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Assessments of specific inherent optical properties (SIOPs) and their variability in highly turbid and productive inland waters are essential for the accurate estimation of water quality. A new optical classification method including two classification criteria [i.e., normalized remote sensing reflectance slope (NS), and normalized remote sensing reflectance depth (ND)] was developed to divide remote sensing reflectance into four classes, i.e., class 1 (NS < −0.0017 and ND < 0.21) is low turbid and productive water; class 2 (NS < −0.0017 and ND > 0.21) is low turbid and high productive water; class 3 (NS > −0.0017 and ND < 0.09) is high turbid and low productive water; and class 4 (NS > −0.0017 and ND > 0.009) is high turbid and high productive water. The relationships between phytoplankton absorption at 440 nm [ a(440)] and chlorophyll- a concentration [ C] as well as between particle backscattering coefficient at 440 nm [ b(440)] and total suspended matter concentration ( C) after classification were obtained from a large number of in situ data in Lake Taihu. The measured specific phytoplankton absorption $$[ {a_{\text{ph}}^{*} \left( \lambda \right)} ]$$ and particle backscattering coefficient $$[ {b_{\text{bp}}^{*} \left( \lambda \right)} ]$$ show significant variations even within the same class. The mean values of $$a_{\text{ph}}^{*} \left( \lambda \right)$$ at 440 nm $$[ {a_{\text{ph}}^{*} \left( {440} \right)} ]$$ for each class are 0.048 ± 0.013, 0.060 ± 0.012, 0.083 ± 0.021, and 0.056 ± 0.017 m/mg, respectively. The mean values of $$b_{\text{bp}}^{*} \left( \lambda \right)$$ at 440 nm $$[ {b_{\text{bp}}^{*} \left( {440} \right)} ]$$ for each class are 0.035 ± 0.01, 0.024 ± 0.004, 0.041 ± 0.009, and 0.038 ± 0.009 m/g, respectively. The power functions of SIOPs and water constituents' concentration indicate that $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ vary with C and C. The validation results show that our proposed values for $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ cover a very wide range of water optical properties, which are characterized from clear water to highly turbid productive water. The validation results also suggest that the retrieval accuracy of C and C bio-optical model was improved after classification. The root mean square error (RMSE) of C was improved from 14.18 to 7.43 μg/L (mean value of all classes) and RMSE of C was improved from 32.98 to 26.10 mg/L (mean value of all classes). Thus, the temporal and spatial variation of $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ should be considered in the bio-optical retrieval model of water quality. Graphical Abstract: In complex optical properties of inland water, retrieving the water constituents with high accuracy needs to classify the water optical properties from the remote sensing spectrum by optical classification method. The figure shows the water color examples of each class[Figure not available: see fulltext.]. [ABSTRACT FROM AUTHOR]

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]

Sediments have a significant influence on the cycling of nutrient elements in lake environments. In order to assess the distribution characteristics and estimate the bioavailability of phosphorus and nitrogen in Dianchi Lake, organic and inorganic phosphorus and nitrogen forms were analysed. The 210Pb radiometric dating method was employed to study temporal changes in the phosphorus and nitrogen pools in Dianchi Lake. The result show that the total phosphorus (TP) and total nitrogen (TN) were both at high concentrations, ranging from 697.5-3210.0 mg/kg and 1263.7-7155.2 mg/kg, respectively. Inorganic phosphorus (IP) and total organic nitrogen (TON) were the main constituents, at percentages of 59%-78% and 74%-95%, respectively, in the sediments. Spatially, there was a decreasing trend in phosphorus and nitrogen contents from the south and north to the lake centre, which is related to the distribution pattern of local economic production. The burial rates of the various phosphorus and nitrogen forms increased in same spatially and over time. Particularly in the past two decades, the burial rates doubled, with that TN reached to 1.287 mg/(cm2·yr) in 2014. As the most reactive forms, nitrate nitrogen (NO3-N) and ammonia nitrogen (NH4-N) were buried more rapidly in the south region, implying that the potential for releasing sedimentary nitrogen increased from north to south. Based on their concentrations and burial rates, the internal loads of phosphorus and nitrogen were analysed for the last century. A TP pool of 71 597.6 t and a TN pool of 81 191.7 t were estimated for Dianchi Lake. Bioavailable phosphorus and nitrogen pools were also estimated at 44 468.0 t and 5429.7 t, respectively, for the last century. [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 isotopic composition of the mainstream is controlled by different sources. • Recharge sources of the mainstream were determined and quantified. • The recharge sources and evaporation cause the temporal and spatial variations of REL. • The emplacement and regulation of TGD changed the contribution ratio of recharge sources. Water and material cycles in rivers are controlled by diverse sources of recharge and flow paths, which exhibit spatial and temporal variations in the contributions of water sources and hydrologic processes. To assess the variation of water recharging, the stable isotope abundances of hydrogen and oxygen (δ2H and δ18O) of 152 water samples collected from the Yangtze River mainstream during May (the flat season) and September (the wet season) in 2021 were analyzed. Bayesian modelling was used to calculate the contribution rates of precipitation, glacier snow meltwater, and groundwater. The isotopic compositions of precipitation and the river exhibited comparable seasonal and spatial characteristics. The Bayesian model results showed that the mainstream was governed by precipitation, with a greater contribution of precipitation in the lower reaches during the wet season. Lakes had a larger contribution during the flat season, as evidenced by the greater increase in the magnitude of δ18O values in the mid-lower reaches during this period. The mid-lower reaches of the river had a decreased river evaporation line (REL) slope, which could be owe to lake replenishment. In addition to intensifying the seasonal variations in the contribution ratios of the lakes, the emplacement of the Three Gorges Dam (TGD) reduced the groundwater contribution of the reservoir. This study enhances our understanding of the hydrological and material cycles in the Yangtze River Basin and provides vital baseline knowledge on the contribution of different recharge sources in the mainstream. [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]

