The dominant influencing factors of desertification and ecological risk changes in Qinghai Area of Qilian Mountains National Park: Climate change or human activity?

Transitional features of desert environments partially determine the risks associated with ecosystems. Influenced by climate change and human activities, the variability and uncertainty of desertification levels and ecological risks in the Qinghai Area of Qilian Mountain National Park (QMNPQA) has become increasingly prominent. As a critical ecological barrier in northwest China, monitoring desertification dynamics and ecological risks is crucial for maintaining ecosystem stability. This study identifies the optimal monitoring model from four constructed desertification monitoring models and analyzes spatiotemporal changes in desertification. The spatial and temporal changes in ecological risks and their primary driving factors were analyzed using methods such as raster overlay calculation, geographic detector, cloud model, and trend analysis. The main conclusions are as follows: The desertification feature spatial model based on GNDVI-Albedo demonstrates better applicability in the study area, with an inversion accuracy of 81.24%. The levels of desertification and ecological risks in QMNPQA exhibit significant spatial heterogeneity, with a gradual decrease observed from northwest to southeast. From 2000 to 2020, there is an overall decreasing trend in desertification levels and ecological risks, with the decreasing trend area accounting for 89.82% and 85.71% respectively, mainly concentrated in the southeastern and northwestern parts of the study area. The proportion of areas with increasing trends is 4.49% and 7.05% respectively, scattered in patches in the central and southern edge areas. Surface temperature (ST), Digital Elevation Map (DEM), and Green normalized difference vegetation index (GNDVI) are the most influential factors determining the spatial distribution of ecological risks in QMNPQA. The effects of management and climatic factors on ecological risks demonstrate a significant antagonistic effect, highlighting the positive contributions of human activities in mitigating the driving effects of climate change on ecological risks. The research results can provide reference for desertification prevention and ecological quality improvement in QMNPQA.

Biomonitoring of polycyclic aromatic hydrocarbons (PAHs) by Murraya paniculata (L.) Jack in South Kolkata, West Bengal, India: spatial and temporal variations.

Attempts have been made in the present study for ascertaining the concentrations of atmospheric polycyclic aromatic hydrocarbons (PAHs) using passive biosamplers in preference to conventional air sampling methods. Mechanical stirring, sonication, Soxhlet technique and microwave-assisted Soxhlet extraction (MASE) were employed to extract PAHs from an evergreen plant (Murraya paniculata) leaves (having long life-span) sampled from polluted places of South Kolkata, India, with dense population and heavy traffic. Effects of extraction methods and operational parameters (solvent and time) on the recovery levels of PAHs were also investigated. Purified extracts, acquired through adsorption chromatography, were subjected to GC-MS and HPLC-UV analyses for qualitative and quantitative assessment of PAHs. Spatio-temporal distribution of accumulated PAHs across the sampling sites was monitored over premonsoon, postmonsoon and winter supported by pollutant source characterization. The results displayed that the extraction yields of Soxhlet (272.07 ± 26.15 µg g-1) and MASE (280.17 ± 15.46 µg g-1) were the highest among the four techniques. Conditions of extraction with toluene for 6 h were found to be most favorable for PAHs. In spatio-temporal analysis, total concentrations of PAHs in the foliar samples varied from 200.98 ± 2.72 to 550.79 ± 10.11 µg g-1 dry weight, and the highest values being recorded in the samples of Exide More because of daylong inexorable traffic flow/crowding increasing the burden of ambient PAHs. Widespread changes in meteorology exerted influence on seasonal concentrations of PAHs in plant leaves, and extent of leaf contamination by PAHs was observed extreme in winter followed by postmonsoon and then, premonsoon. Foliar accretion of PAHs differed in the study sites with diverse sources of emission from motor vehicles, fossil fuel and biomass burning along with other human interferences.

Dimensionless coefficients for assessing human exposure to radio-frequency electromagnetic fields indoors and outdoors in urban areas.

