Variability Of Organic Carbon Stocks Research Articles

Estimation of Carbon Stocks in Soils of Forest Ecosystems as a Basis for Monitoring Climatically Active Substances

The eluvozems and soddy eluvozems on two-layer deposits dominating in the soil cover of the Zvenigorod biostation of Moscow State University contain, on average, 65–83 t/ha of organic carbon in the litter and a meter-deep layer of mineral strata. Carbon stocks are minimal in the soddy eluvozem of the complex spruce forest (59–68 t/ha), which is characterized by a lighter granulometric composition, and reach 76–92 t/ha in the soils of the birch–spruce and complex pine–spruce forests. At the same time, 3.3–5.8 t C/ha or 4–9% of the total organic carbon reserves are concentrated in the litter, and 64–69% in the upper mineral layer (0–20 cm). Different levels and profile distribution of organic carbon reserves in soils are determined by lithological and granulometric features and the nature of vegetation. The contribution of water-extractable organic carbon compounds to their total content in the upper mineral horizons of soils does not exceed 1.3–1.8%, microbial carbon, 1.7–2.4%. In acidic light loamy soils, the enrichment in calcium and potassium, the cation exchange capacity, the content of exchangeable bases, and the degree of saturation can serve as indicators of the content and reserves of organic carbon at the ecosystem level. The relationship with the content of finely dispersed fractions and oxalate-extractable Al and Fe is manifested to a lesser extent due to the similar origin and properties of soils. The variability of organic carbon stocks in soils is determined to the greatest extent by its content, the influence of which decreases with depth. Accounting for spatial heterogeneity, field measurements of the density and proportion of fine earth, and correct analytical determinations are essential components of the assessment of carbon stocks in soils of forest ecosystems as part of a national monitoring system for carbon pools and greenhouse gas fluxes under development.

Estimation of Carbon Stocks in Soils of Forest Ecosystems as a Basis for Monitoring the Climatically Active Substances

—The eluvozems and soddy eluvozems on two-layered deposits dominating in the soil cover of the Zvenigorod Biostation of Moscow State University, contain, on average, 65–83 t/ha of organic carbon in the organic layer and the upper meter of mineral strata. Carbon stock is minimal (59–68 t/ha) in the coarser-textured soddy eluvozem of the spruce forest and reaches 76–92 t/ha in soils of birch–spruce and pine–spruce forests. Organic layers store 3.3–5.8 t C/ha or 4–9% of the total soil organic carbon stock; the upper mineral layer (0–20 cm) stores 64–69%. Different levels and profile distribution of organic carbon in soils are determined by lithological and textural features of the soil profiles and by the nature of vegetation. The contribution of water-extractable organic carbon to the total organic carbon content in the upper mineral horizons does not exceed 1.3–1.8%; the contribution of microbial carbon is 1.7–2.4%. In acidic loamy soils, the enrichment in calcium and potassium, the cation exchange capacity, the content of exchangeable bases, and the degree of base saturation can serve as indicators of the content and stocks of organic carbon at the ecosystem level. The relationship with the content of clay fractions and oxalate-extractable Al and Fe is manifested to a lesser extent due to the similar origin and properties of soils. The variability of organic carbon stocks in soils is largely determined by its content, the influence of which decreases with depth. Accounting for spatial heterogeneity, field measurements of the soil bulk density and proportion of fine earth, and correct analytical determinations are essential components of the assessment of carbon stocks in soils of forest ecosystems as a part of the national monitoring system for carbon pools and greenhouse gas fluxes.

Combining management based indices with environmental parameters to explain regional variation in soil carbon under dryland cropping in South Australia

Identifying drivers of variation in soil organic carbon (OC) at a regional scale is often hampered by a lack of historical management information. Focusing on red-brown-earth soils (Chromosol) under dryland agriculture in the Mid-North and Eyre Peninsula of South Australia, our aims were 2-fold: (i) to provide a baseline of soil OC stocks (0.3 m) and OC fractions (mid-infrared predictions of particulate, humus, and resistant OC in 0.1 m samples) in cropping and crop-pasture systems; and (ii) to evaluate whether the inclusion of management-based indices could assist in explaining regional-level variation in OC stocks and fractions. Soil OC stocks in both regions varied ~20 Mg ha–1, with higher OC stocks in the Mid-North (38 Mg ha–1) than the Eyre Peninsula (29.1 Mg ha–1). The humus OC fraction was the dominant fraction, while the particulate OC was the most variable. Environmental variables only partially explained soil OC variability, with vapour pressure deficit (VPD) offering the greatest potential and likely acting as an integrator of temperature and moisture on plant growth and decomposition processes. Differences between broad-scale cropping and crop–pasture systems were limited. In the Mid-North, variability in soil OC stocks and fractions was high, and could not be explained by environmental or management variables. Higher soil OC concentrations (0.1 m) in the Eyre Peninsula cropping than crop–pasture soils were largely accounted for in the particulate OC fraction and are therefore unlikely to represent a long-term stable OC pool. Use of the management data in index format added some explanatory power to the variability in OC stocks over the main environmental variables (VPD, slope) within the Eyre Peninsula cropping soils only. In the wider context, the management data were useful in interpreting differences between regional findings and highlighted difficulties in using uninformed, broad-scale management categories.

