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Highlights • Critical factors of SWAT were represented digitally and dynamically. • Lake sediment Phosphorus can be designated as an ideal indicative indicator for the watershed non-point source pollution. • Relationship between watershed and sediment P varied apparently among different basins, sediment depths and P states. Abstract An understanding of the quantitative relationship between watershed non-point source (NPS) pollution and lake nutrient enrichment is essential for the environmental management of water bodies. However, a lack of data availability and integration limit our understanding of this relationship. The most critical bottlenecks are the lack of adequate support for watershed-lake integrated data, a lack of data of the nutrient loading from watersheds into a lake as NPS, and the long-term time series data of lake nutrient concentrations. Since lake sediment is the ultimate destination of watershed nutrients, this study aimed to reveal the relationship between watershed phosphorus (P) concentrations that are transported into lakes and lake P concentrations by using inlet sediments as an indicator. Three typical sub-basins within Hongze Lake, China were selected as the study site, and 30-year dataset was calculated using the technology integration of remote sensing, sediment chemical analysis and SWAT model assessment. It can be concluded that, first, the Mineral-P (Min-P) accounted for nearly 65% of the watershed Total P (TP) loss, which varied over different basins and temporal periods. Second, the relationship between watershed P loss into lakes and sediment P concentrations represented obvious variation among different basins, sediment depths and P states. With respect to different basins, the highest correlation appeared in Basin 1, which had a R2 value of 0.65 for Min-P. With respect to different P states, the Inorganic-P (IP) showed a closer relationship between watershed and lake P than Organic-P (OP), and the correlation coefficient (r) was higher than 0.6 in Basin 1 and Basin 3 for IP. In addition, the calcium-phosphorus ratio (Ca-P), which is largely sourced from watershed rock detritus by eroded runoff, played the most critical role among different Min-P states in the relatively ideal relationship of IP. With respect to different sediment depths, a stratification phenomenon existed in Basin 2 and Basin 3, which differed at specific depths. In particular, the ideal relationship only existed within the 7 cm depth from the bottom in basin 2, and this value expands to 10 cm for basin 3. This diversity was influenced by the integration roles from external and endogenous sources. All the findings indicated that lake surface sediment can be used as a proxy to represent NPS P loading under specific conditions. The relationship between watershed P loss and lake sediment P concentration was largely decided by land use/cover change (LUCC), meteorological conditions, and lake resuspension. [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]

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 ± 27.29 g m − 2 yr − 1 after eutrophication. It further increased to 61.98 ± 28.94 g m − 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. [ABSTRACT FROM AUTHOR]

Increased organic carbon and nitrogen accumulation rates (OCAR and ONAR) in lake sediment significantly regulate the global carbon cycle. However, the reasons for and contributors to the increased OCAR and ONAR are unclear. Seven sediment cores, collected in July 2014 from Dianchi Lake, China, were used to evaluate the effects of autochthonous and allochthonous sources on OCAR and ONAR. The results indicate that OCAR and ONAR increased by factors of 4.33 and 7.34 over the past hundred years (1900–2000), particularly after algal blooms began to occur frequently (beginning in the 1980s). Dianchi stored 0.467 ± 0.0055 Tg (mean value ± standard deviation) organic carbon (OC) and 0.033 ± 0.0004 Tg organic nitrogen (ON) after 1986, which is almost equal to the total storage of OC and ON from 1900 to 1985 (OC, 0.468 ± 0.0022 Tg; ON, 0.032 ± 0.0002 Tg). OCAR and ONAR increases were due to increasing autochthonous production and allochthonous loading. Examination of the increased OCAR, which was estimated from a newly developed multi-source mixing model, suggests that > 90% of increased OCAR was caused by allochthonous sources (such as intensified cultivation, land-use cover change, etc.) in southern and eastern Dianchi and that > 70% of the increased OCAR was due to autochthonous sources in western and northern Dianchi Lake. The significant spatial and temporal variation in the contributors to increased OCAR indicates complicated migration and transformation of OC in inland lakes. Land use cover change around Dianchi and the occurrence of algal blooms regulate the contributions of allochthonous and autochthonous sources to the increased OC and ON. [ABSTRACT FROM AUTHOR]

