Temporal Variations In Concentrations Research Articles

Species-specific spatial and temporal variation in foliar nitrogen and phosphorus in mangrove plants

Foliar nitrogen (N) and phosphorus (P) concentrations and stoichiometry affect the productivity and functioning of plants, and they play an important role in biogeochemical processes. We investigated spatial and temporal variation in foliar nutrient concentrations and N:P stoichiometry in mangroves of China, and partitioned the relative importance of taxonomic, climatic and edaphic factors in explaining the variations. To assess spatial patterns, we collected mature leaves of 3 broadly distributed mangrove species in China spanning a latitudinal gradient. To assess temporal variation in leaf stoichiometry, we selected 1 site and sampled leaves of 4 species monthly over 12 mo. Positive relationships were found between foliar nutrient concentrations and latitude or soil nutrient concentrations in individual species. Species accounted for 76, 46 and 18% of the spatial variation in foliar N, P and N:P mass ratio, respectively, while soil nutrients and climate accounted for only small portions of the variation (≤8.3%). Different species showed no consistent patterns across temporal variation in foliar nutrient concentrations or stoichiometry, and species accounted for 94, 86 and 26% of the variations in foliar N, P and N:P ratio, respectively, throughout the year, while climatic factors accounted for only a very small portion of the variations (≤0.5%). Our results suggest that species affect foliar nutrient concentrations and stoichiometry in mangroves more strongly than environmental factors, and that stoichiometric homeostasis in mangroves may play an important role in mitigating the effects of environmental changes in coastal areas.

Long-term Characterization of Urban PM10 in Hungary

Over urban areas in Hungary, the annual average PM10 concentrations are not frequently higher than 40 µg m–3. Despite the mitigation efforts of the local governments, the annual number of exceedances of the daily limit of 50 µg m–3 is higher than what is outlined in EU Directive No 2008/50/EC. The goal of the present study is to assess the characteristics of the temporal (annual, seasonal, daily) variations in PM10 concentrations in selected Hungarian cities with large populations, where most of the exceedances have been reported. The impacts of meteorological conditions on the measured PM10 concentrations and their temporal variations are also evaluated. An important aspect of studying the trends of air pollution is that the tendencies depend not only on the emissions of certain pollutants but also on the meteorological conditions in the area of interest. To analyse emission-related trends, the meteorological signal must be removed from the data series. In this study, the Kolmogorov-Zurbenko (KZ) filter was used for this type of trend separation. Moreover, multiple nonlinear regression analysis was used to find relationships between the PM10 concentration and several meteorological parameters. The goal of this analysis is to estimate the expected daily mean PM10 concentration values. The results of this analysis demonstrate that the regression equation can provide an adequate method for PM pollution forecasting. In addition to the hourly PM10 concentrations and basic meteorological data, global radiation and boundary layer height were considered in the characterization process.

Development and validation of an intra-calibration procedure for MiniDISCs measuring ultrafine particles in multi-spatial indoor environments

