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Using less water to generate more power is a goal of the worldwide power industry, but this is difficult to achieve because of the lack of long-term, operational data-based studies. This challenge is especially severe for megacities facing water shortages. This study used long-term data (2005–2015) from Shenzhen, a megacity of over 20 million people that faces severe water shortages, to determine the relationship between water and energy for different types of power generation. It was found that power generation consumed huge amounts of water and that cooling water was the biggest water use category. Smaller power plants, such as the Yueliangwan power plant, which uses the closed cooling method, consume 2.36 million m3 of tap water per year, equivalent to the water supply of a small reservoir. However, larger power plants, such as the Mawan power plant and Dayawan nuclear power plant (using the open cooling method), use 0.92 and 3.42 billion m3 of seawater for cooling every year, respectively, equivalent to about 60% and 200% of the total annual water supply in Shenzhen, respectively. Therefore, large thermal power plants and nuclear power plants should be built in coastal areas with rich water resources rather than in arid or semi-arid areas. Additionally, the water use efficiency of nuclear power plants was found to be 0.22 m3/kWh, which was significantly lower than that of coal-fired power plants (0.10 m3/kWh) and gas-fired power plants (0.09 m3/kWh). Third, the water use efficiency of the closed cooling method was ten times higher than that of the open cooling method. Therefore, the closed cooling method is suitable for power plants constructed in areas without rich water resources. These results are useful for balancing the water and energy demands in the changing world.

Accurate global terrestrial evapotranspiration (ET) estimation is essential to better understand Earth’s energy and water cycles. Although several global ET products exist, recent studies indicate that ET estimates exhibit high uncertainty. With the increasing trend of extreme climate hazards (e.g., droughts and heat waves), accurate ET estimation under extreme conditions remains challenging. To overcome these challenges, we used 3-hour and 0.25° Global Land Data Assimilation System (GLDAS) datasets (net radiation, land surface temperature (LST), and air temperature) and three-temperature (3T) model, without resistance and parameter calibration, in global terrestrial ET product development. The results demonstrated that the 3T model-based ET product agreed well with both global eddy covariance (EC) tower (root mean square error (RMSE) = 24.9 mm month-1) and basin-scale water balance observations (RMSE =116.0 mm yr-1). The 3T model-based global terrestrial ET product was comparable to other common ET products, i.e., MOD16, P-LSH, PML, GLEAM, GLDAS, and Fluxcom, retrieved from various models, but the 3T model performed better under extreme weather conditions in croplands than did the GLDAS, attaining 9.0–20 % RMSE reduction. The proposed ET product could provide periodic and large-scale information to support water cycle-related studies. The dataset is freely available at the Science Data Bank (http://doi.org/10.57760/sciencedb.o00014.00001, Xiong et al., 2022).

The middle Heihe River Basin (MHRB) in arid areas in China faces the challenge of sustainability, but frequent over-irrigation deteriorated the situation. The water balance and energy budget have not been widely used for the quantifying evaluation of over-irrigation. Although some studies have measured the energy budget and water balance in cropland, the energy and water balance in pepper fields is still unclear. An experiment was conducted using an eddy covariance system, SmartView fluke and other measurements in MHRB. The leaf area index (LAI) for pepper increased in the first two months, then decreased thereafter. After Aug. 4, the daily evapotranspiration (ET) decreased during the maturation stage. The soil moisture was higher than the field capacity frequently, indicating that over-irrigation had occurred. Soil water content was relatively high at 100 cm depth, causing high percolation. The water inputs were 1.5 times ET, and the deep percolations accounted for 74% of the total irrigation inputs. Irrigation water could be conserved 301 mm, in case that percolation was avoided. Therefore, the irrigation amount (per time and total) should be reduced to achieve high water use efficiency (WUE). The latent heat flux (LE) consumed 80% of the net radiation (Rn). In July, the LE/Rn was the highest among all months, whereas H/Rn was the lowest due to the highest value of LAI in July. The net radiation had a significant positive linear correlation with the latent heat flux because of the high water supply. Our study showed that there was considerable room for water conservation in MHRB. Keywords: Sensible heat flux; Soil water content; Evapotranspiration; Latent heat flux; Leaf area index

Quadrat sampling is one of the most widely accepted methods for conducting vegetation surveys over the world for centuries. However, it is difficult to determine an optimal size to adequately repre...