The main objective of this work was to evaluate human exposure to electromagnetic fields in a city of about one hundred thousand inhabitants, both inside and outside dwellings, using exposure quotients. To this end, a personal exposure meter was used, collecting data in different frequency bands, including radio and television broadcasting, mobile telephony, cordless telephones, and wireless communication networks. The indoor measurements were made with the exposure meter in a static position. Those outdoor were made by walking around the building with the exposure meter held by the operator. The median electric field was 0.200 V/m outdoors and 0.102 V/m indoors. The median of the ICNIRP exposure quotients for multiple-frequency sources was 25 10-6 outside and 16 10-6 inside. The proximity of the operator's body caused the readings of the electric field in the FM band to be overestimated by a factor of 1.35, and in the mobile telephony bands by factors from 0.76 to 1.02. The standard deviation of the measurements repeated inside a dwelling over five days was of the order of the exposure meter's standard uncertainty of calibration, but the spatial dispersion at the scale of a dwelling and of the city was much greater. The two main contributors to the exposure were FM radio followed by the "downlink" mobile telephony bands. Inside the dwellings, the DECT and WIFI bands contributed less. Exposure quotients are dimensionless parameters that characterize exposure, and reflect the relative weight of each service to that exposure.

Spatial and temporal variability of soil erosion in the black soil region of Northeast China from 2000 to 2015.

The black soil region in Northeast China is an important production base of commodity grain. However, soil erosion is a major threat that has caused a decline in arable land area and productivity and a series of environmental problems in recent years. To understand the current situation of soil erosion and its changes in the whole black soil region, including six treatment regions, we used the spatial-temporal analysis of soil erosion from 2000 to 2015 and the overlay analysis with its drivers; additionally, soil erosion was evaluated qualitatively with the integrated evaluation method, and its change was indicated by the soil erosion change index (SECI). We found that soil erosion that caused soil loss occurred in each treatment region mainly at the light level in 2015. Water erosion, the most widely distributed erosion type, affected the largest area, while most serious erosion at intensive or higher levels stemmed from wind erosion. Although the situation of water erosion was improved in 2015 compared to that in 2000, the overall situation of soil erosion was worse due to the deterioration of wind and freeze-thaw erosion. Grassland, woodland, and cultivated land changes, such as the conversion from grassland to cultivated land, from woodland to sparse woodland and from dry land to paddy land, revealed these changes to a great extent.

Vertical and Seasonal Patterns Control Bacterioplankton Communities at Two Horizontally Coherent Coastal Upwelling Sites off Galicia (NW Spain).

Analysis of seasonal patterns of marine bacterial community structure along horizontal and vertical spatial scales can help to predict long-term responses to climate change. Several recent studies have shown predictable seasonal reoccurrence of bacterial assemblages. However, only a few have assessed temporal variability over both horizontal and vertical spatial scales. Here, we simultaneously studied the bacterial community structure at two different locations and depths in shelf waters of a coastal upwelling system during an annual cycle. The most noticeable biogeographic patterns observed were seasonality, horizontal homogeneity, and spatial synchrony in bacterial diversity and community structure related with regional upwelling-downwelling dynamics. Water column mixing eventually disrupted bacterial community structure vertical heterogeneity. Our results are consistent with previous temporal studies of marine bacterioplankton in other temperate regions and also suggest a marked influence of regional factors on the bacterial communities inhabiting this coastal upwelling system. Bacterial-mediated carbon fluxes in this productive region appear to be mainly controlled by community structure dynamics in surface waters, and local environmental factors at the base of the euphotic zone.

Spatiotemporal variations and source on black carbon over Chongqing, China: Long-term changes and observational experiments.

