Profile distribution of soil organic carbon fractions under different landforms in the Meghalaya plateau of India

Assessment of organic carbon fractions in soil provides the basis to ascertain vulnerability of an ecosystem to climate change. In the present study, we assessed SOC fractions in four pedons under contrasting landforms i.e., denudational low hill, upper plateau, lower plateau and valley in the Meghalaya plateau, India. Results indicated that soils of the studied pedons were acidic in nature, low in cation exchange capacity and base saturation. Further, surface (0-30 cm) soils were high in Walkley Black C (WBC) content (0.83-1.13%) in the studied pedons located under different landforms. The density of very labile carbon (VLC) fraction up to a depth of 150 cm was highest (49.22 Mg ha?1) in pedon 2 (P2) located in the upper plateau under shifting cultivation while that of less labile carbon (LLC) was highest (50.25 Mg ha?1) in pedon 4 (P4) in the valley under paddy cultivation. Higher densities of WBC and LLC in the valley (P4) as compared to other landforms in the study area indicate higher carbon sequestration potential of valley soil.

Response of Soil Active Organic Carbon and Enzyme Activity to Freeze-Thaw Cycle in Wetlands

Freeze-thaw cycles (FTCs) are an important element of mid and high latitude ecosystems, and significantly influence soil physicochemical properties and microbial activities in the soil active layers. With the global warming, the effects of FTCs on the dissolved organic carbon (DOC) concentration and soil enzyme activity of different types of soil were still uncertain. In this study, soil of undisturbed Deyeuxia angustifolia wetland (UDAW), disturbed Deyeuxia angustifolia wetland (DDAW) and rice paddy field (RP) from three soil layers of (0–10, 10–20 and 20–30 cm) in Sanjiang Plain, Northeast China, were collected, and then subjected to various FTCs with a large (10 to -10℃) and a small (5 to -5℃) amplitudes, respectively. The results indicated that FTCs increased the soil DOC concentration but reduced the concentration of MBC and activities of cellulase, invertase and catalase. Increase in the freeze-thaw frequency, resulted in the DOC concentration increasing initially and then decreasing, and the MBC concentration and soil enzyme activities were opposite. The DOC concentration increment resulting from the freeze-thaw effects was different across different layers and soil type: as the soil depth increased, the average DOC increments decreased, and the average DOC increments varied across different soil types: UDAW > DDAW > RP. The average MBC concentration and soil enzyme activity decreased from 0-10 cm > 10-20 cm > 20-30 cm soil depth; MBC concentration and soil enzyme activities varied across the different soil types: UDAW > DDAW > RP. The freeze-thaw amplitude and soil moisture content interaction had an effect on soil active organic carbon fractions and enzymatic activity. Small amplitude FTCs and higher water content had the greatest effect on DOC concentration, while larger amplitude and higher water content had the greatest effect on MBC concentration and enzymatic activity. In wetland soil, the significant correlations between active organic carbon fractions and enzyme activities indicate that the increased DOC by FTCs plays an important role in soil microbes and enzyme activities. However, active organic carbon fractions and enzyme activities had little correlation in RP, indicating that FTCs has more influence on wetland than farmland.

Application of Inductively Coupled Plasma Spectrometric Techniques and Multivariate Statistical Analysis in the Hydrogeochemical Profiling of Caves—Case Study Cloșani, Romania

The aim of the study was to develop the hydrogeochemical profiling of caves based on the elemental composition of water and silty soil samples and a multivariate statistical analysis. Major and trace elements, including rare earths, were determined in the water and soil samples. The general characteristics of water, anions content, inorganic and organic carbon fractions and nitrogen species (NO3− and NH4+) were also considered. The ANOVA—principal component analysis (PCA) and two-way joining analysis were applied on samples collected from Cloșani Cave, Romania. The ANOVA-PCA revealed that the hydrogeochemical characteristics of Ca2+-HCO3− water facies were described by five factors, the strongest being associated with water-carbonate rock interactions and the occurrence of Ca, Mg and HCO3− (43.4%). Although organic carbon fractions have a lower influence (20.1%) than inorganic ones on water characteristics, they are involved in the chemical processes of nitrogen and of the elements involved in redox processes (Fe, Mn, Cr and Sn). The seasonal variability of water characteristics, especially during the spring, was observed. The variability of silty soil samples was described by four principal components, the strongest influence being attributed to rare earth elements (52.2%). The ANOVA-PCA provided deeper information compared to Gibbs and Piper diagrams and the correlation analysis.