Biochar application to soil has drawn much attention as a strategy to sequester atmospheric carbon in soil ecosystems. The applicability of this strategy as a climate change mitigation option is ...limited by our understanding of the mechanisms responsible for the observed changes in greenhouse gas emissions from soils, microbial responses, and soil fertility changes. We conducted an 8‐wk laboratory incubation using soils from PASTURE (silt loam) and RICE PADDY (silt loam) sites with and without two types of biochar (biochar from swine manure CHAR‐M and from barley stover CHAR‐B). Responses to addition of the different biochars varied with the soil source. Addition of CHAR‐B did not change CO2 and CH4 evolution from the PASTURE or the RICE PADDY soils, but there was a decrease in N2O emissions from the PASTURE soil. The effects of CHAR‐M addition on greenhouse gas emissions were different for the soils. The most substantial change was an increase in N2O emissions from the RICE PADDY soil. This result was attributed to a combination of abundant denitrifiers in this soil and increased net nitrogen mineralization. Soil phosphatase and N‐acetylglucosaminidase activity in the CHAR‐B–treated soils was enhanced compared with the controls for both soils. Fungal biomass was higher in the CHAR‐B–treated RICE PADDY soil. From our results, we suggest CHAR‐B to be an appropriate amendment for the PASTURE and RICE PADDY soils because it provides increased nitrogen availability and microbial activity with no net increase in greenhouse gas emissions. Application of CHAR‐M to RICE PADDY soils could result in excess nitrogen availability, which may increase N2O emissions and possible NO3 leaching problems. Thus, this study confirms that the ability of environmentally sound biochar additions to sequester carbon in soils depends on the characteristics of the receiving soil as well as the nature of the biochar.
Increasing heatwave frequency due to climate change threatens outdoor workers’ health. We aimed to assess the on-site heat strain level of outdoor workers using wearable sensors and identify the ...factors for consideration in developing individual-based heat adaptation strategies. Seven road construction workers were recruited and asked to wear necklace-form temperature loggers and smartwatches monitoring heart rate (HR). The questionnaire was delivered daily to ask about their psychological comfort level during work. Workers were exposed to up to 5.4 °C higher temperature than the official air temperature, indicating that the national heatwave alarm does not reflect on-site heat conditions. Based on the measured HR data, heat strain levels were defined. When HR exceeded the level of “180-age,” we assumed extreme heat strain occurred, which requires immediate cessation of work. When HR exceeded 40% of the individual heart rate reserve (the difference between the maximum and resting HR), we assumed high heat strain occurred, indicating a stressed condition. High heat strain occurred in all workers on 9 of the 13 monitored days, whereas the official heatwave alarms were issued only on four dates. Additionally, three workers experienced extreme heat strain on two dates. The main factor for workers experiencing extreme heat strain was age. Comparing the heat strain levels from HR with the survey results, we found that the older workers considered their condition comfortable even under extreme and high heat strain. Thus, an individual sensor-based early-warning system is needed to prevent heat strain not perceived by outdoor workers. The findings emphasize the need for a personalized adaptation strategy for heatwaves and will be a baseline for developing a new work manual that mainstreams climate change impacts.
•Biochar and slow-release fertilizer reduces CH4 emission but enhances rice yield.•The two treatments have different mechanisms to reduce methane emission.•Methane oxidation may take an important ...role in reduction of CH4 emission.
There has been an increased interest in and wide application of biochar and slow-release fertilizer (SRF) to agricultural soils in recent years because they can reduce greenhouse gas emissions, but increase rice productivity. However, the studies considering combined effects of biochar and SRF are rare. This study examined the combined effects of biochar and SRF on the biogeochemistry, rice productivity, methane emission, and microbial abundances in rice paddy. The study sites included six different treatment combinations: urea (NU), SRF (NS), straw+urea (SU), straw+SRF (SS), biochar+urea (BU), and biochar+SRF (BS). Both the biochar and SRF reduced the methane emission, and the BS paddy soil had the lowest methane emission, while it had the highest rice yield. The biochar inhibited methanogenesis by increasing the soil aeration and oxygen availability. The SRF decreased the plant biomass, thus they may decrease plant-mediated methane transport and carbon substrate from plant debris and root exudates. Increasing in the abundance of methane-oxidizing bacteria was assumed to have critical impact on the reduction in methane emission by biochar. In conclusion, combined application of biochar and SRF highly recommended in rice cultivation, because they can minimize the methane emission but maximize rice yield.