Black carbon (BC), as a critical light-absorbing constituent within aerosols, exerts profound effects on atmospheric radiation balance, climate, air quality and human health, etc. And it is also a long-standing focus in rapidly developing megacities. So, this study primarily focuses on investigating the variation characteristics and underlying causes of BC in Chongqing (31,914,300 population), which is one of the municipalities directly under the central government of China, serving as a pivotal economic hub in southwest China. Utilizing MERRA-2 reanalysis data, we examined the long-term changes of atmospheric BC over Chongqing 20 years (from 2002 to 2021). Moreover, BC mass concentration observations were conducted using an Aethalometer (AE-33) from March 15 to June 14, 2021 in Liangping District, Chongqing. The statistical analysis over the last 20 years reveals an annual mean BC concentration in Chongqing of 3.42 ± 0.20 µg/m3, exhibiting growth from 2002 to 2008, followed by a decline from 2008 to 2021. Monthly concentration displays a "U-shaped" trend, with the lowest values occurring in summer and the highest in winter. Due to topographical and meteorological influences, local emissions primarily contribute to BC pollution, characterized by a spatial distribution pattern of high in the west and low in the east. Ground observation indicates a distinct dual-peaked pattern in the diurnal variation of BC, with peak concentrations aligning with periods of high traffic emissions. The variation in BC is significantly influenced by meteorological conditions (wind, temperature, atmospheric boundary layer) and local pollution sources (predominantly traffic). Furthermore, extreme events analysis suggests that local emissions and regional transport (with higher contributions from Chongqing and the Sichuan Basin) predominantly contributed to BC pollution. This study effectively makes up for the deficiency in analyzing the distribution and sources of BC pollution in Chongqing, providing valuable scientific insights for the atmospheric environment of megacities.

Spatial and temporal variability of dissolved methane concentrations and diffusive emissions in the Three Gorges Reservoir.

Methane (CH4) emissions from freshwater aquatic systems such as rivers and reservoirs are an important component of the global methane budget. However, the estimation can be largely affected by the spatial and temporal resolutions of measurements. Especially, the lack of high-resolution studies in the Three Gorges Reservoir (TGR), one of the largest reservoirs in the world, has led to a longstanding debate on its CH4 emissions. In this study, the spatial distribution and seasonal variations of dissolved CH4 concentrations were measured using a fast-response automated gas equilibrator in the TGR. We observed large spatiotemporal variations of dissolved CH4 (mean ± SD: 0.26 ± 0.19 µM in summer and 0.24 ± 0.17 µM in winter). Higher concentrations with stronger variations were found in the upstream than in the section close to the Three Gorges Dam. The dissolved CH4 concentration in the TGR was mainly influenced by sewage discharge, sedimentation, topographical conditions, tributaries, and spatial and seasonal variations in hydrodynamics. Regression analyses suggest that the concentration can be characterized by sewage discharge, water depth, and electrical conductivity to a certain extent. Mean diffusive CH4 fluxes from the TGR in summer and winter were 16.2 mg m-2 d-1 and 3.1 mg m-2 d-1, respectively. Downsampling simulations show that scaling dissolved CH4 in the TGR from one site likely involves large errors, and at least ∼38 sites and ∼52-58 sites are needed to achieve an accurate estimate in summer and winter, respectively. Due to the large spatial and temporal heterogeneity, high-resolution measurements are key to improving the reliability of CH4 estimates and assessing the contribution of the TGR to regional and global CH4 budgets.

A systems approach to understand microplastic occurrence and variability in Dutch riverine surface waters.

Assessment methods on data quality and environmental variability are lacking for microplastics (MP). Here we assess occurrence and variability of MP number concentrations in two Dutch rivers. Strict QA/QC procedures were applied to identify MP using Fourier-transform infrared (FTIR) microscopy followed by state of the art automated image analysis. For a series of randomly selected, yet ever smaller subareas of filters, we assessed how accurately MP numbers and polymer types are represented during partial filter analysis. Levels of uncertainty were acceptable when analysing 50% of a filter during chemical mapping, and when identifying at least a subset of 50 individual particles with attenuated total reflection (ATR)-FTIR. Applying these guidelines, MP number concentrations between 67 and 11532 MP m-3 were detected in Dutch riverine surface waters. Spatial differences caused MP number concentrations to vary by two orders of magnitude. Temporal differences were lower and induced a maximum variation of one order of magnitude. In total, 26 polymer types were identified, the most common were polyethylene (23%), polypropylene (19.7%) and ethylene propylene diene monomer rubber (18.3%). The highest diversity of polymer types was found for small MPs, whereas MP larger than 1 mm was scarce and almost exclusively made of polyethylene or polypropylene. Virtually all sampling locations revealed MP number concentrations that are considerably below known effect thresholds for anticipated adverse ecological effects.