Quantifying the uncertainties caused by resistance parameterizations is fundamental for understanding, improving, and developing terrestrial evapotranspiration (ET) models. Using high-density eddy covariance (EC) tower observations in a heterogeneous oasis in northwest China, this study evaluates the impacts of resistances on the estimation of latent heat flux (LE), the energy equivalent of ET, by comparing resistance parameterizations with different complexities under one- and two-source Penman–Monteith (PM) equations. The results showed that the mean absolute percent error (MAPE) for the LE estimates from the one- and two-source PM equations varied from 32% to 53%, and the uncertainties were caused mainly by the resistance parameterizations. Calibrating the parameters required in the resistance estimations could improve the performance of the PM equations; specifically, the MAPEs for the one-source PM equations were approximately 16%, whereas they were 38% for the two-source PM equations, emphasizing that multiple resistances result in increased uncertainties. The following conclusions were reached: 1) the empirical and biophysical parameters required in resistance estimations were responsible for the uncertainty; 2) increasingly complex resistance parameterizations resulted in greater uncertainties in LE estimates; and 3) models without resistance parameterizations exhibited reduced uncertainties in LE estimates.

Ammopiptanthus mongolicus, the only drought-resistant, leguminous, evergreen shrub in the desert region of China, is endangered due to climate change and its growth stages urgently need to be non-destructively detected. Although many spectral indexes have been proposed for characterizing vegetation, the relationships are often inconsistent, making it challenging to characterize the status of vegetation across all growth stages. This study investigated the Spectral Features of the endangered desert plant A. mongolicus at different growth stages, and extracted the identified Spectral Features for the establishment of detection and discrimination models using Partial Least Square Regression (PLSR) and Fisher Linear Discriminate Analysis (FLDA), respectively. The results showed spectral reflectance of A. mongolicus differed across different growth stages and it generally increased with the degree of senescence. Poor performance was found in the single factor model, with RMSE ranging from 20.34 to 27.39 or Overall Accuracy of 60% in the validation datasets. The multivariate PLSR model, based on Normalized Difference Vegetation Index (NDVI), Normalized Difference Red Edge Index (NDRE), Physiological Reflectance Index (PhRI) and Plant Senescence Reflectance Index (PSRI), turned out to be accurate in detecting the growth stages, with R2 of 0.89 and RMSE of 12.46, and the performance of the multivariate FLDA model based on 14 Spectral Features was acceptable, with an Overall Accuracy of 89% in the validation datasets. This research provides useful insights for timely and non-destructively discriminating different growth stages by using multivariate PLSR and FLDA analysis.

Climate models predict rising temperatures and more frequent and prolonged urban heat islands (UHI) in southern China. The urban vegetations have become a focal point to mitigate the detrimental effects of UHI and to provide cooling through transpiration. However, transpiration in trees such as Ficus concinna in relation to extreme long-term conditions of UHI is scarcely documented. Here, we investigated the transpiration dynamics and its cooling effects in F. concinna induced by changes in site environmental variables in a subtropical megacity, Shenzhen over five consecutive years (2015–2019) based on continuous sap flow measurements. Seasonally, the transpiration (Tr) and its cooling effect (i.e., heat energy absorbed (Q) and temperature reduction (ΔT) by Tr) were highest in summer, peaking in the month of July with the mean values of 1.98 mm d−1, 4.91 MJ m−2 d−1 and 3.93 °C m−2 d−1, respectively. The highest cooling effect was shown during warmer and wet years. Daily Tr had a positive linear relationship with shortwave radiation (Rs) in May-June, air temperature (Ta) and volumetric soil water content (SWC30) in July-August and vapor pressure deficit (VPD) in September, respectively. Furthermore, the main regulatory variables of Tr within each season were found to be the spring Rs, summer Ta and SWC30, and autumn Rs and VPD, which explain 49, 82 and 74% of the variation, respectively. The influence of these variables (i.e., Ta, Rs and VPD) on Tr was modified by the effect of SWC30. Interannually, Ta, SWC30 and precipitation (PPT) were responsible for most of the observed variation in Tr, individually explaining 72, 81, and 66% of the variation. Furthermore, multiple regression model indicated that together Ta, SWC30 and PPT explained 89% of the variation in Tr. The diminished sensitivity of Tr to environmental variables and enhanced sensitivity to SWC30 during dry years point to species acclimatization to soil dryness. Our findings clearly indicate the temporal dynamics in Tr and its cooling effectiveness for F. concinna over longer timescales. It is suggested that F. concinna could be better suited in response to increasing temperature in subtropical urban areas, as the species may be capable to provide efficient cooling based on its high Tr rate and has the potential to mitigate the UHI effect.

Widely used in croplands, plastic mulch can significantly change land surface properties and energy partitioning. However, the magnitude of these modifications caused by plastic mulch (and its variations) on leaf area index remain largely unclear. Field experiments were, therefore, conducted to analyse the differences in energy partitioning between plastic mulch and non-plastic mulch conditions in cotton fields in arid Tarim Basin. Each component net radiation, surface soil heat flux, sensible heat and latent heat was either measured or estimated at different growth stages of the cotton crop. Results showed that the effects of plastic mulch on field energy partitioning was most evident when leaf area index was less than 1.0. During this period, net radiation decreased mainly due to the increase of surface reflectance. Surface soil heat flux and sensible heat were also increased due to the increase of surface temperature. Finally, latent heat decreased after plastic mulch application. As over 20% of net radiation was allocated to the soil surface under plastic mulch at the seedling stage, this suggests that surface soil heat flux should not be ignored for evaluating surface energy balance at the seedling stage under plastic mulch conditions.

