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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2010.07.023 Byline: Wei Luo (a), Yonglong Lu (a), Yan Zhang (a), Wenyou Fu (a), Bin Wang (a), Wentao Jiao (a), Guang Wang (a), Xiaojuan Tong (b), John P. Giesy (c)(d) Abstract: Concentrations of As and selected metals were determined in surface soils of the Miyun Reservoir watershed of Beijing, China. The degree to which concentrations of As and metals exceeded the corresponding background concentration of soils was: CrCuZnAsNi with no apparent anthropogenic contamination with Cd and Pb. Based on the results of a combination of multivariate statistics and geostatistical analysis, greater concentrations of Cr and Ni in soils were determined to be primarily from iron ore mining near where the Chaohe River enters the northeast portion of the reservoir. Agricultural activities were responsible for the observed elevated concentrations of Cu and Zn in soils. Relatively great concentrations of As were found in soils near the upstream regions of the Baihe River in Chicheng County where small gold mining activities have taken place. The greatest potential for adverse effects of Cr and Cu occurred along the eastern shore of Miyun Reservoir. Author Affiliation: (a) State Key Lab of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China (b) College of Forestry, Beijing Forestry University, Beijing 100083, China (c) Department of Veterinary Biomedical Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada (d) Zoology Dept., Center for Integrative Toxicology, Michigan State University, East Lansing, MI 48824, USA Article History: Received 28 September 2009; Revised 17 June 2010; Accepted 18 July 2010

Diffuse solar radiation plays important role in carbon exchange between forest ecosystems and the atmosphere. Based on a 2-year (2016–2017) dataset of global and diffuse solar radiation, the annual mean diffuse fraction (the proportion of diffuse solar radiation to global solar radiation, DF) was approximately 0.45 over the plantation canopy. A proposed model (BRL-1), including six predictors (half-hourly clearness index CI, solar elevation angle, apparent solar time, daily CI, a persistence of global solar radiation and relative humidity), was developed using the ground-based measurements data of 2016. The DF values estimated by the proposed model were in good agreement with the measured ones. The values of the coefficient of determination (R2), the root mean squared error (RMSE), the mean bias error (MBE) and the t stat for the proposed model were 0.82, 0.12, 0.002 and 1.16, respectively, lower than the results derived from other models. Therefore, the performance of the proposed model estimating half-hourly DF was better than the other models. Moreover, half-hourly diffuse solar radiation in cloudy skies estimated by the proposed model was more consistent with the measured one than that under clear skies. This study aims at helping us understand the change of diffuse solar radiation with clouds. Relationship between clearness index (CI) and solar elevation angle (β). Scatter plots of diffuse fraction (DF) and CI, half-hourly measured diffuse solar radiation and estimated values. Image 10927 • Diffuse fraction was correlated with relative humidity and clearness index. • The performance of the proposed model was better than other eight models. • Estimated diffuse radiation was consistent with measured values in cloudy skies. [ABSTRACT FROM AUTHOR]

To evaluate and improve the ecological benefit of forestation programs, post-forestation estimations of newly sequestrated soil organic carbon (SOC) are necessary. Here, we collected soil samples from three plantations in northeast China and used 13 C natural abundance to measure the amount of SOC sequestrated since 1998. Newly sequestrated SOC decreased with the increasing soil depth in the Larix gmelinii plantation, but increased with soil depth in the Populus trichocarpa plantation. In contrast, newly sequestrated SOC in the Armeniaca sibirica plantation peaked at a soil depth of 30–40 cm. With increasing distance from the tree trunk, average newly sequestrated SOC gradually decreased in the L. gmelinii plantation, did not vary in the P. trichocarpa plantation, and exhibited a gentle unimodal curve in the A. sibirica plantation. Overall, the average density of newly sequestrated SOC in the L. gmelinii , P. trichocarpa , and A. sibirica plantations at a soil depth of 0–50 cm was 0.60, 0.70, and 0.61 g cm −3 , respectively. Determination of δ 15 N and the C/N ratio provided evidence to support the hypothesis that newly sequestrated SOC was primarily regulated by the root-microbial system. Soil depth and tree species should be taken into account when estimating soil carbon sequestration in future studies. [ABSTRACT FROM AUTHOR]

