and with adjacent terrestrial locations. SOC stocks varied most among wetlands but also varied inconsistently within wetlands. Wetland SOC stocks (20.4 ± 0.1 kg C m−2) were significantly greater than adjacent terrestrial locations (13.3 ± 0.1 kg C m−2). Wetland SOC sequestration rates were similar among all locations (i.e., within a wetland, ranging from 70 g C m−2 yr−1 to 87 g C m−2 yr−1). The relative lack of difference in SOC stocks among wetland locations allows for reduced within‐wetland sampling and subsequently greater replication at the wetland level, at least for temperate ephemeral freshwater wetlands, although these findings need to be confirmed over a range of wetland types. This study also produced the first estimates of temperate freshwater wetland SOC stocks and sequestration rates in Australia, and is among the first studies globally to demonstrate that seasonally inundated wetlands can sequester carbon at significant rates. It therefore provides important justification to support the protection and rehabilitation of temperate freshwater wetlands worldwide.

Modeling organic carbon loss from a rapidly eroding freshwater coastal wetland

“…Carbon inventories for both transects are listed by core in Table 2 and range from 10 kg C m −2 to 24 kg C m −2 for Transect A and 11 kg to 20 kg C m −2 for Transect B. These carbon inventories fall outside the range of previously published soil organic carbon inventories for temperate wetlands (30 kg C m −2 to 120 kg C m −2 ), and are closer to the values reported for temperate forests (5 kg C m −2 to 25 kg C m −2 ) 44 . However, cores A3, A7, and B1 all have greater carbon inventories than previously published inventories, possibly due to the greater age of the wetland unit (1,797–2,016 cal years BP compared to 105 cal years BP in Pearse et al .…”

Significant Organic Carbon Accumulation in Two Coastal Acid Sulfate Soil Wetlands

“…Individual two‐tailed student t test results indicate that OC accumulation rates from ~1980 to 2015 are not significantly different ( p > 0.05) between the two studied wetlands (Cattai 267 ± 30 g·m −2 ·year −1 ; Darawakh 195 ± 31 g·m −2 ·year −1 ) nor are they significantly different ( p > 0.05) between seasonally (251 ± 26 g·m −2 ·year −1 ) and permanently inundated (227 ± 50 g·m −2 ·year −1 ) sites. Differences among wetlands in vegetation type, soil classification, and dry bulk densities likely have a larger effect on OC burial than seasonal or permanent inundation (Bernal & Mitsch, ; Pearse et al, ).…”

“…Their highly productive nature and the predominance of anoxic and permanently saturated conditions in these waterlogged soils provide optimum conditions for the sequestration of organic carbon (Bernal & Mitsch, ; McLeod et al, ; Mitsch et al, ). However, coastal freshwater wetlands are often subjected to anthropogenic pressures including drainage and development (Bao et al, ; Pearse et al, ). These pressures have had considerable impacts on the wetland ecosystems services globally (Dodds et al, ).…”

Physical protection in aggregates and organo-mineral associations contribute to carbon stabilization at the transition zone of seasonally saturated wetlands

“…Under the existing understanding of wetland SOC storage, periodic drying of seasonally saturated wetlands might be expected to stimulate C emissions and SOC loss (Miao et al 2017). Contrary to this expectation, seasonally saturated wetland soils can sequester large stocks of SOC (Pearse et al 2018;Tangen and Bansal 2020), though little is known about the mechanisms that could promote long-term SOC storage in seasonally saturated wetlands. As wetting and drying cycles in wetlands are expected to become more extreme with changes in land use and climate (e.g., Fennessy et al 2018;Lee et al 2020), understanding the mechanisms of SOC storage in seasonally saturated wetlands is critical to predicting the vulnerability of SOC to future change.…”