How has carbon storage changed in the Yili-Tianshan region over the past three decades and into the future? What has driven it to change?

Predicting future land use changes and assessing carbon storage remain challenging. Nowadays, how nature and socioeconomics drive changes in carbon storage is a hot topic in research. In this study, through the projection of land use type and the integration of the PLUS, Integrated Valuation of Ecosystem Services and Trade-offs (InVEST), and Geodetector models, we constructed a framework for assessing carbon storage in different land use scenarios. Utilizing this framework, it is possible to project land use change and estimate carbon storage based on different development scenarios. We applied the framework to the Yili Tianshan region and identified the main driving forces for carbon storage change. Further, we estimated the carbon storage in the Yili Tianshan region in 2035 under four scenarios (RE, NE, EP, and CLP). The results showed the following: 1) Between 1990 and 2020, there was an increase in the forest area and water bodies in the Yili-Tianshan region, mainly from bare land. 2) As shown on the time scale, carbon storage increases in the Yili-Tianshan region with a W-shaped fluctuation by converting grasslands and bare land into forests. On a spatial scale, the carbon storage was lower in the center and higher on both sides in the Yili-Tianshan region. 3) In 2035- RE, 2035-ND, and 2035-EP scenarios, the carbon storage was increased by 4.30 Tg, 6.67 Tg, and 12.08 Tg; in the 2035-CLP scenario, it was decreased by 14.63 Tg. The Yili-Tianshan region experienced a notable rise in carbon storage under the 2035-EP scenario compared to the other three scenarios. 4) Soil type played a significant role in the spatial differentiation of carbon storage in Yili-Tianshan (q value 0.5958), followed by population density (0.5394). The changes in carbon storage in the Yili-Tianshan region are the result of synergistic effects of multiple factors, in which the soil type∩soil erosion intensity are the most important. This research could provide a reference method for improving regional carbon storage.

[Seasonal variation of water utilization sources and responses to precipitation in the dominant species of broad-leaved and needle-leaved mixed forests in Mount Lushan, China]. / 庐山针阔混交林优势种水分利用来源季节变化及对降水的响应.

Elucidating the seasonal patterns of water sources for dominant species in the sub-tropical humid mountainous forest, analyzing the eco-hydrological complementarity and competition mechanisms among coexisting species, investigating the responses of plant water utilization to precipitation, could provide a theoretical basis for vegetation restoration and management. Based on the stable hydrogen and oxygen isotope technique, we analyzed the δ2H and δ18O characteristics of precipitation, xylem water from Pinus massoniana and Quercus variabilis, and soil water from 0-100 cm depth in Mount Lushan, China. The MixSIAR model, Levins index, and PS index were used to calculate the relative contribution rate of each water source, the hydrological niche breadth, and niche overlap of P. massoniana and Q. variabilis. The results showed that, in the wet season (March to July), P. massoniana primarily utilized soil water from the 0-20 cm and 20-40 cm depths, while Q. variabilis primarily utilized that from the 20-40 cm and 40-60 cm depths. During the dry season (August to September), P. massoniana and Q. variabilis utilized 40-60 cm and 60-80 cm of soil water, respectively, resulting in an increase in the depth of water absorption. In the early growing season (March to April) and the late growing season (September), there was a high hydrological niche overlap between P. massoniana and Q. variabilis, resulting in intensitive water competition. In the middle of the growing season (May to August), the water source was adequately allocated, and the hydrolo-gical niche was segregated to meet the high transpiration demand. Q. variabilis primarily utilized soil water from a depth of 60-80 cm and 60-80 cm before a precipitation event, and from a depth of 0-20 cm and 20-40 cm after the event. In contrast, P. massoniana primarily utilized soil water from a depth of 0-20 cm and 20-40 cm both before and after a precipitation event. In conclusion, water utilization patterns of P. massoniana and Q. variabilis exhibited a seasonal trend, with shallow water uptake during the rainy season and deep water uptake during the dry season. These species are capable of efficiently allocating water resources during the peak growth season, and their root systems actively respond to change in soil moisture level. They have strong adaptability to extreme precipitation events and exhibit remarkable water conservation capabilities.

[Ecological Environment Assessment and Driving Mechanism Analysis of Nagqu and Amdo Sections of Qinghai-Xizang Highway Based on Improved Remote Sensing Ecological Index].

