Wetland Soil Organic Carbon Research Articles

Combining Artificial Neural Network and Ordinary Kriging to Predict Wetland Soil Organic Carbon Concentration in China's Liao River Basin.

Accurate prediction of wetland soil organic carbon concentration and an understanding of its controlling factors are important for studying regional climate change and wetland carbon cycles; with that knowledge mechanisms can be put in place that are conducive to sustainable ecosystem management for environmental health. In this study, a hybrid approach combining an artificial neural network and ordinary kriging and 103 soil samples at three soil depth ranges (0–30, 30–60, and 60–100 cm) were used to predict wetland soil organic carbon concentration in China’s Liao River Basin. The model evaluation indicated that a combination of artificial neural network and ordinary kriging and limited soil samples achieved good performance in predicting wetland soil organic carbon concentration. Wetland soil organic carbon concentration in the Liao River Basin has apparent spatial and vertical heterogeneities with values decreasing from southeast to northwest and concentrates present mainly in the topsoil (0–30 cm). Mean wetland soil organic carbon concentration values at the three soil depths were 10.43 ± 0.38, 7.93 ± 0.25, and 7.61 ± 0.22 g/kg, respectively, which are smaller than those over other wetland regions in Northeast China. Terrain aspect contributed the most in predicting wetland soil organic carbon concentration at each of the three soil depths, followed by normalized difference vegetation index at 0–30 cm and mean annual precipitation at 30–60 and 60–100 cm. This study provides a framework method and baseline to quantify the soil organic carbon concentration dynamics in response to climatic and anthropogenic drivers.

The Invasion of Alternanthera philoxeroides Increased Soil Organic Carbon in a River and a Constructed Wetland With Different Mechanisms

Wetlands have been considered as a vital reservoir of global carbon and are vulnerable to plant invasion. However, the influence mechanism of plant invasion on soil organic carbon (SOC) in wetlands remains unclear. In this study, we investigated SOC, soil physicochemical properties, and soil microbes in the invaded and non-invaded sites in Xinxue River and Xinxue River Constructed Wetland to research the effects of Alternanthera philoxeroides invasion on SOC and explore the related mechanisms. The invasion of A. philoxeroides increased SOC content and density in both the river and the constructed wetland. SOC in the two types of wetlands was positively correlated with moisture content and negatively correlated with bulk density, dissolved oxygen, water temperature, soil temperature, and pH. The invasion decreased the dissolved oxygen in the river and the soil temperature in the constructed wetland which might be the explanation for the increase of SOC in the two types of wetlands. In the river, the decrease of dissolved oxygen caused by plant invasion could alter the microbial community and limit the decomposition of SOC by microbes, which was confirmed by the increase of microbial α diversity indices and the correlations between soil microbial community in the river and dissolved oxygen showed by RDA analysis. The invasion of A. philoxeroides significantly shifted the soil microbial community in the constructed wetland. Redundancy analysis showed that the variation of soil microbial community structure in the constructed wetland could be mainly explained by soil pH and soil temperature. The decrease of soil temperature in the constructed wetland might inhibit microbial activities and result in the accumulation of SOC. In addition, the indicator species reflecting soil microbial community shifted by plant invasion were highly correlated with SOC, suggesting that the variation of indicator species between invaded sites and non-invaded sites might be another reason for the difference in SOC. The study indicates that A. philoxeroides invasion might increase the carbon storage in rivers and constructed wetlands with different mechanisms.