Purpose
Urban roadside soils are important growth media for roadside trees. However, typical assessment variables are limited in describing the characteristics of roadside soils. We assessed the ...characteristics of roadside soils using the pre- and new suggested variables and recommended optimal soil variables that are representative of roadside tree health.
Materials and methods
Seventy-three roadside soils were collected for measurement, while six urban forest soils were prepared as a control. Samples were used to evaluate both pre-suggested and new variables. The former included bulk density, penetration resistance (PR), pH, organic matter (OM), fluorescein diacetate (FDA) activity, and respiration. To improve the pre-suggested variables, we modified the bulk density using PR and investigated the elemental ratios and stable isotopic signatures of particulate organic matter (POM). Two criteria were used to select the variables for urban roadside soils: (1) the variable should identify distinct characteristics of roadside and urban forest soils and (2) the variable should have a high correlation with urban tree health variables: leaf chlorophyll content and tree vigor.
Results and discussion
The bulk density measured using the conventional method underestimated soil compaction because obtaining intact cores was challenging. The modified bulk density (BD
modified
) obtained from the soil PR is suggested to better represent soil compaction. The roadside soils were affected by de-icing materials, construction debris, and atmospheric alkali particles, which increased the soil pH. The unexpectedly higher OM contents in the roadside soils, where tree origins are limited, possibly due to soil OM sources such as vehicular emissions, animal excreta, and sewer flooding. These OM sources may alter the C/H ratio (POM-C/H) and the stable isotopic signature of POM, leading to OM quality changes. Soil respiration better reflected the changes in the microbial activity of the roadside soils, rather than FDA activity. The newly suggested soil variables, BD
mofieid
, pH, POM-C/H, and RES, were significantly correlated with leaf chlorophyll content and tree vigor (
P
< 0.05).
Conclusions
Using a multiple regression analysis, the newly suggested set of soil variables, including the BD
modified
, soil pH, POM-C/H, and soil respiration, showed high predictive power for the growth of urban roadside trees. Future studies should apply these variables to other cities or broader areas and confirm their predictive ability regarding the health of roadside trees.
Nitrogen leaching from agricultural soils is a major source of pollution for adjacent water systems. Biochar application to agricultural soils was reported to manageably reduce N leaching. For the ...sustainable use of biochar application, a mechanistic understanding of the changes in N leaching induced by biochar treatment is urgently needed. In this study, the effects of biochar rice (Oryza sativa L.) chaff application to rice paddy soil (sandy loam) on leaching and soil structure were investigated. Free‐draining lysimeters (0.2 m in diameter by 0.1 m in height) filled with 500 g of air‐dried soil were treated with biochar at 0, 2, and 10% application rates (BC0, BC2, and BC10, respectively) and N fertilizer (NH4Cl) at 0 and 100 kg ha−1 application rates (Fert0 and Fert100, respectively). During the 9‐wk incubation, the concentration of dissolved C in the leachates was higher in the soils treated with BC2 and BC10 compared with that treated with BC0 in the Fert0 soil while there were no significant differences among the biochar treatments in the Fert100 soil. This result indicated that the labile portion of the applied biochar C was utilized by microbes as the amended N was metabolized. Nitrate contents in leachates from the BC2 and BC10 treatments were significantly smaller than in those from the BC0 soil. Soil analysis showed that NH4+ content decreased and NO3– content increased under BC10 treatment compared with BC0 treatment in the Fert100 soil, indicating that net N mineralization in the soil was enhanced under biochar treatment. We suggested that the NO3– retention in the biochar‐treated soil was related to increased soil aggregation. The C contents in the wet stable aggregates of size 53 to 1000 μm were significantly increased by biochar addition. This size fraction of aggregates is related to soil mesopores, which are involved in the soil's water holding. The water holding capacity (WHC) was higher in the BC2 and BC10 soils than in the BC0 soil, suggesting that application of rice chaff biochar to rice paddy soil could reduce N leaching through the redistribution of soil pores by forming more wet stable aggregates.