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 (TEQcar) 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 TEQcar in the sediment core peaked in the 2010s and 1980s. The spatiotemporal variations in TEQcar and carPAHs were similar. Positive matrix factorization revealed that traffic emissions contributed 35.71 % of the TEQcar, whereas coal and biomass combustion contributed 12.89 % in the surface sediments. The contribution of gasoline and fossil fuel to TEQcar 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. • Spatio-temporal distributions of Σ 16 PAHs, carPAHs, and TEQ in Erhai Lake sediments were investigated. • Sources of PAHs concentrations and TEQcar were quantitatively apportioned via the PMF model. • TEQ BaP and TEQ DbahA increased over last four decades but decreased in recent years. • Energy consumption, especially fossil fuel combustion, greatly contributed TEQ. [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]

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 (210Pb and 137Cs). δ 13C 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. The changes in sediment dissolved organic matter (DOM) by eutrophication and their interplay with bacterial communities. [Display omitted] • δ 13C DOC changes fit well with the historical record of eutrophication. • The properties of sediment DOM were greatly modified by phytoplankton blooms. • Bacterial communities showed heterogeneity of structure and spatial distribution. • There were mutual and complex linkages between bacterial communities and DOM. [ABSTRACT FROM AUTHOR]

Abstract: 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 &y& Elsevier]

Abstract: Methane (CH4) emission from constructed wetland has raised environmental concern. This study evaluated the influence of mono and polyculture constructed wetland and seasonal variation on CH4 fluxes. Methane emission data showed large temporal variation ranging from 0 to 249.29 mg CH4 m−2 h−1. Results indicated that the highest CH4 flux was obtained in the polyculture system, planted with Phragmites australis, Zizania latifolia and Typha latifolia, reflecting polyculture system could stimulate CH4 emission. FISH analysis showed the higher amount of methanotrophs in the profile of Z. latifolia in both mono and polyculture systems. The highest methanogens amount and relatively lower methanotrophs amount in the profile of polyculture system were obtained. The results support the characteristics of CH4 fluxes. The polyculture constructed wetland has the higher potential of global warming. [Copyright &y& Elsevier]

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]

[Display omitted] • Combining R rs (λ) and δ13 C POC can track and monitor the source of POC. • The source of POC in surface water of Taihu Lake in summer is mainly endogenous POC. • Endogenous POC has a certain physiological relationship with water temperature and nutrient (TN, TP), while terrestrial POC was closely related to wind speed. • The a ph (λ) and a nph (λ) can effectively reflect the source of POC. The sources of particulate organic carbon (POC) determine its conversion, thereby playing an important role in the carbon cycle of lakes. Accurate estimation of the sources and dynamic characteristics of POC is important for understanding the migration and transformation of organic carbon. However, the synchronous observation of POC sources with large areas through remote sensing is still challenging because of the complex composition of POC and the optical conditions of inland lakes. In this study, a three-band (1/ R rs (689)–1/ R rs (717)) × R rs (697)) empirical algorithm of POC sources was constructed based on remote sensing reflectance (R rs (λ)) and the proportion of endogenous POC estimated from the field-measured stable isotope (δ13 C POC) values. The validation and calibration results of the three-band algorithm showed robust performance, with MAPE and RMSE of estimated values and measured values of 10% and 0.07, respectively. The three-band algorithm had good simulation results for the Ocean and Land Color Instrument (OLCI), Moderate Imaging Spectroradiometer (MODIS), Geostationary Ocean Color Imager (GOCI), and Medium Resolution Imaging Spectrometer (MERIS) spectra. The POC sources estimated by the three-band algorithm suggest that the endogenous POC of Taihu Lake in August showed a decreasing trend from 2006 to 2019. The variation in terrestrial POC was slow and stable for both annual and monthly variations. The analysis of POC sources with total phosphorus (TP), total nitrogen (TN), water temperature, and wind speed indicated that terrestrial POC was closely related to wind speed (r = 0.33, P < 0.001), while endogenous POC was significantly associated with TP (r = 0.6, P < 0.001), TN (r = 0.56, P < 0.001), and water temperature (r = 0.49, P < 0.001). The use of remote sensing algorithms to evaluate POC from different sources is convenient and effective; furthermore, it helps to better understand the carbon cycle in lacustrine ecosystems. [ABSTRACT FROM AUTHOR]

