Environmental factors affecting greenhouse gas fluxes of green roofs in temperate zone

Archaea rather than bacteria govern green roofs greenhouse gas production

Green roofs are a key solution for increasing green spaces in urban areas covered with impervious surfaces. In recent years, there has been growing interest in the ability of green spaces to reduce greenhouse gas (GHG) emissions and enhance carbon sequestration. To investigate whether green roofs contribute to GHG reduction, it is essential to quantify both carbon sequestration and GHG fluxes. However, few studies have investigated GHG fluxes from green roofs over the long term. To address this gap, this study measured and quantified the annual GHG (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O)) fluxes from a thin-layer rooftop lawn using clear acrylic automatic open/close chambers. In addition, we calculated CO2 sequestration based on the difference between total carbon contents in rooftop lawns (soil and turf) at the beginning and end of the experiment. The annual CO2, CH4, and N2O fluxes were calculated to be −1762 g-CO2• m-2• year-1, 92.33 mg-CH4• m-2• year-1, and 0.53 mg-N2O•m-2• year-1 respectively, and CO2 sequestration by plants and soil was estimated to be −2,626 g-CO2•m-2•year-1 during the first year after construction. The CH4 and N2O fluxes from the rooftop lawn were significantly lower than those reported in other studies conducted on ground-level lawns. Based on these results, annual GHG emission (total of CO2, CH4, and N2O) from the rooftop lawn were calculated to be −1759 to −2,623 g-CO2e (CO2 equivalents). m-2• year-1, indicating that the rooftop lawn acts as GHG sink.

Green (vegetated) roofs have gained global acceptance as a technologythat has the potential to help mitigate the multifaceted, complex environmental problems of urban centers. While policies that encourage green roofs exist atthe local and regional level, installation costs remain at a premium and deter investment in this technology. The objective of this paper is to quantitatively integrate the range of stormwater, energy, and air pollution benefits of green roofs into an economic model that captures the building-specific scale. Currently, green roofs are primarily valued on increased roof longevity, reduced stormwater runoff, and decreased building energy consumption. Proper valuation of these benefits can reduce the present value of a green roof if investors look beyond the upfront capital costs. Net present value (NPV) analysis comparing a conventional roof system to an extensive green roof system demonstrates that at the end of the green roof lifetime the NPV for the green roof is between 20.3 and 25.2% less than the NPV for the conventional roof over 40 years. The additional upfront investment is recovered at the time when a conventional roof would be replaced. Increasing evidence suggests that green roofs may play a significant role in urban air quality improvement For example, uptake of N0x is estimated to range from $1683 to $6383 per metric ton of NOx reduction. These benefits were included in this study, and results translate to an annual benefit of $895-3392 for a 2000 square meter vegetated roof. Improved air quality leads to a mean NPV for the green roof that is 24.5-40.2% less than the mean conventional roof NPV. Through innovative policies, the inclusion of air pollution mitigation and the reduction of municipal stormwater infrastructure costs in economic valuation of environmental benefits of green roofs can reduce the cost gap that currently hinders U.S. investment in green roof technology.

Canopy soil nutrient cycling and response to elevated nutrient levels along an elevation gradient of tropical montane forests

Experimental investigation of summer thermal performance of the green roof system with mineral wool substrate

The main purpose of this study was to explore the dynamic changes of greenhouse gas (GHG) from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China. Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO2, CH4 and N2O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO2, CH4 and N2O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO2, CH4 and N2O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO2 and N2O and the sink for CH4. Compared with CO2 fluxes, N2O and CH4 fluxes were relatively low. The exchange of CO2, N2O and CH4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO2 fluxes of –33.63 –386.36 mg/(m•h), CH4 uptake fluxes of 0.113–0.023 mg/(m•h) and N2O fluxes of –1.68 –19.90 μg/(m•h). Grassland degradation significantly influenced CH4 uptake but had no significant influence on CO2 and N2O emissions. Soil moisture and temperature were positively correlated with CO2 emissions but had no significant effect on N2O fluxes. Soil moisture may be the primary driving factor for CH4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.

