Phytomass and soil carbon storage of different land cover classes in the Usa river basin

This study describes detailed partitioning of phytomass carbon (C) and soil organic carbon (SOC) for four study areas in discontinuous permafrost terrain, Northeast European Russia. The mean aboveground phytomass C storage is 0.7 kg C/m**2. Estimated landscape SOC storage in the four areas varies between 34.5 and 47.0 kg C/m**2 with LCC (land cover classification) upscaling and 32.5-49.0 kg C/m**2 with soil map upscaling. A nested upscaling approach using a Landsat thematic mapper land cover classification for the surrounding region provides estimates within 5 ± 5% of the local high-resolution estimates. Permafrost peat plateaus hold the majority of total and frozen SOC, especially in the more southern study areas. Burying of SOC through cryoturbation of O- or A-horizons contributes between 1% and 16% (mean 5%) of total landscape SOC. The effect of active layer deepening and thermokarst expansion on SOC remobilization is modeled for one of the four areas. The active layer thickness dynamics from 1980 to 2099 is modeled using a transient spatially distributed permafrost model and lateral expansion of peat plateau thermokarst lakes is simulated using geographic information system analyses. Active layer deepening is expected to increase the proportion of SOC affected by seasonal thawing from 29% to 58%. A lateral expansion of 30 m would increase the amount of SOC stored in thermokarst lakes/fens from 2% to 22% of all SOC. By the end of this century, active layer deepening will likely affect more SOC than thermokarst expansion, but the SOC stores vulnerable to thermokarst are less decomposed.

Spatial distribution of the soil carbon pool in a Holm oak dehesa in Spain

Aims Dehesas are agroforestry systems characterized by scattered trees among pastures, crops and/or fallows. A study at a Spanish dehesa has been carried out to estimate the spatial distribution of the soil organic carbon stock and to assess the influence of the tree cover. Methods The soil organic carbon stock was estimated from the five uppermost cm of themineral soil with high spatial resolution at two plots with different grazing intensities. The Universal Kriging technique was used to assess the spatial distribution of the soil organic carbon stocks, using tree coverage within a buffering area as an auxiliary variable. Results A significant positive correlation between tree presence and soil organic carbon stocks up to distances of around 8 m from the trees was found. The tree crown cover within a buffer up to a distance similar to the crown radius around the point absorbed 30 % of the variance in the model for both grazing intensities, but residual variance showed stronger spatial autocorrelation under regular grazing conditions. Conclusions Tree cover increases soil organic carbon stocks, and can be satisfactorily estimated by means of crown parameters. However, other factors are involved in the spatial pattern of the soil organic carbon distribution. Livestock plays an interactive role together with tree presence in soil organic carbon distribution.

Initializing the DSSAT-Century model: inverse calibration of carbon pools from apparent soil N mineralization

The CENTURY soil organic matter model was adapted for the DSSAT (Decision Support System for Agrotechnology Transfer), modular format in order to better simulate the dynamics of soil organic nutrient processes (Gijsman et al., 2002). The CENTURY model divides the soil organic carbon (SOC) into three hypothetical pools: microbial or active material (SOC1), intermediate (SOC2) and the largely inert and stable material (SOC3) (Jones et al., 2003). At the beginning of the simulation, CENTURY model needs a value of SOC3 per soil layer which can be estimated by the model (based on soil texture and management history) or given as an input. Then, the model assigns about 5% and 95% of the remaining SOC to SOC1 and SOC2, respectively. The model performance when simulating SOC and nitrogen (N) dynamics strongly depends on the initialization process. The common methods (e.g. Basso et al., 2011) to initialize SOC pools deal mostly with carbon (C) mineralization processes and less with N. Dynamics of SOM, SOC, and soil organic N are linked in the CENTURY-DSSAT model through the C/N ratio of decomposing material that determines either mineralization or immobilization of N (Gijsman et al., 2002). The aim of this study was to evaluate an alternative method to initialize the SOC pools in the DSSAT-CENTURY model from apparent soil N mineralization (Napmin) field measurements by using automatic inverse calibration (simulated annealing). The results were compared with the ones obtained by the iterative initialization procedure developed by Basso et al., 2011.