Mitigating greenhouse gas emissions and ensuring crop productivity simultaneously is a major challenge that demands the balance of the amounts of nitrogen (N) and straw (S) applied to agricultural soil. This study seeks to determine whether higher grain yields and lower nitrous oxide (N 2 O) emissions could be realized concomitantly by optimizing synthetic N rates and straw returning. The effect of fertilizer N rates and straw application on the inter-annual yield-scaled N 2 O emission variations was measured over a three-year period (2011–2014) in a maize-wheat cropping system on the North China Plain (NCP). Yield-scaled N 2 O emissions were expressed as g N 2 O-N per Mg grain. Six treatments with three synthetic N levels (zero N [N 0 ], optimized N [N opt ] and conventional N [N con ]) and two straw management practices (straw removal [i.e., N 0 , N opt and N con ] and straw return [i.e., N 0 + S, N opt + S and N con + S]) were used. Optimized N (N opt , N opt + S) refers to the use of approximately 50% of the fertilizer N that is used in conventional farming practices (N con , N con + S), with no significant decrease in grain yields ( P > 0.05). Optimized N reduced cumulative N 2 O emissions by 18–37%, which in turn significantly decreased yield-scaled N 2 O emissions by 38–42% ( P < 0.05). The effects of fertilizer N rates and grain yields on cumulative N 2 O emissions are described by linear and exponential models, respectively. Straw return had a positive effect on mean yield-scaled N 2 O emissions both in the maize season and annually. Yield-scaled N 2 O emissions are constructive considering the trade-off between grain yield and N 2 O emission mitigation from intensive crop production. Optimized fertilizer N rate combined with straw return reduced yield-scaled N 2 O emissions significantly in maize-wheat rotations. [ABSTRACT FROM AUTHOR]

• PCA-MLR, PMF, and Unmix receptor models were successfully identified PAHs sources in sediment core. • PAHs reached its peak around 2000 in a remote lake of Tibet Plateau. • Biomass and coal combustion are important soueces of PAHs in sediments. • Temporal trends of factor contributions were consistent with different ring number PAHs. Receptor models are a useful tool for identifying sources of polycyclic aromatic hydrocarbons (PAHs) in multiple environmental media. In this study, three different receptor models (including the principal component analysis-multiple linear regression (PCA-MLR), positive matrix factorization (PMF), and Unmix models) were used to apportion the sources of 16 priority PAHs in a sediment core of Lake Dagze Co. The ∑PAHs (sum of all 16 measured PAHs) concentrations ranged from 51.89 to 132.82 ng/g with an average of 80.39 ng/g. The ∑PAHs were dominated by 2-3 ring PAHs, accounting for 80.12% on average, thereby indicating that they mainly originated from biomass and coal combustion and/or from long-range atmospheric transportation. The three models produced consistent source apportionment results. The greatest contributor to ∑PAHs was biomass combustion, followed by coal combustion, vehicle emissions, and petrogenic sources. Moreover, the temporal variation of the common sources was well-correlated among models. The multi-method comparison and evaluation results showed that all three models were useful tools for source apportionment of PAHs, with the PMF model providing better results than the PCA-MLR and Unmix models. The temporal trends of factor contributions were verified by PAHs with different ring numbers. Significant correlations were found between the simulated concentrations of each source factor and the PAHs with different ring numbers (P <0.01), except for the petrogenic source identified by the Unmix model (P >0.05). This study can provide useful information for further investigation of source apportionment of PAHs in the sediment cores. [Display omitted] [ABSTRACT FROM AUTHOR]