Spatial variability in organic carbon stocks on level sites: Relation to vertical penetration of the A horizon

Understanding the source of spatial variability in soil organic carbon (SOC) stocks will contribute to improved sampling strategies to detect changes in stocks. Most of the variability in SOC stocks in cores collected from small (2 × 3 m) level plots on seven soils with similar cropping histories was related to variation in A horizon depth. Increased variability in horizon depth within plots coincided with the development of zones where the A horizon penetrated to greater depths. Consequently, accurate estimates of SOC stocks cannot be made from shallow measurements at the soil surface (e.g., 10 cm) and minimizing the spatial variability in locations of repeated sampling is necessary when characterizing changes in SOC stocks.Key words: Carbon sequestration, soil organic carbon, spatial variability, soil profile, A horizon

Effects of sampling design on the probability to detect soil carbon stock changes at the Swiss CarboEurope site Lägeren

Soil carbon stock changes are an important element in our attempt to understand and quantify the role of terrestrial carbon sinks. Unfortunately, the large spatial variability of organic carbon stocks in soils complicates their analytical quantification. At a heterogeneous forest site, we conducted a pilot study to estimate whether the choice of a suitable sampling design reduces the uncertainty of the stock estimate to an extent that permits the detection of carbon stock changes within a reasonable time period. Parent material had a strong effect on soil carbon stocks and stratified sampling of parent material classes reduced the error of the carbon stock estimate for the top 10 cm of the mineral soil from 3.1 to 1.7 t C ha − 1 . We estimated that replacing an unpaired sampling approach by a paired sampling approach could improve the detection limit of stock changes approximately by a factor of four. Despite these improvements, we estimate that about 15 years will be necessary to detect carbon stock changes in the top 10 cm if soil carbon sequestration occurs at the rate (0.43 t C ha − 1 a − 1 ) predicted by current carbon cycle models.

Small scale spatial variability of organic carbon stocks in litter and solum of a forested Luvisol

Soil organic carbon (OC) stocks are highly variable at the forest stand level. In order to analyse spatial variability at the stand scale, a study was conducted on a Luvisol developed from loess in Thuringia, Germany. At a 10,000 m 2 beech ( Fagus sylvatica L.) forest site, soil samples were taken at 54 points from the litter layer and the complete solum whose thickness varied between 0.24 m and 0.96 m. With a sampling scheme that incorporated a minimum horizontal sampling distance of 0.2 m, OC stocks in the litter layer and the solum were characterised by ordinary statistics and geostatistics. With respect to the vertical distribution of OC stocks, results showed that the OC stocks were 0.4 kg OC m − 2 in the litter layer, 3.0 kg OC m − 2 in the solum 0–0.12 m depth, and 4.5 kg OC m − 2 in the solum > 0.12 m depth. This highlighted the importance of subsoils in terrestrial carbon balances. No spatial pattern was observed in the litter layer, whereas semivariograms of OC stocks in the solum 0–0.12 m depth and the solum > 0.12 m depth exhibited a range of less than 5.4 m. The nugget variance accounted for around 20% of the sill in the solum 0–0.12 m depth and for over 40% of the sill in the solum > 0.12 m depth. These results emphasised the high small scale variability at the stand scale. Ordinary and spatial correlation indicated that the OC stocks are strongly affected by the thickness of the solum, whereas a relation between the distance to the nearest tree and the magnitude of OC stocks was not found. Considering the variability of the study area, the minimum detectable difference (MDD) of OC stocks for n = 9 was 0.3 kg OC m − 2 in the litter layer, 2.0 kg OC m − 2 in the solum 0–0.12 m depth, and 3.6 kg OC m − 2 in the solum > 0.12 m depth. At this site more than 300 samples would be required to detect a relative OC stock change of 10% in the solum.