The ecological environment along the Qinghai-Xizang highway is an important part of the construction of the ecological civilization in the Xizang region, and current research generally suffers from difficulties in data acquisition, low timeliness, and failure to consider the unique "alpine saline" environmental conditions in the study area due to the unique geographical environment of the Qinghai-Xizang plateau. Based on the GEE platform and the unique geographical environment of the study area, the remote sensing ecological index (RSEI) was improved, and a new saline remote sensing ecological index (SRSEI) applicable to the alpine saline region was constructed by using principal component analysis as an ecological environment quality evaluation index. The spatial distribution pattern and temporal variation trend of ecological environment quality along the Qinghai-Xizang Highway Nagqu-Amdo section were analyzed at multiple spatial and temporal scales using the ArcGIS 10.3 platform and geographic probes, and the driving mechanisms of eight control factors, including natural and human-made, on the spatial and temporal changes in SRSEI were investigated. The results showed that:① compared with RSEI, SRSEI was more sensitive to vegetation and had a stronger discriminatory ability in areas with sparse vegetation and severe salinization, which is suitable for ecological quality evaluation in alpine saline areas. ② The spatial scale of ecological environment quality in the study area had obvious geographical differentiation, and the areas with poor ecological quality were mainly concentrated in the northern Amdo County, whereas the areas with excellent and good quality grades were mainly distributed in the central-western and southeastern Nagqu areas. On the temporal scale, the ecological environment of the study area as a whole showed an improvement trend over 32 years, and the vegetation cover in the central-western and southeastern areas increased significantly, which had a strong improvement effect on the ecological environment. The improvement area was 1 425.98 km2, accounting for 99.82%. The mean value of SRSEI was 0.49, with an overall fluctuating upward trend and an average increase of 0.015 7 a-1. ③ The land use pattern was the most driving influence factor in the change of ecological environment quality in the study area, with an average q value of 0.157 6 over multiple years, and the influence of environmental factors was low. The multi-factor interaction results showed that the ecological environment in the study area was the result of multiple factors acting together, all factors had synergistic enhancement under the interaction, the influence of human factors was gradually increasing, and the interaction of the net primary productivity (NPP) of vegetation and land use pattern was the main interactive control factor of ecological environment quality in the study area. This study can provide a theoretical basis for ecological environmental protection and sustainable development along the Nagqu to Amdo section.

[Enrichment Characteristics, Source Apportionment, and Risk Assessment of Heavy Metals in the Industrial and Mining Area of Northern Guangdong Province].

In order to understand the heavy metal pollution of the industrial and mining area in northern Guangdong Province, topsoil samples (0-20 cm) from 209 sites in study area were collected, and the concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were analyzed. The source and distribution characteristics of Cd, Cr, Hg, Ni, Pb, As, Cu, and Zn in soil samples were analyzed using the geographic information system (GIS) and principal component analysis (PCA), and the geo-accumulation index and potential ecological hazard index were used to evaluate their pollution status and ecological risk. The results showed that:① Except Ni, all seven heavy metal elements exceeded the national soil background value but were below the pollution risk screening value. The soil environment as a whole was relatively clean. ② The spatial distribution of heavy metals in soil differed. The contents of As and Pb showed northwest-southeast zonal distribution. The contents of Cd, Cu, Hg, and Zn generally decreased from the middle to the surrounding, which was consistent with the industrial and mining enterprise locations. However, the spatial distribution of Cr and Ni had no direct relationship with the location of pollution sources such as industrial enterprises. ③ The eight heavy metals could be identified as three principal components (PCs). PC1 (Cd, Cu, Pb, and Zn) was mainly affected by human activities such as lead-zinc deposit dressing, traffic emissions, and agricultural production. However, PC2 (Cr and Ni) was a natural source, mainly affected by soil parent material. In addition, PC3 (As and Hg) was mainly affected by industrial activities such as non-ferrous metal smelting and thermal power generation. ④ According to the geo-accumulation index method, the risk degree of the eight heavy metals was:Cd>As>Zn>Hg>Pb>Cu>Cr=Ni. The contents of Cr and Ni in soil were at a no-risk level; the contents of As, Cu, Hg, Pb, and Zn were at a low-risk level; and the content of Cd was at a high-risk level. Most potential ecological hazards for single elements in the study area were at a mild risk level. In contrast, a small proportion of the surface soils in areas of intense industrial activity were subject to substantial levels of heavy metal stress and require further attention.