Effects of groundwater tables and salinity levels on soil organic carbon and total nitrogen accumulation in coastal wetlands with different plant cover types in a Chinese estuary

Groundwater tables and soil salinity can greatly affect the biogeochemical cycles of carbon and nitrogen by altering soil physicochemical properties. Coastal wetlands with different plant cover types (including bare land, Phragmites australis, and Suaeda salsa wetlands) and groundwater table wetlands (including low groundwater table, medium groundwater table, and high groundwater table wetlands) were investigated in 2012–2013 to characterize the spatial and temporal changes and the effects of groundwater tables on soil organic carbon (SOC) and total nitrogen (TN) in the Yellow River Estuary, China. The results showed that SOCs in 2012 was higher than that in 2013 regardless of the groundwater tables, while TNs was higher in 2013 than in 2012 except in the BL soil with low groundwater tables and the PA wetlands with middle groundwater tables. The SOCs and TNs were mainly concentrated in the top 20 cm soils. SOCc and TNc were fitted very well with soil depth by the general linear fit (p < 0.01). The Lorentz models were ideal for the relationships among SOC, TN and electrical conductivity (EC), indicating that certain EC values could improve carbon and nitrogen accumulation. The theoretical threshold of EC for the maximum SOC and SOCs was 2.2 ms/cm, and the maximum TN and TNs highly depended on groundwater tables (0.9–1.0 ms/cm for LW, 1.6–1.8 ms/cm for MW and 3.0 ms/cm for HW). The general linear model results showed that SOC was positively correlated with TN at the same groundwater table (p < 0.01). Additionally, a positive linear relationship was also observed among SOC, TN and silt + clay contents for all groundwater tables (p < 0.05). These findings indicated that carbon and nitrogen stocks might be regulated by groundwater tables and salinity to improve carbon sinks in coastal wetlands.

Soil organic carbon storage in a tropical freshwater wetland: the influence of vegetation type

The impact of different vegetation communities on soil organic carbon (SOC) in a tropical freshwater wetland in Uganda was investigated. SOC content, density and storage potential were determined under three different dominant vegetation communities: Cyperus papyrus L., Typha latifolia L. and Phragmites mauritianus Kunth. SOC content (123.7 ± 2.6 SE g C kg−1 dry soil) in C. papyrus was significantly higher (p < 0.05) than in both T. latifolia and P. mauritianus, whereas SOC density (kg C m−2) insignificantly varied (p > 0.05) among the three vegetation communities (C. papyrus = 7.2 ± 0.1, T. latifolia = 6.7 ± 0.1 and P. mauritianus = 6.2 ± 0.1). Similarly, for the entire sampled soil depth (0–50 cm), SOC storage potential was significantly higher (p < 0.05) in C. papyrus (36 118.08 ± 552.52 t C km−2), and was in the order of decreasing magnitude: C. papyrus > T. latifolia > P. mauritianus. Plant biomass density, and soil physico-chemical characteristics, bulk density, salinity, pH and temperature were significantly correlated (p < 0.05) with SOC. In conclusion, where climate change mitigation is considered as a wetland ecosystem service, restoration priorities for degraded/lost tropical freshwater wetlands need to consider C. papyrus plants. In addition, comparing SOC storage by ecosystems, Uganda’s wetlands contain three times more SOC than is contained in the country’s forests.

Spatial distribution of soil organic carbon and total nitrogen in disturbed Carex tussock wetland

Disturbance affects the ecological structure and function of wetland ecosystems by altering plant and soil properties. To identify the response of soil carbon and nitrogen to wetland disturbance, this study was conducted in three disturbed and two reference Carex tussock wetlands in Momoge National Natural Reserve, China. The content and stocks of soil organic carbon (SOC) and total nitrogen (TN) were determined to investigate the effects of disturbance on their spatial distribution. Generally, SOC and TN content and stocks gradually decreased with increasing soil depth except for in reference tussock wetlands that had an accumulation peak at 11–20 cm. In disturbed tussock wetlands, a significantly higher SOC content was observed in the top 10 cm of soil, while in disturbed and reference wetlands, no significant differences were found in SOC content and stocks, or in TN levels, in deep soil. Additionally, soil organic carbon and nitrogen were significantly correlated with soil water content (SWC), bulk density, soil porosity, and soil respiration (SR). Redundancy analysis revealed that SWC and SR were major determinants of soil carbon and nitrogen. These findings clarified the dynamic changes of soil carbon and nitrogen of disturbed wetland, which is highly significant for accurate estimation of wetland carbon and nitrogen reserves.