Contrasting temporal dynamics of dissolved and colloidal trace metals in the Pearl River Estuary.

Metal contamination in the Pearl River Estuary (PRE) is persistent-, yet a comprehensive understanding of distribution and behavior of metals in surface water of this large, multi-source estuary is still lacking. In the present study, water samples from 24 sites spanning the whole estuary during the dry and wet season were collected and fractioned. Trace metal concentrations in samples were then determined following a preconcentration technique using Nobias Chelate-PA1 resin. Distribution of trace metals exhibited variability along and across estuary, as a result of estuarine mixing, external metal loadings, addition and removal. Behavior of metals was contrasting between the dry and wet seasons, exhibiting metal-specific intercorrelations and dynamics. Colloidal metals (Mn, Ni and Cd) were primarily present in upper estuary and areas affected by external contaminant loading. Colloidal Cu was the only metal that was ubiquitous in the estuary in both seasons. It showed a high affinity for small-size organic colloids (likely fulvic acid) during the dry season. Overall, the present study demonstrated the multi-source character of the PRE and that the behavior of trace metals was controlled by the coupling of hydrologic and geochemical processes, with anthropogenic perturbations.

Drainage water salinity and quality across nested scales in the Nile Delta of Egypt.

Improving water management depends on understanding the functioning of irrigation and drainage systems across different environmental scales. For this purpose, this study in the Nile Delta of Egypt particularly examines the spatial and temporal variation of drainage water salinity from the system to the plot level. A better understanding of this variation across nested scales is crucial to refine the government's drainage reuse strategy and reduce the adverse effects on agricultural productivity, lagoon ecology, and human health. The study investigates the drainage system of the Meet Yazid study area (82,740 ha) located in the upper central part of the Nile Delta. The parameters measured were electrical conductivity (EC), dissolved oxygen (DO), pH, and temperature. Results showed that salinity and quality of drainage water in the Nile Delta vary highly with space and time. The secondary drains exhibited the highest variability of salinity compared with main drains and subsurface drainage collectors because they accumulate salts from deeper soil layers and seepage of saline groundwater at the time of low flow discharge. In secondary drains, the salinity increased up to four times that of drainage water coming from the collectors. Moreover, DO values were most of the time not meeting standards for reuse in irrigation, especially at main drains that collect not only agricultural drainage but also untreated household sewage water.

Monitoring droughts in Eswatini: A spatiotemporal variability analysis using the Standard Precipitation Index.

The spatiotemporal analysis of drought is of great importance to Eswatini as the country has been facing recurring droughts with negative impacts on agriculture, the environment and the economy. In 2016, the country experienced the most severe drought in over 35 years, resulting in food shortages, drying up of rivers as well as livestock deaths. The frequent occurrence of extreme drought events makes the use of drought indices essential for drought monitoring, early warning and planning. The aim of this study was to assess the applicability of the Standard Precipitation Index (SPI) for near real-time and retrospective drought monitoring in Eswatini. The 3-, 6- and 12-month SPI were computed to analyse the severity and onset of meteorological drought between 1986 and 2017. The results indicated that the climate of Eswatini exhibits geospatial and temporal variability. Droughts intensified in terms of frequency, severity and geospatial coverage, with the worst drought years being 1985-1986, 2005-2006 and 2015-2016 agricultural seasons. Moderate droughts were the most prevalent, while the frequency of severe and very severe droughts was low. Most parts of the country were vulnerable to mild and moderate agricultural droughts. Spatial analysis showed that the most severe and extreme droughts were mostly experienced in the Lowveld and Middleveld agro-ecological zones. The 3-, 6- and 12-month SPI computations conducted in January detected the onset of early season drought, thereby affirming the applicability of the index for monitoring near real-time and retrospective droughts in Eswatini. Drought monitoring using the SPI provides information for early warning, particularly in drought-prone areas, by depicting a drought before the effects are felt.

