Transpiration Induced Changes in Atmospheric Water Vapor δ18O via Isotopic Non-Steady-State Effects on a Subtropical Forest Plantation

Accurate simulation of oxygen isotopic composition (δ18OT) of transpiration (T) and its contribution via isotopic non-steady-state (NSS) to atmospheric water vapor δ18O (δ18Ov) still faces great challenges. High-frequency in-situ measurements of δ18Ov and evapotranspiration (ET) δ18O were conducted for two summer days on a subtropical forest plantation. δ18O of xylem, leaf, and soil water at 3 or 4-h intervals was analyzed. Leaf water δ18O and δ18OT were estimated using the Craig and Gordon (CG), Dongmann and Farquhar–Cernusak models, and evaporation (E) δ18O using the CG model. To quantify the effects of δ18OT, δ18OE, and δ18OET on δ18Ov, T, E, and ET isoforcing was calculated as the product of T, E, and ET fluxes, and the deviation of their δ18O from δ18Ov. Results showed that isotopic steady-state assumption (SS) was satisfied between 12:00 and 15:00. NSS was significant, and δ18OT was underestimated by SS before 12:00 and after 18:00. The Péclet effect was less important to δ18OT simulation than NSS at the canopy level. Due to decreasing atmospheric vertical mixing and the appearance of the inversion layer, contribution from positive T isoforcing increased δ18Ov in the morning and at night. During the daytime, the contribution from positive T isoforcing increased first and then decreased due to strong vertical mixing and variability in T rate

Variability of δ2H and δ18O in Soil Water and Its Linkage to Precipitation in an East Asian Monsoon Subtropical Forest Plantation

The linkage between δ2H and δ18O of soil water and precipitation provides a way of understanding precipitation infiltration, residence time, and soil water source. Soil water at 0–5, 15–20, and 40–45 cm depths and event-based precipitation were collected in a subtropical forest plantation. Correlations between the δ18O of soil water and precipitation on the same day were used to determine the critical threshold of precipitation infiltration. Residence time of precipitation in soil was determined with correlations between the δ18O of soil water and cumulative precipitation before sampling. Soil water source was determined by the intersection points of Soil Water Evaporation Lines (SEL) and local meteoric water lines. The results showed that precipitation >5–6 mm could pass through canopy and litter, and infiltrate into soil. Residence times varied from a few days to several months, and increased with soil depth. The model-based approach for SEL estimation were more robust than the regression-based approach due to the inverse variability in the δ2H and δ18O of soil water source and soil evaporative fractionation. Soil water at a 0–5 cm depth originated mainly from precipitation in the current season, while those at 15–20 and 40–45 cm depths originated mainly from precipitation in the previous season

Transpiration Induced Changes in Atmospheric Water Vapor <i>δ</i>¹⁸O via Isotopic Non-Steady-State Effects on a Subtropical Forest Plantation

Accurate simulation of oxygen isotopic composition (δ18OT) of transpiration (T) and its contribution via isotopic non-steady-state (NSS) to atmospheric water vapor δ18O (δ18Ov) still faces great challenges. High-frequency in-situ measurements of δ18Ov and evapotranspiration (ET) δ18O were conducted for two summer days on a subtropical forest plantation. δ18O of xylem, leaf, and soil water at 3 or 4-h intervals was analyzed. Leaf water δ18O and δ18OT were estimated using the Craig and Gordon (CG), Dongmann and Farquhar–Cernusak models, and evaporation (E) δ18O using the CG model. To quantify the effects of δ18OT, δ18OE, and δ18OET on δ18Ov, T, E, and ET isoforcing was calculated as the product of T, E, and ET fluxes, and the deviation of their δ18O from δ18Ov. Results showed that isotopic steady-state assumption (SS) was satisfied between 12:00 and 15:00. NSS was significant, and δ18OT was underestimated by SS before 12:00 and after 18:00. The Péclet effect was less important to δ18OT simulation than NSS at the canopy level. Due to decreasing atmospheric vertical mixing and the appearance of the inversion layer, contribution from positive T isoforcing increased δ18Ov in the morning and at night. During the daytime, the contribution from positive T isoforcing increased first and then decreased due to strong vertical mixing and variability in T rate

Soil Water Stable Isotopes Reveal Surface Soil Evaporation Loss Dynamics in a Subtropical Forest Plantation

Line-conditioned excess (lc-excess), the deviation of the relationship between &delta;D and &delta;18O in soil water from that of precipitation, is often used to indicate soil evaporation loss, but the conditions of using lc-excess under the influences of precipitation infiltration or percolation had not been identified. The interaction effects of climate, soil and vegetation on soil evaporation in forests are not well known. We collected soil water at 0&ndash;5, 15&ndash;20 and 40&ndash;45 cm depths and event-based precipitation from 2011 to 2015 in a subtropical forest plantation and calculated the lc-excess. Precipitation on the sampling day and percolation of upper soil water with low lc-excess affected the capacity of the lc-excess to indicate the soil evaporation fractionation signals. Lc-excess of soil water at 0&ndash;5 cm depth indicated a reliable soil evaporation loss estimate over 30 days prior to the sampling day. Soil evaporation loss was dominated by the cumulative soil temperature (Tss) during drought periods and was dominated by the relative soil water content (RSWC) during non-drought periods. High Tss decreased soil evaporation loss by increasing transpiration and relative humidity. Our results emphasize the importance of sampling the upper-most soil layer when there is no rain and vegetation during drought periods in forests when studying soil evaporation loss dynamics

