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In this study, the sedimentary records, sources, and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in Dianchi Lake were analyzed. The concentrations of ΣPAH16 in the sediments of Dianchi Lake ranged from 368 to 990 ng/g, with an average value of 572 ng/g, peaking in 1988. Economic development, rapid population growth, and rapid growth of coal consumption have a greater impact on the HMW (high molecular weight) PAHs than on the LMW (low molecular weight) PAHs in the sedimentary environment. The results of the diagnostic ratios and PCA (principal component analysis) model show that the main sources of PAHs were coal and biomass combustion, as well as the fossil fuel combustion in individual years. The risk assessment results showed that the PAH concentrations in the sediment were within a safe range. In the past 100 years of sediment pore water, other 2–3 ring LMW PAHs were within a safe range (except for Phe, which reached chronic toxic pollution levels in some years). With an increase in industrialization and urbanization, the burning of fossil fuels such as coal and petroleum has increased, and some of the 4–6 ring HMW PAHs have reached chronic toxicity or even acute toxicity in the sediment pore water. [ABSTRACT FROM AUTHOR]

An analysis of the correlation between polycyclic aromatic hydrocarbons (PAHs) and economic parameters demonstrates that the total population, gross domestic product, coal consumption, petroleum, temperature, and day consumption significantly affect PAH concentrations in Dianchi Lake, Yunnan province, China. An artificial neural network (ANN) model was developed to predict the trend in PAH concentrations in the sediments of Dianchi Lake over the next 10 years based on current indicators of economic development. The ANN model estimated the concentration of PAHs from 1980 to 2014. The model was evaluated using available observations for the historical trends; concentrations of PAHs in the sediments of Dianchi Lake are calculated to be at 2128.1 ng/g in 2025 and are expected to decline up to 1044.3 ng/g by 2030. These concentrations are considered relatively high because of their impacts on the health of people and aquatic organisms and the development of surrounding industries. We show the importance of the socioeconomic and climate factors in increasing the pollution levels. Our results could support the local government to formulate effective measures to reduce the pollution levels in the lake. [ABSTRACT FROM AUTHOR]

Abstract Estimation of phytoplankton biomass (noted as phytoplankton carbon, C phyto) and evaluation of phytoplankton physiology is central to the estimation of primary productivity and the carbon cycle. This issue has been widely considered in oceans but not in inland water. Here, we develop experiential and semi-analytical models, which validated by independent in situ measurement data, respectively, to derive C phyto and phytoplankton absorption coefficient at 675 nm (a ph (675)) from MODIS. The effects of nutrients and temperature on the seasonal variation of phytoplankton physiology were assessed through a novel proxy of C phyto to a ph (675) ratio (C phyto / a ph (675)) over the Lake Taihu, the third largest lake in China. Significant seasonal climatological cycles of C phyto , a ph (675) and C phyto / a ph (675) were observed in Lake Taihu, especially in Meiliang Bay and Zhushan Bay, where algal blooms occur frequently. The highest C phyto and a ph (675) values were observed in summer due to the growth of phytoplankton biomass and chlorophyll-a concentration. Lower values were observed in winter and spring, which are characterized by relatively high total nitrogen levels and low irradiance, owing to the low temperature astricts the algae growth. However, the C phyto / a ph (675) shows an opposite trend compared to C phyto and a ph (675), which have high values in winter and low values in summer. The analysis of C phyto , a ph (675) and C phyto / a ph (675) with total phosphorus (TP) levels and temperature indicates that TP are the main positive driver of the increase in C phyto and a ph (675) and negatively regulate C phyto / a ph (675). Warming promotes an increase in C phyto and a ph (675) and restricts C phyto / a ph (675) in summer. Biomass and nutrient levels are the primary drivers of the decrease of C phyto / a ph (675) in such a typical eutrophic lake. The results present some new findings compared to previous oceanic studies and expand our knowledge in the study of phytoplankton biomass and physiology in eutrophic lakes. Graphical abstract Image 1 Highlights • Developed the retrieval model of C phyto and a ph (675). • Established an novel proxy (C phyto : a ph (675)) in high turbid inland water to monitor the phytoplankton physiology. • Revealed the regulation effects of temperature and nutrient to C phyto and C phyto : a ph (675). [ABSTRACT FROM AUTHOR]

Sediment resuspension is closely related to the endogenetic release of nutrients in Lake Taihu. Thus, understanding the factors associated with sediment resuspension is important. In this study, a new technology, which integrates a hydrodynamic model and remote sensing techniques, was applied to derive the distribution of the erosion flux and obtain the spatially variable critical shear stress. Then, the spatially variable critical shear stress was used in the sediment simulations at Lake Taihu. Compared to the traditional model, based on uniform values of critical shear stress, the new method, using variable values of critical shear stress calibrated from the Geostationary Ocean Color Imager (GOCI) data, significantly improved the sediment simulations at Lake Taihu. Based on the erosion flux from August 6-8, 2013, the correlations between erosion and wind speed, wind fetch, mud depth, and water depth were analyzed for different subsections and spots in Lake Taihu. The potential sources of error were also addressed. Further improvement of the model is necessary. [ABSTRACT FROM AUTHOR]

Reforestation and afforestation have been implemented over large regions in China for decades, and this has significantly reduced dust storms, desertification and soil/water erosion in China. However, the quantificational evaluation of the reforestation program in China is still incomplete, especially in the southwest China, due to the limitation of survey data. In order to assess the effects of reforestation on soil erosion in southwest China, a subtropical monsoon region with acid red soil, a representative watershed (Dianchi, Yunnan, in southwest China), was selected to study the effect of reforestation on soil erosion over nearly five decades. The land surface soil samples and sedimentary core in this watershed were examined in 2012 to evaluate the soil erosion and sediment deposition during the period of deforestation and reforestation. The results from the multi-source indexes (nutrients, radionuclides, metallic and isotope elements) measurement from soil samples and analyses (composite fingerprinting, remote sensing and geographic information system) indicate that reforestation significantly reduced the presence of sand from surrounding basin via the sedimentary records. Natural forests had the greatest soil conservation capacity, followed by economic forests and farmland, according to a composite fingerprinting. The distribution of total phosphorus, total nitrogen (TN), total organic carbon (TOC) and isotope carbon (δC) presents a high consistency to the results of the composite fingerprinting. The loss rate of TN and TOC in farmland is much greater than that in forest. Reforestation will thus increase the storage of TN and TOC in the long term, although this storage is lower than that in farmland during a short time due to the application of fertilizers. The logging of economic forests will significantly increase soil erosion in this region because of low grass coverage. Recommendations include limiting the period of logging in economic forests to periods outside the rainy season and intercropping other kinds of indigenous trees or grasses to reduce soil erosion. [ABSTRACT FROM AUTHOR]

An integrated system including eutrophication simulation and algal bloom predication was established and applied in Lake Taihu. The mechanic models, which are based on a three-dimensional numerical model coupling hydrodynamic module, pollutant transport module, suspended sediment resuspension module, wind wave module and algal bloom predication module, can simulate not only the single function such as current pattern, nutrient distribution, sediment concentration and wave height field, but also the interaction among them. Using these models, some complex phenomenon such as endogenous pollution can be simulated. In the study, some key technologies are introduced to make the simulation reasonable and feasible. First, a new method for predicting algal bloom is introduced. Differing from the traditional phytoplankton dynamic model, judging the algal bloom through biomass or chlorophyll concentration, the method quantitatively estimates algal growth state switching among bloom, collapse and steady based on algal stability criterion in water column. Second, the sediment resuspension is estimated using calibrated critical shear stresses derived from remote sensing data and the wave-enhanced bottom stress during the windy days. Third, a user-friendly operation environment based on plug-in development and geographic information system is developed. The tests demonstrated that the system could both simulate the reactive solutes such as BOD and DO and the suspended sediment correctly under interaction of gravity and turbulent diffusion. The simulation results demonstrated that the system could obtain reasonable and reliable simulated results in Lake Taihu. [ABSTRACT FROM AUTHOR]

