Soil carbon and nitrogen are essential factors for agricultural production and climate changes. A total of 106 soil samples from three agricultural lands (including two rice fields and one sugarcane field) and four non-agricultural lands (including two forest lands, one wasteland and one built-up land) in the Mun River Basin were collected to determine soil carbon, nitrogen, soil pH, soil particle sizes and explore the influence of pH and soil texture on soil C and N. The results show that total organic carbon (TOC) and nitrogen (TON) contents in topsoil (TOC: 2.78 ~ 18.83 g kg−1; TON: 0.48 ~ 2.05 g kg−1) are much higher than those in deep soil (TOC: 0.35 ~ 6.08 g kg−1; TON: <0.99 g kg−1). In topsoil, their contents of forest lands and croplands (TOC: average 15.37 g kg−1; TON: average 1.29 g kg−1) are higher than those of other land uses (TOC: average 5.28 g kg−1; TON: average 0.38 g kg−1). The pH values range from 4.2 to 6.1 in topsoil, and with increase in soil depth, they tend to increase and then decrease. Soil carbon, nitrogen and the C/N (TC/TN ratio) are negatively correlated with soil pH, demonstrating that relatively low pH benefits the accumulation of organic matter. Most soil samples are considered as sandy loam and silt loam from the percentages of clay, silt and sand. For soil profiles below 50 cm, the TOC and TON average contents of soil samples which contain more clay and silt are higher than those of other soil samples.

The profile distributions of soil organic carbon (SOC), soil organic nitrogen (SON), soil pH and soil texture were rarely investigated in the Lancangjiang River Basin. This study aims to present the vertical distributions of these soil properties and provide some insights about how they interact with each other in the two typical soil profiles. A total of 56 soil samples were collected from two soil profiles (LCJ S-1, LCJ S-2) in the Lancangjiang River Basin to analyze the profile distributions of SOC and SON and to determine the effects of soil pH and soil texture. Generally, the contents of SOC and SON decreased with increasing soil depth and SOC contents were higher than SON contents (average SOC vs. SON content: 3.87 g kg−1 vs. 1.92 g kg−1 in LCJ S-1 and 5.19 g kg−1 vs. 0.96 g kg−1 in LCJ S-2). Soil pH ranged from 4.50 to 5.74 in the two soil profiles and generally increased with increasing soil depth. According to the percentages of clay, silt, and sand, most soil samples can be categorized as silty loam. Soil pH values were negatively correlated with C/N ratios (r = −0.66, p < 0.01) and SOC contents (r = −0.52, p < 0.01). Clay contents were positively correlated with C/N ratios (r = 0.43, p < 0.05) and SOC contents (r = 0.42, p < 0.01). The results indicate that soil pH and clay are essential factors influencing the SOC spatial distributions in the two soil profiles.

Forty-eight suspended particulate matter (SPM) samples were collected from the Mun River, northeast Thailand and its junction with the Mekong River, to investigate the relationship between the distribution of rare earth elements (REE) in SPM and the soils in the watershed. The total REE contents (∑REE) in SPM in the Mun River ranged from 78.5 to 377.8 mg/kg with the average of 189.3 mg/kg, which was lower than ∑REE of 222.3 mg/kg at the Mekong River (one sample at junction). The Post Archean Australia Shale (PAAS)-normalized ratios of light REE (LREE), middle REE (MREE) and heavy REE (HREE) were averaged to 1.0, 1.3 and 1.0, which showed a clear enrichment in MREE. In short, along the Mun River, the REE contents in SPM were decreasing, and the PAAS-normalized patterns of REE showed gradually flat. The REE content in SPM and soils are highest in the upper catchment, indicating that soil/bedrock is the most important source of REE in SPM. Additionally, the positive Eu anomaly was enhanced by the higher Ca content in SPM (R = 0.45), which may be caused by more feldspars or carbonates with Ca and Eu substituting Ca. The results present the REE behaviors of SPM in the Mun River and relationship between REE in SPM and soil/bedrock, the findings may support the other studies in catchment weathering.

Exploring the distributions of rare earth elements (REEs) in soil profiles is essential to understanding how natural and anthropogenic factors influence the geochemical behaviors of REEs. This study aimed to learn about the distribution characteristics of REEs in soils, including their fractionation and enrichment, and to explore the influence of soil pH and soil organic carbon (SOC) on REEs. One hundred and three samples were collected from six soil profiles under different land uses (paddy field: T1, T3; forest land: T2, T6; wasteland: T4; building site: T5) in the Mun River Basin, Northeast Thailand. The average total REE contents (∑REE) are much lower (<80 mg kg−1) than that of Earth’s crust (153.80 mg kg−1) in soil profiles T2, T3, T4, and T6. The contents of REEs tend to increase slightly with depth in all soil profiles. The ratios of (La/Yb)N range from 0.35 to 0.96 in most samples, indicating that the enrichment of heavy REEs (HREEs) relative to light REEs (LREEs) is the main fractionation pattern. Samples from profile T2 show relatively obvious negative Ce anomalies (0.55–0.78) and positive Eu anomalies (1.41–1.56), but there are almost no anomalies of Ce and Eu in other soil profiles. Enrichment factors of LREEs (EFLREEs) range from 0.23 to 1.54 and EFHREEs range from 0.34 to 2.27, which demonstrates that all soil samples show no LREE enrichment and only parts of samples show minor HREE enrichment. Soil organic carbon (SOC) contents positively correlate with the enrichment factors of REEs (EFREE) in soil profiles T1 (R = 0.56, p < 0.01) and T6 (R = 0.71), while soil pH values correlate well with EFREE in soil profiles T2 (R = 0.75) and T4 (R = −0.66, p < 0.01), indicating the important influence of soil pH and SOC on the mobility of REEs in some soil profiles.

Many strategies have been put forward to seek green and low-carbon development, some of which are achieved through land use and cover change (LUCC). A series of land management policies related to LUCC and corresponding changes in carbon dynamics were released with the implementation of the Ecological Conservation Pilot Zone Program (ECPZP) in China. We explored the spatiotemporal dynamics of LUCC and carbon storage in the first ECPZP implementation region (Fujian province) at the time before and after ECPZP implementation using a simplified carbon pools model and quantified the relative impacts of human activities and climate change on net primary productivity (NPP) employing residual analysis. This can fill the gap of land use and vegetation changes and the corresponding carbon dynamics in the ECPZP region and can serve as a reference for future land management policy revisions and ECPZP project extensions. The results showed that: (1) In 1990–2020, woodland, cultivated land, and grassland were the leading land use type in Fujian province. The area of LUCC was 11,707.75 km2, and it was predominantly caused by the conversion from cultivated land to built-up land, and the interconversion between woodland and grassland. (2) An increase of 9.74 Tg in carbon storage was mainly caused by vegetation conversion from 1990 to 2020. (3) The statistically significant increased area of climate change-induced NPP was 2.3% primarily in the northwest, but the decreased area of it statistically significantly was only 0.1%. Correspondingly, the increased area of statistically significant human activity-induced NPP was 8.7% primarily in the southeast, but the decreased area of statistically significance was 6.5%, mostly in the central region. In addition, the statistically significant areas of NPP caused by the combination of human activities and climate change differed by 1.8%. To sum up, ECPZP makes full use of the vertical mountain landscape and property right reform to effectively secure ecological space and local income. Moreover, urbanization-related policies are an essential impetus for LUCC and carbon balance. The impact of other built-up land expansion on environmental change needs to be paid particular attention to. Moreover, land-use activities in the centre of the study region that are not conducive to NPP growth should be judiciously assessed in the future.