Soil Water Stable Isotopes Reveal Surface Soil Evaporation Loss Dynamics in a Subtropical Forest Plantation

Line-conditioned excess (lc-excess), the deviation of the relationship between δD and δ18O in soil water from that of precipitation, is often used to indicate soil evaporation loss, but the conditions of using lc-excess under the influences of precipitation infiltration or percolation had not been identified. The interaction effects of climate, soil and vegetation on soil evaporation in forests are not well known. We collected soil water at 0–5, 15–20 and 40–45 cm depths and event-based precipitation from 2011 to 2015 in a subtropical forest plantation and calculated the lc-excess. Precipitation on the sampling day and percolation of upper soil water with low lc-excess affected the capacity of the lc-excess to indicate the soil evaporation fractionation signals. Lc-excess of soil water at 0–5 cm depth indicated a reliable soil evaporation loss estimate over 30 days prior to the sampling day. Soil evaporation loss was dominated by the cumulative soil temperature (Tss) during drought periods and was dominated by the relative soil water content (RSWC) during non-drought periods. High Tss decreased soil evaporation loss by increasing transpiration and relative humidity. Our results emphasize the importance of sampling the upper-most soil layer when there is no rain and vegetation during drought periods in forests when studying soil evaporation loss dynamics

Systematic and bibliographic review of sustainability indicators for contaminated site remediation: comparison between China and western nations

Sustainable remediation, which promotes the use of more sustainable practices during environmental clean-up activities, is an area of intense international development. While numerous indicators related to sustainable remediation assessment have been utilized and published in related academic literature, they are difficult to unify and vary in emphasis between countries. Following literature retrieval from CNKI, Springer, ScienceDirect, and Wiley Online databases, we present a systematic and bibliometric analysis of relevant national and international literature to define the most frequently considered indicators of sustainability, which play important roles in selecting remediation technologies or site management methods from a sustainability perspective. Following the application of co-occurrence analysis and social network analysis, the results indicate that 1) environmental criteria are most commonly used in evaluating remediation technologies, with significantly less emphasis on social criteria in Chinese publications in particular; 2) with an increasing number of publications in the last 20 years, sustainable remediation has gone through an initial stage, rising stage, and burst or wider adoption stage, characterized by a transformation of the research theme from a predominantly risk-based management approach to a sustainability-based one, with risk management as an underpinning principle; 3) health, resource, cost, and time are the most widely used indicators in terms of social, environmental, economic, and technical criteria, respectively; 4) clear differences exist between China and other nations, particularly in the frequency of usage of each indicator, the application of social criteria, and preferred stakeholders. Nevertheless, China has made significant progress and now makes increasing contributions to sustainable remediation at an international level.</p

Perceptions of Different Stakeholders on Reclaimed Water Reuse: The Case of Beijing, China

Public involvement is critical to the successful implementation of reclaimed water reuse programs. Based on the participatory research method, we studied the attitudes of the stakeholders who are involved in reclaimed water reuse in Beijing, China. Results showed that the general public’s knowledge on water resources was poor, while their awareness on reclaimed water reuse was high. The general public showed a strong acceptance of non-contact and non-potable reclaimed water reuse, but their acceptance of the three major water reuse types of river water supplement, park water supplement, and agriculture irrigation was not high. The beneficial use of reclaimed water was admired by water resource managers, industrial sectors, and researchers, and these stakeholders strongly supported the advancement of reclaimed water reuse. However, some of the stakeholders showed concerns about the potential risks from reclaimed wastewater reuse. Among them, risks from waste water treatment facilities were the biggest concern. Stakeholders’ perception of reclaimed water was influenced by their social-economic attributes. This study will enrich the current survey findings on public perception of reclaimed water reuse, particularly in developing countries

Interannual variability in net ecosystem carbon production in a rain-fed maize ecosystem and its climatic and biotic controls during 2005-2018.

Interannual variability (IAV) in net ecosystem carbon production (NEP) plays an important role in the processes of the carbon cycle, but the long-term trends in NEP and the climatic and biotic control of IAV in NEP still remain unclear in agroecosystems. We investigated interannual variability in NEP, expressed as annual values and anomalies, and its climatic and biotic controls using an eddy-covariance dataset for 2005-2018 for rain-fed spring maize in northeastern China. Average annual NEP was 270±31 g C m-2yr -1, with no significant changes over time. The effects on interannual variability in NEP of gross ecosystem productivity (GEP) that was mainly controlled by soil water content (SWC) and leaf area index (LAI), were more than those of respiration (RE) that was controlled by temperature and LAI. Further, maximum daily NEP (NEPmax) that was dominated by summer vapor pressure deficit explained the largest fraction of annual anomalies in NEP, followed by carbon dioxide uptake period (CUP) that was defined by the beginning date (BDOY) and the end date (EDOY) of CUP. The variability in BDOY was mainly determined by spring precipitation and the effective accumulated temperature, and the variability in EDOY was determined by autumn precipitation, SWC and LAI. NEP may decrease with declining precipitation in the future due to decreasing GEP, NEPmax, or CUP, and irrigation and residues cover may be useful in efforts to maintain current NEP levels. Our results indicate that interannual variability in NEP in agroecosystems may be more sensitive to changes in water conditions (such as precipitation, SWC and VPD) induced by climate changes, while temperature may be an important indirect factor when VPD is dominated