Soil development and establishment of carbon‐based properties in created freshwater marshes

Abstract

The current U.S. wetland mitigation policy of "no net loss" requires that a new wetland be created to replace any natural wetland destroyed under development pressures. This policy, however, may be resulting in a net loss of carbon-based wetland functions. We evaluated the ability of created wetlands to accumulate carbon and to mitigate loss of carbon-based functions in natural wetlands with variable hydrology. Potential limiting factors to carbon accumulation within created systems included soil aggregation, texture, and bulk density. Rates of soil development and the time required for created wetlands to accumulate the amount of carbon found in natural wetlands were estimated by an exponential model. Soils collected from five created (ages 3-8 years) and four natural freshwater marshes, located in central Ohio, USA, were analyzed for soil organic carbon (SOC), mineralizable soil carbon (Cmin), water-stable aggregates (WSA), particle-size fractions (PSD), and bulk density. Peak-standing aboveground plant biomass was also quantified. Created wetlands contained significantly less plant biomass, SOC, and Cmin than natural wetlands (c < 0.05; false discovery rate). Soil physical properties also differed significantly between created and natural wetlands, with fewer macroaggregates, more microaggregates, more silt-clay (0-5 cm only), and higher bulk density in created wetlands (a < 0.05; false discovery rate). Carbon content was positively correlated with macroaggregate content and negatively correlated with microaggregate content, silt-clay fraction, and bulk density. Fit of SOC data to the exponential model indicated that a newly created wetland would require 300 years to sequester the amount of SOC contained in a natural wetland. At this rate of carbon accumulation, a mitigation ratio of 2.7:1 (area) would be necessary for successful mitigation over a 50-year time period. However, other trajectories fit the data equally well and suggested area mitigation ratios of 2.2:1 (logistic) to 4.4:1 (linear regression) to 5.1:1 (exponential regression). Whether created wetlands are on a trajectory toward natural wetland carbon function, however, remains uncertain. Until gaps in the data are filled and a trajectory verified, the best mitigation policy will be a conservative one, with a restrictive permitting process and high mitigation ratios (5.1:1 minimum).

Ecosystem Development After Mangrove Wetland Creation: Plant–Soil Change Across a 20-Year Chronosequence

“…However, many restoration and creation efforts do not follow predicted trajectories or are nonlinear (Zedler 1996;Zedler and Callaway 1999;Matthews and Spyreas 2010;Hossler and others 2011), and where a trajectory is present, ecosystem properties typically develop differentially (Zedler 2000;Craft and others 2003). For example, whereas processes linked to hydrology can be restored relatively rapidly with proper design (for example, within the first year) (Craft and others 2003;Lewis 2005), soil-dependent properties and processes often require much more time to reach equivalency (for example, decades, centuries) (Craft and others 2003;Ballantine and Schneider 2009;Hossler and Bouchard 2010). Furthermore, the rate and trajectory of ecosystem development also varies due to wetland type, landscape position, land-use history, and site-specific starting conditions (Bedford and others 1999;Zedler 2000;Ballantine and Schneider 2009).…”

“…Natural wetland soils are usually very C-rich relative to upland and marine ecosystems; although wetlands cover less than 10% of the earth's terrestrial surface (Zedler and Kercher 2005;Mitsch and Gosselink 2007), wetland soils contain roughly one-third of the global soil C pool (Mitsch and Gosselink 2007). However, there are often large differences between restored, created, and natural wetland soils, and many studies in diverse wetland types indicate that it typically takes much time (for example, decades, centuries) for created and restored wetlands to develop soil properties that are equivalent to natural wetlands (Craft and others 2003;Ballantine and Schneider 2009;Hossler and Bouchard 2010;Hossler and others 2011). Because various international, federal, and state regulations stipulate that, in a mitigation context, created and restored wetlands should be functionally equivalent to the natural wetlands they replace, the slow rate of soil functional and structural development following creation and restoration has caused concern (Bruland 2004;Hossler and Bouchard 2010;Hossler and others 2011).…”

Soil water retention and carbon pools in tropical forested wetlands and marshes of the Gulf of Mexico

“…Craft (2007) found a mean organic carbon content of 10.2% in freshwater marshes in Georgia. Hossler and Bouchard (2010) reported organic carbon content in the range of 3-21% in soils of marshes in Ohio, USA. Carbon storage in soils of studied coastal wetlands is higher than in prairie potholes wetlands in North America, and it is also higher than carbon storage in depressional isolated forested wetlands and riverine marshes in Ohio, USA (Table 4).…”

The effects of the reverse seasonal flooding on soil texture within the hydro-fluctuation belt in the Three Gorges reservoir, China

“…in the process of wetland evolution and recovery (Zheng et al 2011;Wolf et al 2011). The conditions of change in soil texture are difficult to isolate due to the influence of flooding in wetlands (Wang et al 2005;Hossler and Bouchard 2010). While some studies suggest that flooding increased the percentage of clay particles and porosity of soil, leading to overall improvement soil texture (Lu et al 2007;Hossler and Bouchard 2010;Lee et al 2014), other studies indicate that flooding increased sand particle Different letters in the columns indicate significant differences (P < 0.05).…”