Greenhouse gas emissions from intact riparian wetland soil columns continuously loaded with nitrate solution: a laboratory microcosm study

Spatial and Temporal Variability and Driving Factors of Carbon Dioxide and Nitrous Oxide Fluxes in Alpine Wetland Ecosystems

Plants regulate greenhouse gas (GHG) fluxes in wetland ecosystems, but the mechanisms of plant removal and plant species that contribute to GHG emissions remain unclear. In this study, the fluxes of carbon dioxide (CO2) and nitrous oxide (N2O) were measured using the static chamber method from an island forest dominated by two different species, namely Betula platyphylla (BP) and Larix gmelinii (LG), in a marsh wetland in the Great Xing’an Mountains. Four sub-plots were established in this study: (1) bare soil after removing vegetation under BP (SBP); (2) bare soil after removing vegetation under LG (SLG); (3) soil with vegetation under BP (VSBP); and (4) soil with vegetation under LG (VSLG). Additionally, the contributions of the dark respiration from plant aerial parts under BP (VBP) and LG (VLG) to GHG fluxes were calculated. We found that the substantial spatial variability of CO2 fluxes ranged from −25.32 ± 15.45 to 187.20 ± 74.76 mg m−2 h−1 during the study period. The CO2 fluxes decreased in the order of SBP > VSLG > VSBP > SLG > VLG > VBP, indicating that vegetation species had a great impact on CO2 emissions. Particularly, the absence of vegetation promoted CO2 emission in both BP and LG. Additionally, CO2 fluxes showed dramatically seasonal variations, with high CO2 fluxes in late spring (May) and summer (June, July, and August), but low fluxes in late summer (August) and early autumn (September). Soil temperatures at 0−20 cm depth were better predictors of CO2 fluxes than deeper soil temperatures. N2O fluxes were varied in different treatments with the highest N2O fluxes in SLG and the lowest N2O fluxes in VBP. Meanwhile, no significant correlation was found between N2O fluxes and air or soil temperatures. Temporally, negative N2O fluxes were observed from June to October, indicating that soil N2O fluxes were reduced and emitted as N2, which was the terminal step of the microbial denitrification process. Most of the study sites were CO2 sources during the warm season and CO2 sinks in the cold season. Thus, soil temperature plays an important role in CO2 fluxes. We also found that the CO2 flux was positively related to pH in a 10 cm soil layer and positively related to moisture content (MC) in a 50 cm soil layer in VSBP and VSLG. However, the CO2 flux was negatively related to pH in a 30 cm soil layer in SBP and SLG. Our findings highlight the effects of vegetation removal on GHG fluxes, and aid in the scientific management of wetland plants.

A latest review on the application of microcosm model in environmental research

Microcosms are used experimentally to simulate ecosystems. This technology has received increasing attention and is widely used for environmental research. This review briefly introduces the origin and development of microcosm theory, summarizes classification and applications of microcosms across decades, and describes the advantages and limitations of microcosm technology in comparison with other methods. Finally, trends in the development of microcosm models are discussed.

Greenhouse gas emissions from riparian zones are related to vegetation type and environmental factors

Riparian zones provide multiple benefits, including streambank stabilization and nutrient abatement. However, there is a knowledge gap on how the type of vegetation and environmental factors (e.g., soil temperature, moisture) within the riparian zone influence CO₂ and CH₄ emissions. Our objective was to quantify and compare CO₂ and CH₄ emissions from a herbaceous (grass) riparian zone (GRS), a rehabilitated riparian zone composed of deciduous trees, an undisturbed natural forested riparian zone with deciduous trees (UNF-D) or coniferous trees (UNF-C), and an agricultural field. Cumulative soil CO₂ emission ranged from 23 to 105 g CO₂ -C m^-2 . Carbon dioxide emissions were greatest (p < .05) in the GRS zone and lowest (p < .05) in the UNF-C riparian zone. The best predictors for CO₂ emissions were soil temperature and soil organic carbon (SOC) content. Cumulative CH₄ emission ranged from -23 to 253 g CH₄ -C m^-2 . Methane emissions were greatest (p < .05) in the UNF-D and lowest (p < .05) in the GRS riparian zone. The best predictors for CH₄ emissions were soil moisture, SOC, and photosynthetic photon flux density. The total CO₂ -C equivalent (i.e., CH₄ + CO₂ ) was greatest (p < .05) for the GRS and lowest (p < .05) for the UNF-C riparian zone. The environmental factors controlling CO₂ and CH₄ emissions within the various riparian zones did not change; instead, changes were due to how vegetation within riparian zones influenced these controls.

Effective treatment of greywater via green wall biofiltration and electrochemical disinfection

Low energy and cost solutions are needed to combat raising water needs in urbanised areas and produce high quality recycled water. In this study, we investigated key processes that drive a unique greywater treatment train consisting of a passive green wall biofiltration system followed by disinfection using a Boron-doped diamond (BDD) electrode with a solid polymer electrolyte (SPE). In both systems, the treatment was performed without any additional chemicals and pollutants of concern were monitored for process evaluation. The green wall system removed over 90% of turbidity, apparent colour, chemical oxygen demand, total organic carbon, and biological oxygen demand, and 1 log of E. coli and total coliforms, mostly through biological processes. The green wall effluent met several proposed greywater reuse guidelines, except for E. coli and total coliform treatment (below 10 MPN/100 mL). Further disinfection of treated greywater (contained 28 mg/L Cl¯ and electrical conductivity (EC) of 181.3 µS/cm) by electrolysis at current density 25 mA/cm² inactivated over 3.5 logs of both E. coli and total coliforms, in 10 - 15 min of electrolysis, resulting in recycled water with less than 2 MPN/100 mL. A synergistic effect between electrochemically-generated free chlorines and reactive oxygen species contributed to the inactivation process. Although the treated water contained diluted chloride and had low EC, estimated energy consumption was just 0.63 - 0.83 kWh/m³. This is the first study to show the effectiveness of a low energy and a low cost greywater treatment train that combines green urban infrastructure with BDD electrochemical treatment process with SPE, offering a reliable and an environmentally-friendly method for greywater reuse.