Monitoring droughts in Eswatini: A spatiotemporal variability analysis using the Standard Precipitation Index.

The spatiotemporal analysis of drought is of great importance to Eswatini as the country has been facing recurring droughts with negative impacts on agriculture, environment and economy. In 2016, the country experienced the most severe drought in over 35 years resulting in food shortages, drying up of rivers as well as livestock deaths. The frequent occurrence of extreme drought events makes the use of drought indices essential for drought monitoring, early warning and planning. The aim of this study was therefore to assess the applicability of the Standard Precipitation Index (SPI) for near real-time and retrospective drought monitoring in Eswatini. The 3-, 6- and 12-month SPI were computed to analyse severity and onset of meteorological drought between 1986 and 2017. The results indicated that the climate of Eswatini exhibits geospatial and temporal variability. Droughts intensified in terms of frequency, severity and geospatial coverage, with the worst drought years being 1985-1986, 2005-2006 and 2015-2016 agricultural seasons. Moderate droughts were the most prevalent, while the frequency of severe and very severe droughts was low. Most parts of the country were vulnerable to mild and moderate agricultural droughts. Spatial analysis showed that the most severe and extreme droughts were mostly experienced in the Lowveld and Middleveld agro-ecological zones. The 3-, 6- and 12-month SPI computations conducted in January detected the onset of early season drought, thereby affirming the applicability of the index for monitoring near real-time and retrospective droughts in Eswatini. Drought monitoring using SPI provides information for early warning, particularly in drought-prone areas, by depicting a drought before the effects have begun to be felt.

[Comparing the responses of radial growth between Quercus mongolica and Phellodendron amurense to climate change in Xiaoxing'an Mountains, China.] / å°å ´å®‰å²­è’™å¤æ Žå’Œé»„è èå¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å˜åŒ–çš„å“åº”æ¯”è¾ƒ.

Quercus mongolica and Phellodendron amurense are two important broad-leaved species in temperate forests of Northeast China. It is critical to explore their responses to climate change for supporting management, protection, and restoration of the broad-leaved forest in Northeast China under the future climate change scenario. Three sampling sites along a longitude gradient, Heilun, Tieli and Yichun, were set up in the Xiaoxing'an Mountains. Dendrochronological methods were used to establish standard chronologies for Q. mongolica and P. amurense. Correlation analyses were conducted between these chronologies and local climatic factors to establish the spatial and temporal variations in growth-climate relationship of Q. mongolica and P. amurense. The results showed that the radial growth of P. amurense was sensitive to temperature, while that of Q. mongolica was limi-ted by both temperature and precipitation. The temperature sensitivities of these two species were different. High spring temperature inhibited the radial growth of Q. mongolica, but promoted that of P. amurense. The limiting effect of high maximum temperature in summer on radial growth of Q. mongolica was significantly higher than that of P. amurense. With the increases of longitude (water availability), the correlation coefficients between radial growth of Q. mongolica and precipitation gradually weakened, while P. amurense didn't change. The physiological characteristics of those tree species was the key factors affecting their growth-climate relationship. With the significant warming since the 1976, the growth trend of P. amurense increased, whilst that of Q. mongolica decreased. Deteriorated drought stress caused by warming and difference in the species' ability to cope with water deficits might be the main reasons for different responses of two species, and for the divergence phenomenon occurring for Q. mongolica. If warming continues or worsens in the future, the growth of Q. mongolica may decline due to the intensified drought stress, while that of P. amurense may be less affected or be slightly enhanced.

Estimating individual-level exposure to airborne polycyclic aromatic hydrocarbons throughout the gestational period based on personal, indoor, and outdoor monitoring.