Since the real exposure to indoor ultrafine particles depends on temporal and spatial variation of aerosol concentration, particles dynamic behavior becomes relevant in studying indoor pollution. With this aim, the characterization of Ultrafine Particles (UFPs) variability within different environments (multi-spatial indoor environments) can be regarded as a specific tool in assessing the human exposure. In the case of urban indoor environments, instruments able to measure UFPs at high time resolution with high sensitivity are needed, lightweight and silent. For this purpose, personal monitors unipolar diffusion charging based could be used for their ease of use. Among them, Miniature DIffusion Size Classifier (MiniDISC), a small, silent and wearable analyzer measures particle number concentration, particle modal size and lung deposited surface area of nanoparticles at high time resolution, for dynamic or static use. Nevertheless, the typical ±30% accuracy specified by the manufacturer does not make this sensor reliable enough to measure gradients of urban doses of UFPs occurring in multi-spatial indoor environments.The presented work aims at improving the performances of MiniDISCs for their use in simultaneous measurement of urban UFPs by a multiple set-up, such as in indoor environments inside a building.For this purpose, a new intra-calibration procedure has been developed among MiniDISCs, named Best Intra-calibration (BIC), which corrects data of electrical signals of two or more instruments to those of one selected as reference. Compared to a linear regression analysis for PNC of UFPs, BIC procedure has two main advantages. First, it makes it possible to improve simultaneously the precision of particle number concentration (PNC) and particle modal size (PMS). Secondly, it allows multiple instruments to operate as a fleet, such as a spatial delocalization of an instrument in multiple environments.The procedure was tested in realistic environmental conditions, evaluating indoor PNC and PMS of UFPs by both parallel samplings and multi-spatial samplings. Three types of monitoring campaigns were carried out: inter-comparisons between PNC of UFPs from three MiniDISCs and one Condensation Particle Counter; intra-comparisons between PNC and PMS of UFPs from three MiniDISCs; urban monitoring in-field campaign of UFPs with three MiniDISCs in an indoor workplace, a physic laboratory, in the next hallway and outside. The latter campaign aimed at evaluating how UFPs are influenced by the interaction among different environments inside the building and by the work activity. For these purposes, the dynamical behavior and the ratios Indoor to Outdoor were investigated, in addition to a novel ratio Indoor to Hallway. The BIC procedure allows increasing the precision measured by the weighted coefficients of variation CVs of about 7 times. The results support the novel Intra-calibration procedure to improve the intra variability of MiniDISCs in parallel sampling, making them attractive for measuring UFPs by both the metrics PNC and PMS in multi-spatial indoor environments.

Quantification of the radiative impact of light-absorbing particles during two contrasted snow seasons at Col du Lautaret (2058 m a.s.l., French Alps)

Abstract. The presence of light-absorbing particles (LAPs) in snow leads to a decrease in short-wave albedo affecting the surface energy budget. However, the understanding of the impacts of LAPs is hampered by the lack of dedicated datasets, as well as the scarcity of models able to represent the interactions between LAPs and snow metamorphism. The present study aims to address both these limitations by introducing a survey of LAP concentrations over two snow seasons in the French Alps and an estimation of their impacts based on the Crocus snowpack model that represents the complex interplays between LAP dynamics and snow metamorphism. First, a unique dataset collected at Col du Lautaret (2058 m a.s.l., above sea level, French Alps) for the two snow seasons 2016–2017 and 2017–2018 is presented. This dataset consists of spectral albedo measurements, vertical profiles of snow specific surface area (SSA), density and concentrations of different LAP species. Spectral albedos are processed to estimate SSA and LAP absorption-equivalent concentrations near the surface of the snowpack. These estimates are then compared to chemical measurements of LAP concentrations and SSA measurements. Our dataset highlights, among others, large discrepancies between two measurement techniques of black carbon (BC) concentrations in snow (namely thermal-optical and laser-induced incandescence). Second, we present ensemble snowpack simulations of the multi-physics version of the detailed snowpack model Crocus, forced with in situ meteorological data, as well as dust and BC deposition fluxes from an atmospheric model. The temporal variations of near-surface LAP concentrations and SSA are most of the time correctly simulated. The simulated seasonal radiative forcing of LAPs is 33 % higher for the 2017–2018 snow season than for the 2016–2017 one, highlighting a strong variability between these two seasons. However, the shortening of the snow season caused by LAPs is similar with 10 ± 5 and 11 ± 1 d for the first and the second snow seasons, respectively. This counter-intuitive result is attributed to two small snowfalls at the end of the first season and highlights the importance in accounting for meteorological conditions to correctly predict the impact of LAPs. The strong variability of season shortening caused by LAPs in the multi-physics ensemble for the first season (10 ± 5 d) also points out the sensitivity of model-based estimations of LAP impact on modelling uncertainties of other processes. Finally, the indirect impact of LAPs (i.e. the enhancement of energy absorption due to the acceleration of the metamorphism by LAPs) is negligible for the 2 years considered here, which is contrary to what was found in previous studies for other sites.