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] − [AVS])/foc, and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

Agriculture consumes a huge amount of energy every year and then emits lots of greenhouse gases (GHG). Reduction of agricultural energy consumption is important to sustainable agriculture and mitigation of climate change. Groundwater is the main irrigation source in north China’s main food production plains, North China Plain (NCP). Many studies have shown that the groundwater levels here have declined a lot during past decades. However, the related environmental and economic impacts have been rarely researched. This study carries out a detailed research on the changes in energy cost and GHG emissions caused by groundwater level declines on the NCP. Results indicate that during 1996–2013, total agricultural groundwater consumption here has increased by 20%. Over-exploitation of groundwater has caused severe groundwater declines (0.6 m yr−1) and the decline rate has become faster in recent years. As a result, energy use rate for pumping unit water has increased from 0.50 to 0.61 kWh m−3, by nearly 22%. Therefore, GHG emissions have increased from 6.16 to 8.72 Mt CO2e, by 42%. Hebei suffers the most serious groundwater level declines and emits most GHG from pumping, accounting for 47% of the total emissions in the NCP. The economic cost of energy consumption and emission reduction for pumping irrigation is US$ 1.25 billion in 2013, reaching up to 10.3% of GDP in this region. The increasing cost is a great threat to sustainable development of agriculture. Water-saving irrigation is one of the most effective ways to reduce water and energy consumption without loss of grain output. To reduce GHG emissions and pressures on energy and groundwater resources, water-saving irrigation should be greatly promoted in this region. The study would contribute to the development of water-saving and energy-saving agriculture.

Jiuzhaigou Valley (JZG) has been rated as World Heritage, National Nature Reserves and world-class places of interests, due to its fantastic beauty of water. In recent years, however, JZG is losing its beauty with runoff decreasing and stream drying up. An increase of evapotranspiration (ET) over the rehabilitating forest is assumed to be the main reason for runoff decreasing, however, this assumption remained untested for lack of long-term observing data. To test this assumption, a long-term field experiment was carried out from August 2013 to December 2015 in JZG over a typical secondary forest. Meteorological parameters and energy fluxes were measured by eddy covariance system, soil moisture by time-domain reflectometry probes, and ET by eddy covariance method and soil water budget. Results showed that (1) despite the limitation of high elevation, high atmospheric humidity and low annual air temperature, annual ET was quite large. It was 700 mm and 739 mm, respectively for 2014 and 2015, while the corresponding precipitation (P) was 1003 mm and 782 mm. ET/P was close or over 1, which meant that P was mostly used for forest ET and only a very small proportion of P contributed to runoff. (2) The ratio of latent heat flux (LE) to net radiation (Rn) was 0.69 and 0.75 in the growing season of 2014 and 2015, respectively. These high LE/Rn ratio values were considerably higher in JZG than in other areas of the Tibetan Plateau, which could be attributed to better forest rehabilitation in JZG. Our results also showed that ET at the forest site was limited by available energy. We conclude that ET in JZG was energy-limited, whereas forest ET consumed most precipitation. (3) The above assumption is verified to be true. The high ET rate after forest rehabilitation in JZG comes at a cost of decreasing runoff and leads to streams drying up. These results will be useful for sustainable managements of water and forest in JZG.

A study was conducted to quantify temporal variations in physiological responses of Kandelia obovata under multiple heavy metal stress. The results showed that plant growth was not significantly affected by multiple heavy metal stress during the 120-days experiment. At the start, levels of net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) showed effects of "low-promotion, high-inhibition", but Pn and Gs reduced with increasing heavy metal stress at the end. Temporary lipid oxidation was shown by high levels of malondialdehyde (MDA) under high heavy metal stress at the start but was unaffected at the end of the experiment. MDA negatively correlated with biomass and photosynthetic parameters and acted as a sensitive indicator. Proline also shared similar trend and indicated its temporary role in osmotic adjustment. Negative correlations between osmotic adjustment matter and photosynthetic parameters further confirmed the significant role of osmotic adjustment under heavy metal stress.

