Biomass, carbon and nitrogen in single tree components of grey poplar (Populus × canescens) in an uncultivated habitat in Van, Turkey

Mechanistic understanding of perfluorooctane sulfonate (PFOS) sorption by biochars

Biochar has recently emerged as a cost-effective solution to combat per- and polyfluoroalkyl substances (PFAS) pollution in water, but mechanistic understanding of which physicochemical properties of biochars dictate PFAS sorptive removal from water remains elusive. Herein, 15 biochars were pyrolyzed from five feedstocks (corn, Douglas fir, eucalyptus, poplar, and switchgrass) at three pyrolysis temperatures (500, 700, and 900 °C) to investigate their removal efficiencies and mechanisms of perfluorooctane sulfonate (PFOS) from water. A commercial biochar was also included for comparison. Biochar physiochemical properties, including elemental composition, pH, specific surface area (SSA), pore structure, hydrophobicity, surface charge, surface functional groups, and crystalline structure were systematically characterized. Batch sorption data showed that the Douglas fir 900 biochar (Douglas fir and 900 are the feedstock type and pyrolysis temperature, respectively; this naming rule applies to other biochars), poplar 900 biochar, and commercial biochar can remove over 95% of PFOS from water. Structural equation model (SEM) was used to elucidate which biochar properties affect PFOS sorption. Interestingly, biochar pore diameter was identified as the most critical factor controlling PFOS removal, but pore diameter/pore volume ratio, SSA, pyrolysis temperature, hydrophobicity, and elemental composition all played variable roles. Hypothetically, biochars with small pore diameters and large pore volumes had a narrow yet deep pore structure that traps PFOS molecules inside once already sorbed, resulting in an enhanced PFOS sorption. Biochars with small pore diameter, low nitrogen content, and high pyrolysis temperature were also favorable for enhanced PFOS sorption. Our findings advance the knowledge of using biochars with optimized properties to remove PFOS and possibly other similar PFAS compounds from water.

Long-term ecological effects of two artificial forests on soil properties and quality in the eastern Qinghai-Tibet Plateau

Afforestation is an essential process of ecological restoration, landscape reconstruction, and environmental improvement. While large-scale plantations have restored the fragile ecosystems of the Qinghai-Tibet Plateau, they have also changed local soil characteristics. A 30-year-old typical planted forest on the eastern Qinghai-Tibet Plateau was selected to determine the long-term ecological effects of artificial forests on the soil in this study. Physicochemical soil characteristics at varying soil depths and relative soil parameters, such as element stoichiometry and growing stock, were quantified on the different plantations. This soil quality information was used to construct an MDS-SQI Model. Our findings revealed that soil TN, TK, TP, and AP content was higher than pre-afforestation baseline values, while SOC and pH values were lower. Amounts of soil nutrients SOC, TN, TP, TK, AP, and AK, were positively correlated in the artificial forests. The ratio of soil C/N was higher and ratios C/P and N/P were lower in poplar than the Chinese pine plantation. The soil quality index values calculated from the MDS model were 0.31 and 0.40 for poplar and Chinese pine plantations in the top 30 cm and 0.55 and 0.46 in the 100 cm depth, respectively, which indicated that the two plantations had low-quality soil. LiDAR satellite imagery was used to estimate a growing stock of 7723 m³ and 435 m³ in the poplar and Chinese pine plantations. The results suggest that the artificial forest improves soil properties overall but that different stand forests have discrete effects on the soil environment.