Carbon (C) sequestration potential of biochar should be considered together with emission of greenhouse gases when applied to soils. In this study, we investigated CO2 and N2O emissions following the ...application of rice husk biochars to cultivated grassland soils and related gas emissions tos oil C and nitrogen (N) dynamics. Treatments included biochar addition (CHAR, NO CHAR) and amendment (COMPOST, UREA, NO FERT). The biochar application rate was 0.3% by weight. The temporal pattern of CO2 emissions differed according to biochar addition and amendments. CO2 emissions from the COMPOST soils were significantly higher than those from the UREA and NO FERT soils and less CO2 emission was observed when biochar and compost were applied together during the summer. Overall N2O emission was significantly influenced by the interaction between biochar and amendments. In UREA soil, biochar addition increased N2O emission by 49% compared to the control, while in the COMPOST and NO FERT soils, biochar did not have an effect on N2O emission. Two possible mechanisms were proposed to explain the higher N2O emissions upon biochar addition to UREA soil than other soils. Labile C in the biochar may have stimulated microbial N mineralization in the C-limited soil used in our study, resulting in an increase in N2O emission. Biochar may also have provided the soil with the ability to retain mineral N, leading to increased N2O emission. The overall results imply that biochar addition can increase C sequestration when applied together with compost, and might stimulate N2O emission when applied to soil amended with urea.
Selection of an appropriate biochar as a soil amendment requires a thorough investigation of the effects on soil ecosystems and adjacent water systems via leaching. Different biochar characteristics ...influence retention or leaching of different soil and biochar components. A lab lysimeter study was conducted to investigate carbon (C) balance and leachate quality with biochar additions. Biochar made from wood pellets (WP) and sewage sludge (SS) produced at 400 °C (WP400 and SS400) and 700 °C (WP700 and SS700), respectively, were applied to silt loam soil at an application rate of 4%. Fluorescence excitation-emission spectrophotometry (EEMs) was utilized to understand the compositional changes in leachate dissolved organic carbon (DOC). Our results show that DOC contributed the largest portion of C leaching loss. The WP treatments increased DOC mass loss, but did not significantly change leachate DOC quality. SS400, in comparison, increased mass loss of DOC and SS700 decreased it probably due to its higher adsorptive capacity to DOC. Unlike WP treatments, SS treatments significantly changed leachate DOC quality. Chemical oxygen demand (COD) was reduced with SS400 and SS700 biochar additions, which is assumed to be related to SS biochar's high oxygen-containing surface functional groups. Reduction in total nitrogen (TN) leaching by WP700 and SS700 treatments might be related to the higher micropore surface area. Over all, our findings imply that changes in the different components of the leachate from biochar-amended soil are related to different biochar properties, such as labile matter content, total surface area, micropore volume and cation exchange capacity.
•DOC contributed the largest portion of C leaching loss from biochar added soils.•Leachate properties of biochar addition were related to biochar characteristics.•Wood pellet biochar increased DOC leaching but did not influence DOC quality.•Sewage sludge biochar (700 °C) reduced COD/TN leaching and retained humic substances.
Green areas are thought to reduce particulate matter (PM) concentrations in urban environments. Plants are the key to PM reduction via various mechanisms, although most mechanisms do not lead to the ...complete removal of PM. Ultimately, PM falls into the soil via wind and rainfall. However, the fallen PM can re-entrain the atmosphere, which can affect plants capacity to reduce PM. In this study, we simulated an urban green floor and measured the resuspension of PM from the surface using a new experimental system, a wind tunnel-mounted closed chamber.