Consideration of dissolved organic carbon flux reduces estimated wetland carbon losses in response to warming

Wetland gaseous carbon (C) emissions have been widely used to evaluate temperature sensitivity of soil organic carbon (SOC) decomposition (indicated by Q10). However, dissolved organic carbon (DOC) flux as an important pathway for soil solid-phase organic carbon losses has seldom been considered in such estimations, which may introduce bias in predictions of wetland soil C-climate feedback. Hence, this study aimed to explore whether and how the temperature sensitivity of wetland SOC decomposition is affected by DOC flux. We carried out an anaerobic microcosm experiment using diverse wetland soils to assess the feedback of wetland SOC decomposition to temperature change with and without considering DOC flux. The contribution of DOC flux to wetlands SOC decomposition at a low temperature was significantly (p 0.05) for low-SOC wetland soils. In addition, the overestimation for alkaline wetland soils was much higher than that of acid wetland soils, with a significantly (p < 0.01) positive correlation between the ratios of Q10 (gaseous C emissions) to Q10 (SOC decomposition) and soil pH across all wetland soil samples. Our finding suggested that the sensitivity of wetland SOC decomposition to temperature change might be overestimated if DOC flux is not considered, especially in alkaline or high-SOC soils. Thus, C-climate models should incorporate DOC flux when predicting wetland C loss in response to warming.

Molecular Fingerprints of Soil Organic Carbon in Wetlands Covered by Native and Non-native Plants in the Yellow River Delta

This study compared soil organic carbon (SOC) in wetlands dominated by native and one invasive plant specie to better understand how short-term Spartina alterniflora colonization affected carbon circulation in the Yellow River Delta (YRD). Freshwater marsh dominated by Phragmites australis (FM) had the highest SOC, total nitrogen (TN), and water-extractable organic carbon (WEOC) contents, whereas SOC contents varied only slightly among salt marshes covered by Suaeda salsa (SM2), S. alterniflora (SM3) and bare flat (MD). Invasion by S. alterniflora substantially changed the molecular characteristics of SOC. The spectral characteristics of Fourier-transform infrared spectroscopy (FTIR) of humic acids (HAs) were similar from 4000 to 1800 cm−1 but differed greatly from 1800 to 1000 cm−1 among four wetlands. Pyrolysis-gas chromatography/mass spectrometry technology (Py-GC/MS) was used to characterize molecular fingerprints of HAs. Aliphatics (27.38%), lignin (16.64%), nitrogen-containing compounds (Nc) (16.16%), polysaccharides (16.93%), and phenol (13.42%) were dominant in FM, and aliphatics, alkyl, and Nc were primary in HAs from MD, SM2, and SM3. Lignin moieties were only found in HAs from FM and SM3, which accounted for about 16.64% and 1.6% of the total ion current, respectively. The absorption bands of the FTIR spectrum around 3340 and 1650 cm−1 in FM samples were much larger than those in the other three wetlands. However, the ratio of the peak areas at 1620 and 2930 cm−1 (R1620/2930) in SM3, was lower than that in MD and SM2, and it meant carbon in SM3 was less stable. Proportions of lignin and phenol moieties to total ion counts (TIC) in MD and SM2 were 3.3% and 3.4%, while these proportions in FM and SM were 30% and 7.5%, respectively. It showed S. alterniflora invasion into salt marsh would increase SOC contents and its stability, while it will inverse if freshwater marsh was supplanted by S. alterniflora in the YRD.