Experimental Study on Dispersion of Unconfined Aquifer in a Site of Jilin City

Dispersion parameter is an important parameter for the establishment of groundwater solute transport model.The dispersion test uses sodium chloride as a tracer,which was conducted in a site in Jilin City.The standard curve comparison method was used to solve the dispersion parameters of the aquifer under the natural flow field.The test results show that under the natural flow field,the longitudinal dispersion of unconfined aquifer in Jilin City is 0.400m,and the lateral dispersion is 1.933×10-5~6.557×10-3m;while the vertical dispersion coefficient is 0.246m2d,the lateral dispersion coefficient is 1.191×10-5~4.039×10-3m2d.The above results can provide an important parameter basis for the establishment of groundwater solute transport model,the accurate prediction of temporal and spatial variation of pollutant concentration in groundwater and the formulation of groundwater pollution prevention and control scheme.

Concentration of Black Carbon in the Near-Surface Atmosphere in the Pechora-Ilych Natural Reserve: Measurements and Merra-2 Reanalysis

The concentration of black carbon (BC), measured in near-surface air on the territory of the Pechora-Ilych State Natural Biosphere Reserve (PISNBR) on the western side of the Northern Ural Mountains, far from sources, is presented for two years (December 2017–November 2019). The temporal variations in BC concentration throughout a year and the location of its main sources are analyzed. The average values for two cold and two warm half-years were 128 and 62 ng/m3, respectively. The BC concentration in near-surface atmosphere was compared with MERRA-2 reanalysis data. On a monthly scale, the anomalous increase in BC concentration during short-term smoke aerosol transport across the observation area is more clearly revealed from the reanalysis data, rather than by values measured at a single point. Daily monitoring allows us to detect the specific dates of such situations.

Ambient exposure of O3 and NO2 and associated health risk in Kuwait.

Ozone (O3) and nitrogen dioxide (NO2), indissoluble air pollutants in the atmosphere, have been confirmed in various parts of the world to have detrimental health effects on humans. Currently, such information is lacking in Kuwait. The objectives of this study are to investigate the spatial and temporal variations of O3 and NO2 concentrations in Kuwait during a 4-year period (2014-2017) and to quantify the associated short- and long-term health effects, including all-cause, respiratory, and cardiovascular mortalities and morbidities during the same study period. Exposure assessment showed that the annual levels (22.5-26.4 ppb), SOMO35, and the 8-hour 4-year mean (38 ppb) of O3 were very low and below the World Health Organization (WHO) (50 ppb) and Kuwaiti (70 ppb) regulatory limits. The annual mean levels of NO2 ranged from 30.3 to 43.8 ppb and were significantly higher than both WHO and Kuwait limits (21 ppb). As expected, O3 and NO2 levels showed opposing trends, with higher concentrations of NO2 recorded in early morning and mid-evening, during autumn and winter, and during Saturdays (the so-called weekend effect). Health effects indicated high respiratory diseases due to short-term exposure to NO2. Contrary to the western countries' pollution levels, Kuwait showed lower O3 and higher NO2 levels. There is potential for substantial health improvements in Kuwait by reducing NO2 pollution through stringent control measures of stationary and mobile sources.

Impact of Hydrometeorological Events for the Selection of Parametric Models for Protozoan Pathogens in Drinking-Water Sources.

Temporal variations in concentrations of pathogenic microorganisms in surface waters are well known to be influenced by hydrometeorological events. Reasonable methods for accounting for microbial peaks in the quantification of drinking water treatment requirements need to be addressed. Here, we applied a novel method for data collection and model validation to explicitly account for weather events (rainfall, snowmelt) when concentrations of pathogens are estimated in source water. Online in situ β-d-glucuronidase activity measurements were used to trigger sequential grab sampling of source water to quantify Cryptosporidium and Giardia concentrations during rainfall and snowmelt events at an urban and an agricultural drinking water treatment plant in Quebec, Canada. We then evaluate if mixed Poisson distributions fitted to monthly sampling data ( = 30 samples) could accurately predict daily mean concentrations during these events. We found that using the gamma distribution underestimated high Cryptosporidium and Giardia concentrations measured with routine or event-based monitoring. However, the log-normal distribution accurately predicted these high concentrations. The selection of a log-normal distribution in preference to a gamma distribution increased the annual mean concentration by less than 0.1-log but increased the upper bound of the 95% credibility interval on the annual mean by about 0.5-log. Therefore, considering parametric uncertainty in an exposure assessment is essential to account for microbial peaks in risk assessment.

