Elevated levels of environmental radioactivity in fluvial sediment: origin and health risk assessment.

To study the geogenic processes of naturally occurring radioactive materials' (NORMs') distribution, a transboundary Himalayan river (Punarbhaba) is chosen due to its trivial anthropogenic impacts. In explaining the genesis of radionuclides, transition elements (Sc, Ti, V, and Fe), rare-earth-elements (REEs: La, Eu, Ce, Yb, Sm, and Lu), Ta, Hf, Th, and U were analysed in 30 riverbed sediments collected from the Bangladeshi portion of the river. Elemental abundances and NORMs' activity were measured by neutron activation analysis and HPGe-gamma-spectrometry, respectively. Averagen=30 radioactivity concentrations of 226Ra (68.4 Bq kg-1), 232Th (85.7 Bq kg-1), and 40K (918 Bq kg-1) were 2.0-2.3-fold higher, which show elevated results compared to the corresponding world mean values. Additionally, mean-REE abundances were 1.02-1.38-times higher than those of crustal origin. Elevated (relative to earth-crust) ratios of Th/U (=3.95 ± 1.84) and 232Th/40K and statistical demonstrations invoke Th-dominant heavy minerals, indicating the role of kaolinite clay mineral abundance/granitic presence. However, Th/Yb, La/V, Hf/Sc, and Th/Sc ratios reveal the presence of felsic abundances, hydrodynamic sorting, and recycling of sedimentary minerals. Geo-environmental indices demonstrated the enrichment of chemical elements in heavy minerals, whereas radiological indices presented ionizing radiation concerns, e.g., the average absorbed-gamma-dose rate (123.1 nGy h-1) was 2.24-fold higher compared to the threshold value which might cause chronic health impacts depending on the degree of exposure. The mean excess lifetime cancer risk value for carcinogen exposure was 5.29 × 10-4 S v-1, which is ∼2-times greater than the suggested threshold. Therefore, plausible extraction of heavy minerals and using residues as building materials can alleviate the two-reconciling problems: (1) radiological risk management and (2) fluvial navigability.

Radiation exposure and health concerns associated with the environmental geochemistry of relatively higher radioactivity in a fresh water basin.

This study was carried out on a negligible anthropogenically impacted Indo-Bangla transboundary river basin (Atrai, Bangladesh) to elicit radionuclides' and elemental distributions. Thirty sediment samples were collected from the Bangladesh portion of the river, and instrumental neutron activation analysis and HPGe γ-Spectrometry techniques were used to determine environmental radionuclides (e.g., 232Th, 226Ra, 40K) and associated elemental concentrations, respectively. Metal concentrations (Sc, V, Fe, Eu, Sm, La, Yb, Ce, Lu, Ta, Hf) were determined to comprehend the genesis of greater radioactivity. Recognizing the mean concentration of absorbed gamma dose rate (158.7 hGyh-1) is 2.88-times more than the recommended value (55 hGyh-1) that describes ionizing radiation concerns regarding potential health risks to the surrounding communities and the houses of native residents, which are constructed by Atrai river sediment. This work will assist relevant policymakers in exploring valuable heavy minerals and provide information regarding radiological health risks from a fluvial system.

Characteristics of soil N2O emission and N2O-producing microbial communities in paddy fields under elevated CO2 concentrations.

The effects of elevated carbon dioxide (CO2) concentration (e[CO2]) on nitrous oxide (N2O) emissions from paddy fields and the microbial processes involved in N2O emissions have recently received much attention. Ammonia-oxidizing microorganisms and denitrifying bacteria dominate the production of N2O in paddy soils. To better understand the dynamics of N2O production under e[CO2], a field experiment was conducted after five years of CO2 fumigation based on three treatments: CK (ambient atmospheric CO2), T1 (CK + increase of 40 ppm per year until 200 ppm), and T2 (CK + 200 ppm). N2O fluxes, soil physicochemical properties, and N2O production potential were quantified during the rice-growth period. The functional gene abundance and community composition of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were analyzed using quantitative polymerase chain reaction (qPCR) and those of ammonia-denitrifying bacteria (nirS- and nirK-type) were analyzed using Illumina MiSeq sequencing. N2O emissions decreased by 173% and 41% under the two e[CO2] treatments during grain filling and milk ripening, respectively (P < 0.05). N2O emissions increased by 279% and 172% in the T2 treatment compared with T1 during the tillering and milk-ripening stages, respectively (P < 0.05). Furthermore, the N2O production potential was significantly higher in the CK treatment than in T1 and T2 during the elongation stage. The N2O production potential and abundance of AOA amoA genes in T1 treatment were significantly lower than those in CK treatment during the high N2O emission phase caused by mid-season drainage (P < 0.05). Although nirK- and nirS-type denitrifying bacteria community structure and diversity did not respond significantly (P > 0.05) to e[CO2], the abundance of nirK-type denitrifying bacteria significantly affected the N2O flux (P < 0.05). Linear regression analysis showed that the N2O production potential, AOA amoA gene abundance, and nirK gene abundance explained 47.2% of the variation in N2O emissions. In addition, soil nitrogen (N) significantly affected the nirK- and nirS-type denitrifier communities. Overall, our results revealed that e[CO2] suppressed N2O emissions, which was closely associated with the abundance of AOA amoA and nirK genes (P < 0.05).