OBJECTIVES: Current understanding on health effects of long-term polycyclic aromatic hydrocarbon (PAH) exposure is limited by lack of data on time-varying nature of the pollutants at an individual level. In a cohort of pregnant women in Krakow, Poland, we examined the contribution of temporal, spatial, and behavioral factors to prenatal exposure to airborne PAHs within each trimester and developed a predictive model of PAH exposure over the entire gestational period. METHODS: We monitored nonsmoking pregnant women (n = 341) for their personal exposure to pyrene and eight carcinogenic PAHs-benz[a]anthracene, chrysene/isochrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene [B(a)P], indeno[1,2,3-c,d]pyrene, dibenz[a,h]anthracene, and benzo[g,h,i]perylene-during their second trimester for a consecutive 48-hr period. In a subset (n = 78), we monitored indoor and outdoor levels simultaneously with the personal monitoring during the second trimester with an identical monitor. The subset of women was also monitored for personal exposure for a 48-hr period during each trimester. We repeatedly administered a questionnaire on health history, lifestyle, and home environment. RESULTS: The observed personal, indoor, and outdoor B(a)P levels we observed in Krakow far exceed the recommended Swedish guideline value for B(a)P of 0.1 ng/m(3). Based on simultaneously monitored levels, the outdoor PAH level alone accounts for 93% of total variability in personal exposure during the heating season. Living near the Krakow bus depot, a crossroad, and the city center and time spent outdoors or commuting were not associated with higher personal exposure. During the nonheating season only, a 1-hr increase in environmental tobacco smoke (ETS) exposure was associated with a 10-16% increase in personal exposure to the nine measured PAHs. A 1 degrees C decrease in ambient temperature was associated with a 3-5% increase in exposure to benz[a]anthracene, benzo[k]fluoranthene, and dibenz[a,h]anthracene, after accounting for the outdoor concentration. A random effects model demonstrated that mean personal exposure at a given gestational period depends on the season, residence location, and ETS. CONCLUSION: Considering that most women reported spending < 3 hr/day outdoors, most women in the study were exposed to outdoor-originating PAHs within the indoor setting. Cross-sectional, longitudinal monitoring supplemented with questionnaire data allowed development of a gestation-length model of individual-level exposure with high precision and validity. These results are generalizable to other nonsmoking pregnant women in similar exposure settings and support reduction of exposure to protect the developing fetus.

Indoor air quality in two French hospitals: Measurement of chemical and microbiological contaminants.

In addition to being influenced by the environment, the indoor air pollution in hospitals may be associated with specific compounds emitted from various products used, health care activities and building materials. This study has enabled assessment of the chemical and microbiological concentrations of indoor air in two French hospitals. Based on an integrated approach, the methodology defined aims to measure concentrations of a wide range of chemical compounds (>50 volatile and semi-volatile organic compounds), particle concentrations (PM10 and PM2.5), microorganisms (fungi, bacteria and viruses) and ambient parameters (temperature, relative humidity, pressure and carbon dioxide). Chemical and microbiological air concentrations were measured during two campaigns (winter and summer) and across seven rooms (for spatial variability). The results have shown that indoor air contains a complex mixture of chemical, physical and microbiological compounds. Concentrations in the same order of magnitude were found in both hospitals. Compared to dwelling indoor air, our study shows low, at least equivalent, contamination for non-hospital specific parameters (aldehydes, limonene, phthalates, aromatic hydrocarbons), which is related to ventilation efficiency. Chemical compounds retrieved at the highest concentration and frequencies are due to healthcare activities, for example alcohol - most commonly ethanol - and hand rubbing (median concentration: ethanol 245.7 µg/m3 and isopropanol 13.6 µg/m3); toluene and staining in parasitology (highest median concentration in Nancy laboratory: 2.1 µg/m3)).

Within-room and within-home spatial and temporal variability in concentrations of legacy and "novel" brominated flame retardants in indoor dust.