Temporal variation of iodine-129 concentrations in kelps (Saccharina) from coastal waters off northern Japan

Concentrations of 129I and 127I in kelps (Saccharina) collected from coastal waters off northern Japan were monitored from 2007 to 2019. During the 2007–2008 test operation of the Rokkasho nuclear fuel reprocessing plant, 129I discharge from the plant increased, and the 129I concentration and 129I/127I atom ratio in the kelps reached maxima of 42 μBq/g-dry and 264 × 10−11, respectively. By 2009, both had decreased by one order of magnitude. After the Fukushima Dai-ichi Nuclear Power Plant accident in 2011, the 129I concentration and 129I/127I atom ratio in the kelps increased to 2.24 μBq/g-dry and 11.6 × 10−11, respectively. After 2012, the ratio in kelps decreased to (2.1–8.9) × 10−11, which is almost the same as the seawater value off Aomori Prefecture before the test operation. The 129I/127I atom ratio in kelps thus represents the ambient seawater ratio during the growth period of the kelps.

Spatial and Temporal Variability in Trihalomethane Concentrations in the Bromine-Rich Public Waters of Perth, Australia.

High concentrations of trihalomethanes (THMs) in public water supplies potentially pose a health hazard, but exposure assessment remains a complex task. To interpret research findings and monitoring data for THMs, it is important to evaluate spatial and temporal variations in both total THM and the individual constituent compounds (including brominated species). We therefore aimed to determine the concentrations, and spatial and temporal variability of concentrations, of THMs public water supplies in Perth, Western Australia, which is known historically to have high brominated THM concentrations. We analysed water samples from 21 water distribution zones around Perth (including Busselton and Bunbury) across different seasons over a period of two years. A total of 250 samples provided a median total THM of 72 µg/L (range of 0–157 µg/L), which falls well within Australia’s National Health and Medical Research Council guidelines. The concentration of all species, including brominated forms, also fell the World Health Organization’s guidelines. Total THM concentrations were typically higher in spring and summer. A high degree of spatial variability was detected and appears to relate to the source water. Both the temporal and spatial variability in THM concentrations have implications for epidemiological studies, and monitoring.

Trace element fractionation and isotope ratio variation during melting of a spatially distributed and lithologically heterogeneous mantle

The source region of basalts in the mantle is chemically and lithologically heterogeneous. During decompression melting of a spatially distributed and lithologically heterogeneous mantle, mineral modes of distinct mantle sources vary continuously, resulting in spatial and temporal variations in the bulk partition coefficient of a trace element in different lithologies in the melting column, which in turn affects the fractionation of the trace element in partial melt and residual solid. This problem can be quantified by following the motion of solid in the melting column. This study presents a new melting model that can be used to keep track of spatial and temporal variations of mineral mode, melting reaction, bulk partition coefficient, and trace element concentration in the lithologically heterogeneous melting column. Simple analytical solutions for a time-dependent perfect fractional melting model are obtained. Essential features of the new model are elucidated through case studies of melting a two-lithology mantle that consists of blobs of orthopyroxene-rich lithology in the upwelling lherzolitic mantle; and an application to Sr-Nd-Hf isotope ratio variations in basalts from the Mid-Atlantic Ridge is presented. Fractional melting of the two-lithology mantle results in large temporal variations in incompatible trace element concentrations and Sr-Nd-Hf isotope ratios in the pooled melt. Mixing of fractional melts derived from different lithologies in the melting column produces enriched and depleted melts that form mixing loops in Sr-Nd-Hf isotope ratio correlation diagrams. These mixing loops rotate away from mixing lines defined by the binary mixing model and are a unique feature of melting a spatially heterogeneous mantle. Formation of the mixing loop can be traced to the location and spacing of the enriched lithological units in the melting column. The role of lithological heterogeneity is to change the bulk partition coefficient of a trace element from its values in the lherzolitic mantle to new values in the pyroxenitic mantle, which alters the extent of depletion of the trace element in the melting column. Changing bulk partition coefficient with time and space through lithological heterogeneity can result in greater variabilities in Sr-Nd-Hf isotope ratios and highly incompatible trace element concentrations in the pooled melt. Results from this study establish a framework for systematic studies of trace element fractionation and isotope ratio variation during decompression melting of a spatially distributed and lithologically heterogeneous mantle.