Loss-On-Ignition Estimates for Soil Organic Carbon in Great Lakes Freshwater Coastal Wetlands

Soil organic carbon (SOC) is an important component of freshwater wetlands that may be used to quantify ecosystem services and prioritize conservation efforts. Measuring SOC directly via elemental analysis is often time and cost-prohibitive. Loss-on-ignition (LOI) is a rapid and low-cost method for determining soil organic matter; however, LOI data must be converted to SOC data using a soil type-specific regression model and no models currently exist for freshwater coastal wetlands. To address this gap, we performed regression analyses that convert percent organic matter measured from LOI to SOC for freshwater coastal wetlands in the southern basin of Lake Michigan. Analyses across 6 Lake Michigan wetlands provide a regression model capable of estimating SOC within ±3.5% uncertainty (r2 = 0.757), a threshold useful for wetland management and large-scale soil surveys. Future research should explore the LOI-SOC relationship at other freshwater coastal wetlands – to investigate whether the correlation values found here are typical of these systems and to refine our regression model using data from disparate freshwater locales.

Investigating Spatial and Vertical Patterns of Wetland Soil Organic Carbon Concentrations in China’s Western Songnen Plain by Comparing Different Algorithms

Investigating the spatial and vertical patterns of wetland soil organic carbon concentration (SOCc) is important for understanding the regional carbon cycle and managing the wetland ecosystem. By integrating 160 wetland soil profile samples and environmental variables from climatic, topographical, and remote sensing data, we spatially predicted the SOCc of wetlands in China’s Western Songnen Plain by comparing four algorithms: random forest (RF), support vector machine (SVM) for regression, inverse distance weighted (IDW), and ordinary kriging (OK). The predicted results of the SOCc from the different algorithms were validated against independent testing samples according to the mean error, root mean squared error, and correlation coefficient. The results show that the measured SOCc values at depths of 0–30, 30–60, and 60–100 cm were 15.28, 7.57, and 5.22 g·kg−1, respectively. An assessment revealed that the RF algorithm was most accurate for predicting SOCc; its correlation coefficients at the different depths were 0.82, 0.59, and 0.51, respectively. The attribute importance from the RF indicates that environmental variables have various effects on the SOCc at different depths. The land surface temperature and land surface water index had a stronger influence on the spatial distribution of SOCc at the depths of 0–30 and 30–60 cm, whereas topographic factors, such as altitude, had a stronger influence within 60–100 cm. The predicted SOCc of each vertical depth increased gradually from south to north in the study area. This research provides an important case study for predicting SOCc, including selecting factors and algorithms, and helps with understanding the carbon cycles of regional wetlands.

Effects of water and salinity on soil labile organic carbon in estuarine wetlands of the Yellow River Delta, China

Changes in labile organic carbon in wetland soils as indicators of soil quality and climate change have received many attention worldwide. Soil samples were collected in 2012 and 2013 in estuarine wetlands with different groundwater tables in the Yellow River Delta, and soil salinity, water content (WC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC) were determined to investigate the effects of water and salinity on labile organic carbon in wetland soils. Our results showed that the response of labile organic carbon to salt and water conditions varied varied in soil samples with different groundwater tables. The MBC in soils with low groundwater tables (LW) was the lowest when soil WC was 25% and then exhibited an increase with increasing WC. The DOC in LW soils has increased and MBC and DOC contents in soils with middle groundwater tables (MW) and high groundwater tables (HW) has decreased with increasing WC. MBC in three wetlands presented a “decreasing before increasing” tendency with increasing salinity, whereas DOC showed an “increasing before decreasing” tendency. Soil microbial biomass and soil fertility in estuarine wetlands with salinity between 1.8 and 2.0 ppt were relatively high, which was conducive to plant growth. The findings of this study provide a better understanding of the relationships between soil labile organic carbon and water and salt conditions as also deliver basic data for carbon sequestration and blue carbon management in estuarine wetlands.