Understanding changes in climate and environment on a regional scale can provide useful guidance for regional socio-economic development. The present study characterizes changes in the environment, climate, land use and cover types via in situ observed, statistical data and remote sensing images for Jiangsu Province, China, during the period 1980–2012. Statistical and spatial analyses indicate that the pace of urbanization in southern Jiangsu is more rapid than that in northern Jiangsu. Urbanization (92.7%) results primarily from the loss of farmland. While emissions of pollutants from industrial sources were well controlled, and wastewater, which more frequently derives from urban domestic sources, was found to be increasing. The rates of wastewater to population increased from 0.17 ± 0.017 to 0.32 ± 0.090 (billion ton/million persons) during the two periods of 1980–2000 and 2000–2012. However, the rates of wastewater to Gross Domestic Product (GDP) decreased from 0.26 ± 0.20 to 0.014 ± 0.009 (billion ton/billion Yuan), respectively. The significant increase in scattering radiance and Earth's albedo caused by the urbanization and its process (Pearson correlation coefficient (r) between urban land and scattering radiance = 0.86, p < 0.0001; r between farmland and scattering radiance = − 0.92, p < 0.0001) aggravates the warming in the regional scale. This correlation analysis indicates that temperature will decrease with the increase of woodland, grassland and farmland, and will increase with the increase of urbanized and unexploited lands. Added to warming caused by an increase in CO 2 , land use/cover change and human activities may be the primary reason for the rising temperatures in Jiangsu Province. The change in regional thermal conditions reduces both local humidity and land atmosphere flux exchange. The low atmosphere flux exhange contributes to the spread of atmospheric pollutants and the deposition of atmospheric particles. [ABSTRACT FROM AUTHOR]

Black carbon (BC), the highly recalcitrant aromatic carbonaceous from the incomplete combustion of fossil fuel and biomass, is an important carbon sink in carbon cycle. Char and soot, the main components of BC, have significantly different origin and physicochemical characteristics (particle sizes and resultant transportability). The limited understanding of char and soot sources leads to poor insight into the effect of BC on carbon cycle. Sources of char and soot were investigated in this study using stable carbon isotopes to study the effect of BC on the organic carbon pool in a lake, thereby improving the knowledge of lacustrine carbon cycling. The concentration of BC in Taihu Lake ranged from 0.0 to 0.7 mg·L−1and accounted for 10.9 ± 4.7% of the particulate organic carbon. The spatial-mean δ13C values of BC, char, and soot were −23.2 ± 2.0‰, −23.5 ± 2.2‰, and −22.9 ± 1.6‰, respectively. The BC in water was primarily derived from fossil fuels (66.0 ± 9.3%), with liquid fossil fuel accounting for 48.2 ± 13.2% of the BC. The contribution of liquid fossil fuel to soot (49.3%) was much higher than that to char (36.1%); correspondingly, the contributions of biomass and coal to soot (29.2% and 21.5%) were lower than those to char (38.1% and 25.8%). The contribution of liquid fossil fuel combustion to organic carbon (OC), char, and soot gradually increased from 31.9% to 49.3%. Biomass and coal combustion primarily contributed to char (38.1% and 25.8%) and OC (37.5% and 30.6%). The source apportionment of BC, char, and soot revealed the influence of anthropogenically driven BC, char, and soot on the lake and, by extension, to the global carbon cycle. [Display omitted] • Char and soot equally contribute to BC with a mean char/soot ratio of 1.2 ± 0.7. • The contribution of fossil fuels to BC in Taihu Lake is 66.0 ± 9.3%. • Soot is mainly derived from liquid fossil fuels combustion, and char is mainly derived from biomass burning. [ABSTRACT FROM AUTHOR]

Humans have had a significant impact on the terrestrial pedosphere through activities such as agriculture and urbanization. The effects of human activities on land use and the related environmental changes were investigated through point and areal studies surrounding Meiliang Bay, which is an open area of extreme eutrophication in Taihu Lake, China. This study used remote sensing and environmental-tracer profiles [total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), grain size, and geochemical parameters] to determine the causes of changes in land use and the associated environmental parameters. The results of LUCCs (Land use/cover changes) indicate that over the past three decades, total farmland decreased by 862.49 km2, with an annual decrement rate of 28.75 km2/year, and total urbanized land increased by 859.71 km2, with an annual growth rate of 28.66 km2/year. The geochemical results indicate that the trophic state of Taihu Lake was persistently intensifying and that the TN, TP, and TOC concentrations increased twofold, threefold, and twofold, respectively, from 1949 to 2010. The sources of TN, TP, and TOC were highly similar after 1975. However, before 1974, TN and TP originated from different sources than TOC. The grassland and woodland around the lake retain nutrients and sand from the land of study area. The increase in urbanized land and tertiary industries significantly increased the sediment concentrations of TN, TP, and TOC after 1980. [ABSTRACT FROM AUTHOR]

Abstract: It has been proven that empirical (two-band) and semi-analytical (three-band) algorithms based on near-infrared and red (NIR-red) wavelengths can be used for estimating C chl-a in highly turbid productive waters with satisfactory performance. However, the optimal spectral bands and parameters of algorithms vary significantly because of the different optical properties of datasets. Using a comprehensive dataset, we validate and evaluate the applicability of empirical and semi-analytical algorithms for deriving C chl-a for inland lakes in China. The comprehensive dataset contains 993 in situ samples collected from five inland lakes in China between 2006 and 2013. The optimal algorithms, R rs(706)/R rs(685) and , are calibrated using an in situ dataset, with root mean square errors (RMSEs) of 10.66mg/m3 and 8.47mg/m3, respectively. The RMSEs of the NIR-red two- and three-band algorithms for the validation data are 11.1mg/m3 and 8.82mg/m3, respectively. The RMSEs increase to 13.17mg/m3 and 12.58mg/m3 when the algorithms are applied to Medium Resolution Imaging Spectrometer (MERIS) and Geostationary Ocean Color Imager (GOCI) centre wavelengths. The RMSEs for the validation data decrease to 8.80mg/m3 and 7.78mg/m3 when the optimal spectral band (λ 1) shifts to 671nm. The RMSEs decrease to 10.03mg/m3 and 9.09mg/m3 as a result of optimization of the model parameters when the algorithms are applied to MERIS and GOCI centre wavelengths. The shifting of the optimal spectral band (the difference between 671nm and 685nm) increases the RMSEs from 8.80mg/m3 to 11.1mg/m3 for the two-band algorithm, and slightly increases the RMSEs from 7.78mg/m3 to 8.82mg/m3 for the three-band algorithm. This indicates that the three-band algorithm is much more suitable for high-turbidity water than the two-band algorithm. Nevertheless, the two-band model can be used for extremely turbid and low C chl-a waters for analysis of the retrieval results after cluster analysis of remote sensing reflectance. Meanwhile, shifting of the optimal spectral bands (λ 1) is highly correlated with the total suspended matter concentration (C TSM) (the Pearson correlation coefficient between λ 1 and C TSM can reach 0.95). In conclusion, the results indicate that both the two- and three-band algorithms have high potential applicability for derivation of C chl-a in high-turbidity inland waters in China. [Copyright &y& Elsevier]