To test the hypothesis that assessments of human exposure to PBDEs and NBFRs (PBEB, EH-TBB, BEH-TEBP, BTBPE and DBDPE) via dust ingestion should take into account spatial and temporal variability in dust contamination; 238 dust samples were collected from nine different rooms within three homes in Birmingham UK. In each room, three different dust samples were taken at monthly intervals for nine months, one sample from elevated surfaces and two samples from two different floor areas. Substantial within-room and within-home spatial variability in BFR concentrations was apparent between two floor areas and between different rooms due to the varying distances of sampled surfaces from potential BFR sources. With the exception of DBDPE, BFR concentrations in elevated surface dust exceeded significantly those in floor dust. Considerable within-room and within-home temporal variability in BFR concentrations was also apparent over a nine month sampling period. This is likely attributable to changes in room contents. Based on observed spatial and temporal variability, exposure estimates based on analysis of a single dust sample taken from one specific floor area at one specific point in time may not be entirely representative of human exposure in that room. Noticeable variability in BFR concentrations was also observed between colder and warmer seasons. In 13 out of 17 floor areas, concentrations of Σ8tri-deca-BDEs were higher in colder seasons, while those of Σ5NBFRs were higher in warmer seasons. Significant negative correlation was observed in two rooms between concentrations of BDE-99, Σ7tri-hepta-BDEs and BEH-TEBP and dust loading (g/m2).

CO2 oversaturation and degassing using chambers and a new gas transfer velocity model from the Three Gorges Reservoir surface.

Reservoirs are considered as important carbon source of the atmosphere, whilst, regional and global reservoir CO2 quantification is hampered by data limitation and bias in spatial and temporal sampling. By deploying chamber measurements and employing the newly developed model of gas transfer velocity, CO2 partial pressure (pCO2) and evasion in the main stem of the Three Gorges Reservoir (TGR) were investigated. The pCO2 ranged from 429 to 8668 µatm with an average of 2511.6 ±â€¯1721.3 µatm, 6.1-fold higher than the ambient air pCO2 (mean: 410 µatm). All the samples were net CO2 sources via water-air interface, displaying pronounced spatial and monthly variability. The CO2 areal flux averaged 212.5 ±â€¯120.1 mmol/m2/d in June, 123.3 ±â€¯78.5 mmol/m2/d in July in the lotic TGR main stream, much higher than its lentic system, i.e., 79.6 ±â€¯41.3 mmol/m2/d in November, and 76.3 ±â€¯88.1 mmol/m2/d in March. Much lower k levels in the lentic reservoir surface resulted in lower CO2 evasion rates. Furthermore, dam impoundment considerably altered the riverine carbon cycle, as reflected by the changing magnitude of CO2 efflux and environmental controls of dissolved CO2. Precipitation and concurrent soil CO2 influx exhibited a central role in controlling riverine pCO2, and respiration of allochthonous organic carbon was a secondary factor in the TGR lotic system, whilst, both in-stream metabolism and terrestrial inputs played crucial roles in controlling aqueous CO2 in the TGR lentic system. In comparison, we provided key findings of k model and more reliable CO2 quantification with a consideration of water level shifts and a complete coverage of spatial sampling. Our higher CO2 emission (1.47 (1.16-2.13) Tg CO2/y) than previous studies called more field measurements to assess the resulting changes in CO2 flux owing to dam operation and changing environment, and their implications for regional carbon budgets should be warranted.

[Spatial and Temporal Variability of Soil C-to-N Ratio of Yugan County and Its Influencing Factors in the Past 30 Years].