Reconciling the geogenic and non-crustal origins of elements in an Indo-Bangla transboundary river, Atrai: Pollution status, sediment quality, and preliminary risk assessment.

This study has been conducted on an anthropogenically less influenced transboundary river (Atrai: Indo-Bangladesh) to comprehend the inherent geochemistry and identify potential elemental sources. In doing so, across the Bangladeshi portion, 30 river-bed samples were culled and studied by neutron activation analysis to quantify the abundances of 15 geochemically and toxicologically significant elementals (Na, Al, K, Ti, Cr, Mn, Co, Zn, As, Rb, Sb, Cs, Ba, Th, and U). The results revealed that the mean concentrations (µg/g) of Rb (154.6), Cs (7.53), Th (20.90), and U (4.88) were 1.5-2.0 times higher than crustal values. Besides, geo-environmental indices revealed 'uncontaminated to moderately contaminated' pollution status with minor enrichment or contamination for Rb, Th, Sb, U, and Cs, relatively concentrated in the mid-to-downstream zone possessed geogenic and non-crustal origins. The positive matrix factorization and other statistical approaches revealed predominant geogenic enrichment of Na, K, Al, Ti, Zn, Cs, Rb, As, Th, and U from differential mineralogical compositions via weathering, elemental fractionations, and biogeochemical mobilization. Contrariwise, several anthropogenic sources (for Cr, Sb, Co, Mn, Th) were also ascertained in the vicinity of Atari River. However, sediment characterization based on SQG threshold values manifested that Cr and Mn possess rare biological effects on local aquatic organisms. Nevertheless, SQGs-based and ecological risk indices invoked minor to no potential ecotoxicological intimidations for the considered metal(oid)s (Cr, Mn, Co, Zn, As, and Sb). Hence, this study manifested the usefulness of a less anthropogenically affected river to reckon geogenic and non-crustal elemental origins in the compounded riverine sediment.

Characteristics and influencing factors of carbon fluxes in winter wheat fields under elevated CO2 concentration.

Elevated carbon dioxide (ECO2) concentration has profound impacts on ecosystem carbon fluxes, with consequent changes in carbon sequestration and its feedback to climate change. Agroecosystem plays an essential role in global carbon sequestration. However, it is not well understood how the carbon fluxes of agroecosystem respond to increasing atmospheric CO2 concentrations. In this study, an in-situ 2-year field experiment was conducted using open-top chamber with treatments including ambient CO2 concentration (CK) and ambient plus 200 µmol mol-1 (T) to investigate the characteristics and main factors influencing carbon fluxes during the 2017-2019 winter wheat growing seasons. Results showed that the dynamics of CO2 fluxes under different treatments had similar seasonal trends, with the peak flux observed at the heading-filling stage. Compared to the CK, T treatment increased the cumulative amount of CO2 (CAC) by 17.2% and 24.0% in 2017-2018 and 2018-2019 growing seasons, respectively. In addition, the seasonal CAC was highly dependent on treatment and varied with year, while there was no interactive effect of treatment and year (p > 0.05). ECO2 concentration increased the biomass of wheat by an average of 8.28% over two growing seasons. There was a significant positive correlation between biomass and CAC, with biomass elucidating 52% and 76% of the variations in CAC under CK and T treatments, respectively. A good correlation was found between net ecosystem exchange (NEE) and environmental variables under different treatments. During the pre-milk ripening period, the NEE mainly depended on photosynthetically active radiation (PAR) and air temperature (Ta), while NEE was mainly controlled by PAR and soil water content (SWC) during the post-milk ripening period. Overall, the findings presented here demonstrate that the carbon exchange in wheat fields under different treatments serves as carbon sequestration, while ECO2 concentration enhances the capacity of winter wheat fields to act as carbon sinks, which may have feedback to the climate system in the future.