Redistribution of Soil Organic Matter by Permafrost Disturbance in the Canadian High Arctic

With increased warming in the Arctic, permafrost thaw may induce localized physical disturbance of slopes. These disturbances, referred to as active layer detachments (ALDs), redistribute soil across the landscape, potentially releasing previously unavailable carbon (C). In 2007–2008, widespread ALD activity was reported at the Cape Bounty Arctic Watershed Observatory in Nunavut, Canada. Our study investigated organic matter (OM) composition in soil profiles from ALD-impacted and undisturbed areas. Solid-state 13C nuclear magnetic resonance (NMR) and solvent-extractable biomarkers were used to characterize soil OM. Throughout the disturbed upslope profile, where surface soils and vegetation had been removed, NMR revealed low O-alkyl C content and biomarker analysis revealed low concentrations of solvent-extractable compounds suggesting enhanced erosion of labile-rich OM by the ALD. In the disturbed downslope region, vegetation remained intact but displaced material from upslope produced lateral compression ridges at the surface. High O-alkyl content in the surface horizon was consistent with enrichment of carbohydrates and peptides, but low concentrations of labile biomarkers (i.e., sugars) suggested the presence of relatively unaltered labile-rich OM. Decreased O-alkyl content and biomarker concentrations below the surface contrasted with the undisturbed profile and may indicate the loss of well-established pre-ALD surface drainage with compression ridge formation. However, pre-ALD profile composition remains unknown and the observed decreases may result from nominal pre-ALD OM inputs. These results are the first to establish OM composition in ALD-impacted soil profiles, suggesting reallocation of permafrost-derived soil C to areas where degradation or erosion may contribute to increased C losses from disturbed Arctic soils.

Soil carbon dynamics in primary and secondary tropical forests in Colombia

Soils play a central role in the dynamics of biospheric carbon and in climate change. They contain the largest carbon stock of terrestrial ecosystems and return to the atmosphere a significant proportion of carbon fixed by photosynthesis. Soils of tropical forests are tremendously important in the carbon cycle because they receive the largest organic matter inputs, they have the largest respiration rates, and they are among the largest carbon reservoirs among world soils. This research assesses the main components of the soil carbon dynamics in primary (PF) and secondary (SF) tropical forests in Colombia. I evaluated the production, stocks, and decomposition rates of aboveground detritus as well as the stocks, growth, mortality, and decomposition of fine roots in these two forest types. Soil carbon outputs were evaluated as total soil, heterotrophic, and root respiration. The stocks of soil organic carbon down to 4 m deep in these two cover types and in degraded pastures (PAS) were also evaluated. ^ Soil inputs of organic carbon from above and belowground sources were lower in SF than in PF. Litterfall in SF was 58% and production of fine root detritus was 60% of that in PF. When production of woody detritus and palm fronds was considered, the difference between these forest types was even larger. However, outputs of mineral carbon through heterotrophic soil respiration were similar; in SF they equaled 97% of those in PF. As a result, soil carbon balance was positive in PF and negative in SF. Despite that soil carbon balances suggest that soils of SF are losing carbon, soil carbon stocks of SF were higher than of degraded pastures, suggesting that they have already started to recover soil carbon stocks lost under degraded pastures. This discrepancy can be partially explained by the effect of drier conditions on heterotrophic soil respiration as a consequence of a moderate El Niño event during the period of soil respiration measurements. The positive carbon balance in soils of PF despite the El Niño event, suggests that soils of PF accumulated about 664 Kg C ha−1 yr−1. Therefore, soil carbon dynamics mainly depended on successional status of vegetation and on climatic conditions. ^

Flux of organic carbon in a riverine mangrove wetland in the Florida Coastal Everglades

Short-term (daily) and seasonal variations in concentration and flux of dissolved organic carbon (DOC) were examined over 15 tidal cycles in a riverine mangrove wetland along Shark River, Florida in 2003. Due to the influence of seasonal rainfall and wind patterns on Shark River’s hydrology, samplings were made to include wet, dry and transitional (Norte) seasons. We used a flume extending from a tidal creek to a basin forest to measure vertical (vegetated soil/water column) and horizontal (mangrove forest/tidal creek) flux of DOC. We found significant (p < 0.05) variations in surface water temperature, salinity, conductivity, pH and mean concentration of DOC with season. Water temperature and salinity followed seasonal patterns of air temperature and rainfall, while mean DOC concentration was highest during the dry season (May), followed by the wet (October) and ‘Norte’ (December) seasons. This pattern of DOC concentration may be due to a combination of litter production and inundation pattern of the wetland. In contrast to daily (between tides) variation in DOC flux between the mangrove forest and tidal creek, daily variations of mean water quality were not significant. However, within-tide variation of DOC flux, dissolved oxygen content and salinity was observed. This indicated that the length of inundation and water source (freshwater vs. saltwater) variation across tidal cycles influenced water quality and DOC flux in the water column. Net DOC export was measured in October and December, suggesting the mangrove forest was a source of DOC to the adjacent tidal creek during these periods. Net annual export of DOC from the fringe mangrove to both the tidal creek and basin mangrove forest was 56 g C m−2 year−1. The seasonal pattern in our flux results indicates that DOC flux from this mangrove forest may be governed by both freshwater discharge and tidal range.