[Effects of CO2 concentration and soil water content on short-term water-use efficiency at whole-plant level]. / CO2浓度和土壤含水量对植物个体尺度短期水分利用效率的影响.

Uncovering the variations of short-term water-use efficiency (WUEp) at whole-plant level in response to CO2 concentration (Ca) and soil water content (SWC) can improve the understanding of plant survival strategies under climate change. In this study, Platycladus orientalis saplings were cultured in simulated climate chambers.There were totally 15 treatments, including Ca of 400 (C400), 600 (C600) and 800 (C800) µmol·mol-1 and SWC of 35%-45% field water holding capacity (FC), 50%-60%FC, 60%-70%FC, 70%-80%FC and 95%-100%FC. The WUEp was measured by mini-lysimeters, weighting method, and static assimilation chamber. The results showed that both daytime (0.12-1.87 mol·h-1) and nighttime transpiration rates (0.01-0.16 mol·h-1) at whole-plant level reached the maximum at C400×70%-80%FC, while the whole-plant daytime net photosynthetic rate (2.12-22.10 mmol·h-1) reached the maximum at C800×70%-80%FC. In contrast, nighttime respiration rate (0.84-4.41 mmol·h-1) increased with increasing SWC, but decreased with increasing of Ca, reaching the maximum at C400×95%-100%FC. For WUEp (5.37-24.35 mmol·mol-1), it reached the maximum at C800×50%-60%FC, indicating that plants could use less water and fixed more carbon by adjusting adaptation strategies under high Ca and drought conditions. In addition, leaf instantaneous water-use efficiency was a good predictor of WUEP when the canopy structure was similar.

Soil water stress overrides the benefit of water-use efficiency from rising CO2 and temperature in a cold semi-arid poplar plantation.

The counteractive effect of atmospheric CO2 (ca ) enrichment and drought stress on tree growth results in great uncertainty in the growth patterns of forest plantations in cold semi-arid regions. We analysed tree ring chronologies and carbon isotopes in Populus simonii plantations in cold semi-arid areas in northern China over the past four decades. We hypothesized that the hydraulic stress from drought would override the stimulating effect of increasing ca and temperature (T) on stem growth (basal area increment [BAI]). We found the stimulating effect of rising ca and T on the growth, indicated by continuous increase of intrinsic water-use efficiency in all stands and a positive correlation between T and BAI. However, these effects failed to alleviate the negative impacts of drought on tree growth. Concurrent acceleration of BAI reversed during the intensive drought episodes. Water stress resulted from inaccessibility of roots to deep soil water rather than from lack of precipitation, suggested by the decoupling of BAI from precipitation and vapour pressure deficit. Local soil water limitation might also cause greater stomatal regulation in declining trees, indicated by lower intercellular CO2 concentration. Thus, site-specific soil moisture conditions growth sensitivity to global warming resulting in site-specific decline episodes in drought-prone areas.

[Erosion process of loess slope and influencing factors in the loess hilly-gully region, China]. / é»„åœŸä¸˜é™µæ²Ÿå£‘åŒºé»„åœŸå¡é¢ä¾µèš€è¿‡ç¨‹åŠå ¶å½±å“å› ç´ .