The estimation of particulate organic carbon (POC) concentrations from satellite images can provide crucial spatiotemporal continuous observation data for the carbon cycle and ecological environmental governance. Here, we developed a novel inversion algorithm for deriving POC in inland water based on remote sensing and geochemical isotopes, which is summarized as follows. First, we developed empirical relationships between the phytoplankton absorption coefficient and endogenous POC concentration (C endPOC) and between the nonalgal particulate absorption coefficient and terrestrial POC concentration (C terPOC). Second, based on the valid relationships, semianalytical retrieval models were established to estimate C endPOC and C terPOC. Third, the proportions of endogenous POC (R endPOC) and terrestrial POC (R terPOC) to the total POC concentration (C POC) were derived using a three-band empirical model. Finally, C POC was obtained by dividing C endPOC by R endPOC (R endPOC ≥ 0.5) or dividing C terPOC by R terPOC (R endPOC < 0.5). Validation with field data shows that our proposed algorithm can accurately derive C POC (0–20 mg/L), with a root mean square deviation (RMSD), median bias (MB), median absolute percent difference (MAPD), and median ratio (MR) of 1.15 mg/L, −0.05 mg/L, 24%, and 0.98, respectively. Synchronous validation based on Sentinel-3/OLCI images confirmed the accuracy, with RMSD, MB, MAPD, and MR values of 0.41 mg/L, −0.16 mg/L, 28%, and 0.91, respectively. The algorithm was applied to ocean and land color sensor (OLCI) images to reveal the temporal and spatial variations in POC in Lake Taihu. • A novel bio-optical based POC semi-analytical inversion algorithm for inland water. • We improved POC estimation strategy by estimating POC terminal members. • a ph (674) and a nap (443) can be used to drive C endPOC and C terPOC , respectively. • Endogenous POC dominance in Lake Taihu increased significantly in summer. [ABSTRACT FROM AUTHOR]

[Display omitted] • PAHs concentration in sediments was the highest (C 3 , 1.88E-03–2.64E-03 mol/m3). • PAHs transport from air to water and then to sediment. • Lowest PAH concentration was found under SSP3 (2025–2035) in future projections. This study analyzed the fate and transfer of PAHs through multiple media in Dianchi Lake and the sediment records of polycyclic aromatic hydrocarbons (PAHs) in sediments. The model simulation results showed the simulated concentrations to be in good agreement with the measured values. The concentration and total amount of PAHs were the highest in the sediment, which is an important sink for PAHs in lake systems. The main transport direction of the PAHs in the three phases was from the atmosphere to the water to the sediment. Advection and emission inputs were the primary input pathways for PAHs in the atmosphere, and advection output was the main removal path. The main input sources pathways for PAHs in sediments was the sedimentation of particulate matter in water, with diffusion and degradation being the primary methods of removal. Advection and atmospheric dry and wet deposition were the main sources of PAHs in water, with particulate deposition being the primary removal process. The range of PAHs was 336–3520 ng/g in sediments in Dianchi Lake, with an average of 1569 ng/g, peaking in 2012. Among the predicted future PAH concentrations in the sediments under the five shared socioeconomic pathways (SSPs), the lowest PAH concentration was found under SSP3 from 2025 to 2035, whereas the lowest PAH concentration was found under SSP4 from 2035 to 2050. In the sustainable path of SSP1, although the concentration of PAH pollutants showed an increasing trend in the short term, the increase in PAHs concentration in sediments slowed in the long run. [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]