Comparison of Modeled-to-Monitored PM2.5 Exposure Concentrations Resulting from Transportation Emissions in a Near-Road Community

Residents living in near-road communities are exposed to traffic-related air pollutants, which can adversely affect their health. Near-road communities are expected to observe significant spatial and temporal variations in pollutant concentrations. Determining these variations in the surrounding areas can help raise awareness among government agencies of these underserved communities living near highways. This study conducted traffic and air quality measurements along with emission and dispersion modeling of the exposure to transportation emissions of a near-road urban community adjacent to the US 54 highway (US 54), with annual average daily traffic (AADT) of 107,237. The objectives of this study were (i) to develop spatial and temporal patterns of pollutant concentration variation and (ii) to apportion the differences in exposure concentrations to background concentrations and those that are contributed from major highways. It was observed that: (a) particulate matter (PM2.5) in near-road communities is dominated by the regional background concentrations which account for more than 85% of the pollution; and (b) only near-road receptors are affected by the traffic-related air pollutant emissions from major highways while spatial and temporal variations of PM2.5 concentrations in near-road communities are less influenced by local traffic, subsiding rapidly to negligible concentrations at 300 m from the road. Modeled PM2.5 concentrations were compared with monitored data. For better air quality impact assessments, higher quality data such as time-specific traffic volume and fleet information as well as site-specific meteorological data could help yield more accurate concentration predictions. Modeled-to-monitored comparison shows that air quality in near-road communities is dominated by regional background concentrations.

Kriging-Based Land-Use Regression Models That Use Machine Learning Algorithms to Estimate the Monthly BTEX Concentration.

This paper uses machine learning to refine a Land-use Regression (LUR) model and to estimate the spatial–temporal variation in BTEX concentrations in Kaohsiung, Taiwan. Using the Taiwanese Environmental Protection Agency (EPA) data of BTEX (benzene, toluene, ethylbenzene, and xylenes) concentrations from 2015 to 2018, which includes local emission sources as a result of Asian cultural characteristics, a new LUR model is developed. The 2019 data was then used as external data to verify the reliability of the model. We used hybrid Kriging-land-use regression (Hybrid Kriging-LUR) models, geographically weighted regression (GWR), and two machine learning algorithms—random forest (RF) and extreme gradient boosting (XGBoost)—for model development. Initially, the proposed Hybrid Kriging-LUR models explained each variation in BTEX from 37% to 52%. Using machine learning algorithms (XGBoost) increased the explanatory power of the models for each BTEX, between 61% and 79%. This study compared each combination of the Hybrid Kriging-LUR model and (i) GWR, (ii) RF, and (iii) XGBoost algorithm to estimate the spatiotemporal variation in BTEX concentration. It is shown that a combination of Hybrid Kriging-LUR and the XGBoost algorithm gives better performance than other integrated methods.

A hydrogel/particle composite with gradient in oxygen releasing microparticle for oxygenation of the cartilage-to-bone interface: Modeling and experimental viewpoints