Water table management with controlled drainage and subsurface-irrigation (SI) has been identified as a Beneficial Management Practice (BMP) to reduce nitrate leaching in drainage water. It has also been shown to increase crop yields during dry periods of the growing season, by providing water to the crop root zone, via upward flux or capillary rise. However, by retaining nitrates in anoxic conditions within the soil profile, SI could potentially increase greenhouse gas (GHG) fluxes, particularly N2O through denitrification. This process may be further exacerbated by high precipitation and mineral N-fertilizer applications very early in the growing season. In order to investigate the effects of water table management (WTM) with nitrogen fertilization on GHG fluxes from corn (Zea mays) agro-ecosystems, we conducted a research study on a commercial farm in south-western Quebec, Canada. Water table management treatments were: free drainage (FD) and controlled drainage with subsurface-irrigation. GHG samples were taken using field-deployed, vented non-steady state gas chambers to quantify soil CO2, N2O and CH4 fluxes weekly. Our results indicate that fertilizer application timing coinciding with intense (≥24 mm) precipitation events and high temperatures (>25 °C) triggered pulses of N2O fluxes, accounting for up to 60% of cumulative N2O fluxes. Our results also suggest that splitting bulk fertilizer applications may be an effective mitigation strategy, reducing N2O fluxes by 50% in our study. In both seasons, pulse GHG fluxes mostly occurred in the early vegetative stages of the corn, prior to activation of the subsurface-irrigation. Our results suggest that proper timing of WTM mindful of seasonal climatic conditions has the potential to reduce GHG emissions.

The study characterized the temporal and spatial variability in greenhouse gas (GHG) fluxes (CO2, CH4, and N2O) between December 2020 and November 2021 and their regulating drivers in the subtropical wetland of the Indian Himalayan foothill. Five distinct habitats (M1-sloppy surface at swamp forest, M2-plain surface at swamp forest, M3-swamp surface with small grasses, M4-marshy land with dense macrophytes, and M5-marshy land with sparse macrophytes) were studied. We conducted in situ measurements of GHG fluxes, microclimate (AT, ST, and SMC(v/v)), and soil properties (pH, EC, N, P, K, and SOC) in triplicates in all the habitat types. Across the habitats, CO2, CH4, and N2O fluxes ranged from 125 to 536mgm-2h-1, 0.32 to 28.4mgm-2h-1, and 0.16 to 3.14mgm-2h-1, respectively. The habitats (M3 and M5) exhibited higher GHG fluxes than the others. The CH4 flux followed the summer > autumn > spring > winter hierarchy. However, CO2 and N2O fluxes followed the summer > spring > autumn > winter. CO2 fluxes were primarily governed by ST and SOC. However, CH4 and N2O fluxes were mainly regulated by ST and SMC(v/v) across the habitats. In the case of N2O fluxes, soil P and EC also played a crucial role across the habitats. AT was a universal driver controlling all GHG fluxes across the habitats. The results emphasize that long-term GHG flux monitoring in sub-tropical Himalayan Wetlands has become imperative to accurately predict the near-future GHG fluxes and their changing nature with the ongoing climate change.

No-till farming and greenhouse gas fluxes: Insights from literature and experimental data

Abstract. We here present a detailed dataset of automated greenhouse gas (GHG) net soil and ditch fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from a drained fen in Denmark covering a full year. The dataset resolves small scale spatial and hourly-daily-seasonal dynamics of GHG soil fluxes. The GHG flux dataset is accompanied by simultaneous time series of soil temperature and moisture, as well as groundwater table depth and covers spatiotemporal gradients in soil hydrological and climatic variability. The GHG fluxes of CO2, CH4 and N2O were measured simultaneously by a high-precision cavity ring down laser spectrometer connected with a novel automated GHG system platform called SkyLine2D (Earthbound Scientific Ltd., UK) that allowed up to 27 individual chamber measurement points along a 24 meter transect. In total 47.483 chamber measurements were completed and after quality control 44.631 CO2 fluxes, 44.099 N2O and 42.515 CH4 fluxes remained. The average net soil CO2 efflux observed at the site (2.55 μmol CO2 m-2 s-1 or 35 tCO2 ha-1 y-1) aligns with findings from similar drained fens in northern Europe. However, this transect average masks substantial spatial variability and highlights the role of episodic emission bursts related to hydrological variability. N2O fluxes measured at this site were similarly variable in space, but displayed a more dynamic flux behaviour than CO2, where increasing groundwater table depth in response to precipitation during warmer seasons lead to emission bursts of N2O that dominated the annual budget and decreased to near-zero fluxes in drier periods. Soil CH4 fluxes were near-zero and the site overall acted as a small net source, although net uptake was observed as well especially in drier conditions. Diurnal and seasonal patterns of net soil CO2 and N2O fluxes align with expectations of soil temperature driven processes, but no clear patterns were observed for CH4. Compared to soil GHG fluxes, ditch CO2 and N2O fluxes were 4-fold and 27-fold lower, respectively, while CH4 fluxes were more than two orders of magnitude larger, confirming earlier findings that ditches can be CH4 hotspots, where the CH4 is emitted in bursts with little seasonal variability, including emissions as ebullitions. The data set is well suited for testing and developing biogeochemical models, with emphasis on the soil thermal-hydrology interactions with the peat C and N cycles.