Rainfall intensity, slope length, and slope gradient are the important factors affecting runoff and sediment yield. In order to quantitatively analyze the effects of rainfall intensity, slope length, and slope gradient on the erosion process of Ansai loess slope in loess hilly and gully region, we analyzed the variation of runoff and sediment yield on Ansai loess with two slope lengths (5, 10 m), three slopes (5°, 10°, 15°) and two rainfall intensities (60, 90 mm·h-1) in an indoor simulated rainfall experiment. The results showed that the initial runoff generation time decreased with the increases of slope length, though the overall change was not significant. The initial runoff generation time decreased with the increases of rainfall intensity. Compared with the intensity of 60 mm·h-1, the initial runoff generation time decreased by 5.7-18 min under the intensity of 90 mm·h-1. Among them, the runoff initiation time on the slope of 10° was the fastest. With the duration of rainfall, runoff yield rate increased rapidly at first, and then gradually fluctuated around a certain value. The sediment yield rate increased rapidly in a short period of time at the initial stage of runoff generation, and then decreased after reaching the maximum, and being gradua-lly stable. The rates of runoff and sediment yield increased with the increases of slope length and rainfall intensity, but the law of change with slope was not obvious. With the increases of rainfall intensity, slope length and gradient, the total sediment yield increased accordingly. Under the rainfall intensity of 90 mm·h-1, the slope surface with the length of 10 m and slope of 15° generated rill, leading to the highest total erosion amount (11885.66 g). Under the rainfall intensity of 60 mm·h-1, the erosion amount per unit area decreased with the increases of slope length, and there was a critical erosion slope length in 5-10 m slope section. Slope length, slope and rainfall intensity all played a promoting role in runoff process. Rainfall intensity, slope length, and their interaction contributed more to runoff yield rate and total erosion amount. Rainfall intensity contributed the most to runoff yield rate, with a contribution rate of 49.8%. The contribution rate of slope length to the total erosion was the largest, which reached 37.8%.

[Quantitative separation of evapotranspiration components of Platycladus orientalis ecosystem based on multiple isotope models]. / åŸºäºŽå¤šç§åŒä½ç´ æ¨¡åž‹çš„ä¾§æŸæž—ç”Ÿæ€ç³»ç»Ÿè’¸æ•£ç»„åˆ†å®šé‡æ‹†åˆ†.

To fully understand the changes in the evapotranspiration components in forest ecosystem and their contribution to evapotranspiration at daily scale, we used the hypothesis theory of isotopic steady state and non-steady state combined with the water isotope analyzer system to quantitatively split and compare the evapotranspiration components of Platycladus orientalis ecosystem during the growing season. Results showed that the 18O of water from different sources during the four mea-surement days (August 5, 8, 10, 11, 2016) all showed surface soil water and oxygen isotope composition (δS) > branch water and oxygen isotope composition (δX) > atmospheric water vapor oxygen isotopes composition (δV), with obvious differences due to the isotope fractionation. Oxygen isotopes composition of soil evaporated water vapor (δE) was between -26.89‰ï½ž-59.68‰ at the daily scale, showing a pattern of first rising and then decreasing. The oxygen isotopic composition of evapotranspiration water vapor in forest ecosystem (δET) was between -15.99‰ï½ž-10.04‰. The oxygen isotopic composition of transpired water vapor under steady state(δT-ISS) was between -12.10‰ï½ž-9.51‰. The oxygen isotopic composition of transpired water vapor under non-steady state (δT-NSS) was between -13.02‰ï½ž-7.23‰. δET and δT-NSS had the same changing trend throughout the day at the daily scale, while the trend of δET, δT-ISS and δT-NSS was approximately the same during 11:00-17:00. In general, the contribution rate of plant transpiration to total evapotranspiration showed that FT-ISS was between 79.1%-98.7%, and FT-NSS was between 88.7%-93.7%. Our results suggested that water consumption through soil evaporation was far less than that of vegetation transpiration in the study area, and that vegetation transpiration dominated forest evapotranspiration.

Effects of thinning intensity on the understory water-holding capacity of Pinus sylvestris var. mongolica plantation in the Bashang area of north China.

The complex terrain and poor climatic conditions in Bashang area of Hebei Province result in water and soil loss and geological disasters, which pose a serious threat to ecological safety in North China. In order to improve local environmental quality, barren-resistant and fast-growing tree species such as Pinus sylvestris var. mongolica and Larix gmelinii are planted with large areas. However, unreasonable plantation density will lead to inefficient utilization of rainfall and intensify the conflict between forest and water. In this study, we analyzed the effects of five thinning intensities (0, 20%, 40%, 60%, 80%) of P. sylvestris var. mongolica plantation on herbs, litter, soil and overall water-holding capacity, with the aim to provide scientific basis for management of P. sylvestris var. mongolica. The results showed that water-holding rate of herb varied from 47.7% to 90.7%, and that the water-holding capacity of herb decreased with increasing thinning intensity. When the thinning intensity was less than 40%, water-holding capacity decreased slowly, and then decreased rapidly. With the increase of thinning intensity, natural water-holding rate and maximum water-holding rate of undecomposed layer and semi-decomposed layer decreased gradually, with the effective water-holding rate being 60%>40%>20%>80%>0, and the water-holding capacity of semi-decomposed layer being better than that of undecomposed layer. The water-holding capacity of soil decreased gradually with the increases of thinning intensity. Thinning intensity less than 40% promoted water holding capacity. Under different thinning intensities, the total water-holding rate of understory was 8.3%-14.3%, with an order of 20%>0>40%>60%>80%. In view of understory all layers and overall changes, the thinning intensity at 20% in the study area could effectively improve the understory water-holding capacity and achieve better ecological benefits.