The Secchi disk depth (Z SD ) plays a critical role in describing water clarity. Several studies have shown linkages between Three Gorges Dam (TGD) and the downstream lacustrine ecosystem in the middle and lower Yangtze River basin. However, the potential influence on the Z SD fluctuation in the entire anthropogenic reservoirs of Three Gorges (ER) and Dongting Lake (DTL) has not been reported, possibly due to technical obstacles in obtaining statistically significant spatial and temporal results. We addressed this challenge by using remote sensing technology: the Landsat 8 Operational Land Imager (OLI). We proposed a new, robust remote-sensing algorithm to estimate Z SD from OLI imagery using red and green band-ratio, leading to MAPE of 21.68% and RMSE of 0.076 m for Z SD ranging from 0.1 m to 1.05 m. After satisfactory image-based validation, the algorithm was implemented on OLI data to derive Z SD patterns over ER and DTL from 2013 to 2017. Several crucial findings can be drawn: 1) Spatial-temporal patterns of Z SD exhibited notable fluctuations over both ER and DTL, and they also demonstrated a significant correlation with each other because of the opposite temporal cycle of Z SD fluctuations between ER and DTL; 2) Temporally, monthly fluctuations of Z SD between ER and DTL had opposite temporal cycles, which was mainly attributed to the surface runoff and sediment discharge driven by the outbound runoff variations of TGD. Spatially, the heterogeneity of the Z SD pattern in ER might have resulted from the different geographical regions being divided by large anthropologic hydrological facilities, such as TGD; 3) The relationship between Z SD and total suspended matter (TSM) showed a significant negative correlation, as did the relationship between Z SD and K d (490). These findings demonstrate that TSM often plays a principal role in light attenuation of extremely turbid inland waters; 4) An inversed phenomenon of water clarity was observed at the intersection of DTL and the Yangtze River around Chenglingji site (YRAC), which was due to the opposite temporal cycle of Z SD fluctuations between DTL and ER after the impoundment of TGD; and 5) Owing to the analysis of noise-equivalent Z SD , OLI data can be used to derive Z SD, since the imagery uncertainty is 0.07 m by means of our band-ratio algorithm, which demonstrates similar results to MODIS. The proposed Z SD -derived algorithm in this study could be suitable for other turbid lakes or reservoirs to formulate related strategies of water quality management in the middle and lower Yangtze River basin, and the unveiled findings here improve our understanding of Z SD spatiotemporal fluctuations in large river-connected lakes, such as Poyang Lake. [ABSTRACT FROM AUTHOR]

• Allochthonous organics are the major sources for DOM pool in the Yangtze River. • Natural conditions and anthropogenic forces modify riverine DOM chemo-diversities. • Aromatic, unsaturated and humic-like DOM fractions dominate in up-midstream reaches. • Seasonal phytoplankton growth produces labile aliphatic and protein-like compounds. The Yangtze River, the largest river in Asia, plays a crucial role in linking continental and oceanic ecosystems. However, the impact of natural and anthropogenic disturbances on composition and transformation of dissolved organic matter (DOM) during long-distance transport and seasonal cycle is not fully understood. By using a combination of elemental, isotopic and optical techniques, as well as Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), we investigated DOM abundance and composition along the whole mainstream at highly spatial resolution in the dry and early wet seasons. Our findings showed that the concentration and flux of dissolved organic carbon (DOC) in the Yangtze River was much lower compared with other worldwide larger rivers. The distribution of δ 13C DOC and higher abundance of humic-like fluorescent component and highly unsaturated and phenolics (HUPs) compound reflected a prominent contribution of allochthonous DOM. Further optical and molecular analysis revealed humic-like fluorescent components were coupled with CHO molecules and HUPs compound with higher aromatic, unsaturated, molecular weight and stable characteristics between upstream and midstream reaches. With increasing agricultural and urban land downstream, there were more heteroatomic formulae and labile aliphatic and protein-like compounds which were derived from human activities and in situ primary production. Meanwhile, DOM gradually accumulates with slow water flow and additional autochthonous organics. Weaker solar radiation and water dilution during the dry/cold season favours highly aromatic, unsaturated and oxygenated DOM compositions. Conversely, higher discharge during the wet/warm season diluted the terrestrial DOM, but warm temperatures could promote phytoplankton growth that releases labile aliphatic and protein-like DOM. Besides, chemical sulfurization, hydrogenation and oxygenation were found during molecular cycling processes. Our research emphasizes the active response of riverine DOM to natural and anthropogenic controls, and provides a valuable preliminary background to better understand the biogeochemical cycling of DOM in a larger river. Highlighted characteristics and compositions of riverine DOM pool of three reaches and two seasons. [Display omitted] [ABSTRACT FROM AUTHOR]