At the cartilage-to-bone interface, the residing cells are different with respects to metabolic requirements. Fabrication of a scaffold affording different metabolic needs of these cells can be taken account of a promoting step for regeneration of cartilage- to-bone interface. In the present study, a scaffold with a depth-dependent gradient of oxygen releasing microparticles was developed. To this end, oxygen releasing microparticles were fabricated from polylactic acid (PLA) and calcium peroxide and then dispersed in hydrogel precursor of functionalized pectin and fibroin. The microparticles were loaded in a hydrogel precursor solution in a gradient manner using a gradient mixing chamber. The mixing chamber was composed of two compartments filled with hydrogel precursors with different microparticle contents (10 and 30% w/w) and an interfacial mixing port. The velocity of microparticle loaded solution inside the gradient chamber was modeled using momentum balance Navier–Stokes equations. Moreover, spatial and temporal variations of microparticle concentration in the gradient chamber were modeled using mass transfer Navier–Stokes equations. Chemical, morphological and structural variations across the composite thickness were evaluated using microscopy and spectroscopy analyses. The model proposed by Navier–Stokes equation corroborated that the flow velocity was different in various domains of the mixing chamber and in the vicinity of the mixing port the velocity was substantially higher than the bulk flow. Moreover, the velocity profile showed gradual velocity changes from bulk to the mixing port. The model represented for microparticle concentration proved that microparticle content of precursor solution varied both spatially and temporally. As time goes by, the microparticle concentration gradually increased from about 10% w/w and approached to about 30% w/w at the end of the process. SEM micrographs from the cross-section of composite corroborated that microparticle density gradually increased from the lower to the upper surface. Spectroscopy confirmed that the oxygen releasing component, i.e. calcium peroxide, increased across the said direction. Oxygen measurement from successive sections of composite revealed that the amount of produced oxygen increased from the lowermost to the uppermost section. In conclusion, the hydrogel/particle composite with a gradient in oxygen releasing component can be a promising scaffold to satisfy the different metabolic needs of cells at the cartilage- to-bone interface. Statement of significanceNumerous tissue engineering scaffolds have been so far fabricated to recapitulate the gradient nature of cartilage- to-bone interface. Chemical, mechanical, structural and even electrical gradients of cartilage- to-bone interface have been tried to imitate by those scaffolds. However, scaffold with a gradient in metabolic features has not been developed yet. At the cartilage-to-bone interface, the residing cells are different with respects to metabolic requirements. Therefore, fabrication of a scaffold affording different metabolic needs of these cells can be taken account of a promoting step for regeneration of cartilage- to-bone interface. In the present study, a scaffold with a depth-dependent gradient of oxygen releasing microparticles was developed using a gradient making chamber. In addition to mathematical modeling of flow velocity and microparticle concentration in gradient making device, the depth-dependent changes in morphology, chemistry and structure of hydrogel/particle composite were experimentally evaluated.

Reconstruction of temporal variations of metal concentrations using radiochronology (239+240Pu and 137Cs) in sediments from Kizilirmak River, Turkey

Sediment cores retrieved from rivers, lakes, and coastal marine environment have been widely utilized to reconstruct historical variations of anthropogenic pollutants. A sediment core was collected in the Kizilirmak River, Turkey during 2014 and analyzed for a suite of metals (Cu, Pb, Zn, Ag, Ni, Co, Mn, As, Cd, Sb, V, Cr, Hg and Se) to reconstruct their temporal variations. Chronology was attempted using excess 210Pb (210Pbxs), 137Cs and 239,240Pu in the sediment cores. The vertical profile of excess 210Pb indicates that this core is not datable using excess 210Pb method. The 137Cs-based linear and mass apparent accumulation rates were estimated to be 0.84 cm year−1 and 0.93 g cm−2 year−1, respectively. These values are in agreement with the 239+240Pu peak-based linear (0.88 cm year−1) and mass apparent accumulation (0.97 g cm−2 year−1) rates. There is considerable broadening in the peaks of both 137Cs and 239,240Pu, likely due to post-depositional mixing processes. The measured sediment inventories of 210Pbxs, 137Cs and 239+240Pu were 38, 29, and 0.42 dpm cm−2, respectively, which were generally higher than the expected inventories based on local atmospheric depositional inventories. We attribute these enhanced inventories to potential sediment focusing and additional watershed erosional input. The Al-normalized enrichment factors (ANEF) were used to evaluate the contribution from natural versus anthropogenic sources. The ANEF of Ag, Ni, As, Cd and Se were > 1.5, which suggests a significant contribution of anthropogenic sources for these trace metals varied between 226% and 1163%. The geoaccumulation index (Igeo) values of the sediment column suggest that Cu, Pb, Zn, Co, Mn, Sb, V and Hg were in an unpolluted level and the others were in a polluted level. Besides, both the ANEF and Igeo values of Cu, Pb, Zn, Ag, As, Se, Cd and Hg showed a peak at 28–30 cm layer (corresponds to 1978–1981), which is attributed to maximum metal release during 1970s.