For optically complex turbid productive waters, the optical behavior of suspended particles is the keynote of characterizing the unordered variations of inherent optical properties (IOPs). Multiple bio-optical measurements and sampling of optically active substances were performed in Lake Taihu, Lake Chaohu, and Lake Dianchi, and Three Gorges reservoir of China, in 2008, 2009, and 2010. On the basis of obtaining adequate observation data, we developed an improved and robust water classification approach, by which complex water conditions were divided into three types, i.e., Type 1 (Normalized Trough Depth at 675 nm, hereafter NTD675, ≥0.092), Type 2 (0 ＜ NTD675 ＜ 0.092), and Type 3 (NTD675 ≤ 0). Furthermore, the specific inherent optical quantities for suspended particles, including the specific absorption coefficient of non-algal particles (a*nap), the specific absorption coefficient of phytoplankton (a*ph), and the specific scattering coefficient of the suspended particles (b*p), were determined for the three classified types of waters. The validation results showed that our proposed values for these specific inherent optical quantities presented relatively high predictive accuracies, with most mean absolute percentage errors (MAPE) near 30%, and more importantly, performed much better than that of non-classified waters. Additionally, relative contributions of phytoplankton and non-algal particles to the total particulate absorption and scattering, as well as the spectra, were also analyzed, and the differences among the three classified types of waters were clarified. Overall, the results obtained in this study provide us with new knowledge for understanding complex varied inherent optical properties of highly turbid productive waters. [ABSTRACT FROM AUTHOR]

This study develops a novel support vector regression (SVR) model for retrieving the specific cyanobacterial pigment C-phycocyanin (C-PC) concentrations in cyanobacteria-dominated large turbid lakes of China. Lake Taihu, Lake Chaohu, and Lake Dianchi in China were our study areas. Five field cruises were carried out to collect data sets of optical and water quality parameters. To retrieve the C-PC, three types of reflectance forms, including single band, band ratio, and three-band-combination, were compared. The band ratio was the best candidate to serve for algorithm development. On this basis, two types of models, including linear models and a SVR model, were originally established. The previous typical algorithms were also examined. The obtained results showed that the best-performing model was the SVR model. By our validation data set, the proposed SVR model also presented accurate prediction results, with the lowest errors among all methods. The novelty of the SVR model compared to the previous ones lies in the inclusion of band ratios that are located outside of the main pigment absorption peaks but hold information on inflection points, curvature, etc., into empirical optimization. The implications of these findings indicates the potential applicability of the SVR models in lakes of the similar type. [ABSTRACT FROM AUTHOR]

Water spectral absorption characteristics of eutrophic lakes are largely different from those of ocean and coastal waters. We therefore studied them with the aim of establishing an analytical model for inland water colour, to be used in remote sensing. Field measurements were carried out on 16 and 17 August 2006 (summer), 5 and 6 November 2006 (winter), and 29 and 30 March 2007 (spring) at 15 stations in northern Lake Taihu (China). Chromophoric dissolved organic matter (CDOM) absorption coefficients (a CDOM) are higher in summer than in spring and winter, with the ratios of a CDOM in spring, summer and winter being approximately 1 : 4.0 : 1.2 at both UV-C and UV-B. The spectral slope S CDOM values change with wavelength and season, and covary with CDOM concentration, as shown by regression analysis. For the CDOM absorption spectrum in the wavelength region 500-700 nm (important for water colour remote sensing), a linear method simulates better than an exponential method. Seasonal variations in non-algal particulate (NAP) absorption (a NAP) at blue, green and red wavelengths show better consistency, in the order winter>spring>summer. The average S NAP is 0.0065±0.0009 nm-1, which is lower than that in other types of waters. Phytoplankton absorption (a ph) peak height changes with the season, with the pattern summer>winter>spring, and phytoplankton absorption spectra can be expressed with high accuracy by a quadratic model. CDOM absorption contributions in the three seasons are low compared to phytoplankton and NAP. [ABSTRACT FROM AUTHOR]

In this study, the influencing factors and sources of historical changes in polycyclic aromatic hydrocarbons (PAHs) in the sediment core of Fuxian Lake were analyzed. Before 1970, the Σ 16 PAH concentration fluctuated widely, with one or more maximum values. During 1971–2004, the Σ 16 PAH concentration showed a slow growth trend, while during 2005–2017, the concentration increased sharply, reaching a peak value of 821 ng g−1. dw in 2017. The results of a positive matrix factorization (PMF) model demonstrated that before 1970, PAHs were mainly derived from biomass burning in the Fuxian Lake sediment core, with an overall contribution of 40 %. During 1971–2004, the source of PAHs was mainly coal combustion, with an overall contribution of 34 %. During 2005–2017, PAHs primarily originated from traffic, with an overall contribution of 33 %. Population, coal, GDP, motor, and petroleum had a significant influence on low molecular weight (LMW) PAHs in 1980–2004 and 2005–2017. Motor, coal, population, and GDP had a greater impact on high molecular weight (HMW) PAHs. Before 1970 and in 1971–2004, meteorological factors had little effect on PAHs in the sediment core in Fuxian Lake. During 2005–2017, day and rainfall were significantly negatively correlated with HMW PAHs, while temperature and wind were not correlated with PAH concentrations. During 2005–2017, total organic carbon (TOC) and total nitrogen (TN) had greater adsorption effects on HMW PAHs than on LMW PAHs. Before 1970 and in 1971–2004, the adsorption effects of TOC and TN on 3–4-ring PAHs were greater than those of 2-ring and 5–6-ring PAHs. Total phosphorus (TP) had no adsorption effect on PAHs in the entire sedimentary column. [Display omitted] • Coal combustion and vehicle emissions have been the main sources of PAHs since 1970s. • The contributions of coal and motor to HMW PAHs have gradually increased. • The decrease in day and rainfall will reduce the removal of HMW PAHs. • The adsorption effects of TOC, TN and TP on HMW PAHs are greater than on LMW PAHs. [ABSTRACT FROM AUTHOR]

• Lake CO 2 and CH 4 concentrations varied with seasons and mixing regimes on a regional scale. • System productivity directly affected the carbon concentrations in the dry season and stratified sites. • Direct impacts of lake morphology and geoclimatic factors were found except for the dry season. • The effects of season and mixing regime should be considered in estimating lake carbon emissions. Due to the large spatiotemporal variability in the processes controlling carbon emissions from lakes, estimates of global lake carbon emission remain uncertain. Identifying the most reliable predictors of CO 2 and CH 4 concentrations across different hydrological features can enhance the accuracy of carbon emission estimates locally and globally. Here, we used data from 71 lakes in Southwest China varying in surface area (0.01‒702.4 km2), mean depth (< 1‒89.6 m), and climate to analyze differences in CO 2 and CH 4 concentrations and their driving mechanisms between the dry and rainy seasons and between different mixing regimes. The results showed that the average concentrations of CO 2 and CH 4 in the rainy season were 23.9 ± 18.8 μmol L−1 and 2.5 ± 4.9 μmol L−1, respectively, which were significantly higher than in the dry season (10.5 ± 10.3 μmol L−1 and 1.8 ± 4.2 μmol L−1, respectively). The average concentrations of CO 2 and CH 4 at the vertically mixed sites were 24.1 ± 21.8 μmol L−1 and 2.6 ± 5.4 μmol L−1, being higher than those at the stratified sites (14.8 ± 13.4 μmol L−1 and 1.7 ± 3.5 μmol L−1, respectively). Moreover, the environmental factors were divided into four categories, i.e., system productivity (represented by the contents of total nitrogen, total phosphorus, chlorophyll a and dissolved organic matter), physicochemical factors (water temperature, Secchi disk depth, dissolved oxygen and pH value), lake morphology (lake area, water depth and drainage ratio), and geoclimatic factors (altitude, wind speed, precipitation and land-use intensity). In addition to the regression and variance partitioning analyses between the concentrations of CO 2 and CH 4 and environmental factors, the cascading effects of environmental factors on CO 2 and CH 4 concentrations were further elucidated under four distinct hydrological scenarios, indicating the different driving mechanisms between the scenarios. Lake morphology and geoclimatic factors were the main direct drivers of the carbon concentrations during the rainy season, while they indirectly affected the carbon concentrations via influencing physicochemical factors and further system productivity during the dry season; although lake morphology and geoclimatic factors directly contributed to the carbon concentrations at the vertically mixed and stratified sites, the direct effect of system productivity was only observed at the stratified sites. Our results emphasize that, when estimating carbon emissions from lakes at broad spatial scales, it is essential to consider the influence of precipitation-related seasons and lake mixing regimes. [Display omitted] [ABSTRACT FROM AUTHOR]