Effects of watershed char and climate variables on annual runoff in different climatic zones in China.

The complex interactions between climate and watershed characteristics lead to diverse annual runoff responses. Understanding the mechanism by which different climatic and watershed factors affect annual runoff is helpful in understanding the resulting changes in the hydrological process. In this study, the characteristics of 73 watersheds were analyzed. The basins were divided into three categories according to their climatic regions: temperate continental climate (n = 7); temperate monsoon climate(n = 36); and subtropical monsoon climate(n = 30). Correlation analysis, linear regression, and path analysis were used to quantify the effects of selected watershed characteristics and meteorological conditions on long-term runoff. Results showed that the average annual runoff coefficient was strongly correlated with basin area, showing a scale effect. The average annual runoff depth was strongly positively correlated with precipitation for the all watersheds. As the drought index (DI, the ratio of annual evaporation capacity to annual precipitation) increased, the annual runoff depth decreased logarithmically. The average annual rainfall and runoff depth of watersheds in the subtropical monsoon climate zone were significantly higher than those in other climatic zones, and there was no significant difference in potential evaporation between the temperate monsoon climate and subtropical monsoon climate zones. With increases in both the drought index (Ep/P) and moisture index (E/P), the vegetation distribution in the basin showed an increasing trend in farmland area and decreasing trend in forest area. Path analysis showed that rainfall had a positive effect on annual average runoff depth (ranging from 31 to 62%) while actual evapotranspiration had a negative impact (ranging from 17 to 47%). For all basins, a negative effect (13-25%) of basin area on runoff depth was observed, while forestland area had a positive effect (7-39%) on runoff depth. This study further quantified the effects of climatic and geographical factors on the long-term water balance in different climatic regions.

Comparison of agricultural wastes and synthetic macromolecules as solid carbon source in treating low carbon nitrogen wastewater.

This paper investigated the feasibility of using agricultural wastes and synthetic macromolecules as solid carbon sources and studied the effects of improvement of denitrification by the selected agricultural wastes. The carbon release capacity and denitrification performance of corncob (CC), peanut shell (PS), obsolescent rice (OR) and polycaprolactone (PCL), poly butylene succinate (PBS), polyvinyl alcohol sodium alginate (PVA-SA) were systematically analyzed. The results showed that for each carbon source, the first-order kinetic equation was basically followed during the carbon release process. PVA-SA, CC and PS had higher carbon release capacity with accumulative dissolved organic carbon (DOC) of 16.22-20.63 mg·g-1 and chemical oxygen demand (COD) of 100.86-134.10 mg·g-1. Correspondingly, they showed excellent denitrification performance with almost no residual NO3--N, and the denitrification process well followed the Monod equation. PCL, PBS and OR had lower carbon release capacity with accumulative DOC of 2.06-3.14 mg·g-1 and COD of 13.29-24.13 mg·g-1, respectively. Nevertheless, these materials can also improve the denitrification performance, with the residual NO3--N in the range of 6.02-6.36 mg·L-1, and the effluent DOC was in the range of 10-15 mg·L-1. Synthetic polymers are more suitable for nitrogen removal in groundwater treatment, while agricultural wastes are ideal carbon sources for secondary effluent treatment.

Environmental and physiological controls on diurnal and seasonal patterns of biogenic volatile organic compound emissions from five dominant woody species under field conditions.