The biomarker composition and stable carbon isotope values of organic matter (OM) in sediment cores from Shuanglong catchment of the Dianchi watershed show an unimodal n -alkane distribution ranging from C 15 –C 33 with a strong predominance of odd-numbered n -alkanes, maximizing at n -C 27 , n -C 29 and n -C 31 . Organic carbon to nitrogen (OC/N) ratio indicates a strong terrestrial influence on the OM. The values of δ 13 C 27 , δ 13 C 29 and δ 13 C 31 of n -alkanes range from −36.1‰ to −26.1‰, −34.1‰ to −30.1‰ and −33.8‰ to −28.7‰, respectively, suggesting a mainly C 3 land plants origin. The carbon preference index (CPI 25–31 ), odd-even preference (OEP 27–31 ), average chain length (ACL 25–33 ), pristine/phytane (pr/ph), Paq, (C 27 + C 29 )/2C 31 , n C 16–23 / n C 24–33 and 3C 17 /(C 21 + C 23 + C 25 ) values are also consistent with the predominance of C 3 land plant-derived OM. Different sources of OM are reflected by the peak of n -C 15 , ascribed to a contribution by aquatic algae and photosynthetic bacteria. Eutrophication seems to be enhanced by both autochthonous (weak) and allochthonous (strong) contributions of OM. A major factor affecting the OM accumulation in the catchment and OM transportation to the Dianchi Lake may be increased by human activities from 1871 to 2011. [ABSTRACT FROM AUTHOR]

Abstract: Remote sensing detection of suspended particulate composition is of importance for understanding variability of water optical properties, especially in complex-material loading turbid inland waters. To achieve this goal, this study carried out multiple in situ bio-optical investigations during the period of 2008~2010, covering Lake Taihu, Chaohu, Dianchi, and Three Gorges reservoir in China. Using the collected in situ observed datasets, a semi-analytical approach was developed based on theoretical derivation of the water radiative transfer theory. This algorithm showed relatively high calibration accuracy, and was further evaluated by means of an independent validation dataset, producing low predictive errors (mean absolute percentage error, MAPE =29.5%, and root mean square error, RMSE =0.23, 10−3). Then, the developed algorithm was applied into a new hyperspectral satellite data, namely the HJ1A/HSI image, mapping spatio-temporal distribution of suspended particulate composition for Lake Taihu waters. The findings in the present study indicate that the proposed approach has a great potential in detecting particulate composition of water bodies. This study provides us improved understanding of particulate composition characteristics and corresponding spatio-temporal distribution for complex turbid inland waters. [Copyright &y& Elsevier]

Abstract: Accurate assessment of phytoplankton chlorophyll a (Chla) concentration in turbid waters by means of remote sensing is challenging due to optically complexity and significant variability of case 2 waters, especially in inland waters with multiple optical types. In this study, a water optical classification algorithm is developed, and two semi-analytical algorithms (three- and four-band algorithm) for estimating Chla are calibrated and validated using four independent datasets collected from Taihu Lake, Chaohu Lake, and Three Gorges Reservoir. The optical classification algorithm is developed using the dataset collected in Taihu Lake from 2006 to 2009. This dataset is also used to calibrate the three- and four-band Chla estimation algorithms. The optical classification technique uses remote sensing reflectance at three bands: Rrs(G), Rrs(650), and Rrs(NIR), where G indicates the location of reflectance peak in the green region (around 560nm), and NIR is the location of reflectance peak in the near-infrared region (around 700nm). Optimal reference wavelengths of the three- and four-band algorithm are located through model tuning and accuracy optimization. The three- and four-band algorithm accuracy is further evaluated using other three independent datasets. The improvement of optical classification in Chla estimation is revealed by comparing the performance of the two algorithms for non-classified and classified waters. Using the slopes of the three reflectance bands, the 138 reflectance spectra samples in the calibration dataset are classified into three classes, each with a specific spectral shape character. The three- and four-band algorithm performs well for both non-classified and classified waters in estimating Chla. For non-classified waters, strong relationships are yielded between measured and predicted Chla, but the performance of the two algorithms is not satisfactory in low Chla conditions, especially for samples with Chla below 30mg m−3. For classified waters, the class-specific algorithms perform better than for non-classified waters. Class-specific algorithms reduce considerable mean relative error from algorithms for non-classified waters in Chla predicting. Optical classification makes that there is no need to adjust the optimal position to estimate Chla for other waters using the class-specific algorithms. The findings in this study demonstrate that optical classification can greatly improve the accuracy of Chla estimation in optically complex waters. [Copyright &y& Elsevier]