The soil carbon-to-nitrogen (C/N) ratio of soils is a sensitive indicator of soil quality and an indicator for assessing the carbon and nitrogen nutrition balance of soils. Its variation is significant in reflecting the carbon and nitrogen cycling of soils. An accurate knowledge of how the C/N ratio varies spatially and temporally and the driving factors at county scale is of great significance to the extrapolation of balanced fertilization based on soil C/N ratio regulation as well as to the protection of the ecological environment. This study was based on 200 points of surface soil samples (0-20 cm) collected during the second National Soil Survey in 1982 and 423 points of surface soil samples (0-20 cm) collected during the soil test-based formulated fertilization project in 2012 in Yugan County. Combined with the soil parent material, soil type, farmland-use type, terrain factors, pH, straw incorporation pattern, and nitrogen fertilizer rate over the past 30 years, spatial and temporal variability characteristics of the soil C/N ratio were analyzed by using ordinary kriging methods, and the effects of the influencing factors were quantified by regression analysis. The results indicated that the mean value of the C/N ratio was 10.05 and 11.18 in 1982 and 2012, respectively. The coefficient of variation was 19.40% and 25.04%, respectively, which suggested the soil C/N ratio had moderate variability in the study area. The ratios of nugget to sill were 15.91% and 71.25% in 1982 and 2012, respectively. This means that the leading factor from the structural factors (parent material and soil type) into the stochastic factors (nitrogen fertilizer rate and straw incorporation pattern). In the past 30 years, most of the regional soil C/N ratio increased significantly especially the eastern region. The spatial variability of soil C/N in 1982 was mainly affected by soil parent material, soil type, terrain factor, and pH, with the degree of influence of each variable at 17.3%, 14.2%, 7.4%, and 2.3%. In 2012, the spatial variability was mainly affected by soil parent material, soil type, farmland-use type, terrain factor, straw incorporation pattern, and nitrogen fertilizer rate, with the degree of influence of each variable of 8.7%, 23.5% 28.2%, 12.2%, 12.6%, and 42.3%, respectively. To maintain the steady growth of the soil C/N ratio, it is suggested that the return of carbon be incorporated with the input of nitrogen, such as incorporating crop residues into the soil and inputting more organic fertilizers into the soil in future farming practices.

Spatiotemporal variability of soil respiration in a seasonal tropical forest.

We monitored soil CO 2 effluxes for over 3 years in a seasonally wet tropical forest in Central Panama using automated and manual measurements from 2013 to 2016. The measurements displayed a high degree of spatial and temporal variability. Temporal variability could be largely explained by surface soil water dynamics over a broad range of temporal scales. Soil moisture was responsible for seasonal cycles, diurnal cycles, intraseasonal variability such as rain-induced pulses following dry spells, as well as suppression during near saturated conditions, and ultimately, interannual variability. Spatial variability, which remains largely unexplained, revealed an emergent role of forest structure in conjunction with physical drivers such as soil temperature and topography. Mean annual soil CO 2 effluxes (±SE) amounted to 1,613 (±59) gC m-2 year-1 with an increasing trend in phase with an El Niño/Southern Oscillation (ENSO) cycle which culminated with the strong 2015-2016 event. We attribute this trend to a relatively mild wet season during which soil saturated conditions were less persistent.

Spatial and temporal variability among marine Bacteroidetes populations in the NW Mediterranean Sea.

The abundance and structure of Bacteroidetes populations at diverse temporal and spatial scales were investigated in the Northwestern Mediterranean Sea. At a temporal scale, their relative abundance exhibited a marked seasonality, since it was higher in spring and decreased in winter. Similarly, Bacteroidetes community structure encompassed three main groups (winter, spring and summer-fall), which mimicked global bacterioplankton seasonality. At the spatial scale, relative abundances were similar in all surface samples along an inshore-offshore transect, but they decreased with depth. Analysis of the community structure identified four markedly different groups mostly related to different depths. Interestingly, seasonal changes in abundance and community structure were not synchronized. Furthermore, richness was higher when Bacteroidetes were less abundant. The variability of Bacteroidetes contributions to community structure in the temporal and spatial scales was correlated with different environmental factors: day length was the most important factor at the temporal scale, and salinity at the spatial scale. The community composition in terms of phylotypes changed significantly over time and along the depth gradients, but season or depth-specific phylogenetic clusters were not identified. Delineation of coherent Bacteroidetes sub-clusters should help to uncover higher resolution patterns within Bacteroidetes, and explore associations with environmental and biological variables.