Effects of Land Use on Sources and Ages of Inorganic and Organic Carbon in Temperate Headwater Streams

The amounts, sources and relative ages of inorganic and organic carbon pools were assessed in eight headwater streams draining watersheds dominated by either forest, pasture, cropland or urban development in the lower Chesapeake Bay region (Virginia, USA). Streams were sampled at baseflow conditions six different times over 1 year. The sources and ages of the carbon pools were characterized by isotopic (δ13C and ∆14C) analyses and excitation emission matrix fluorescence with parallel factor analysis (EEM–PARAFAC). The findings from this study showed that human land use may alter aquatic carbon cycling in three primary ways. First, human land use affects the sources and ages of DIC by controlling different rates of weathering and erosion. Relative to dissolved inorganic carbon (DIC) in forested streams which originated primarily from respiration of young, 14C-enriched organic matter (OM; δ13C = −22.2 ± 3 ‰; ∆14C = 69 ± 14 ‰), DIC in urbanized streams was influenced more by sedimentary carbonate weathering (δ13C = −12.4 ± 1 ‰; ∆14C = −270 ± 37 ‰) and one of pasture streams showed a greater influence from young soil carbonates (δ13C = −5.7 ± 2.5 ‰; ∆14C = 69 ‰). Second, human land use alters the proportions of terrestrial versus autochthonous/microbial sources of stream water OM. Fluorescence properties of dissolved OM (DOM) and the C:N of particulate OM (POM) suggested that streams draining human-altered watersheds contained greater relative contributions of DOM and POM from autochthonous/microbial sources than forested streams. Third, human land uses can mobilize geologically aged inorganic carbon and enable its participation in contemporary carbon cycling. Aged DOM (∆14C = −248 to −202 ‰, equivalent14C ages of 1,811–2,284 years BP) and POM (∆14C = −90 to −88 ‰, 14C ages of 669–887 years BP) were observed exclusively in urbanized streams, presumably a result of autotrophic fixation of aged DIC (−297 to −244 ‰, 14C age = 2,251–2,833 years BP) from sedimentary shell dissolution and perhaps also watershed export of fossil fuel carbon. This study demonstrates that human land use may have significant impacts on the amounts, sources, ages and cycling of carbon in headwater streams and their associated watersheds.

The Effect of Nutrient-Rich Effluents from Shrimp Farming on Mangrove Soil Carbon Storage and Geochemistry Under Semi-Arid Climate Conditions in Northern Brazil

A semi-arid mangrove estuary system in the northeast Brazilian coast (Ceará state) was selected for this study to (i) evaluate the impact of shrimp farm nutrient-rich wastewater effluents on the soil geochemistry and organic carbon (OC) storage and (ii) estimate the total amount of OC stored in mangrove soils (0–40 cm). Wastewater-affected mangrove forests were referred to as WAM and undisturbed areas as Non-WAM. Redox conditions and OC content were statistically correlated (P < 0.05) with seasonality and type of land use (WAM vs. Non-WAM). Eh values were from anoxic to oxic conditions in the wet season (from − 5 to 68 mV in WAM and from < 40 to > 400 mV in Non-WAM soils) and significantly higher (from 66 to 411 mV) in the dry season (P < 0.01). OC contents (0–40 cm soil depth) were significantly higher (P < 0.01) in the wet season than the dry season, and higher in Non-WAM soils than in WAM soils (values of 8.1 and 6.7 kg m− 2 in the wet and dry seasons, respectively, for Non-WAM, and values of 3.8 and 2.9 kg m− 2 in the wet and dry seasons, respectively, for WAM soils; P < 0.01). Iron partitioning was significantly dependent (P < 0.05) on type of land use, with a smaller degree of pyritization and lower Fe-pyrite presence in WAM soils compared to Non-WAM soils. Basal respiration of soil sediments was significantly influenced (P < 0.01) by type of land use with highest CO2 flux rates measured in the WAM soils (mean values of 0.20 mg CO2 h− 1–g− 1 C vs. 0.04 mg CO2 h− 1–g− 1 C). The OC storage reduction in WAM soils was potentially caused (i) by an increase in microbial activity induced by loading of nutrient-rich effluents and (ii) by an increase of strong electron acceptors [e.g., NO3−] that promote a decrease in pyrite concentration and hence a reduction in soil OC burial. The current estimated OC stored in mangrove soils (0–40 cm) in the state of Ceará is approximately 1 million t.