Seasonal Variation of Dissolved Oxygen in the Southeast of the Pearl River Estuary

Dissolved oxygen (DO) concentration in estuaries is highly variable at different spatial and temporal scales, which is affected by physical, chemical and biological processes. This study analyzed the spatial–temporal distributions of dissolved oxygen concentration and bottom hypoxia in the southeast of the Pearl River Estuary (PRE) using monthly water quality monitoring and hydrographic data covering the period 2000–2017. The seasonal spatial–temporal variation of DO concentration was studied using various methods, such as rotated empirical orthogonal functions, harmonic analysis, and correlation analysis. The results showed that DO stratification was significant in summer, but it was not distinct in winter, during which DO concentration peaked. DO stratification exhibited a significantly positive correlation with water stratification. In the south and west of Hong Kong (SHK and WHK, respectively), DO concentration fields exhibited distinct seasonal changes in the recent 18 years. In SHK, the main periods of the surface DO variation were 24, 12, and 6 months, whereas the main period was 12 months in WHK. The main period of the bottom DO variation was 12 months in both SHK and WHK. In SHK, the spatial–temporal variations in surface and bottom DO were highly related to the variations of salinity, dissolved inorganic nitrogen (DIN), and active phosphorus, and the variation of surface DO was also connected to the variation of temperature and chlorophyll a. In WHK, the variations in surface and bottom DO were highly related to the variations of salinity and temperature, and the variation of surface DO was also connected to the variation of DIN. The river discharge and wind had a different important influence on the temporal variability of DO in WHK and SHK. These findings suggested that the variations of DO may be controlled by coupled physical and biochemical processes in the southeast of PRE. From 2000 to 2017, bottom hypoxia in the southeast of PRE occurred in the summers of 7 years. SHK appeared to be more vulnerable to hypoxia than WHK.

Investigation of black carbon climate effects in the Arctic in winter and spring

Black carbon (BC) exerts a potential influence on climate, especially in the Arctic, where the environment is very sensitive to climate change. Therefore, the study of climate effects of BC in this region is particularly important. In this study, numerical simulations were performed using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) in the Arctic in winter and spring for two years to investigate the atmospheric BC causing changes in surface radiation, meteorology, and atmospheric stability. Generally, WRF-Chem well reproduced the temporal variations of meteorological variables and BC concentration. Numerical simulations showed that BC concentrations in the Arctic in winter were mostly higher than those in spring, and the BC-induced near-surface temperature changes were also stronger. The effects of BC on near-surface water vapor mixing ratio were consistent with the spatial pattern of near-surface temperature changes. That was probably the result of the regional circulation anomaly due to the temperature changes. Additionally, the distributions of near-surface temperature changes and horizontal wind changes also reflected in the distribution of planetary boundary layer height. Ultimately, this study revealed that the downward longwave radiation related to cloudiness changes played an important role for driving near-surface temperature in the Arctic in winter. While in spring, the relatively less changes in near-surface temperature may be the result of the mutual compensation between the surface longwave and shortwave radiation effects.

Spatial and Temporal Variations of Arctic Sea Ice From 2002 to 2017

AbstractThe variation of polar sea ice is an indicator of polar environmental change, which plays an important role in the study of regional and global climate change. In this paper, the latest sea ice data sets from the European Space Agency Climate Change Initiative were firstly combined to comprehensively analyze the spatial and temporal variation of Arctic sea ice concentration (SIC) and sea ice thickness (SIT) from 2002 to 2017. The results show that during this period, the SIC of the Kara Sea and the Barents Sea decreases the most significantly, reaching −1.11%·year−1. The Arctic annual average sea ice extent (SIE) and sea ice area (SIA) exhibit noticeable decreasing trends, reaching −0.0592 × 106 km·year−1 and −0.0628 × 106 km·year−1, respectively. Both of Arctic SIE and SIA vary seasonally, and they reach the minimum values of 4.97 × 106 km2 and 3.96 × 106 km2 in September and the maximum values of 14.58 × 106 km2 and 13.35 × 106 km2 in March, respectively. Moreover, the Arctic SIE and SIA anomaly series from 2002 to 2017 were analyzed based on the linear regression method. It is found the most noticeable decreasing trends of the Arctic SIE and SIA are from July to October. The maximum variation of the SIE is −1.06 × 106 km2(10a)−1, and the maximum variation of the SIA is −1.09 × 106 km2(10a)−1. The Arctic SIE and SIA present the smallest decreasing trends from April to May, which are −0.19 × 106 km2(10a)−1 and −0.2 × 106 km2(10a)−1, respectively. The Arctic SIT also displays a pronounced decreasing trend with −0.015 m·year−1 in autumn and −0.018 m·year−1 in winter. The annual average SIT reaches a minimum of 1.28 m in 2013 and a maximum of 1.66 m in 2005. Particularly, the SIT of the Hudson Bay decreases the most significantly, reaching −0.051 m·year−1. Finally, the Arctic average SIT was tested by the Mann‐Kendall method. It is found that the SIT has a sudden change in 2007, from a slight increase in 2003–2007 to a significant decrease in 2007–2017. Overall, the decreasing trend of the Arctic sea ice (both SIC and SIT) is significant in the past decade. These findings can contribute to future research on polar regions and global climate change.

