Wetland Soil Organic Carbon Research Articles

Five-year changes in soil organic carbon and total nitrogen in coastal wetlands affected by flow-sediment regulation in a Chinese delta.

Changes in the sources and sinks of soil organic carbon (SOC) and total nitrogen (TN) in wetland soils as indicators of soil quality and climate change have received attention worldwide. Soil samples were collected in 2007 and 2012 in the coastal wetlands of the Yellow River Delta and the SOC and TN were determined to investigate a five-year change in their content and stock in these wetlands as affected by flow-sediment regulation. Our results revealed that the soils in 2007 exhibited greater electrical conductivities, SOC content and density, and ammonium nitrogen (NH4+-N) levels in the top 10 cm soils (p < 0.05) compared with the soils in 2012. In general, the SOC and TN contents decreased with increasing soil depth. However, the highest ratios of soil organic carbon and total nitrogen (molar C/N ratios) were observed in the 30–40 cm soil layer. A significant SOC loss occurred (p < 0.05) in top 10 cm soils, but only a small change in SOC in the top 50 cm soils. Comparatively, TN levels did not show significant differences in the study period.

Comparison of the quantitative determination of soil organic carbon in coastal wetlands containing reduced forms of Fe and S

The performance of the Walkley–Black wet oxidation chemical method for soil organic carbon (SOC) determination in coastal wetland soils (mangroves, coastal lagoons, and hypersaline tidal flats) was evaluated in the state of Ceara along the semiarid coast of Brazil, assessing pyrite oxidation and its effects on soil C stock (SCS) quantification. SOC determined by the chemical oxidation method (CWB) was compared to that assessed by means of a standard elemental analyzer (CEA) for surficial samples (<30 cm depth) from the three wetland settings. The pyrite fraction was quantified in various steps of the chemical oxidation method, evaluating the effects of pyrite oxidation. Regardless of the method used, and consistent with site-specific physicochemical conditions, higher pyrite and SOC contents were recorded in the mangroves, whereas lower values were found in the other settings. CWB values were higher than CEA values. Significant differences in SCS calculations based on CWB and CEA were recorded for the coastal lagoons and hypersaline tidal flats. Nevertheless, the CWB and CEA values were strongly correlated, indicating that the wet oxidation chemical method can be used in such settings. In contrast, the absence of correlation for the mangroves provides evidence of the inadequacy of this method for these soils. Air drying and oxidation decrease the pyrite content, with larger effects rooted in oxidation. Thus, the wet oxidation chemical method is not recommended for mangrove soils, but seems appropriate for SOC/SCS quantification in hypersaline tidal flat and coastal lagoon soils characterized by lower pyrite contents.

Soil recovery across a chronosequence of restored wetlands in the Florida Everglades.

The restoration project in the Hole-in-the-Donut of Everglades National Park in Florida, USA is to reestablish native wetlands by complete removal of the invasive plants and the associated soil. However, there is little information available about changes in properties of the newly formed Marl soils in restored wetlands. In this study, we measured soil physicochemical properties, soil enzymatic activities, and stable isotopes of carbon (δ13C) in plants and soil organic carbon (SOC) in an undisturbed natural wetland (UNW) and three wetlands restored respectively in 1989, 1996 and 1999 (WR89, WR96 and WR99). The older restored wetlands (WR89 and WR96) are characterized by greater SOC and mineral nitrogen. The values of soil dehydrogenase and phosphatase activities in the four wetlands follow the order: UNW > WR89 > WR96 > WR99, and are consistent with changes in vegetation coverage. The principal component analysis shows that dehydrogenase and phosphatase activities are the vital variables contributing to the soil of UNW. The similar δ13C values of SOC and plants in the restored wetlands suggest the formation of SOC during restoration is mainly derived from the associated plants. These results indicate that the newly restored soils develop toward the soil in the UNW with time since restoration.

What happens to soil organic carbon as coastal marsh ecosystems change in response to increasing salinity? An exploration using ramped pyrolysis

AbstractCoastal wetlands store vast amounts of organic carbon, globally, and are becoming increasingly vulnerable to the effects of anthropogenic sea level rise. To understand the effect of sea level rise on organic carbon fate and preservation in this global sink, it is necessary to characterize differences in the biogeochemical stability of coastal wetland soil organic carbon (SOC). Here we use ramped pyrolysis/oxidation decomposition characteristics as proxies for SOC stability to understand the fate of carbon storage in coastal wetlands comprising the Mississippi River deltaic plain, undergoing rapid rates of local sea level rise. Soils from three wetland types (fresh, brackish, and salt marshes) along a salinity gradient were subjected to ramped pyrolysis analysis to evaluate decomposition characteristics related to thermochemical stability of SOC. At equivalent soil depths, we observed that fresh marsh SOC was more stable than brackish and salt marsh SOC. Depth, isotopic, elemental, and chemical compositions, bulk density, and water content of SOC all exhibited different relationships with SOC stability across the marsh salinity gradient, indicative of different controls on SOC stability within each marsh type. The differences in stability imply stronger preservation potential of fresh marsh soil carbon, compared to that of salt and brackish marshes. Considering projected marsh ecosystem responses to sea level rise, these observed stability differences are important in planning and implementing coastal wetland carbon‐focused remediation and improving climate model feedbacks with the carbon cycle. Specifically, our results imply that ecosystem changes associated with sea level rise will initiate the accumulation of less stable carbon in coastal wetlands.