• Organic matter is an important source of DIC in the Yangtze River, accounting for 36.99±11.19 %. • Nitrogen-containing formulae accounted for 41.77±2.55 % of DOM, showed superior oxidation state. • Nitrogen-containing components significantly accelerated the degradation of DOM to organic-sourced DIC. Dissolved inorganic carbon (DIC) represents a major global carbon pool and the flux from rivers to oceans has been observed to be increasing. The effect of weathering with respect to increasing DIC has been widely studied in recent decades; however, the influence of dissolved organic matter (DOM) on increasing DIC in large rivers remains unclear. This study employed stable carbon isotopes and Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) to investigate the effect of the molecular composition of DOM on the DIC in the Yangtze River. The results showed that organic matter is an important source of DIC in the Yangtze River, accounting for 40.0 ± 12.1 % and 32.0 ± 7.2 % of DIC in wet and dry seasons, respectively, and increased along the river by approximately three times. Nitrogen (N)-containing DOM, an important composition in DOM with a percentage of ∼40 %, showed superior oxidation state than non N-containing DOM, suggesting that the presence of N could improve the degradable potential of DOM. Positive relationship between organic sourced DIC (DIC OC) and N-containing DOM formulae indicated that N-containing DOM is crucial to facilitate the mineralization of DOM to DIC OC. N-containg molecular formular with low H/C and O/C ratio were positively correlated with DIC OC further verified these energy-rich and biolabile compounds are preferentially decomposed by bacteria to produce DIC. N-containing components significantly accelerated the degradation of DOM to DIC OC , which is important for understanding the CO 2 emission and carbon cycling in large rivers. [Display omitted] [ABSTRACT FROM AUTHOR]

Owing to their bioavailability and toxicity, the dissolved polycyclic aromatic hydrocarbons (PAHs-d) loaded in rivers are harmful to both inland and marine ecosystems. Thus, exploring the changes in PAHs-d levels and sources is important for controlling PAHs pollution. In this study, the concentration of PAHs-d in the mainstream of the Yangtze River during dry and wet seasons was investigated and the source was analyzed using the positive matrix factorization (PMF) model to assess the response of PAHs-d to hydrological and anthropogenic activities changes. The concentration of PAHs-d in the wet season (166.2 ± 52.51 ng/L) was significantly higher than that in the dry season (89.05 ± 20.89 ng/L) (ANOVA, P < 0.001), and the sampling sites with high pollution were mainly distributed in the downstream urban agglomeration. Herein, 2–3 rings were identified to play a dominant role in the composition of PAHs-d. Compared with the dry season, the proportion of the low molecular weight (LMW) PAHs-d were relatively depleted and the high molecular weight (HMW) PAHs-d were accumulated in the wet season. Coal and coke combustion were identified as the main sources of PAHs-d (65.9% in the dry season and 59.2% in the wet season), followed by vehicle emissions, petroleum sources, and biomass combustion. Owing to the change in energy consumption structure and climate characteristics, the sources of PAHs-d displayed seasonal variation and spatial heterogeneity. Further, flow was identified as the most important factor affecting PAHs-d in the hydrological parameters. Increases of flow, pH, and SPM decreased the proportion of LMW PAHs-d, and increased that of HMW PAHs-d. The increase in anthropogenic activities intensified the residual levels of 2-3rings and 5–6 rings in water, but had no significant impact on the levels of 4 rings. • Dissolved PAHs in the Yangtze River were studied by using 0.7 μm filter. • PAHs-d residual levels and structures displayed seasonal changes and spatial heterogeneity. • PAHs-d in the Yangtze River mainly generated from coal and coke combustion. • Flow accelerated the accumulation of PAHs-d in river. • Anthropogenic activities had the most significant impact on 2–3 ring PAHs-d. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is a retarder in carbon cycle, and the proportion of char and soot in BC restricts the significance of BC as a sink in carbon cycle. Tracing the sources of char and soot is helpful for in-depth understanding the anthropogenic-driven burial and pattern of BC, and is crucial for regulating emissions of BC and impact of BC on carbon cycle/climate change. This study investigated source-driven BC via the concentration and δ13C of BC (char and soot) in a Plateau lake sediment. The burial rate of BC (mean: 6.42 ± 5.09 g m−2 yr−1) showed an increasing trend (3.7 times after 1977 compared with before), and the growth rate of char (4.1 times) was faster than soot (2.5 times). The source trace results, showing faster growth of coal combustion ratio in char (increased 21% after 1980 compared with before) than soot (13%), proved that coal combustion promoted faster growth of char in BC. Redundancy analysis confirmed that more low-temperature utilization of coal urged a stronger driving force for char than soot, which caused BC to have lower aromatic content and higher reactivity in organic carbon pool from the past to present, further impact the effects of BC on carbon cycle. [Display omitted] • BC in sediment core witnessed the advancement of regional urbanization and industrialization. • Faster burial of char than soot was discovered in BC of Dianchi sediment core. • Coal combustion facilitated faster burial of char than soot in BC. • Source of char and soot were estimated via stable carbon isotopic signature. [ABSTRACT FROM AUTHOR]

Accurate estimation of phytoplankton chlorophyll a (Chla) concentration from remotely sensed data is particularly challenging in turbid, productive waters. The objectives of this study are to validate the applicability of a semi-analytical three-band algorithm in estimating Chla concentration in the highly turbid, widely variable waters of Taihu Lake, China, and to improve the algorithm using a proposed four-band algorithm. The improved algorithm is expressed as [Rrs(λ 1)−1 −Rrs(λ 2)−1][Rrs(λ 4)−1 −Rrs(λ 3)−1]−1. The two semi-analytical algorithms are calibrated and evaluated against two independent datasets collected from 2007 and 2005 in Taihu Lake. Strong linear relationships were established between measured Chla concentration and that derived from the three-band algorithm of [Rrs−1(660)−Rrs−1(692)]Rrs(740) and the four-band algorithm of [Rrs−1(662)−Rrs−1(693)][Rrs−1(740)−Rrs−1(705)]−1. The first algorithm accounts for 87% and 80% variation in Chla concentration in the 2007 and 2005 datasets, respectively. The second algorithm accounts for 97% of variability in Chla concentration for the 2007 dataset and 87% of variation in the 2005 dataset. The three-band algorithm has a mean relative error (MRE) of 43.9% and 34.7% for the 2007 and 2005 datasets. The corresponding figures for the four-band algorithm are 26.7% and 28.4%. This study demonstrates the potential of the four-band model in estimating Chla even in highly turbid case 2 waters. [Copyright &y& Elsevier]