Above-ground biomass (AGB) is an essential indicator for assessing ecosystem health and carbon storage in desert shrub-related research. Above-ground volume (AGV) of vegetation is a crucial parameter to estimate the AGB. In unmanned aerial vehicle (UAV) remote sensing, the AGV and AGB are mainly estimated by vegetation feature metrics (for example, spectral indices, textural, and structural metrics). However, there is limited study on the AGV and AGB estimation in desert shrub communities by using UAV, and it is difficult to determine the contribution of these metrics to AGV models under eliminating the influence of background factors. Taking a typical desert shrub area in Inner Mongolia, China as an example, this study develops an improved approach to extracted three types of feature metrics simultaneously using UAV RGB (Red, Green, Blue) images. First, digital orthophoto map (DOM) and digital surface model (DSM) were created through the photogrammetric procedure based on UAV RGB images. Second, the digital terrain model (DTM) for canopy height calculation was generated based on DOM and DSM by object-oriented image binary classification and ground elevation interpolation. Here, we recommended the ENVI Landsat Gap-fill tool to interpolate the ground elevation of vegetation areas. Meanwhile, 21 spectral indices, eight textural metrics, and five structural metrics were extracted. Finally, single-variable and multi-variable commonly used regression models were established based on these metrics and measured AGV with a leave-one-out cross-validation. Results showed that: (1) in the proposed model, the contribution of structural, textural, and spectral metric to shrub AGV models was 86.68, 7.08, and 6.24%, respectively. (2) The horizontal and vertical structural metrics, textural metrics, or spectral indices reflected the one-dimensional change of AGV, which had a saturation effect. (3) The canopy volume, combining the horizontal and vertical characteristics of vegetation canopy, could describe the overall change of AGV and played the most essential role in AGV modelling (R2 = 0.928, relative RMSE = 26.8%). The study findings provide a direct reference in determining suitable vegetation feature metrics for monitoring shrub AGV. The proposed approach for DTM generation and AGV estimation is more efficient, accurate and low-cost than before, and it can be a useful bridge between ground-based investigation and satellite remote sensing.

Water resources, which are considerably affected by land use/land cover (LULC) and climate changes, are a key limiting factor in highly vulnerable ecosystems in arid and semi-arid regions. The impacts of LULC and climate changes on water resources must be assessed in these areas. However, conflicting results regarding the effects of LULC and climate changes on runoff have been reported in relatively large basins, such as the Jinghe River basin (JRB), which is a typical catchment (> 45 000 km2) located in a semi-humid and arid transition zone on the central Loess Plateau, northwest China. In this study, we focused on quantifying both the combined and isolated impacts of LULC and climate changes on surface runoff. We hypothesized that under climatic warming and drying conditions, LULC changes, which are primarily caused by intensive human activities such as the Grain for Green Program, will considerably alter runoff in the JRB. The Soil and Water Assessment Tool (SWAT) was adopted to perform simulations. The simulated results indicated that although runoff increased very little between the 1970s and the 2000s due to the combined effects of LULC and climate changes, LULC and climate changes affected surface runoff differently in each decade, e.g., runoff increased with increased precipitation between the 1970s and the 1980s (precipitation contributed to 88 % of the runoff increase). Thereafter, runoff decreased and was increasingly influenced by LULC changes, which contributed to 44 % of the runoff changes between the 1980s and 1990s and 71 % of the runoff changes between the 1990s and 2000s. Our findings revealed that large-scale LULC under the Grain for Green Program has had an important effect on the hydrological cycle since the late 1990s. Additionally, the conflicting findings regarding the effects of LULC and climate changes on runoff in relatively large basins are likely caused by uncertainties in hydrological simulations.

Many remotely sensed evapotranspiration (ET) calculations are based on algorithms that include an aerodynamic resistance-related parameter, which is significantly affected by heterogeneity and could cause the ET to be underestimated as the scale increases, and it is challenging to verify the ET estimation because of the lack of a bridge between satellite-based remote sensing and ground-based measurements. To address this issue, an approach using a “thermal infrared remote sensing + three-temperature model” is proposed and applied under multi-scale conditions. It is hypothesized that good consistency exists between multi-scale aggregations and ET estimates using the proposed method because it does not include aerodynamic resistance. The mothed was verified in the Zhangye Oasis during the first thematic experiment launched under the HiWATER project using extensive eddy correlation (EC) tower observations (a total of 16 EC towers) and multi-scale thermal infrared datasets, including aerial photos (3 m, as a bridge between the ground and satellite measurements), ETM+ (60-m resolution), ASTER (90 m), and MODIS (1000 m). The results show that good agreement is obtained between the EC-measured ET and that using remote sensing techniques under multi-scale conditions. The determination coefficients (R 2 ) between the measured and estimated latent heat flux (LE) values were 0.72, 0.81, 0.61, and 0.53 for the aerial photos, ETM+, ASTER and MODIS, respectively. The respective mean absolute errors (MAEs) were 63.64, 56.56, 59.32, and 80.34 W m −2 , and the mean absolute percent errors (MAPEs) were 12.00, 11.18, 10.78, and 14.60%, respectively. However, the estimated ET became slightly overestimated as the sensor resolution decreased. In addition, the variability of the heterogeneous landscape represented by the range of LE values and the standard deviation decreased gradually as the sensor resolution decreased. Aggregation (up-scaling) of ET from higher-resolution images could better represent the heterogeneity over land surfaces than the original (unaggregated) ET maps, and there is high consistency between multi-scale aggregation and estimation, with a minimum R 2 of 0.76 and a maximum root-mean-square error (RMSE) of 64.80 W m −2 . The proposed methodology is concluded to be a feasible method for estimating ET under multi-scale conditions over heterogeneous landscapes.