Risk assessment of drought disaster in summer maize cultivated areas of the Huang-Huai-Hai plain, eastern China.

Agricultural drought risk analysis is useful for reducing probable drought risk in the background of global warming. This study aims to identify spatiotemporal characteristics of drought and drought disaster risk in the summer maize growth period under climate change condition. In this research, we use daily datasets from 79 meteorological stations and the maize yield data in the Huang-Huai-Hai (HHH) plain, eastern China during the period 1960-2015. The drought disaster risk index (DDRI) model was applied to assess the drought disaster risk. The maize drought disaster risk maps were drawn under current and future climate change conditions. The results showed that the high DDRI was distributed in northern region and low DDRI was distributed in most of southern region in the HHH plain. During the summer maize growth period, the DDRI decreased gradually from the northern to southern region. The results also exhibited that under the RCP4.5 (Representative Concentration Pathway 4.5) scenario, about one half of the HHH plain belonged to the slight and sub-slight DDRI region in the future 80 years. Overall, our results demonstrated that the DDRI model provided an accurate assessment in both spatial and temporal scales and had a theoretical guidance for improving the adaptation of crop production. Elevating maize drought risk management helps to lessen the anticipated risk to crop production in the HHH plain under the context of climate change.

The process of methanogenesis in paddy fields under different elevated CO2 concentrations.

Understanding the process of methanogenesis in paddy fields under the scenarios of future climate change is of great significance for reducing greenhouse gas emissions and regulating the soil carbon cycle. Methyl Coenzyme M Reductase subunit A (mcrA) of methanogens is a rate-limiting enzyme that catalyzes the final step of CH4 production. However, the mechanism of methanogenesis change in the paddy fields under different elevated CO2 concentrations (e[CO2]) is rarely explored in earlier studies. In this research, we explored how the methanogens affect CH4 flux in paddy fields under various (e[CO2]). CH4 flux and CH4 production potential (MPP), and mcrA gene abundance were quantitatively analyzed under C (ambient CO2 concentration), C1 (C + 160 ppm CO2), and C2 (C + 200 ppm CO2) treatments. Additionally, the community composition and structure of methanogens were also compared with Illumina MiSeq sequencing. The results showed that C2 treatment significantly increased CH4 flux and MPP at the tillering stage. E[CO2] had a positive effect on the abundance of methanogens, but the effect was insignificant. We detected four known dominant orders of methanogenesis in this study, such as Methanosarcinales, Methanobacteriales, Methanocellales, and Methanomicrobiales. Although e[CO2] did not significantly change the overall community structure and diversity of methanogens, C2 treatment significantly reduced the relative abundance of two uncultured genera compared to C treatment. A linear regression model of DOC, methanogenic abundance, and MPP can explain 67.2% of the variation of CH4 flux under e[CO2]. Overall, our results demonstrated that CH4 flux in paddy fields under e[CO2] was mainly controlled by soil unstable C substrate and the abundance and activity of methanogens in rhizosphere soil.

A highly agricultural river network in Jurong Reservoir watershed as significant CO2 and CH4 sources.

Freshwaters are receiving growing concerns on atmospheric carbon dioxide (CO2) and methane (CH4) budget; however, little is known about the anthropogenic sources of CO2 and CH4 from river network in agricultural-dominated watersheds. Here, we chose such a typical watershed and measured surface dissolved CO2 and CH4 concentrations over 2 years (2015-2017) in Jurong Reservoir watershed for different freshwater types (river network, ponds, reservoir, and ditches), which located in Eastern China and were impacted by agriculture with high fertilizer N application. Results showed that significantly higher gas concentrations occurred in river network (CO2: 112 ± 36 µmol L-1; CH4: 509 ± 341 nmol L-1) with high nutrient concentrations. Dissolved CO2 and CH4 concentrations were supersaturated in all of the freshwater types with peak saturation ratios generally occurring in river network. Temporal variations in the gas saturations were positively correlated with water temperature. The saturations of CO2 and CH4 were positively correlated with each other in river network, and both of these saturations were also positively correlated with nutrient loadings, and negatively correlated with dissolved oxygen concentration. The highly agricultural river network acted as significant CO2 and CH4 sources with estimated emission fluxes of 409 ± 369 mmol m-2 d-1 for CO2 and 1.6 ± 1.2 mmol m-2 d-1 for CH4, and made a disproportionately large, relative to the area, contribution to the total aquatic carbon emission of the watershed. Our results suggested the aquatic carbon emissions accounted for 6% of the watershed carbon budget, and fertilizer N and watersheds land use played a large role in the aquatic carbon emission.