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.

Experimental data on acoustical performances, in particular on sound absorption, of several green roof systems were evaluated and discussed. Measurements were performed on samples of three green roof systems, different for maintenance, plant setting and containment criteria, and categorized in extensive green roof (sample A), semi-intensive green roof (sample B), and common soil (sample C). Experimental values of normal incidence acoustic absorption coefficient and acoustic impedance were evaluated for each sample in one-third octave frequency bands from 160 to 1600 Hz by using a standing wave tube. Then, diffusive sound absorption coefficients and normal and diffusive weighted sound absorption coefficients were calculated in the same frequency range. Results show that green roofs provide high sound absorption, mostly if compared with the typical performances of traditional flat roofs. Curves of sound absorption coefficients result strongly dependent on the stratigraphy. Comparison between the different systems performed on the base of weighted sound absorption coefficients shows a better behavior for the sample B. Results obtained suggest that green roof technology, in addition to energy and environmental benefits, can contribute to noise control in urban areas by means of high sound absorption performances in relation to the size of the surface area.

Deciduous tree stems can become an important source of methane (CH4) and nitrous oxide (N2O) emissions especially in case of flooding or increase of the soil water-table level. So far, studies were mainly implemented in forests with organic soils, while limited information is available about mineral soils. Within this study we estimated the CH4 and N2O fluxes from the stem surface of silver birch, black alder and aspen in 16 study sites (forest stands) with drained and naturally wet mineral soils in Latvia to evaluate the impact of soil moisture conditions. We found that in forest stands with drained mineral soil, the mean CH4 fluxes from the tree stems were 10.2 ± 3.2 µg CH4-C·m-2·h-1 for aspen, 1.3 ± 2.6 µg CH4-C·m-2·h-1 for black alder, 4.5 ± 2.9 µg CH4-C·m-2·h-1 for silver birch. In forest stands with wet mineral soil, CH4 fluxes from the tree stems were higher for all tree species (21.1 ± 5.5 µg CH4-C·m-2·h-1 for aspen, 6.3 ± 2.4 µg CH4-C·m-2·h-1 for black alder, 10.3 ± 2.3 µg CH4-C·m-2·h-1 for silver birch) than in stands with drained soil. Similarly, higher N2O fluxes from the stem surface were found in forest stands with wet mineral soils for aspen and silver birch (4.1 ± 1.5 and 4.0 ± 1.5 µg N2O-N·m-2·h-1, respectively) than in forest stands with drained mineral soil (-0.8 ± 1.4 and 1.9 ± 1.5 µg N2O-N·m-2·h-1, respectively), while N2O fluxes for black alder were similar under drained and wet condition (3.8 ± 1.3 and 3.6 ± 1.3 µg N2O-N·m-2·h-1, respectively). However, high variation in CH4 and N2O fluxes was observed and the difference in mean fluxes between drained and wet conditions was not statistically significant. In general, the study shows that forest drainage can reduce CH4 and N2O fluxes from the surface of tree stems; however, due to the high variation of the fluxes more data are necessary to increase accuracy of projections of the studied greenhouse gases.

Effects of dredging wastewater input history and aquaculture type on greenhouse gas fluxes from mangrove sediments along the shorelines of the Jiulong River Estuary, China

Malaysia is the developing country, which develop in contraction, agriculture, and many more kinds of activities. The construction activities for Malaysia is less implemented the green materials technology and the Environmental Management. The Environmental Management Practices is not usually applied by the construction workers. The government also show no enforcement and awareness on the Environmental Management Practices in Malaysia. There are some importance of the Environmental Management Practices is described and also the plan to improve the implementation of Environmental Management Practices under construction of Malaysia. The green roof is one of the technologies of green materials. There three kinds of green roof system as intensive green roof system, semi-intensive green roof system, and extensive green roof system. These three different systems have its own advantages and this advantages. The green materials that can be used for the green roof construction are bamboo, stones, and recycled bricks. The green materials or green roof system help to reduce the environment impact, social impact, and economic impact of Malaysia. The better environment, social life and economic can lead to sustainable development in Malaysia.