Quantification and molecular characterization of organo-mineral associations as influenced by redox oscillations

Organo-mineral association is one of the most important stabilization mechanisms of soil organic matter. However, few studies have been conducted to assess the retention, transformation, and transportation of colloids (1–1000 nm) and associated organic carbon (OC) in soil. Given the particularly significant role that wetland soils play in carbon storage and cycling, we quantified the dynamics of organo-mineral association within colloidal size range by conducting three consecutive 35-day redox (reduction-oxidation) oscillation experiments using a wetland soil. Molecular compositions of natural nanoparticle (NNP, 2.3–100 nm), fine colloid (100–450 nm), and particulate (450–1000 nm) fractions were measured using isotope ratio mass spectrometry (IRMS) and x-ray photoelectron spectroscopy (XPS). Results showed that NNP and fine colloids constituted up to 8.94 ± 0.50% and 22.19 ± 7.52% of bulk C concentration (2.3–1000 nm), respectively; indicating substantial contributions of these two fractions to the operationally defined “dissolved” (<450 nm) fraction. There was significant enrichment in heavier δ13C isotopes (p < 0.001) with size: NNP (−29.64 ± 0.32‰) < fine colloid (−28.81 ± 0.31‰) < particulate (−28.34 ± 0.25‰) fractions. NNP had the highest percentages of carbonyl/carboxyl C (C=O); while fine colloid and particulate fractions contained more reduced aromatic or aliphatic C (C–C, C=C, C–H). OC became more enriched (‰) in microbial-derived C (higher δ13C) with increasing particle size as well as with repeated redox oscillations. Our findings clearly demonstrate limitations of using the operationally defined “dissolved” fraction (<450 nm) to assess C cycling in ecosystems such as wetlands. Increase in colloid and OC concentrations and presence of more microbial-derived C in larger size fractions additionally imply that redox oscillations promote the formation of molecularly diverse sub-colloid sized organo-mineral associations. Being a composite unit of soil microaggregates, organic-mineral associations can thus influence the overall stability of OC in wetland soils that undergo frequent redox oscillations.

Environmental Controls on the Distribution of Tidal Wetland Soil Organic Carbon in the Continental United States

AbstractTidal wetlands are among the most valuable ecosystems in the world in terms of ecosystem service value, and the strategic management of their carbon resources is an important part of climate change mitigation. Tidal wetland soils contain relatively high quantities of soil organic carbon (SOC); yet there is little information about whether this SOC can be predicted based on easily identifiable environmental factors. We investigated how tidal wetland SOC density was distributed across the continental United States among various coastal locations, estuarine typologies, vegetation types, water regimes, and management regimes and found that knowledge of a wetland's coastal affiliation provided the most differentiation (whether on the East Coast, West Coast, or Gulf Coast). We then sought to identify whether SOC density was correlated with 47 different environmental variables and found that knowledge based on latitude and precipitation explained ~46% of the variance in SOC density for wetlands on the West Coast and Gulf Coast, respectively. Several other geographic, oceanic, terrestrial, and atmospheric factors were cross‐correlated along these axes, including oceanic salinity, temperature, and average catchment elevation. For the U.S. East Coast, SOC density was not simple to explain and was likely dependent on a wide range of interacting and complex factors. This synthetic work can provide a better understanding of how changing environmental and social conditions can lead to enhanced or degraded carbon sequestration rates in times of rapid global change.

Aggregation but Not Organo‐Metal Complexes Contributed to C Storage in Tidal Freshwater Wetland Soils

Core Ideas Water‐stable aggregates may assist in the preservation of organic carbon in wetland soils. Soil C was more evenly distributed among the aggregate‐size classes in the restored but not the natural site. Macroaggregate‐C more closely resembled plan detritus whereas mineral‐C was enriched with N‐containing compounds. One of the many goals of wetland restoration is to promote the long‐term storage of carbon (C) in the terrestrial biosphere. Unfortunately, soil C reservoirs in restored wetlands are slow to accumulate even after hydrology and plant communities are reestablished. Oftentimes wetland restoration changes the soil matrix and thus can dramatically alter how soil C is stored and processed. Our research investigated whether soil organic matter (SOM) preservation theories derived from studies in non‐wetland soil systems can be extended to wetland soils. We examined C associated with water‐stable soil aggregates, minerals, and metal oxides within habitats of one natural and one restored tidal freshwater wetland. This study revealed that a majority of the soil C in the natural site was associated with large macroaggregates (&gt;2000 μm), and soils from the restored site stored more C in small macroaggregates (≥250 to &lt;2000 μm). Despite these different associations, the chemical composition of SOM followed similar patterns across each aggregate‐size class. Results from the sequential extraction procedure suggest organo‐metal oxide complexes do not contribute to C stabilization in these habitats. This research is one of the few studies that have examined C stabilization related to soil structure in wetland soils. Our results suggest soil aggregate formation may be an important mechanism driving C stabilization, and that disruption to macroaggregates may limit C accumulation in restored wetlands. Additional empirical research and long‐term field monitoring are needed to confirm linkages between aggregate‐C stabilization and accumulation in wetland soils.