Evapotranspiration (ET) is crucial to arid and semiarid environments because it substantially affects the energy and water cycles. Based on the estimation of continuous ET from barren or sparsely vegetated areas, this letter investigated how ET affects the regional land surface temperature (LST) in the Shiyanghe river catchment area, a typical inland river catchment in Northwest China. ET was estimated during 2008–2011 using a three-temperature model and MODIS data sets. LST was retrieved from the MODIS product (MOD11A2). Results taken from transects that began in the oasis area and ended in the desert reveal that ET decreased, with the daily average ET in the oasis being approximately 1.4 mm larger than that in the desert. By contrast, the LST in the oasis was 8 K lower than that in the desert. Statistical results suggested that ET and LST showed a negative relationship ( $R^{2}=0.83$ ). Further analysis showed that the correlation was strongly dependent on the water availability in barren or sparsely vegetated areas. It is concluded that in water-limited barren or sparsely vegetated regions, the negative correlation between ET and LST may provide alternative information for water management, such as identifying groundwater recharge in arid regions.

To investigate the influence of Sonneratia apetala on nutrients and heavy metals in intertidal sediments, sediment cores of S. apetala marsh and mudflat in Shenzhen Bay, China were analyzed. The results showed that S. apetala improved sediment nutrient properties due to increased total carbon (TC), total nitrogen (TN), and total sulfur (TS). The levels of heavy metals were higher in S. apetala site than in mudflat, including chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg). In S. apetala site, TC, TN, and TS were not positively correlated with Cr, Ni, As, Cd, and Pb, indicating their less important roles in trapping heavy metals. There were positive correlations among Ni, Cu, Zn, and Cd in both sites, suggesting similar anthropogenic source. Levels of As were higher than the probable effect level at both sites, indicating their toxicological importance. The geo-accumulation index and potential ecological risk index revealed higher metal contaminations in S. apetala site, especially for Cd, Hg, and As. Multivariate analysis implied that S. apetala alter the biogeochemical cycle of Cd and Cr to a certain extent. These findings indicate that S. apetala may improve soil nutrient properties and facilitate heavy metal accumulation in intertidal sediments.

Quantifying the uncertainties induced by resistance parameterization is fundamental to understanding, improving, and developing terrestrial evapotranspiration (ET) models. Using high-density eddy covariance (EC) tower observations in a heterogeneous oasis in Northwest China, this study evaluates the impact of resistances on latent heat flux (LE) estimations, the energy equivalent of ET, by comparing resistance parameterizations with varied complexity under one- and two-source Penman-Monteith (PM) equations. We then discuss possible solutions for reducing such uncertainties by employing a three-temperature (3T) model, which does not explicitly include resistance-related parameters. The results show that the mean absolute percent error (MAPE) varied from 32 % to 39 % for the LE estimates from the one- and two-source PM equations. When only surface resistance (rs) was parameterized under the one-source network, then the uncertainty (defined as the difference between MAPEs) dropped to 12 %. When both rs and aerodynamic resistance (ra) were parameterized differently under the one- and two-source networks, then the uncertainties in the estimates were 11~23 %, emphasizing that multiple resistances add uncertainties. Additionally, the 3T model performed better than the PM equations, with MAPE of 19 %. The results suggest that 1) although prior calibration of the parameters required in resistance estimations can improve the PM-based LE estimates, resistance parameterization process can generate obvious uncertainties, 2) more complex resistance parameterizations leads to more uncertainty in the LE estimation, and 3) the relatively simple 3T model avoids resistance parameterization, thus introducing less uncertainty in the LE estimation.