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]

Dissolved organic matter (DOM) in sediment pore water plays a key role in lake water quality, complexation of the contaminants, biogeochemical cycles, and even climate. To better understand the vertical dynamics and characteristics of DOM among pore water profiles, we investigated concentrations, chemical structures, and benthic fluxes of DOM in plateau lake sediments via stoichiometric analysis, ultraviolet–visible (UV–vis) absorption, three-dimensional fluorescence matrix spectroscopy (EEMs), and parallel factor model (PARAFAC). The results revealed that dissolved organic carbon (DOC), concurrent with chromophoric DOM (CDOM) and fluorescent DOM (FDOM), tended to accumulate in the anaerobic deeper layers. These trends also demonstrated a good agreement with the ammonium nitrogen (NH 4 +-N) concentration, implying that the pathway of DOM dynamics was closely related to the redox state. The EEMs-PARAFAC model revealed that DOM in pore water mostly consisted of two terrestrial humic-like components (average contribution:> 60%) followed by microbial and tryptophan-like components, respectively. Terrestrial humic-like components were relatively stable, and their abundance was positively correlated with the FDOM level (p < 0.05). The changes of aromatic, molecular weight, and humification degree of DOM were possibly driven by microbial activities at different depths. Moreover, benthic flux estimations indicated that DOM and the total dissolved nitrogen (TDN) in inland sediments were potential sources for the overlying water and possibly affected the quality and ecological safety of lake water bodies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Lakes are important organic carbon (OC) traps in the global carbon cycle. Recent studies have shown that the rate of OC burial in lacustrine sediments is influenced by factors such as climate change, land-use change, and eutrophication. In this study, we use multiproxy methods to reveal the mechanisms of lacustrine sediment OC burial in an alpine lake (Cuopu Lake), in southwest China. Combined with the dating from 210Pb ex and n -alkanes distribution analysis using the Positive Matrix Factorization model, the sedimentary history was divided into five stages: religious activity (the 1840s–1880s), earthquake (the 1880s–1910s), garrison (the 1910s–1960s), transition (the 1960s–1990s), and ecotourism (the 1990s–2010s). During the earthquake stage, OC burial was dominated by terrestrial solids (>40%) and co-precipitated algae (>30%), with a rapid deposition rate (>4 mm a−1) and low OC concentration (<4 mg g−1). During the other stages, when the level of disturbance was relatively low, a change in nutrient conditions either promoted or inhibited plant growth, which influenced the type of buried OC. The contribution of OC derived from combustion sources varied from stage to stage. Severe anthropogenic disturbances have led to a significant increase in nutritional levels in the lake water, leading to an increase in the OC burial rate. Climate change, which leads to changes in temperature and rainfall, did not significantly influence OC burial, whereas nitrogen deposition (and associated ecological changes) was a significant determinant. When the general mechanism is dominant, the total nitrogen to inorganic phosphorus ratio is an effective indicator of OC burial due to its selective promotion of different plant types. In conclusion, our results suggest that lacustrine sediment OC burial is closely linked to physical and anthropogenic factors in Cuopu Lake, as well as similar montane lakes. Unlabelled Image • Sedimentary records of biomarkers and nutrients in Cuopu Lake were investigated. • Human activities indirectly increase OC burial by improving nutrient conditions. • Earthquakes promote OC burial by enhancing terrestrial input and co-deposition. • TN/IP affects OC burial by selectively promoting and inhibiting plant growth. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) is a ubiquitous group of organic compounds in rainwater that plays vital roles in the biogeochemical cycle. However, little is known about its chemical composition, optical characterization, potential sources, and controlling mechanisms in peri-urban atmospheric rainwater. One-year rainfall samples were collected between September 2018 and August 2019 in a Nanjing suburb. Stoichiometric, ultraviolet–visible (UV–Vis) absorption, and three-dimensional fluorescence excitation-emission matrix (EEM) with parallel factor analysis (PARAFAC) analyses were utilized to characterize DOM. Several proxies for DOM concentration, including dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and absorption coefficient (a254), exhibited power-function relationships with the rainfall amount (r2 = 0.33–0.55, p < 0.001). Particularly, the DOC and a254 value showed significant seasonal variability, with lower value in two wet seasons (winter and summer) than in the dry seasons (autumn and spring). The annual wet depositional (WD) flux of DOC in the Xianlin (XL) site was calculated as 1.68 g C m−2 yr−1, agreeing with the range of global WD flux values. Two terrestrial humic-like components (C1–C2), one microbial humic-like component (C3), and one tryptophan-like component (C4) were identified by EEM-PARAFAC in rainwater DOM. The results of the specific absorption indices (SUVA 254, S R) and PARAFAC component analyses revealed that summer DOM samples had lower fluorescence intensities, aromatic contents, and molecular sizes. Principal component analysis (PCA) based on DOM indices showed that rainwater DOM had predominantly terrestrial humic origins, while this characteristic became slightly weaker in summer. The quantity and quality of rainwater DOM were closely related to meteorological variables (i.e., air mass, rainfall amount, and solar radiation) as well as anthropogenic activities. This study could improve the understanding of the quantity and quality of rainwater DOM on carbon budgets and biogeochemical cycling from some new insights of optical proxies about different fates of rainwater DOM under complex controlling mechanisms. Image 1 • Concentration and chemical structure of rainwater DOM showed seasonal variations. • Climatic factors and human activities were dominant effects on rainwater DOM. • Rainwater DOM components were mainly generated from humic substances. • Wet inorganic N in atmosphere was closely coupled with rainwater DOM. [ABSTRACT FROM AUTHOR]