Effect of salinity on the decomposition of soil organic carbon in a tidal wetland

Climate warming and sea level rise have the potential to change the salt level of soil in tidal wetlands. And it is important to clarify the process and the mechanism of decomposition of soil organic carbon in a tidal wetland under varying salinities. The aim of this study was to evaluate the impacts of soil salinity on the decomposition rate of organic carbon (DROC) and dissolved organic carbon (DOC) in a tidal wetland. Two types of soil (surface soil in Suaeda salsa and bare tidal flat) were collected, air-dried, and homogenized. After adding different content of salt (0 g/L, 3 g/L, 6 g/L, 9 g/L, and 12 g/L), the soils were incubated for 28 days at stable room temperature (25 ± 2 °C) and added by deionized water to maintain the stability of soil moisture. The gases (CO2 and CH4) emission rates of each salt treatment were measured during 28-day incubation. DROC was determined by the sum of daily CO2-C emission rates and daily CH4-C emission rates in this study. Salt addition inhibited the process of gas emissions and DROC. Gases emission rates and DROC of two types of soil showed similar temporal trends, with distinctive drop in the beginning of experiment and no significant decrease followed. Significant difference of DOC among salt treatments was found in the bare tidal flat soil. Variations of partial correlation between DROC and soil salinity and DOC showed similar trends (e.g., in days 9–18, the positive effect of DOC on DROC was greatly promoted (R2 = 0.80, p < 0.001), and the negative effect of soil salinity was highly improved (R2 = 0.93, p < 0.001)). Soil properties, in particular DOC, may be primary factors accounting for the discrepancy of gases emission rates and DROC of two types of soil. Increased soil salinity had a negative effect on DROC during 28-day incubation. The impact of soil salinity and DOC on DROC were varied in different phases of laboratory experiment (soil salinity generally had increasingly negative relationship with DROC, but DOC showed most significantly positive relationship in the middle stage of incubation). Both the formation and consumption of DOC may be valuable for more detail research regarding to decomposition of soil organic carbon.

Predicting landscape effects of Mississippi River diversions on soil organic carbon sequestration

AbstractLarge Mississippi River (MR) diversions (peak water flow &gt;1416 m3/s and sediment loads &gt;165 kg/s) have been proposed as part of a suite of coastal restoration projects and are expected to rehabilitate and rebuild wetlands to alleviate the significant historic wetland loss in coastal Louisiana. These coastal wetlands are undergoing increasing eustatic sea‐level rise, land subsidence, climate change, and anthropogenic disturbances. However, the effect of MR diversions on wetland soil organic carbon (SOC) sequestration in receiving basins remains unknown. The rate of SOC sequestration or carbon burial in wetlands is one of the variables used to assess the role of wetland soils in carbon cycling and also to construct wetland carbon budgets. In this study, we examined the effects of MR water and sediment diversions on landscape‐scale SOC sequestration rates that were estimated from vertical accretion for the next 50 yr (2010–2060) under two environmental (moderate and less optimistic) scenarios. Our analyses were based on model simulations taken from the Wetland Morphology model developed for Louisiana's 2012 Coastal Master Plan. The master plan modeled a “future‐without‐action” scenario as well as eight individual MR diversion projects in two of the hydrologic basins (Barataria and Breton Sound). We examined the effects that discharge rates (peak flow) and locations of these individual diversion projects had on SOC sequestration rates. Modeling results indicate that large river diversions are capable of improving basin‐wide SOC sequestration capacity (162–222 g C·m−2·yr−1) by up to 14% (30 g C·m−2·yr−1) in Louisiana deltaic wetlands compared to the future‐without‐action scenario, especially under the less optimistic scenario. When large river diversions are placed in the upper receiving basin, SOC sequestration rates are 3.7–10.5% higher (6–24 g C·m−2·yr−1) than when these structures are placed in the lower receiving basin. Modeling results also indicate that both diversion discharge and location have large effects on SOC sequestration in low‐salinity (freshwater and intermediate marshes) as compared to high‐salinity marshes (brackish and saline marshes).