Radiocarbon dating, carbon storage and soil properties of samples from Tulemalu Lake, central Canadian Arctic

We investigated total storage and landscape partitioning of soil organic carbon (SOC) in continuous permafrost terrain, central Canadian Arctic. The study is based on soil chemical analyses of pedons sampled to 1 m depth at 35 individual sites along three transects. Radiocarbon dating of cryoturbated soil pockets, basal peat and fossil wood shows that cryoturbation processes have been occurring since the Middle Holocene and that peat deposits started to accumulate in a forest-tundra environment where spruce was present (~6000 cal yrs BP). Detailed partitioning of SOC into surface organic horizons, cryoturbated soil pockets and non-cryoturbated mineral soil horizons is calculated (with storage in active layer and permafrost calculated separately) and explored using principal component analysis. The detailed partitioning and mean storage of SOC in the landscape are estimated from transect vegetation inventories and a land cover classification based on a Landsat satellite image. Mean SOC storage in the 0-100 cm depth interval is 33.8 kg C/m**2, of which 11.8 kg C/m**2 is in permafrost. Fifty-six per cent of the total SOC mass is stored in peatlands (mainly bogs), but cryoturbated soil pockets in Turbic Cryosols also contribute significantly (17%). Elemental C/N ratios indicate that this cryoturbated soil organic matter (SOM) decomposes more slowly than SOM in surface O-horizons.

Redistribution of Soil Organic Matter by Permafrost Disturbance in the Canadian High Arctic

With increased warming in the Arctic, permafrost thaw may induce localized physical disturbance of slopes. These disturbances, referred to as active layer detachments (ALDs), redistribute soil across the landscape, potentially releasing previously unavailable carbon (C). In 2007–2008, widespread ALD activity was reported at the Cape Bounty Arctic Watershed Observatory in Nunavut, Canada. Our study investigated organic matter (OM) composition in soil profiles from ALD-impacted and undisturbed areas. Solid-state 13C nuclear magnetic resonance (NMR) and solvent-extractable biomarkers were used to characterize soil OM. Throughout the disturbed upslope profile, where surface soils and vegetation had been removed, NMR revealed low O-alkyl C content and biomarker analysis revealed low concentrations of solvent-extractable compounds suggesting enhanced erosion of labile-rich OM by the ALD. In the disturbed downslope region, vegetation remained intact but displaced material from upslope produced lateral compression ridges at the surface. High O-alkyl content in the surface horizon was consistent with enrichment of carbohydrates and peptides, but low concentrations of labile biomarkers (i.e., sugars) suggested the presence of relatively unaltered labile-rich OM. Decreased O-alkyl content and biomarker concentrations below the surface contrasted with the undisturbed profile and may indicate the loss of well-established pre-ALD surface drainage with compression ridge formation. However, pre-ALD profile composition remains unknown and the observed decreases may result from nominal pre-ALD OM inputs. These results are the first to establish OM composition in ALD-impacted soil profiles, suggesting reallocation of permafrost-derived soil C to areas where degradation or erosion may contribute to increased C losses from disturbed Arctic soils.

Effects of Soil Organic Matter Properties and Microbial Community Composition on Enzyme Activities in Cryoturbated Arctic Soils

Enzyme-mediated decomposition of soil organic matter (SOM) is controlled, amongst other factors, by organic matter properties and by the microbial decomposer community present. Since microbial community composition and SOM properties are often interrelated and both change with soil depth, the drivers of enzymatic decomposition are hard to dissect. We investigated soils from three regions in the Siberian Arctic, where carbon rich topsoil material has been incorporated into the subsoil (cryoturbation). We took advantage of this subduction to test if SOM properties shape microbial community composition, and to identify controls of both on enzyme activities. We found that microbial community composition (estimated by phospholipid fatty acid analysis), was similar in cryoturbated material and in surrounding subsoil, although carbon and nitrogen contents were similar in cryoturbated material and topsoils. This suggests that the microbial community in cryoturbated material was not well adapted to SOM properties. We also measured three potential enzyme activities (cellobiohydrolase, leucine-amino-peptidase and phenoloxidase) and used structural equation models (SEMs) to identify direct and indirect drivers of the three enzyme activities. The models included microbial community composition, carbon and nitrogen contents, clay content, water content, and pH. Models for regular horizons, excluding cryoturbated material, showed that all enzyme activities were mainly controlled by carbon or nitrogen. Microbial community composition had no effect. In contrast, models for cryoturbated material showed that enzyme activities were also related to microbial community composition. The additional control of microbial community composition could have restrained enzyme activities and furthermore decomposition in general. The functional decoupling of SOM properties and microbial community composition might thus be one of the reasons for low decomposition rates and the persistence of 400 Gt carbon stored in cryoturbated material.