Biogenic volatile organic compounds (BVOCs) play essential roles in tropospheric chemistry, on both regional and global scales. The emissions of large quantities of species-specific BVOC depend not only on environmental (temperature, T; photosynthetically active radiation, PAR), but also physiological parameters (i.e. net photosynthetic rate, Pn; transpiration rate, Tr; stomatal conductance, gs and intercellular CO2 concentration, Ci). Here, isoprene, monoterpene and sesquiterpene emissions were determined from five dominant mature woody tree species in northern China, which are two evergreen conifers (Pinus tabuliformis and Platycladus orientalis) and three broad-leaved deciduous trees (Quercus variabilis, Populus tomentosa and Robinia pseudoacacia). A dynamic enclosure technique combined with GC-MS was used to sample BVOCs and analyse their fractional composition at daily and annual scales. The diurnal data showed that both isoprene and monoterpene emissions increased with increasing temperature, and reached their maximum emission rates in the peak of growing season for both coniferous and broad-leaved species. The emissions of individual compound within the monoterpenes and sesquiterpenes were statistically correlated with each other for all species. Furthermore, some oxygenated monoterpene emissions were highly correlated to sesquiterpenes in all tree species. Linking BVOC emissions to environmental and leaf physiological parameters exhibited that monoterpene emissions were linearly and positively correlated to the variation of T, PAR, Pn and Tr, while their relationship to gs and Ci is more complex. Collectively, these findings provided important information for improving current model estimations in terms of the linkage between BVOC emissions and plant physiological traits. The data presented in this study can be used to update emission capacity used in models, as this is the first time of reporting BVOC emissions from five dominant species in this region. The whole-year measurement of leaf-level BVOCs can also advance our understanding of seasonal variation in BVOC emissions.

[Effects of soil water stress and atmospheric CO2 concentration on photosynthetic and post-photosynthetic fractionation].

Analysis of plant photosynthesis and post-photosynthetic fractionation can improve our understanding of plant physiology and water management. By measuring δ13C in the atmosphere, and δ13C of soluble compounds in leaves and branch phloem of Platycladus orientalis, we examined discrimination pattern, including atmosphere-leaf discrimination during photosynthesis (ΔCa-leaf) and leaf-twig discrimination during post-photosynthesis (ΔCleaf-phlo), in response to changes of soil water content (SWC) and atmospheric CO2 concentration (Ca). The results showed that ΔCa-leaf reached a maximum of 13.06‰ at 95%-100% field water-holding capacity (FC) and Ca 400 µmol·mol-1, and a minimum of 8.63‰ at 35%-45% FC and Ca 800 µmol·mol-1. Both stomatal conductance and mesophyll cell conductance showed a significant linear positive correlation with ΔCa-leaf, with a correlation coefficient of 0.43 and 0.44, respectively. ΔCleaf-phlo was not affected by SWC and Ca. Our results provide mechanism of carbon isotopes fractionation and a theoretical basis for plant survival strategies in response to future climate change.

[Assessing water sources for Populus simonii with different degrees of degradation based on stable isotopes].

Water availability is the key factor limiting plant growth in arid regions. Populus simonii is a typical shelterbelt tree species in Zhangbei County, Hebei Province, with an important role in constructing ecological barrier. With stable isotope technique, graphical method, and multiple linear mixing model, we analyzed water sources and water use strategies of P. simonii in different growth periods with four different degrees of degradation (non-degraded, slightly degraded, modera-tely degraded and severely degraded) in Zhangbei County. Results would help improve our understanding on the cause and mechanism of the large-scale degradation of P. simonii in this area. The results showed that water sources of P. simonii in the early growth stage (May-June) from all four degradation degrees were relatively simple. P. simonii mainly used soil water in 0-40 cm, with the utilization rates being 34.2%, 50.1%, 41.6%, and 55.7% for the four degradation degrees, respectively. At the middle growth stage (July-August), non-degraded P. simonii utilized soil water from layers of 200-280 cm and 280-400 cm, with utilization rates of 20.2% and 30.9%, respectively. Soil water at 200-280 cm and 280-400 cm layers was utilized by slightly degraded poplar, with the contribution rates of each layer being 33.2% and 27.9%, respectively. Moderately degraded P. simonii utilized soil water from the depths of 0-40 cm and 40-120 cm, with the rates of 30% and 26.9%, respectively. Water utilization rate of severely degraded P. simonii to 0-40 cm depth was 55.4%. At the late growth stage (September-October), water sources of non-degraded P. simonii transferred to the upper-middle soil layers, with the utilization rate of 0-40 cm, 40-80 cm, and 80-120 cm being 23.3%, 17.2%, and 16.5%, respectively. The utilization rate of the slightly degraded P. simonii was 35.7% at 0-40 cm and 20.6% at 80-200 cm. The moderately and severely degraded P. simonii mainly utilized soil water at 0-40 cm layer, with the contribution rates of soil water being 43.7% and 51.8%, respectively. With the exacerbation of degradation, the main water source of P. simonii gradually transferred from deep to surface soil water.