Soil organic carbon variability in Australian temperate freshwater wetlands

AbstractGlobally, 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.

Can Soil Organic Carbon Fractions Be Used as Functional Indicators of Wetlands?

This work aimed to determine whether the organic carbon in wetland soils correlated with physico-chemical characteristics of wetlands (e.g. nutrient content, pH) and differentiated wetlands accordi ...

Iron-mediated soil carbon response to water-table decline in an alpine wetland

The tremendous reservoir of soil organic carbon (SOC) in wetlands is being threatened by water-table decline (WTD) globally. However, the SOC response to WTD remains highly uncertain. Here we examine the under-investigated role of iron (Fe) in mediating soil enzyme activity and lignin stabilization in a mesocosm WTD experiment in an alpine wetland. In contrast to the classic ‘enzyme latch’ theory, phenol oxidative activity is mainly controlled by ferrous iron [Fe(II)] and declines with WTD, leading to an accumulation of dissolvable aromatics and a reduced activity of hydrolytic enzyme. Furthermore, using dithionite to remove Fe oxides, we observe a significant increase of Fe-protected lignin phenols in the air-exposed soils. Fe oxidation hence acts as an ‘iron gate’ against the ‘enzyme latch’ in regulating wetland SOC dynamics under oxygen exposure. This newly recognized mechanism may be key to predicting wetland soil carbon storage with intensified WTD in a changing climate.

Distribution and storage of soil organic carbon in a coastal wetland under the pressure of human activities

Purpose Soil organic carbon (SOC) stock is one of the most important carbon reservoirs on the earth and plays a vital role in the global climate change. However, research on the carbon sequestration and storage of coastal wetland soil is very scarce. Therefore, a study in the coastal wetland was conducted to investigate the SOC distribution, storage, and variation under the influence of human activities.

Spatial distribution of soil organic carbon in the Zoige alpine wetland, northeastern Qinghai–Tibet Plateau

Regional-scale soil organic carbon (SOC) field investigations would significantly improve our understanding of national and global SOC sequestration and carbon (C) cycles. The Zoige wetland is the world's largest high-altitude wetland. It is located in northeastern Qinghai–Tibet Plateau. Although considered sensitive to global climate change, little is known of its wetland SOC stocks and spatial distribution patterns. Accordingly, we investigated SOC stocks and spatial distribution patterns in the uppermost 1m soil layer in Ruoergai and Hongyuan counties in the Zoige wetland. We found that SOC decreased with increasing soil depth, which was highest in the topmost 0.3m soil layer. Total nitrogen and water content were positively correlated to SOC content while bulk density was negatively correlated to SOC content in both wetland and grassland areas. Wetlands had a higher SOC density than grassland. In the uppermost 1m of wetland soil, average SOC density was 69.5kgCm−3, greater by a factor of three compared to mean wetland SOC density in China and greater by a factor of six compared to the national average. SOC stock in the uppermost 1m of wetland soils totaled 514Tg C, of which 50% was stored in the topmost 0.3m. This indicated that the two counties in the Zoige wetland stores from 8.3 to 10.2% of the total SOC in China in the topmost 1m of wetland soils. This vast SOC pool and high SOC density requires sound land use practices to sustain and protect Zoige wetland ecosystem services and C stocks.