Distribution Characteristics of Soil Organic Carbon in Estuarine Wetland of Qingdao Dagu River

Distribution characteristics of content of soil organic carbon in wetland were studied by the analysis of four soil samples from areas, which were at different depths of soil, collected in the Dagu River estuary of Qingdao during summer of 2014. The result showed that the content of soil organic carbon in coastal wetland of Jiaozhou bay had an overall downward trend with the increase of soil depth. Because of the influence of hydro-salinity environment and tidal action, in regions near the sea, the content of soil organic carbon was less than its counterpart in regions away from the ocean.

Burning, biomass removal and tillage effects on soil organic carbon and nutrients in seasonal wetlands (Dambos) of Chiota smallholder farming area, Zimbabwe

Seasonal wetland (dambo) cultivation in smallholder farming areas is important because it improves household food security. However, most farming practices, such as burning of vegetation and conventional tillage in dambo gardens, may reduce soil organic carbon (SOC) and nutrient dynamics. We evaluated the effects of simulated burning, vegetation clearing and clipping, and conventional tillage in dambo gardens on SOC, nutrient contents and biomass production over a 3-year period. The results showed that clearing and clipping of vegetation and conventional tillage reduced SOC, soil nutrient contents and biomass yields, while burning increased SOC and soil nutrient contents. For the 0–10 cm depth, conventional tillage, clearing and clipping resulted in a 37%, 34% and 18% decrease in SOC, respectively, after three seasons, burning resulted in a 25% increase in SOC, while there were no changes in the control after 3 years. For the 0–40 cm depth, the average change in SOC was 32%, 25% and 16% for conventional tillage, clearing and clipping, respectively. Locally and regionally, conventional tillage, clearing and clipping reduce SOC, nutrient contents and biomass production in dambos. Though annual burning increased SOC and nutrient contents in the short term, the long-term effects are uncertain, hence there is a need for long-term studies.

The Accumulation and Seasonal Dynamic of the Soil Organic Carbon in Wetland of the Yellow River Estuary, China

The wetland of the Yellow River estuary is a typical new coastal wetland in northern China. It is essential to study the carbon pool and its variations for evaluating the carbon cycle process. The study results regarding the temporal-spatial distribution and influential factors of soil organic carbon in four typical wetlands belonging to the Yellow River estuary showed that there was no significant difference in the contents of the surface soil TOC to the same season among the four types of wetlands. For each type of wetlands, the TOC content in surface soils was significantly higher in October than that in both May and August. On the whole, the obvious differences in DOC contents in surface soils were not observed in the different wetland types and seasons. The peak of TOC appeared at 0–10 cm in the soil profiles. The contents of TOC and DOC were significantly higher in salsa than those in reed, suggesting that the rhizosphere effect of organic carbon in salsa was more obvious than that in reed. The results of the principal component analysis showed that the nitrogen content, salinity, bulk density, and water content were dominant influential factors for organic carbon accumulation and seasonal variation.

Spatiotemporal Distribution Characteristics of Soil Organic Carbon in Newborn Coastal Wetlands of the Yellow River Delta Estuary

The distribution and seasonal variation of soil organic carbon (SOC) in newborn coastal wetland of the Yellow River Delta (YRD) estuary at eastern China were studied based on monitoring data in 2009 at two transects from the bank of the Yellow River to the seaside. The results showed that SOC contents of 0–60 cm soil layer in transects ranged from 0.46 to 10.15 g kg−1 and average values of soil profiles ranged from 2.15 to 5.00 g kg−1. The SOC contents tended to increase from the river flood land to the salt beach, which could be accounted for the organic matters including large algae, the bodies and excretion of marine animals due to the feedback of tides. The significant difference of SOC contents at different vegetation communities was observed, while the difference of SOC in soil profiles was not obvious. The SOC contents in 0–30 cm soil layers decreased with plant growth period, while in 40–60 cm soil layers were relatively stable. The mean soil organic carbon density was 3.05 kg C m−2 in study region, which was much lower than that reported in other ecosystems, and its spatiotemporal variations were consistent with that of SOC content. Further analysis revealed that SOC was positively correlated with total nitrogen and clay contents. Our findings indicated that the newborn coastal wetland in the YRD should be a potential sink of SOC.