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]

Accurate remote assessment of phytoplankton chlorophyll- a (Chl a) concentration in turbid case-2 waters is a challenge, owing largely to terrestrial substances (such as minerals and humus) that are optically significant but do not co-vary with phytoplankton. Here, we propose an improved Quasi-Analytical Algorithm (QAA) (denoted as TC2) for retrieving Chl a concentrations from remote sensing reflectance (R rs (λ)) which can be applied to Sentinel-3 Ocean and Land Colour Instrument (OLCI) images in turbid case-2 waters. TC2 has two main extensions when compared with QAA. First, TC2 makes an additional assumption to separate the total non-water absorption at 665 nm (a nw (665)) into phytoplankton absorption (a ph (665)) and yellow matter (a ym (665)), which is the sum of colored dissolved matter (CDOM) and detritus. Second, for selecting the position of the near-infrared (NIR) band which is used to estimate the signal of total backscattering coefficient (b b (λ 0)) at QAA reference band (λ 0), we take into account the assumption that the absorption of pure water should be dominant at this band, as well as the impact of the signal-to-noise ratio (SNR) in the NIR band on the Chl a concentration estimating model. When applied to in situ R rs (λ) and OLCI match-up R rs (λ) data in this study, TC2 provided more accurate Chl a estimation than previous Ch a concentration retrieval algorithms for turbid case-2 waters. TC2 has the potential for use as a simple and effective algorithm for monitoring Chl a concentrations in the turbid case-2 waters at a global scale from space. • A new algorithm for estimating Chl a concentrations for turbid case-2 waters. • It makes an additional assumption to isolate Chl a absorption at the phytoplankton absorption peak of the red band. • The algorithm considers the impact of the SNR in the NIR band on the water total backscattering coefficient estimation. • It outperformed previous Chl a concentration retrieval algorithms using OLCI remote sensing reflectance. [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]