Urban shrubs are one of the main components of urban vegetation and play a significant role in mitigating the urban heat island (UHI) through transpiration. As there are no suitable methods to measure the transpiration rate of urban shrubs, many issues related with urban transpiration rate and UHI are still not properly understood. In this study, the two-dimensional (2D) three-temperature (3T) model is extended to three-dimensional (3D) scale and applied to estimate the transpiration rate of typical urban shrubs from May to December in 2018. Three common species of shrubs are observed in this study, namely Lagerstroemia indica cv “Bush”, Podocarpus macrophyllus var. angustifolius, and Ligustrum vicaryi. Estimated transpiration rates are proofed by isotope method. Results show that (1) the modified 3D-3T model is a reliable method for estimating urban shrub transpiration (R2 = 0.61, MAE = 0.10 mm·h−1); (2) urban shrubs have a quite high transpiration rate, ranging from 0.2 to 0.6 mm·h−1 in the daytime; (3) the rate of transpiration varies greatly in different directions of the shrub canopy (top, south, north, east, and west); (4) the 3D-3T model is able to better reflect transpiration characteristics under the heterogeneous condition in urban environments. To the best of our knowledge, the improved 3D-3T model is one of the very few methods that can measuring the transpiration rate of urban shrubs. The results from this study provide meaningful information and a useful tool for measuring urban evapotranspiration and urban planning.

To investigate the rate of sediment accumulation and mercury (Hg) flux in Avicennia marina forest of Deep Bay, China, sediment cores were analyzed. The results showed that Hg concentrations were much higher at all depths compared to the background level. A high correlation between Hg and total organic carbon (TOC) indicated their similar anthropogenic origin. Sedimentation rate was estimated to be 1.38 cm a−1 by 210Pb geochronology. The increase in the mass sediment accumulation rates was rapid (range: 0.5–0.94 g cm−2 a−1), and the Hg fluxes ranged between 76 and 116 ng cm−2 a−1 during the last three decades. The reduction in both Hg concentrations and flux during the last decade may be due to the adoption of contamination control policies. Our results support the notion that the Hg fluxes determined from the sediment cores reveal the effects of anthropogenic influences from the areas around Deep Bay.

Remotely estimating evapotranspiration (ET) and partitioning of its two components, soil evaporation (E) and vegetation transpiration (T), have been challenges for ET studies and their applications. In this study, we reviewed the three-temperature model (3T model) and its applications for thermal remote sensing under multi-scale conditions. There are two submodels in the 3T model: the soil evaporation submodel and the vegetation transpiration submodel. E and T can be separately estimated with these two submodels, and then ET can be obtained by putting E and T together. One of the most significant advantages of the 3T model is that only a minimum number of parameters are required. The necessary parameters for E estimation are net radiation, soil heat flux, surface temperature (drying soil and dry soil), and air temperature, while the parameters for T estimation are net radiation, surface temperature (canopy and dry canopy), and air temperature. Verifications and applications were carried out using ground-based and space-based thermal remote sensing from chamber scale to catchment scale. Verifications were carried out by comparing the estimated results with estimated ET from the Penman-Monteith method and measured ET from weighing lysimeter, Bowen ratio, eddy covariance, and water budget methods. Results showed that the “3T model + thermal remote sensing” approach is a reliable and practical method for remotely estimating ET, especially in arid and semi-arid regions. Therefore, it can be applicable for irrigation water management, water and energy budget monitoring, thermal environment monitoring and evaluation, and other applications.

Study region: The Qilian Mountain, northwestern China. Study focus: Land degradation is a global eco-environmental issue. To minimize soil erosion and land degradation, China has implemented several ecological engineering such as “Grain for Green” program (GFG) since 1999. Relationship between vegetation and water budgets in catchments has been widely studied, however very few studies addressed the effects of eco-environmental restoration on water balance in mountain areas, especially with a focus on soil moisture content. Therefore SWAT model was used to quantify the effects of ecological engineering actions (taken place in 2005) on water balance in Qilian Mountain. New hydrological insights for the region: After the ecological engineering, water yield and soil water content experienced an increment of 32%, and 46%. The opposite trend was monitored in runoff and evapotranspiration, which decreased by 48% and 4%, respectively. Therefore ecosystem restoration have increased soil water retention capacity, a greater proportion of precipitation reaching the catchment is absorbed by the soil rather than flowing out of the region as runoff. Therefore trade-offs between environmental sustainability and water resources security should be carefully addressed in arid region that experienced severe water shortages. Keyword: SWAT, Water balance, Ecosystem restoration, Qilian Mountain

Surface sediments in the Futian mangrove forest (South China) were analyzed for heavy metals including cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn). The heavy metal distributions varied greatly in surface sediments, reflecting some sediment heterogeneity. The heavy metal concentrations decreased in the order of Zn>Cr>Pb>Cu>Cd. According to the mean probable effects level quotient, the combination of studied metals had a 21% probability of being toxic. The potential ecological risk index and geo-accumulation index also revealed high metal contamination. Cd was of primary concern due to its higher assessment values and potential for adverse biological effects. Multivariate analysis implied that clay and silt played a significant role in raising the levels of Cr, Cu and Zn. The percentage of mobile heavy metals was relatively higher, without considerable ecological risk to the biota based on the risk assessment code.