[Simulation of δ18O in Platycladus orientalis leaf water with different kinetic fractionation coefficients].

Clarifying 18O isotope composition of leaf water (δL,b) would provide theoretical refe-rence for the study of leaf physiology and forest hydrology. We continuously monitored the concentration of atmospheric water vapor (Wa) and 18O isotope composition of atmospheric water vapor (δv) at the canopy of Platycladus lateralis plantation in the mountain area of Beijing. We analyzed the effects of kinetic fractionation coefficients Δk1(32%) and Δk2(28%) on the prediction of δL,b by combining the measured leaf water 18O isotope (δx) and δL,b of P. lateralis. The results showed that the diurnal variation of Wa was irregular. Atmospheric relative humidity (RH) showed a "V" shape of diurnal variation, and stomatal conductance (gs) increased first and then decreased at the diurnal scale. Wa, RH, and gs showed a significant negative correlation with δL,b when isotopes approached a steady-state equilibrium around noon. The kinetic fractionation coefficient Δk1 and Δk2 were applied to the Craig-Gordon model to predict δL,b under the isotopic quasi-steady-state condition. The results showed that the predicted values of Δk2 approached the observed values of δL,b. This result indicated that the application of Δk2 to the model was more consistent with the change of water isotope concentration in the leaves of P. lateralis in the mountain area of Beijing. These results would improve our understanding of water isotope enrichment model and evapotranspiration resolution model in leaves.

[Partitioning ecosystem respiration of a Platycladus orientalis forest in the west mountainous area of Beijing, China using stable carbon isotope].

Based on stable carbon isotope, we quantitatively partitioned ecosystem respiration in a Platycladus orientalis forest in the west mountainous area of Beijing. Results from this study could lay the foundation for carbon exchange research in forest ecosystems of this region. The spectroscopy technique was used to continuously measure CO2 concentrations and δ13C values at different height of the forest. Soil and branch chambers were used for measuring nighttime δ13C values in underground and aboveground respiration, and then the proportions of respiration components were calculated. Combined with soil respiration efflux measurement, ecosystem respiration was then quantitatively partitioned. The results showed that δ13C values of respiratory components fluctuated, which ranged from -31.74‰ to -23.33‰ in aboveground respiration of plants and from -32.11‰ to -27.74‰ in soil respiration. The δ13C values of ecosystem respiration was at the middle of those ranges. Soil respiration averaged 1.70 µmol·m-2·s-1 at night, accounting for 47%-91% of ecosystem respiration. Aboveground respiration averaged 0.72 µmol·m-2·s-1, contributing less to ecosystem respiration. Daytime respiration based on isotope mixing model calculation had greater variability than that based on temperature response model, with a mean value of 2.31 µmol·m-2·s-1 and 2.28 µmol·m-2·s-1, respectively.

Effects of Simulated Gravel on Hydraulic Characteristics of Overland Flow Under Varying Flow Discharges, Slope Gradients and Gravel Coverage Degrees.

To quantify the hydraulic characteristics of overland flow on gravel-covered slopes, eight flow discharges (Q) (8.44-122 L/min), five slope gradients (J) (2°-10°) and four gravel coverage degrees (Cr) (0-30%) were examined via a laboratory flume. The results showed that (1) gravel changed flow regime. Gravel increased the Reynolds number (Re) by 2.94-33.03%. Re were less affected by J and positively correlated with Cr and Q. Gravel decreased the Froude number (Fr) by 6.83-77.31%. Fr was positively correlated with Q and J and negatively correlated with Cr. (2) Gravel delayed the flow velocity (u) and increased the flow depth (h) and flow resistance (f). Gravel reduced u by 1.20-58.95%. u was positively correlated with Q and J and negatively correlated with Cr. Gravel increased h by 0.12-2.41 times. h was positively correlated with Q and Cr and negatively correlated with J. Gravel increased f by 0.15-18.42 times. f were less affected by J, positively correlated with Cr and negatively correlated with Q. (3) The relationships between hydraulic parameters and Q, J and Cr identified good power functions. Hydraulic parameters were mainly affected by Cr. These results can guide the ecological construction of soil and water conservation.