Abstract: In recent decades, forest area in China increased rapidly by afforestation and reforestation, especially in its temperate parts. However, lack of information on carbon exchange in temperate plantations in China reduced the accuracy of estimation on regional carbon budget. In this study, CO2 flux was measured using the eddy covariance method over a broadleaf dominant mixed plantation in the lithoid hilly area of the North China. The results showed that annual maximum photosynthetic capacity (A max) varied from 0.81 to 1.22 mg CO2 m−2 s−1 and annual initial light use efficiency (α) from 0.014 to 0.026. Net CO2 uptake was depressed when vapor pressure deficit (VPD) was more than 2.5 kPa. Annual temperature sensitivity coefficient (Q 10) for ecosystem respiration, ranged from 1.84 to 2.35, was negatively correlated with base ecosystem respiration (R 0) (P < 0.05). Annual R 0 decreased but Q 10 increased evidently when winter drought occurred. From 2006 to 2010, annual net ecosystem carbon exchange (NEE), Gross primary productivity (GPP) and ecosystem respiration (R ec) were −355 ± 34, 1196 ± 21 and 841 ± 43 g C m−2 yr−1, respectively. The warm-temperate mixed plantation in the lithoid hilly area of the North China was a strong carbon sink of the atmosphere, which was usually weaken when spring drought happened. [Copyright &y& Elsevier]

N2O fluxes in a wheat/maize rotation system were measured using flux gradient methods combined with gas chromatograph (GC) technique. The mean precision of two repeated GC analyses for N2O concentration achieved to 0.27–0.46ppbv, which could resolve N2O concentration differences in a low range of 0.39–0.65ppbv. To maximize measurable N2O concentration differences, gradient measurements were conducted only after fertilization or under low wind conditions. During observation period, N2O flux ranged from −4.41 to 4.84mgN2Om−2 h−1 for maize field, and from −2.82 to 3.59mgN2Om−2 h−1 for wheat field. When gradient observation changed from two layers to four layers, the temporal variation of N2O flux reduced but the mean value changed less. Many negative N2O fluxes were found in maize and wheat fields even after fertilization. Nearly all of them were caused by negative N2O concentration differences. During four days'' observation in maize field, a mean N2O flux of −0.75mgN2Om−2 h−1 was found in the daytime and could not be simply attributed to the temporal variation of N2O flux. N2O flux determined by the aerodynamic method (F a) and the Bowen ratio/energy balance method (F b) were in a good agreement and statistically significant. The ratio of F a to F b increased linearly with energy balance ratio (EBR) obtained by the aerodynamic method in the daytime when EBR is larger than 0.3. It is the first time to give a quantitative description for the impact of energy closure on N2O flux, and show a possible way to improve the data quality under the condition of poor energy balance. [Copyright &y& Elsevier]

• GCC, GCC MODIS , and EVI-estimated phenology presented comparable performance in estimating phenological events. • Both GCC MODIS and EVI performed better than GCC in simulating GPP at the DBF and GRA sites. • GCC MODIS could be utilized as an effective tool for extracting vegetation phenology and estimating ecosystem GPP. Vegetation phenology serves as an important indicator for climate change and plays a crucial role in affecting the terrestrial water, energy, and carbon cycles. The green chromatic coordinate (GCC) obtained from digital repeat photographs has been widely applied in estimating phenology from the perspective of greenness, while the performance of satellite derived GCC is not well understood. We used flux tower GPP from seven deciduous broadleaf forest (DBF) and three grassland (GRA) sites over the Northern Hemisphere. The aim was to compare phenological events with GCC (obtained from digital repeat photographs and satellite remote sensing (GCC MODIS)) and the enhanced vegetation index (EVI). Meanwhile, we also explored the performance of these three indices in simulating GPP utilizing the light use efficiency (LUE) model at the DBF and GRA sites. Phenology retrieved by GCC, GCC MODIS , and EVI was all significantly correlated with GPP-estimated values at all sites (P < 0.001). It indicates the comparable performance of GCC, GCC MODIS , and EVI in estimating phenological events. The RMSE values between the GPP and three indices-estimated phenological events revealed that the three indices excelled in estimating the start of growing season (SOS) compared to the end of growing season (EOS) and the length of growing season (GSL). In terms of GPP estimation performance, the R2 values of GCC MODIS and EVI-estimated GPP increased by 2 % and 1 %, respectively, compared to GCC-simulated GPP. Meanwhile, the RMSE values for GCC MODIS and EVI reduced by 0.08, and the bias values were reduced by 0.06 and 0.12, respectively. This study showed that GCC obtained from satellite remote sensing data could be utilized as an effective tool in extracting phenology and has a great potential to estimate GPP, at least across the DBF and GRA regions. [ABSTRACT FROM AUTHOR]