Sixteen polycyclic aromatic hydrocarbons (PAHs) in a sediment core from Dianchi Lake, southwest China, were analysed. The influence of changes in China's energy structure for 2–6 ringed PAHs was investigated to assess sources and the impact of socioeconomic development on temporal changes in concentrations. The concentration of the ΣPAH 16 ranged from 746 to 2293 ng g−1. Prior to the 1960s relatively low concentrations of the ΣPAH 16 and a larger proportion of 2–3-ring PAHs indicated that biomass combustion was the main source of PAHs. A rapid increase in the concentrations of 2–3 ring PAHs between 1975 and 2004 was attributed to population growth and coal consumption. A declining trend since 2004 was interpreted as being due to local changes in household energy usage. Increased concentrations of 4-ring PAH between 1975–2005 and 5–6-ring PAHs between the 1980s to 2004 showed correlations with increased coal consumption and the number of motor vehicles, respectively. These were caused by rapid urbanization and industrialization in the Dianchi watershed following the implementation of the Reform and Open Policy in 1978. A subsequent decline in the concentrations of 4-ring and 5–6-ring PAHs may have been due to decreased coal consumption and improvements in emission standards, respectively. Source apportionment by a PMF model revealed that coal combustion (29.2%), vehicle emissions (24.2%), petrogenic sources (21.8%), and biomass combustion (24.9%) were the sources of PAHs in the lake sediment core, and that coal combustion was the most important regional source of PAHs pollution. Image 1 • Sixteen PAHs from Dianchi lake sediment, a plateau lake in China, were studied. • Sediment record of PAHs reflect trends in GDP and total energy consumption. • Sediment records of different PAH rings can reflect the changes of energy structure. • Coal and biomass combustion, vehicle emissions and petrogenic were the PAHs sources. • Time trend of factor contributions are consistent with economic parameters. [ABSTRACT FROM AUTHOR]

Observations and models suggest a latitudinal redistribution of precipitation as a result of ongoing global climatic warming. However, the dynamic link between temperature and regional precipitation in the course of natural climatic variability during the current interglacial period remains unclear, especially in the monsoon regions of China. Here we present a reconstruction of a ∼5 year-resolution summer monsoon rainfall record for the past 3200 years, based on 622 pairs of δ18O and δ13C and 29 230Th dates from a stalagmite (Wu37) from Wulu Cave in southern China. A close similarity between the δ18O and δ13C records on centennial to decadal timescales suggests that calcite δ18O is most likely a proxy associated with monsoon precipitation. The record reveals that the Little Ice Age (650 - 100 yr B.P.) was a relatively humid period, with two centennial-scale wet events, compared with the Medieval Warm Period (1050 - 650 yr B.P.). In contrast with previous observations in India and northern China, monsoon precipitation variations indicated by our record and other cave records nearby were inversely related to changes in Northern Hemisphere (NH) temperature over the past two millennia, in particular to variations in the thermal gradient between the Northern and Southern hemispheres. This suggests that NH temperature has an important influence on summer precipitation in southern China, via the interhemispheric thermal gradient and land-ocean thermal contrast. In addition, we find that variations of monsoon rainfall in southern China on multi-centennial to centennial timescales are inversely correlated with observed rainfall in the core monsoon region of India and in the northern fringe of the Asian summer monsoon region in China. This spatial pattern of rainfall variability can be interpreted as a result of the migration of the intertropical convergence zone that is likely dominated by the interhemispheric thermal gradient via cross-equatorial airflows. • Increase of monsoon precipitation in southern China (SC) since the LIA. • Anti-phase relationship between SC precipitation and NH temperature. • A negative correlation between precipitation in SC and India, northern China. • A direct control of NH temperature on the shifts of the ITCZ rainbelt. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and sulfur (S) deposition rates have changed rapidly in China during recent years. But few studies have simultaneously measured wet N and S deposition rates on different land use types in the same region. In present study, 238 precipitation samples were collected between May 2016 and April 2017 using wet-only auto-samplers, and the wet N and S deposition rates were measured at three sites with different land use types (urban, agriculture, and lake) in the Yangtze River Delta (YRD), Eastern China. The annual wet deposition rates of total N (TN), ammonium (NH 4 +), nitrate (NO 3 −), dissolved organic N (DON), water-insoluble particulate N (WIPN), and sulfate (SO 4 2−) were 16.87–26.64, 6.38–10.81, 5.92–11.11, 1.43–1.96, 2.23–2.67, and 9.07–22.53 kg N (S) ha−1 yr−1, respectively. The wet N and S deposition rates were in the order: agriculture > urban > lake sites, and the seasonal variations in wet N and S deposition were similar at all sites. DON and WIPN contributed 6.4–11.8% and 10.7–16.2% of the total wet N deposition, respectively. Chemical N fertilization and fossil fuel were important sources of wet N and S deposition. Annual wet N and S deposition are important nutrient sources that stimulate the eutrophication and soil/water acidification in the YRD. To minimize the environmental cost of wet N and S deposition in the YRD, it is critical to investigate the sources of N and S. Image 1 • Wet N and S deposition at three sites in the Yangtze River Delta were investigated. • Wet N and S deposition rates were in the order: agricultural > urban > lake sites. • DON provided 6.4–11.8% and WIPN provided 10.7–16.2% of the total wet N deposition. • Chemical N fertilizer and fossil fuel were major sources of wet N and S deposition. • N and S deposition caused a high risk of eutrophication and acidification. [ABSTRACT FROM AUTHOR]

Combustion-driven particulate black carbon (PBC) is a crucial slow-cycling pool in the organic carbon flux from rivers to oceans. Since the refractoriness of PBC stems from the association of non-homologous char and soot, the composition and source of char and soot must be considered when investigating riverine PBC. Samples along the Yangtze River continuum during different hydrological periods were collected in this study to investigate the association and asynchronous combustion drive of char and soot in PBC. The results revealed that PBC in the Yangtze River, with higher refractory nature, accounts for 13.73 ± 6.89% of particulate organic carbon, and soot occupies 37.53 ± 11.00% of PBC. The preponderant contribution of fossil fuel combustion to soot (92.57 ± 3.20%) compared to char (27.55 ± 5.92%), suggested that fossil fuel combustion is a crucial driver for PBC with high soot percentage. Redundancy analysis and structural equation modeling confirmed that the fossil fuel energy used by anthropogenic activities promoting soot is the crucial reason for high-refractory PBC. We estimated that the Yangtze River transported 0.15-0.23 Tg of soot and 0.15-0.25 Tg of char to the ocean annually, and the export of large higher refractory PBC to the ocean can form a long-term sink and prolong the residence time of terrigenous carbon.