The developed system is capable of quantifying the resuspension rate at the millimeter scale, which is measured by using the 1 mm node chain. This is adequate for simulating in situ green floors, including fallen branches and leaves. This addressed limitations from previous studies which focused on micrometer-scale surfaces. In this study, the surfaces consisted of three types: bare sand soil, broadleaves, and coniferous leaves. The resuspended PM was measured using a light-scattering dust detector.
The resuspension rate was highest of 14.45×10
s
on broad-leaved surfaces and lowest on coniferous surfaces of 5.35×10
s
(
< 0.05) and was not proportional to the millimeter-scale surface roughness measured by the roller chain method. This might be due to the lower roughness density of the broad-leaved surface, which can cause more turbulence for PM resuspension. Moreover, the size distribution of the resuspended PM indicated that the particles tended to agglomerate at 2.5 µm after resuspension.
Our findings suggest that the management of fallen leaves on the urban green floor is important in controlling PM concentrations and that the coniferous floor is more effective than the broadleaved floor in reducing PM resuspension. Future studies using the new system can be expanded to derive PM management strategies by diversifying the PM types, surfaces, and atmospheric conditions.
The soils in urban greenery considerably contribute to providing ecosystem services. However, appropriate tools to assess and manage urban soil quality under consideration of ecosystem services and ...soil functions are unavailable. In this study, we aimed to 1) provide detailed instructions for assessing a novel urban soil quality index (uSQI) and 2) propose the application of uSQI in urban soil quality management. The uSQI is the average of the scores for six soil functions. Each soil function was estimated by several measurable indicators that have high correlation with soil functions. The measurable soil indicators are bulk density, saturated hydraulic conductivity, litter-layer depth, mineral-associated organic matter, clay + silt content, inorganic nitrogen concentration, fluorescein diacetate hydrolytic activity, cation exchange capacity, concentrations of potentially toxic elements, and pH. The uSQI effectively identified the soils with low quality due to disturbances. The radar chart of six soil functions comprising uSQI could suggest the direction of management for urban stakeholders.•The uSQI represents soil functions necessary for urban greenery to provide ecosystem services.•The uSQI successfully identified the soils with low quality due to disturbances.
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The assessment of environmental vulnerability is a sound basis for environmental management measures because it provides an objective standard for the priorities for implementation. Although several ...methods have been used by international agencies to assess and compare national environmental vulnerabilities, relatively few methodologies have been proposed to assess vulnerability on the local scale. In this study, we developed a methodology to assess the environmental vulnerability of a coastal city, with the goal of overcoming the limitations of a previous method that compared countries' vulnerabilities on a global scale. We applied this methodology to Jakarta, Indonesia, to identify its utility in providing a basis for the development of environmental policy measures. We assessed the relative environmental vulnerabilities of Jakarta's five districts, using a conceptual diagram composed of exposure, sensitivity, and adaptive capacity. For environmental exposure, we considered inundation due to heavy rainstorm, flood from sea level rise, and environmental pollution. For sensitivity, sectors of human and natural systems were considered using a land cover map from GIS data. To examine adaptive capacity, we addressed environmental awareness, policy foundation, economic status, and infrastructure. The assessment results showed that the East and North districts are more vulnerable than other districts. We suggested environmental policy measures for each district using radial graphs that show the dominant indicators within the composite index. Our proposed methodology has a significant relevance in the sense that it extracts key indicators of environmental vulnerability by considering local conditions, and provides a useful tool to compare results within a vulnerability assessment and to inform appropriate environmental policy measures.
•A new methodology to assess environmental vulnerability for coastal cities was developed considering land use pattern and policy utilization.•Using GIS data is turned out to be very useful to reflect local conditions.•We suggest radial graphs as a policy supporting tool to visualize important sectors for overall environmental vulnerabilities.
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