Antarctic Adélie penguin feathers as bio-indicators of geographic and temporal variations in heavy metal concentrations in their habitats

Seabird feathers are effective indicators of heavy metal contamination. To propose a biological detection method suitable for the long-term monitoring of heavy metals in the Antarctic environment, eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in Adélie penguin feathers from different body parts, years, and molting grounds in the Antarctic were investigated in this study. It is found that the concentrations of heavy metals in the feathers showed differences among the body part of origin. The levels of the eight elements in the abdomen and back feathers were approximately the same, but some elements of them were significantly higher than those in the tail feathers. The Hg and Cd concentrations in the abdomen and back feathers increased from root to tip, regardless of the sampling year or molting ground. Based on a structural analysis of the feathers, Hg and Cd were mainly distributed in the feather vane rather than the shaft. The methylmercury content accounted for 83%–97% of the total mercury content in all feather samples, regardless of location, year, or body part, thereby supporting the assumption that mercury entering the feather was predominantly methylated and indicating that a relatively toxic form of Hg is excreted through the feathers. The heavy metals in feathers from the same molting ground showed significant differences over the sampling years. The average concentrations of As, Cr, Cu, Ni, and Zn increased significantly from 2015 to 2019, whereas those of Cd, Hg, and Pb tended to decrease. The concentrations of the eight elements in Adélie feathers from three molting grounds varied greatly, possibly in relation to their living areas and dietary structures. Feathers from the Ross Sea site had the highest Cd, Cu, Hg, Ni, and Zn concentrations, the highest As and Cr concentrations were detected in feathers from the Zhongshan site, and feathers from the Great Wall site showed higher Pb concentrations than those from the other two sites. This study established a long-term, nondestructive, and efficient method for monitoring heavy metal contamination in the polar environment in the future.

Co-relation of Arsenic contamination with water table fluctuations and groundwater flow dynamics: A case study in a part of Bengal basin

ABSTRACT Temporal and seasonal variations of groundwater arsenic concentration are very significant for the exploration of its mobilisation mechanisms and to frame the policies of viable usage of arsenic-contaminated groundwater. Much less is known about the temporal and seasonal pattern of variation of arsenic contamination in shallow groundwater from the present study area (Karimpur blocks, Nadia district, West Bengal, India). So, to extend the understanding, the present study encompasses the steady monitoring of 15 wells of shallow depth from the study area for the period of 2014–2016. It has been observed that geochemical components were varying extensively during the period and the same trends follow for both Fe and As. During the period, the groundwater levels oscillated seasonally which promotes the reductive dissolution of Fe-oxides and/or oxy-hydroxides (As bearing minerals) which is aided by less dispersion of atmospheric oxygen into the shallow aquifers maintaining the reducing environment in the aquifers. The supply of dissolved organic matter into shallow aquifers was also evident by variation of Cl− ion concentration which may help to enhance arsenic mobilisation into shallow groundwater. Moreover, groundwater recharge from both regional rivers and perennial sources influences the evolution of anoxic conditions in the areas with low aquifers permeability consisting mainly of clayey and/or silty intercalations. Likewise, irrigation practices have been augmented to understand its role in arsenic mobilisation.