Surface sediments and sediment core had been collected from Erhai Lake, Southwest China to study the concentrations, toxicity risks, and sources of polycyclic aromatic hydrocarbons (PAHs). The average concentrations of Σ 16 PAHs, seven carcinogenic PAHs (carPAHs), and carcinogenic toxic equivalents (TEQ car ) in the surface sediments and sediment core were 1634.50 ± 488.56 ng g -1 and 436.72 ± 128.17 ng g -1 , 67.18-293.65 ng g -1 and 91.07-265.90 ng g -1 , and 34.89 ± 13.17 ng g -1 and 36.99 ± 7.52 ng g -1 , respectively. The Σ 16 PAHs and carPAHs concentrations in surface sediments were higher in the southern lake. The Σ 16 PAHs and TEQ car in the sediment core peaked in the 2010s and 1980s. The spatiotemporal variations in TEQ car and carPAHs were similar. Positive matrix factorization revealed that traffic emissions contributed 35.71 % of the TEQ car , whereas coal and biomass combustion contributed 12.89 % in the surface sediments. The contribution of gasoline and fossil fuel to TEQ car significantly increased from 19.2 % (1890s) to 66.5 % (1990s), that of benz[a]pyrene (coal combustion) decreased, and those of benz[b]fluoranthene and indeno[1,2,3-cd]pyrene (petroleum combustion and traffic emissions) increased from 1.92 % to 3.93 % and from 1.54 % to 2.52 % in the sediment cores, respectively, owing to changes in energy consumption., Competing Interests: Declaration of competing interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Polycyclic aromatic hydrocarbons (PAHs) have received worldwide attention due to their potential teratogenic, persistent, and carcinogenic characteristics. In this study, the PAHs concentrations in two dated sediment cores taken from central Tibetan Plateau (TP) were analyzed to study the deposition history, potential sources, ecological risks, and influencing factors. Total concentration of PAHs (∑PAHs) ranged from 50.0 to 195 ng g -1 and 51.9-133 ng g -1 in sediments of Pung Co (PC) and Dagze Co (DZC), respectively. 2-3-ring PAHs were dominant in the two lake sediments, accounting for an average of 77.5% and 80.1%, respectively. The historical trends of ∑PAHs in the two lakes allowed to distinguish three periods, namely, relative stability before the 1950s, a gradual increase between the 1950s and the 1990s, and then a decline to the present-day. In addition, the trend in the concentration level of each PAH composition was consistent with ∑PAHs before the 1990s, while they exhibited different trends since the 1990s, which may be the result of a combination of anthropogenic activities and climate change in recent years, whereas before the 1990s the PAH profile was mainly influenced by atmospheric deposition. The results of source apportionment examined according to diagnostic ratios and positive matrix factorization were consistent and revealed that PAHs were primarily derived from biomass and coal combustion. Significant correlations between PAHs and organic carbon (OC) indicate that OC might be a key factor influencing the concentration of PAHs in sediments. The ecological risk assessment demonstrated that PAHs in TP sediments occurred at a low risk level. Results of this study could be helpful to develop a deeper insight into the deposition history of PAHs in remote lakes of the TP region and explore the response of these variations to climate change and human activities., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The regulation of lacustrine organic carbon (OC) burial by nutrient is an outstanding knowledge gap in the current understanding of lake carbon cycles. In this study, we determined how nutrients quantitatively correspond with OC burial using the parallel factor analysis (PARAFAC) method in Dianchi Lake, southwest China. Factors were classified into three types according to their historical sedimentation characteristics: the background factor (BF), response factor (RF), and contingency factor (CF). The BF represented the original OC input combination in the lake and was insensitive to nutrient changes. The RF represented the OC input combination that was induced or promoted by nutrient changes in the lake. The CF represented short-term discontinuous factors in sedimentary history, which may be related to unique historical events. The results indicate that changes in the total nitrogen (TN) to total phosphorus (TP) ratio correlated with changes in the BF contribution; whereas the quantity of OC was mainly correlated with TN. The >90% of OC buried in sediment was quantitatively simulated by BF and RF; the driving effect of RF on OC burial was approximately 13 times higher than that of BF. It was observed that a 1 mg kg -1 increase in TN led to approximately 2.2 units increase in RF contribution in Dianchi Lake, while the BF was insensitive to changes in TN. Thus, changes in lake nutrients may effectively change the composition and quantity of OC buried in lake sediment., Competing Interests: Declaration of competing interest I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is enclosed. We declare that we have no financial and personal relationships with other people of organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature of kind in any product, service or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Sediment dissolved organic matter (DOM) in inland waters is commonly affected by environmental changes. However, knowledge about how sediment DOM responds to eutrophication and the associations between sediment DOM and bacterial communities requires further investigation. We selected a sediment core from Dianchi Lake (China) that was dated from 1864 to 2019 by the activity of radionuclides ( 210 Pb and 137 Cs). δ 13 C DOC changes fit well with the historical record that heavy eutrophic status in Dianchi Lake were observed since 1980s. Large amounts of dissolved organic carbon (DOC), chromophoric (CDOM) and fluorescent (FDOM) DOM accumulated at the top of the sediments during the eutrophication period (1982-present). The additional algae sources with a higher degradation rate altered the composition, aromaticity and humification of DOM. After long-term mineralization, the remaining DOM became more and more recalcitrant and kept a relatively stable level at older sediments. A co-occurrence network analysis revealed that Proteobacteria, Chloroflexi, Acidobacteriota, Bacteroidota and Desulfobacterota were the most abundant species at the phylum level and clustered into three primary modules. Different microbes shared unique preferences for niches, causing a heterogeneous bacterial distribution at different depths. We conducted Spearman's correlation and redundancy analysis (RDA) to explore potential interactions between bacterial community and sediment DOM. The richness and diversity of bacterial communities were positively related to DOM content, suggesting abundant DOM can produce more available resources for bacteria. RDA results showed some specific species might modify DOM composition and structure. This study suggests that sediment DOM properties were regulated by source transformation during eutrophication, and emphasizes the importance of microbial role on sediment biogeochemical process., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The long-term accumulation, burial and release of nutrients, such as carbon (C), nitrogen (N), and phosphorus (P) in lacustrine sediments are responsible for the global lake eutrophication. Interpretation of the spatiotemporal sedimentary record of nutrients (C, N, and P) in contrasting trophic level of lakes is helpful for understanding the evolutionary process of water eutrophication. Based on the radiochronology of 210 Pb ex and 137 Cs, a comparative study of spatial and temporal concentrations, burial of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP), the sources of organic matter were conducted using sediment cores from two plateau lakes Dianchi (DC) and Fuxian (FX) of SW China. Results showed that concentrations and burial of C, N, and P in sediments of DC, a shallow hypertrophic lake with the maximum depth of 5.8 m, were both higher than those in FX, an oligotrophic deep lake with the maximum depth of 155.0 m. For both lakes the molar ratio of TOC/TN increased in the sediments moving from north to south. The values of TOC/TN molar ratios increased over time in DC and were higher than in FX. The extremely high values of TOC/TN appeared in the central and southern parts of FX, indicating the impacts of accumulation effect and sediment focusing in the deeper region and indirect supplement from the Lake Xingyun (XY), an adjoining lake connected with FX via the Gehe River. Time-integrated sources identification in DC indicated the contribution of allochthonous sources was dominant over the past few decades, which contributed to the increased trophic level of the lake. The comparison of relationships of carbon accumulation rates (CAR), nitrogen accumulation rates (NAR), and phosphorous accumulation rates (PAR), the ratios of N/P and the utilizations of N and P fertilizer between DC and FX implied that both of N and P inputs should be limited for reducing the trophic level, but N control was predominant in comparison with P for both lakes. The results indicated that caution is required in plateau lakes to limit transition from oligotrophic to eutrophic in these lakes., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

High ammonia (NH 3 ) and nitrogen oxide (NO x ) emissions are related to serious air pollution in urban areas and the negative impacts of excessive reactive nitrogen (N) deposition on many ecosystems. However, whether there is a relationship between N deposition rates and their sources with urbanization or not remains unclear in many areas. Here, we investigated the deposition rates of ammonium (NH 4 + ), nitrate (NO 3 - ), dissolved organic N, and water-insoluble particular N from July 2017 to June 2018 at two urban and two suburban sites in the Yangtze River Delta (YRD). The δ 15 N values of precipitation NH 4 + and NO 3 - were measured, and major sources were analyzed using a Bayesian isotope mixing model. Wet N deposition rates were higher in Yangzhou (developing city, 20.3-22.7 kg N ha -1  yr -1 ) than those in Nanjing (developed city, 19.4-20.5 kg N ha -1  yr -1 ), and were higher at urban sites (20.4-22.5 kg N ha -1  yr -1 ) than those at suburban sites (18.7-20.3 kg N ha -1  yr -1 ). δ 15 N values of precipitation NH 4 + increased with an increase in precipitation pH because ambient acidity affects the equilibrium isotope fractionation between NH 3 and NH 4 + and wet scavenging coefficients of NH 3 and particulate NH 4 + . For NH 4 + , combustion-related NH 3 sources (62%-65% with 5.5-6.4 kg N ha -1  yr -1 , including coal combustion, vehicle exhaust, and biomass burning) contributed more than volatilization NH 3 sources (35%-38% with 2.9-3.9 kg N ha -1  yr -1 , including fertilizer application and waste volatilization). For NO 3 - , non-fossil fuel NO x sources (50%-63% with 3.4-4.1 kg N ha -1  yr -1 , including biomass burning and microbial N cycle) were comparable to fossil fuel NO x sources (37%-50% with 2.4-3.4 kg N ha -1  yr -1 , including coal combustion and vehicle exhaust). This study evidenced high N deposition rates and the importance of combustion-related NH 3 emissions and non-fossil fuel NO x emissions in city areas of the YRD., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2021. Published by Elsevier B.V.)