Size distribution of particulate matter in runoff from different leaf surfaces during controlled rainfall processes.

The presence of plant leaves has been shown to lower the risks of health problems by reducing atmospheric particulate matter (PM). Leaf PM accumulation capacity will saturate in the absence of runoff. Rainfall is an effective way for PM to "wash off" into the soil and renew leaf PM accumulation. However, little is known about how PM wash-off varies with PM size and health problems caused by particulate pollution vary with PM size. This study thus used artificial rainfall with six plant species to find out how size-fractioned PM are washed off during rain processes. Total wash-off masses in fine, coarse and large fractions were 0.6-10.3 µg/cm2, 1.0-18.8 µg/cm2 and 4.5-60.1 µg/cm2 respectively. P. orientalis (cypress) and E. japonicus (evergreen broadleaved shrub) had the largest wash-off masses in each fraction during rainfall. P. cerasifera (deciduous broadleaved shrub) had the largest cumulative wash-off rates in each fraction. Rainfall intensity had more influence on wash-off masses and rates of large particles for six species and for small particles in evergreen species, but limited effect on wash-off proportions. Wash-off proportions decreased in large particles and increased in small particles along with rainfall. The results provide information for PM accumulation renewal of plants used for urban greening.

Scale effects on runoff and a decomposition analysis of the main driving factors in Haihe Basin mountainous area.

Catchment runoff scale relationships comprise an important theoretical support for water resource management. However, previous understandings of the scale effect were mostly based on empirical summaries and quantitative research, while interpretation based on measured data was rare. The purpose of this paper was to quantitatively reveal the causes of runoff scale impacts in the Haihe mountainous area over a 20-year period. Fifty-seven catchments (92-15803 km2) were selected from the available hydrological sites. Multi-year average values for17 environmental variables were calculated in each catchment over the study period, including data on hydrology, meteorology, vegetation, land use, topography, and soil. Based on these data, the quantitative relationship between runoff and catchment area was first established. Then the correlation between environmental factors and runoff scale impacts was assessed. Finally, catchments were divided into three groups by area, and the dominant factors influencing runoff at different scales, as well as the direct and indirect effects of these factors on runoff, were obtained using stepwise regression and path analysis. The results showed that: 1) Runoff coefficients decreased logarithmically as catchment area increased and the scale distribution characteristics of the variables closely related to runoff were an important reason for the runoff scale effect. 2) Larger river basins had fewer sensitivity factors for runoff and the impacts of vegetation and land use factors were mainly reflected in small and medium catchments. 3) Vegetation and land use primarily had indirect effects, which determined the proportion of factors in the total effect. Among these, the indirect effects of farmland were very prominent, which implied that human activities have had an important influence on runoff scale effects. This study emphasized the importance of farmland management in the upstream areas of Haihe mountainous area, and provides important theoretical support for catchment scale effects and water resource management in water-limited regions.

Biological denitrification using polycaprolactone-peanut shell as slow-release carbon source treating drainage of municipal WWTP.

The development of slow-release carbon source is an effective way to reduce the total nitrogen (TN) in low carbon to nitrogen ratio wastewater. In this study, a novel solid slow-release carbon source (PPP) was prepared using polycaprolactone (PCL) and peanut shell (PS) as carbon sources with polyvinyl alcohol-sodium alginate (PVA-SA) as hybrid scaffolds. The carbon release properties of PPP and each carbon source materials were compared. The performances of nitrogen removal and microbial community structure using PPP as external carbon source were investigated. The results showed that PPP had the best slow-release performance, and its release process followed the first-order release equation. The ratio of acetic acid, propionic acid and butyric acid in released organic matter was stable at (75.73 ±â€¯4.62)%:(17.22 ±â€¯4.53)%:(7.06 ±â€¯1.02)%. When using PPP as an external carbon source for denitrification, the relative abundance of Gammaproteobacteria increased from 39.32% to 46.66%, while the Shannon index decreased from 8.59 to 8.29. The utilization efficiency of PPP was determined by the ratio of the organic matter releasing rate to the released organic matter consumption rate. By optimizing the PPP dosage, both high nitrogen removal efficiency and low residual organic matter could be achieved.