An accurate estimation of evapotranspiration (ET) is crucial to better understand the water budget and improve related studies. Satellite remote sensing provides an unprecedented opportunity to map the spatiotemporal distribution of ET. However, ET values from barren or sparsely vegetated areas in arid regions are often assumed to be zero in typical ET products because of their low values. In addition, separating ET into soil evaporation (E-s) and vegetation transpiration (E-c) is difficult. To address these challenges, we developed an ET product (MOD3T) based on a three-temperature model and thermal remote sensing, specifically Moderate Resolution Imaging Spectroradiometer (MODIS) data. MOD3T has a spatial resolution of 1 km and a temporal resolution of 8 days. All input parameters except air temperature were obtained from MODIS datasets. Validation in two adjacent arid river basins in northwestern China showed that the mean absolute errors (mean absolute percent errors) between the MOD3T and flux tower ET were 0.71 mm d(-1) (18.5%) and 0.16 mm d(-1) (24.9%) for a densely vegetated area and sparsely vegetated sandy desert, respectively. The error between the MOD3T and water balance ET was 24 mm y(-1) (8.1%). The E-c/ET or E-s/ET of MOD3T was comparable to the observed stable oxygen and hydrogen isotopes. Unlike the MODIS ET (MOD16), MOD3T could not provide continuous ET values (as 70% of the MOD16 area lacked data) but exhibited relatively low uncertainty, particularly in cold seasons. Therefore, MOD3T can provide ET, E-s and E-c estimates for arid regions within acceptable ranges. (C) 2015 Elsevier B.V. All rights reserved.

Water quality in China is becoming a severe challenge for agriculture and food safety, and it might also impact health of population via agriculture and food. Thus, it is causing widespread concern. Based on extensive literatures review and data mining, current situation of water pollution in China and its effects on food safety were analyzed. The 2nd National Water Resource Survey in China show that the surface water all over the country was under slight pollution and about 60% of groundwater is polluted. Drinking water quality is basically guaranteed in urban area but it is worrisome in rural areas. In addition, China is the largest consumer of fertilizer and pesticide in the world and the amounts of application still show increasing trends. Fertilizers and pesticides are the most important sources of pollution, which affect human health as persistent organic pollutants and environmental endocrine disruptors. Eutrophication of surface water and nitrate pollution of groundwater are serious threats to drinking water safety. Sewage irrigation is becoming a pollution source to China's water and land because of lacking of effective regulations. Although, with the advance in technology and management level, control of nitrogen and phosphorus emissions and reducing water pollution is still a major challenge for China.

Mitigation of the urban heat island (UHI) effect by regulating the transpiration rate of urban vegetation is one of the most important aspects for adapting to global warming and urbanization. Accurate estimation of the transpiration rate of urban trees is critical for it. Urban trees are usually geographically dispersed (e.g., street trees) and the only feasible method to measure the transpiration rate is the sap flow method, which is seriously limited owing to its destructiveness and lack of representativeness. To overcome this challenge, this study developed an advanced approach based on the three-temperature (3T) model by extending its energy balance from two-dimensional (2D) to three-dimensional (3D). The advanced approach was thus named as the 3D-3T model and verified by the sap flow method. The results showed that: (1) there was a good agreement between the results of the two methodologies in the daytime, with a determination coefficient (R2) of 0.88 and root mean square error (RMSE) of 0.01 mm h−1. This is the first result worldwide to successfully measure the transpiration rate for a large tree without contact or damage. (2) The leaf transpiration rate measured by a LI 6400XT and the plant transpiration transfer coefficient of Ficus concinna from the 3D-3T model also showed a good agreement at nighttime (R2 = 0.97). (3) The urban F. concinna could consume not only most of the net radiation, but also the sensible heat from the surrounding air, thereby helping to reduce the ambient temperature and mitigate the UHI effect. These results provide a feasible way to accurately estimate the transpiration rate of individual urban trees and may be useful for urban environmental management and urban planning.

Jiuzhaigou Valley, a subalpine river valley located in the transition zone between the Tibetan Plateau and the Sichuan Basin, is characterized by fragile ecosystems, strong climate change, and high-intensity human activities which might have changed the energy and water exchange of the wetlands. However, little is known about the seasonal and interannual variability of the surface fluxes and their driving forces in these wetlands owing to the lack of long-term continuous observations. We studied the dynamics of surface fluxes and their controlling factors based on the five-year data collected from July 2013 to April 2019. Our results showed that: (1) the dominant turbulent flux in this ecosystem shifted from sensible heat flux (H) in the frozen period to latent heat flux (LE) in the non-frozen period, especially in the growth period. This fluctuation, which was also reflected by Bowen ratio, highlighted the seasonality of precipitation in the monsoon climate. (2) The energy partitioning with each year was similar across years: LE accounted for approximately 58% of the net radiation, while H accounted for 41% and ground heat flux accounted for 1%. (3) Although the annual precipitation fluctuated between 870 mm and 1089 mm, the interannual fluctuations in evapotranspiration (ET) were less than 41 mm. (4) The wetland ET was predominantly driven by atmospheric demand and was limited to some extent by physiological factors. We then concluded that official management efforts by the local government to increase vegetation cover as well as climate change may lead to an increase in wetland ET, and this change will likely affect local hydrology, climate and the existence of this unique hydrological landscape.