Black carbon (BC), characterized by high aromaticity and stability, has been recognized as a substantial fraction of the carbon pool in soil and sediment. The effect of BC on the particulate organic carbon (POC) pool in lake water, which is an important medium of carbon transmission and transformation, has not been thoroughly studied. The investigations of BC composition and distribution, POC, polycyclic aromatic hydrocarbons (PAHs), and stable carbon and nitrogen isotopes were conducted in a eutrophic urban lake, Taihu Lake, which is the third largest freshwater lake in China. The results indicate that the BC is composed of 55 ± 12% char and 45 ± 12% soot and accounted for 12 ± 6% of POC (the maximum value is 31%). The comparatively high levels of BC and char are distributed in the northern Taihu Lake, especially in Meiliang Bay (0.72 ± 0.38 mg L -1 and 0.45 ± 0.24 mg L -1 ). The distribution of soot presents a declining trend from the lakeshore to the central lake, particularly in the northern, western, and southern lakes. Source apportionment results from positive matrix factorization of PAHs suggest that consumption of fossil fuel (79 ± 20%) is the dominant source of BC, which agrees with the low ratio of char/soot (1.41 ± 0.71) and relatively depleted δ 13 C. The covariation of BC and PAHs and terrestrial dissolved organic carbon indicate that the effect of terrestrial input significantly regulates the distribution of BC in Taihu Lake, which is reflected in the high BC value along the lakeshore., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Particulate organic carbon (POC) sources, which regulate dissolved organic carbon, sediment organic carbon, and inorganic carbon via deposition, degradation, and mineralization, play an important role in lake ecosystems. Linear or Bayesian algorithms on isotope and n-alkanes have been widely used to identify the source proportion of organic carbon. However, the applicability of these methods is ambiguous because of the unilateral advantages of each model and trace factors. To test the applicability of the various methods for identifying POC sources, we analyzed dual isotopes and n-alkanes in surface water samples of Lake Taihu, and Multi-source mixing model and Bayesian mixing model were used to distinguish between endogenous and exogenous contributions. Carbon isotope presented a clear advantage in West Taihu (-21.85 ± 0.78‰) and Southwest Taih (-22.61 ± 1.35‰); nitrogen isotope also showed high values in Meiliang Bay (9.76 ± 0.92‰). The majority of the lake was dominated by short-chain n-alkanes, except for East Taihu Lake (dominated by medium-chain n-alkanes) and areas with riverine input (dominated by long-chain n-alkanes). Different principles between the Bayesian mixing model (based on the Markov Chain Monte Carlo algorithm) and the Multi-source mixing model (based on linear estimation) caused discrepancies in the estimations of source contributions. But the fraction of chemical compounds during the migration process, and the overlap of potential sources play important role in the inconsistency of results. The estimations from the different models were consistent in indicating the dominance of endogenous organic carbon in Lake Taihu (mean of 60.18 ± 20.26%), particularly in the north and western regions (West Taihu, Meiliang Bay, and Southwest Taihu). This was likely due to algal aggregation influenced by human activities and climatic factors., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier Ltd.)

The total amount and morphology of nitrogen and phosphorus in sediments have important environmental significance. The study of the ecological risk assessment of nitrogen and phosphorus in sediments is important to understand the environmental quality of water body in the basin. In this study, taking the Futunxi Basin of Fujian Province as an example, the single factor index and bioavailability coefficient method were used to evaluate the ecological risk of nitrogen and phosphorus in the sediments, and reveal the spatial change and environmental significance of the nitrogen and phosphorus forms. The results showed that different morphological components of the bio-available nitrogen were distributed as organic sulfide bound nitrogen (SOEF-N) > iron-manganese oxidized nitrogen (SAEF-N) > weak acid leached nitrogen (WAEF-N) > ion exchange nitrogen (IEF-N). The inorganic phosphorus included the highest proportion of metal oxide bound phosphorus (NaOH-P), followed by calcium bound phosphorus (HCl-P). The proportion of reduced phosphorus (BD-P) was even lower, and the proportion of weakly adsorbed phosphorus (NH4Cl-P) was the lowest. The results of single factor pollution index showed that the sediment nitrogen in the study area mainly caused moderate pollution and phosphorus mainly caused light pollution. By contrast, the results of the bioavailability index method indicated that nitrogen mainly caused light pollution, and phosphorus mainly caused clean pollution in sediments. Combined with the characteristics of social economy and environment in the study area, it can be inferred that the bioavailability index method based on comprehensive evaluation of total amount and morphology can better characterize the spatial change and ecological risk of nitrogen and phosphorus in sediments.

The continuous flux of organic carbon (OC) from terrestrial ecosystems into inland water is an important component of the global carbon cycle. The buried OC pool in inland water sediments is considerable, and black carbon (BC) is a significant contributor to this OC pool because of the continuous growth in BC emissions. Therefore, determining the effect of BC on total OC burial and variations in the structure of BC during the burial process will contribute significantly to our understanding of lacustrine carbon cycling. This study investigated BC burial and its structural variations in response to anthropogenic drivers using four dated sedimentary cores from a deep plateau lake in China. The BC burial rate rose from 0.96 ± 0.64 g·m -2 ·y -1 (mean of sedimentary cores pre-1960s) to 4.83 ± 1.25 g·m -2 ·y -1 (after 2000), which is a 5.48 ± 2.12-fold rise. The increase of char was similar to those of BC. The growth rate of soot was 7.20 ± 4.30 times, which is higher than that of BC and char, increasing from 0.12 ± 0.08 to 0.64 ± 0.23 g·m -2 ·y -1 . There was a decreasing trend in the ratio of char and soot at a mean rate of 62.8 ± 6.46% (excluding core 3) in relation to increased fossil fuel consumption. The contribution of BC to OC burial showed a significant increasing trend from the past to the present, particularly in cores 3 and 4, and the mean contribution of the four cores was 11.78 ± 2.84%. Source tracer results from positive matrix factorization confirmed that the substantial use of fossil fuels has promoted BC burial and altered the BC structure. This has resulted in BC with a higher aromatic content in the lake sediment, which exhibits reduced reactivity and increased stability. The strong correlation between BC and allochthonous total OC indicates that the input pathways of the buried BC in this plateau lake sediment were terrestrial surface processes and not atmospheric deposition.