Forecasting the Effects of Coastal Protection and Restoration Projects on Wetland Morphology in Coastal Louisiana under Multiple Environmental Uncertainty Scenarios

ABSTRACT Couvillion, B.R.; Steyer, G.D.; Wang, H.; Beck, H.J., and Rybczyk, J.M., 2013. Forecasting the effects of coastal protection and restoration projects on wetland morphology in coastal Louisiana under multiple environmental uncertainty scenarios. Few landscape scale models have assessed the effects of coastal protection and restoration projects on wetland morphology while taking into account important uncertainties in environmental factors such as sea-level rise (SLR) and subsidence. In support of Louisiana's 2012 Coastal Master Plan, we developed a spatially explicit wetland morphology model and coupled it with other predictive models. The model is capable of predicting effects of protection and restoration projects on wetland area, landscape configuration, surface elevation, and soil organic carbon (SOC) storage under multiple environmental uncertainty scenarios. These uncertainty scenarios included variability in parameters such as eustatic SLR (ESLR), subsidence rate, and Mississippi River disc...

Changes in labile soil organic carbon fractions in wetland ecosystems along a latitudinal gradient in Northeast China

article i nfo Wetlands in mid-high latitude regions play a vital role in climate change, due to their high organic carbon density. Nonetheless, the stabilization of soil organic carbon (SOC) and its fractions in these regions is largely unknown. The objectives of this study were to examine the changes in SOC and its fractions along a latitudinal gradient and to analyze the influencing factors in the southern margin of the permafrost region on the Eurasian continent. Topsoil (0-20 cm) was collected from five wetlands along a latitudinal gradient in Northeast China. We analyzed SOC and some labile fractions. Our results demonstrated that wetland SOC and its labile fractions concentration declined with decreasing latitude. The Permafrost regions had greater organic carbon content than the regions with seasonally frozen ground. The light fraction organic carbon and particulate organic carbon accounted for 5-83% and 21-32%, respectively, of the SOC and were particularly enriched in the permafrost region. Microbial biomass carbon and dissolved organic carbon showed a similar decreasing trend to that of SOC. At the same latitude, vegetation affected SOC stock and the dynamics of its labile fractions. Therefore, wetlands in mid-high latitudes contain a large carbon pool, and carbon stock varies with latitude. Although the labile fractions were higher in the permafrost region, their activities were lower, due to low temperature and poor nutrient status. Under global warming, the labile carbon pool may be mobilized and contribute to the greenhouse effect. Moreover, vegetation differences should be considered in obtaining an accurate carbon calculation.

Risk of Inundation to Coastal Wetlands and Soil Organic Carbon and Organic Nitrogen Accounting in Louisiana, USA

Exceeding 1.2 million acres (4856 km(2)) since the 1930s, coastal wetland loss has been the most threatening environmental problem in Louisiana, United States. This study utilized high-resolution LiDAR (Light Detection and Ranging) and DEM (Digital Elevation Model) data sets to assess the risk of potential wetland loss due to future sea level rises, their spatial distribution, and the associated loss of soil organic carbon (SOC) and organic nitrogen (SON) estimated from the State Soil Geographic (STATSGO) Database and National Wetlands Inventory (NWI) digital data. Potential inundation areas were divided into five elevation scales: < 0 cm, 0-50 cm, 50-100 cm, 100-150 cm, and 150-200 cm above mean sea level. The study found that southeastern Louisiana on the Mississippi River Delta, specifically the Pontchartrain and Barataria Basins, are most vulnerable to sea-level rise induced inundation. Accordingly, approximately 42,264,600 t of SOC and 2,817,640 t of SON would be inundated by 2050 using an average wetland SOC density (203 t per hectare) for the inundation areas between 0 and 50 cm. The estimated annual SOC and SON loss from Louisiana's coast is 17% of annual organic carbon and 6-8% of annual organic nitrogen inputs from the Mississippi River.

Freeze-thaw effects on sorption/desorption of dissolved organic carbon in wetland soils

The effects of freeze-thaw cycles on sorption/desorption of dissolved organic carbon (DOC) in two wetland soils and one reclaimed wetland soil were investigated. DOC concentrations added were 0–600 mg/L. Laboratory incubations of sorption/desorption of DOC had been carried out at −15C ° for 10 h, and then at +5°C for 13 h. Soil samples were refrozen and thawed subsequently for 5 cycles. Initial Mass model was used to describe sorption behavior of DOC. The results indicate that freeze-thaw cycles can significantly increase the sorption capacity of DOC and reduce the desorption capacity of DOC in the three soils. The freeze-thaw effects on desorption of DOC in soils increase with the increasing freeze-thaw cycles. The conversion of natural wetlands to soybean farmland can decrease the sorption capacity and increase the desorption capacity of DOC in soils. Global warming and reclamation may increase DOC release, and subsequently increase the loss of carbon and the emission of greenhouse gas.