Increasing vegetation is considered one of the most efficient ways to mitigate the urban heat island (UHI) effect due to the cooling effect of evapotranspiration. Considering the adverse consequences of the UHI effect on sustainable development and health problems among city dwellers, the effectiveness of urban vegetation on regulation of the UHI effect should be quantitatively evaluated and analyzed to satisfy the needs of urban planning and policy making. Therefore, in this study we analyzed an one-year field experiment data along an 8-km-long belt transect with various land use types and measured the air temperature at 2-h intervals in Shenzhen, a subtropical megacity in China. The results showed that (1) a higher UHI intensity (UHII) was found during the nighttime throughout the year, with a maximum UHII of 4.02 °C during a heat wave night. (2) Both UHI intensity and the Discomfort Index showed a significant negative linear relationship to vegetated area ratio, especially during nighttime with a strong UHI effect. (3) The UHII decreases by 0.16–0.55 °C during nighttime and 0.05–0.15 °C during daytime, when the vegetated area ratio increases by 10%. (4) Increasing vegetation coverage could significantly reduce air temperature fluctuations and areas with vegetation coverage greater than 55% could maintain a relative stable thermal environment for the dwellers. These results could be useful for urban thermal environmental management and urban planning.

Mangrove forests worldwide are mostly degrading and the degradation can be monitored by the leaf chlorophyll (Chl) content, which can be estimated from a quick non-destructive remote measurement. Although there are extensive studies on spectrometric remote sensing methods, few studies on intertidal mangroves are available, and the non-destructive Chl content monitoring method for mangrove with unique leaf characteristics has not been proposed. To develop a valid, non-destructive method for Chl estimation, this study examined nine commonly used vegetation indexes (VIs) for both adaxial and abaxial leaf surfaces of four mangrove species with different leaf thicknesses. Results showed that the modified Datt index (MDATT) was the most effective for estimating the Chl content for both leaf surfaces of various species. An improved MDATT index (IMDATT), in the form of (R527 − R746)/(R527 − R747), performed best with r = −0.88 and RMSE = 8.70 µg/cm2, among all the optimal VIs tested, and proved to be applicable to monitor Chl content with low sensitivity to the variations of leaf surfaces. It proved to be applicable to monitor Chl content in the validation data sets of all species (r = 0.87 and RMSE = 8.20 µg/cm2) and it could be more effective for specific species, with larger r and smaller RMSE. In addition, the different performances of IMDATT could be attributed to the species, as well as the leaf thickness. In conclusion, IMDATT could be broadly applicable to intertidal mangrove plants, especially for species with thin leaves. The research provides a robust tool for monitoring mangrove Chl content.

Based on the five typical mangrove species in the mangrove wetland of Shenzhen Bay, the contents and distributional characteristics of iron plaques (Fe) and the Mn, Pb, Zn, Cu, As, Cr, Cd, Ni, Co, and Sb enrichment of the iron plaques on mangrove plant roots were investigated. The results show that:① There is a significant difference in the contents of iron plaques among the five mangrove species, and the contents in the species follow the order

BACKGROUND The use of cell-surface display technology to express recombinant proteins on a microbial cell surface can enhance metal adsorption to microbial cells. The transcription factor CadR of Pseudomonas putida shows highly selective affinity with Cd2+. RESULTS CadR was genetically engineered by truncating 47 N-terminal amino acids and 21 C-terminal amino acids in order to maximize its expression efficiency while maintaining its metal-binding domain. The redesigned CadR (named T68CadR) was then displayed with Saccharomyces cerevisiae a-agglutinin cell-surface display system. This engineering approach enhanced the H+/OH− buffering capacity and the Cd2+ adsorption capacity of yeast cells. The surface-engineered cells also performed well at mesophilic and higher temperatures (30–50 °C) under neutral or alkalescent conditions. With an initial concentration of 1.0 mg L−1, the Cd2+ removal efficiency remained 85% when the concentration of Na+ changed from 0 to 400 mmol L−1 (pH 7.8). The surface-engineered cells also showed highly selective adsorption to Cd2+ in the presence of Zn2+ and Pb2+. CONCLUSIONS T68CadR displayed yeast cells constructed in this study provide an option to selectively remove Cd in water. It also might be promising as a tool to determine CadR's Cd-binding mechanism and to improve its selectivity and affinity to Cd2+. © 2015 Society of Chemical Industry