The concentration, source and composition of dissolved organic matter (DOM) in aquatic ecosystems are associated with land use and hydrological connectivity between terrestrial and aquatic systems. However, direct evidence of the effects of rainfall and land use on the variability of DOM in aquatic ecosystems is very limited. In this study, chromophoric DOM (CDOM) absorption and fluorescence spectroscopy were used to elucidate how rainfall and land use affect the variability of CDOM in the watershed of Lake Tianmu, a key drinking water reservoir in the Yangtze River Delta. The mean values of the fluorescence intensity (F max ) of parallel factor analysis-derived humic-like components (C1, C3, C6) and tryptophan-like components C5 were higher in the southeastern inflowing river mouths than those downstream of the lake outlet regions. The upstream tributaries were mainly dominated by humic-like materials, while the lake was mainly dominated by protein-like materials. The F max values of four humic-like components and two tryptophan-like components all increased significantly as the %woodland decreased, but %anthropogenic land use (%cropland+%urban construction area) increased. The F max of the humic-like components at the inflowing tributaries and the lake increased with increasing rainfall during storm events, and the value was especially pronounced at the inflowing river mouths. We concluded that land use and hydrological conditions play an important role in influencing the CDOM source and optical composition, and these findings provide insights for the understanding of aquatic ecosystem metabolism and reservoir water quality management., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Analyzing the association between fine particulate matter (PM 2.5 ) pollution and socio-economic factors has become a major concern in public health. Since traditional analysis methods (such as correlation analysis and geographically weighted regression) cannot provide a full assessment of this relationship, the quantile regression method was applied to overcome such a limitation at different spatial scales in this study. The results indicated that merely 3% of the population and 2% of the Gross Domestic Product (GDP) occurred under an annually mean value of 35 μg/m³ in mainland China, and the highest population exposure to PM 2.5 was located in a lesser-known city named Dazhou in 2014. The analysis results at three spatial scales (grid-level, county-level, and city-level) demonstrated that the grid-level was the optimal spatial scale for analysis of socio-economic effects on exposure due to its tiny uncertainty, and the population exposure to PM 2.5 was positively related to GDP. An apparent upward trend of population exposure to PM 2.5 emerged at the 80th percentile GDP. For a 10 thousand yuan rise in GDP, population exposure to PM 2.5 increases by 1.05 person/km² at the 80th percentile, and 1.88 person/km 2 at the 95th percentile, respectively., Competing Interests: The authors declare no conflict of interest.

Two sediment cores were collected from Dianchi Lake, a plateau lake in Southwest China, to study the temporal trends and to investigate the sources of sedimentary deposited polycyclic aromatic hydrocarbon. The ΣPAH16 concentration in the two sediment cores ranged from 172.5 to 2244.8 ng/g and from 211.4 to 1777.8 ng/g, with mean values of 1106.2 and 865.1 ng/g, respectively. Three temporal trends for the ΣPAH16 concentration and the composition of PAHs in Dianchi Lake all showed three typical changing stages: (1) slight changes in deeper segments before the 1950s; (2) a rapid increase in PAH concentrations between the 1960s and 1990s; and (3) a slight reduction from the 1990s onward. These trends differ from those observed in developed countries due to differences in the timing of industrialization and urbanization processes. According to the results of the molecular ratios and principal component analysis, the PAH deposition was dominated by coal combustion, wood combustion, and vehicle emissions before and after the 1960s, respectively.

Organic carbon (OC) buried in lake sediment is an important component of the global carbon cycle. The impact of eutrophication on OC burial in lakes should be addressed due to worldwide lake eutrophication. Fourteen 210 Pb- and 137 Cs-dated sediment cores taken in Dianchi Lake (China) in August 2006 (seven cores) and July 2014 (seven cores) were analyzed to evaluate the response of the organic carbon accumulation rate (OCAR) to eutrophication and algal blooms over the past hundred years. The mean value of OCAR before eutrophication occurred in 1979, 16.62±7.53 (mean value±standard deviation), increased to 54.33±27.29gm -2 yr -1 after eutrophication. It further increased to 61.98±28.94gm -2 yr -1 after algal blooms occurred (1989). The accumulation rate of organic nitrogen (ONAR) is coupled with OCAR. The high loss rate of OC and organic nitrogen (ON) leads to a long-term burial efficiency of only 10% and 5% of OC and ON. However, this efficiency can still lead to an increase in OCAR by a factor of 4.55 during algal blooms in Dianchi Lake. Dianchi Lake stored 1.26±0.32 Tg carbon and 0.071±0.018 Tg nitrogen, including 0.94±0.23 Tg OC and 0.32±0.14 Tg inorganic carbon, 0.066±0.018 Tg ON, 0.002±0.001 Tg nitrate nitrogen (NO 3 -N) and 0.003±0.001 Tg ammonium nitrogen (NH 4 -N) between 1900 and 2012., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Human activities contribute highly to water eutrophication. In this study, the relationship between human activities and water eutrophication in Dianchi Lake in China was characterized using a combination of satellite imaging, sedimentary physicochemical and meteorological data analyses. The heavy eutrophic status and algal bloom in Dianchi Lake were first observed by satellite in 1977 and 1989, respectively. The C/N ratio, an indicator of organic sources in sediments, also showed that the planktonic organic source in the sediment significantly increased beginning in 1989. The land use cover in the Dianchi basin showed that both farm lands and forests, but particularly farmlands, were reduced during the period from 1974 to 2009. The urbanized land area increased from 1974 to 2009, particularly after 2000. The effects of human activities on water eutrophication were expressed by land use cover, population, gross domestic product (GDP; separated into primary, secondary and tertiary industries) and wastewater discharge. For land use cover, farm and urbanized lands were the main sources of water nutrients; forest contributed slightly to these nutrients. For GDP, primary (correlation coefficient=0.94, P<0.001) and tertiary (correlation coefficient=0.95, P<0.001) industries were highly correlated with total nitrogen. Secondary (correlation coefficient=0.95, P<0.001) and tertiary (correlation coefficient=0.96, P<0.001) industries were highly correlated with total phosphorus. The algal bloom area was significantly correlated with wastewater discharge (correlation coefficient=0.78, P<0.005) (except industrial wastewater), which was primarily led by the non-agricultural population, from 2000 to 2009. This study suggests that the protection of water environments requires a comprehensive protection policy in addition to a unilateral protection policy., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Light scattering properties in such a highly turbid productive lake as Lake Taihu in China were examined through 118 samples collected during three cruises in November 2006, March 2007, and November 2007. The particulate scattering and backscattering coefficients were observed using WETLabs AC-S and ECO-BB9. A power model with a spectral exponent of -0.729 was used to simulate the particulate scattering coefficient (b(p)) spectra. It has a better performance than the linear model. Scattering parameters are more closely related to inorganic suspended matter (ISM) concentration than to other water components, such as total suspended matter (TSM), organic suspended matter (OSM), and chlorophyll a (Chla). This indicates that ISM dominates the scattering signal in the lake. Three discrepancies with oceanic/coastal waters are observed: (a) the backscattering ratio (b (bp)) decreases with an increase in the ISM concentration because of a highly strong contribution by ISM to b(p); (b) the mass-specific scattering coefficient (b(p) (m)) exhibits a wider range of variability than that reported in previous studies, which can be attributed to considerable variation in the OSM and ISM distributions; (c) the particle size distribution slope (xi) is mostly larger than 4.0 in Lake Taihu, whereas it is usually within 3.5-4.0 for marine particles. In addition, the bulk refractive index (n (p)) calculated according to the Twardowski et al. model [J. Geophys. Res. 106, 14129 (2001)JGREA20148-0227] indicates that some stations (n (p)<1.07) can be regarded as organic-particle dominant. Other stations with high ISM concentrations have a very small n (p) value mostly within 1.10-1.17. Overall, the knowledge on the scattering properties gained in this study broadens our understanding of water optics in highly turbid productive water columns.