• VCI showed an increasing trend in China from 2001 to 2020. • The time lag and cumulative effects of drought on VCI increased with latitude. • Warming and decreased precipitation at high altitudes improved vegetation growth condition. Vegetation can reduce the adverse effect of climate change. Under the frequent droughts and global warming, it is critical to clear vegetation dynamics and response to climatic variables. However, it is unclear how drought and climatic variables affect vegetation dynamics. In this study, we used the vegetation condition index (VCI) to examine vegetation dynamics in China between 2001 and 2020. The average annual value of VCI had increased during the period of 2001 to 2020, and 90.63% of the study regions had a rising trend in VCI. A large portion of the area had a 3-month time lag between VCI and temperature and precipitation. The time-lag response of VCI to drought was mainly 9 months, with a cumulative effect on drought of 1 month and 12 months. The VCI of evergreen needleleaf forests (ENF), deciduous needleleaf forests (DNF), deciduous broadleaf forests (DBF), and mixed forests (MF) in northern China displayed long time-lag response to drought. Except for DBF in the north and DNF in the central south regions, the cumulative effect of drought on other forest VCI was great in northern China. Except for DNF, DBF, and MF in the central south and DBF in the southwest regions, drought had less time-lag effects on VCI for ENF, evergreen broadleaf forests (EBF), DNF, and MF in southern China. The cumulative effect of drought on VCI of forests in southern China was short. The responses of various types of the grassland and shrubland to drought were similar as those of forests. However, the time-lag effect of drought on grassland and shrubland VCI was shorter than that of forests, making the grassland and shrubland more vulnerable to the short-term cumulative effects of drought. The result of this study can help us understand how the vegetation responds to climate change and drought under global warming scenarios. [ABSTRACT FROM AUTHOR]

• RMSD between EVI- and GPP-based phenology dates was 8 and 13 days for SOS and EOS. • MODIS EVI was more effective at estimating EOS and GSL than MCD12Q2. • Preseason temperature and precipitation explained 40% of SOS variation. Vegetation phenology is an integrated indicator of vegetation growth and development in response to climate, and it is one of the important variables regulating carbon flux in forest ecosystems. Land surface phenology derived from different remote sensing products and their relationships with flux tower gross primary production (GPP) data have been paid much attention. Remotely sensed phenology was retrieved based on greenness, while GPP-based phenology was extracted based on photosynthesis. However, exploring the differences between remotely sensed and GPP-based phenology are limited. In this study, we compared phenological metrics obtained from flux tower GPP of a mixed plantation with phenological metrics derived using MODIS EVI and MCD12Q2 from 2006 to 2017. We also explored phenological transitions and the response of phenology to climatic variables. The results showed that the 16-day composited EVI time series was in agreement with the 16-day composited GPP time series (R 2 = 0.86, p < 0.001). The root mean squared deviation values between flux tower GPP- and the MODIS EVI- and MCD12Q2-retrieved phenology dates were 8, 13, 34, and 16 days and 8, 19, 28, and 18 days for the start of the growing season (SOS), end of the growing season (EOS), peak of the growing season (POS), and growing season length (GSL), respectively, suggesting that MODIS EVI and MCD12Q2 were valuable products for retrieving the vegetation phenological dynamics, except for POS. The partial correlation analysis showed that temperature had a more important role in phenophase than precipitation. Rising temperatures in spring triggered earlier SOS. Significant correlations were found between EOS EVI , EOS MCD12Q2 , EOS GPP , and preseason temperature (60 d prior to EOS) (p < 0.05), indicating that warming over the preseason resulted in earlier EOS. These findings help to understand the discrepancies between MODIS EVI, MCD12Q2, and flux tower GPP-based phenologies, their responses to climatic factors, and further confirm that precipitation should be taken into account to improve the accuracy of phenology models. [ABSTRACT FROM AUTHOR]