Effects of warming and elevated O3 concentrations on N2O emission and soil nitrification and denitrification rates in a wheat-soybean rotation cropland.

The effects of warming and elevated ozone (O3) concentrations on nitrous oxide (N2O) emission from cropland has received increasing attention; however, the small number of studies on this topic impedes understanding. A field experiment was performed to explore the role of warming and elevated O3 concentrations on N2O emission from wheat-soybean rotation cropland from 2012 to 2013 using open-top chambers (OTCs). Experimental treatments included ambient temperature (control), elevated temperature (+2 °C), elevated O3 (100 ppb), and combined elevated temperature (+2 °C) and O3 (100 ppb). Results demonstrate that warming significantly increased the accumulative amount of N2O (AAN) emitted from the soil-winter wheat system due to enhanced nitrification rates in the wheat farmland and nitrate reductase activity in wheat leaves. However, elevated O3 concentrations significantly decreased AAN emission from the soil-soybean system owing to reduced nitrification rates in the soybean farmland. The combined treatment of warming and elevated O3 inhibited the emission of N2O from the soybean farmland. Additionally, both the warming and combined treatments significantly increased soil nitrification rates in winter wheat and soybean croplands and decreased denitrification rates in the winter wheat cropping system. Our results suggest that global warming and elevated O3 concentrations will strongly affect N2O emission from wheat-soybean rotation croplands.

Effect of Warming and Elevated O3 Concentration on CO2 Emissions in a Wheat-Soybean Rotation Cropland.

A deeper understanding of the effects of experimental warming and elevated ozone (O3) concentration on carbon dioxide (CO2) fluxes is imperative for reducing potential CO2 emissions in agroecosystems, but are less understood particularly in rotational wheat (Triticum aestivum)-soybean (Glycine max) croplands. In order to understand such effects on CO2 fluxes from winter wheat-soybean rotation, a field experiment was conducted by using the open-top chamber (OTCs) during the growing seasons of 2012 and 2013 at an agro-ecological station in southeast China. The experimental treatments included the control (CK), experimental warming (T, crop canopy temperature increased by ~2 °C), elevated O3 concentration (O, O3 concentration about 100 ppb) along with temperature enhancement (OT, elevated ~2 °C temperature plus 100 ppb O3). The results showed that warming significantly increased the mean CO2 fluxes (MCF) and the cumulative amount of CO2 (CAC) from soil and soil-crop systems, while elevated O3 and warming enhancement (OT) significantly reduced MCF and CAC. Besides, warming significantly reduced the biomass of winter-wheat, but it insignificantly decreased the biomass of soybean in the harvest period. The O and OT treatments significantly reduced the biomass of winter-wheat and soybean cropping systems in the harvest time. Both warming and elevated O3 concentration decreased the temperature sensitivity coefficients (Q10) in soil respiration during the experimental period. Overall, our results indicate that elevated O3 concentration compensates the effect of warming on CO2 emission to some extents, which has a positive feedback impact on the climate system.

Spatiotemporal analysis the precipitation extremes affecting rice yield in Jiangsu province, southeast China.

With the increasing risk of meteorological disasters, it is of great importance to analyze the spatiotemporal changes of precipitation extremes and its possible impact on rice productivity, especially in Jiangsu province, southeast China. In this study, we explored the relationships between rice yield and extreme precipitation indices using Mann-Kendall trend test, Pettitt's test, and K-means clustering methods. This study used 10 extreme precipitation indices of the rice growing season (May to October) based on the daily precipitation records and rice yield data at 52 meteorological stations during 1961-2012 in Jiangsu province. The main findings were as follows: (1) correlation results indicated that precipitation extremes occurred in the months of July, August, and October, which had noticeable adverse effects on rice yield; (2) the maximum 7-day precipitation of July and the number of rainy days of August and October should be considered as three key indicators for the precipitation-induced rice meteorological disasters; and (3) most of the stations showed an increasing trends for the maximum 7-day precipitation of July and the number of rainy days of August, while the number of rainy days of October in all the stations demonstrated a decreasing trend. Moreover, Jiangsu province could be divided into two major sub-regions such as north and south areas with different temporal variations in the three key indicators.