The influence of organic amendments on soil aggregate stability from semiarid sites

Restoring the native vegetation is the most effective way to regenerate soil health. Under these conditions, vegetation cover in areas having degraded soils may be better sustained if the soil is amended with an external source of organic matter. The addition of organic materials to soils also increases infiltration rates and reduces erosion rates; these factors contribute to an available water increment and a successful and sustainable land management. The goal of this study was to analyze the effect of various organic amendments on the aggregate stability of soils in afforested plots. An experimental paired-plot layout was established in southern of Spain (homogeneous slope gradient: 7.5%; aspect: N170). Five amendments were applied in an experimental set of plots: straw mulching; mulch with chipped branches of Aleppo Pine (Pinus halepensis L.); TerraCotten hydroabsobent polymers; sewage sludge; sheep manure and control. Plots were afforested following the same spatial pattern, and amendments were mixed with the soil at the rate 10 Mg ha-1. The vegetation was planted in a grid pattern with 0.5 m between plants in each plot. During the afforestation process the soil was tilled to 25 cm depth from the surface. Soil from the afforested plots was sampled in: i) 6 months post-afforestation; ii) 12 months post-afforestation; iii) 18 months post-afforestation; and iv) 24 months post-afforestation. The sampling strategy for each plot involved collection of 4 disturbed soil samples taken from the surface (0–10 cm depth). The stability of aggregates was measured by wet-sieving. Regarding to soil aggregate stability, the percentage of stable aggregates has increased slightly in all the treatments in relation to control. Specifically, the differences were recorded in the fraction of macroaggregates (≥ 0.250 mm). The largest increases have been associated with straw mulch, pinus mulch and sludge. Similar results have been registered for the soil organic carbon content. Independent of the soil management, after six months, no significant differences in microaggregates were found regarding to the control plots. These results showed an increase in the stability of the macroaggregates when soil is amended with sludge, pinus mulch and straw much. This fact has been due to an increase in the number cementing agents due to: (i) the application of pinus, straw and sludge had resulted in the release of carbohydrates to the soil; and thus (ii) it has favored the development of a protective vegetation cover, which has increased the number of roots in the soil and the organic contribution to it.

Potential mitigation of midwest grass-finished beef production emissions with soil carbon sequestration in the United States of America

Beef production can be environmentally detrimental due in large part to associated enteric methane (CH4) production, which contributes to climate change. However, beef production in well-managed grazing systems can aid in soil carbon sequestration (SCS), which is often ignored when assessing beef production impacts on climate change. To estimate the carbon footprint and climate change mitigation potential of upper Midwest grass-finished beef production systems, we conducted a partial life cycle assessment (LCA) comparing two grazing management strategies: 1) a non-irrigated, lightly-stocked (1.0 AU/ha), high-density (100,000 kg LW/ha) system (MOB) and 2) an irrigated, heavily-stocked (2.5 AU/ha), low-density (30,000 kg LW/ha) system (IRG). In each system, April-born steers were weaned in November, winter-backgrounded for 6 months and grazed until their endpoint the following November, with average slaughter age of 19 months and a 295 kg hot carcass weight. As the basis for the LCA, we used two years of data from Lake City Research Center, Lake City, MI. We included greenhouse gas (GHG) emissions associated with enteric CH4, soil N2O and CH4 fluxes, alfalfa and mineral supplementation, and farm energy use. We also generated results from the LCA using the enteric emissions equations of the Intergovernmental Panel on Climate Change (IPCC). We evaluated a range of potential rates of soil carbon (C) loss or gain of up to 3 Mg C ha-1 yr-1. Enteric CH4 had the largest impact on total emissions, but this varied by grazing system. Enteric CH4 composed 62 and 66% of emissions for IRG and MOB, respectively, on a land basis. Both MOB and IRG were net GHG sources when SCS was not considered. Our partial LCA indicated that when SCS potential was included, each grazing strategy could be an overall sink. Sensitivity analyses indicated that soil in the MOB and IRG systems would need to sequester 1 and 2 Mg C ha-1 yr-1 for a net zero GHG footprint, respectively. IPCC model estimates for enteric CH4 were similar to field estimates for the MOB system, but were higher for the IRG system, suggesting that 0.62 Mg C ha-1 yr-1 greater SCS would be needed to offset the animal emissions in this case.