Human activity has fundamentally altered the global phosphorus (P) cycle. Yet our understanding of when and how humans influenced the P cycle has been limited by the scarcity of long-term P sequestration records, particularly outside Europe and North America. Lake sediments provide a unique archive of past P burial rates and allow the human-mediated disruption of the global P cycle to be examined. We compiled the first global-scale and continentally resolved reconstruction of lake-wide Holocene P burial rates using 108 lakes from around the world. In Europe, lake P burial rates started to increase noticeably after ∼4000 calendar years before 1950 CE (cal BP), whereas the increase occurred later in China (∼2000 cal BP) and in North America (∼550 cal BP), which is most likely related to different histories of population growth, land-use and associated soil erosion intensities. Anthropogenic soil erosion explains ∼86% of the observed changes in global lake P burial rates in pre-industrial times. We also provide the first long-term estimates of the global lake P sink over the Holocene (∼2686 Tg P). We estimate that the global mean lake sediment P sequestration since 1850 CE (100 cal BP) is ∼1.54 Tg P yr−1, representing approximately a six-fold increase above the mean pre-industrial value (∼0.24 Tg P yr−1; 11,500 to 100 cal BP) and around a ten-fold increase above the Early-Middle Holocene low-disturbance baseline of 0.16 Tg P yr−1. This study suggests that human activities have been affecting the global P cycle for millennia, with substantial alteration after industrial times (1850 CE). • We estimated Holocene phosphorus (P) burial rates in sediments of 108 global lakes. • Global lake P burial rates increased notably in the Late Holocene. • Human-induced soil erosion caused early increases in lake sediment P burial rates. • We observed different patterns of lake P burial rates among continents since the Late Holocene. • We provide the first estimates of long-term, global P sequestration in lake sediments throughout the Holocene. [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]

With the ensemble Empirical Mode Decomposition Method (EEMD) and the non-parametric Mann-Kendall Test, the quasi-periodic and abrupt changes of sedimentation rate at multiple time scales, and their relations to climate changes and human activities from 1951 to 2010 in Meiliang Bay of Lake Taihu (China) were studied. The results showed the following. (1) The change in sedimentation rate can be completely decomposed into three quasi-periodic changes on 3.7, 6.4, and 24-yr time scales, and a long-term trend. (2) The quasi-periodic changes in sedimentation rate are significantly and positively related to changes in annual average temperature at 6.4 and 24-yr time scales and human activities at 3.7-yr time scales, and not significantly related to precipitation at these time scales. The trend of sedimentation rate has a negative relation with temperature, but positive relations with precipitation and human activities. As a whole, the total variance contribution of climate changes to the quasi-periodic changes of sedimentation rate is close to that of human activities; (3) Temperature and precipitation are possibly related to the abrupt change of sedimentation rate as a whole. Floods have significant impacts on abrupt changes in the sedimentation rate at 3.7, 6.4 and 24-yr time scales. Moreover, some abrupt changes of sedimentation rate at 3.7- and 6.4-yr time scales are partly related to the changes of precipitation at 3.1-yr time scale and temperature at 5-yr time scale. The results of this study will help identify the impacts of climate change and human activities on lake sedimentation at different time scales, and will be available for use as a guide for reasonable development and effective protection of lake resources. [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]

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. • Sediment cores in remote lakes from the Tibetan Plateau were analyzed for PAHs. • 2–3-ring PAHs were predominant in the sediments. • Biomass and coal combustion were the main sources of PAHs. • OC was a key factor influencing the concentrations of PAHs in sediments. • Climate change and anthropogenic activities have influenced PAH composition since the 1990s. [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]

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]

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]

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]

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]

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.

Microbial communities in freshwater lake sediments exhibit a distinct depth-dependent variability. Further exploration is required to understand their biodiversity pattern and microbial interactions in vertical sediments. In this study, sediment cores from two freshwater lakes, Mugecuo (MGC) and Cuopu (CP), on the Tibetan plateau were sampled and subsequently sliced into layers at a depth of every centimeter or half a centimeter. Amplicon sequencing was used to analyze the composition, diversity, and interaction of microbial communities. Results showed that sediment samples of both lakes could be clustered into two groups at a sediment depth of about 20 cm, with obvious shifts in microbial community compositions. In lake MGC, the richness component dominated β-diversity and increased with depth, indicating that the microbial communities in the deep layer of MGC was selected from the surface layer. Conversely, the replacement component dominated β-diversity in CP, implying a high turnover rate in the surface layer and inactive seed banks with a high variety in the deep layer. A co-occurrence network analysis showed that negative microbial interactions were prevalent in the surface layers with high nutrient concentrations, while positive microbial interactions were more common in the deep layers with low nutrient concentrations, suggesting that microbial interactions are influenced by nutrient conditions in the vertical sediments. Additionally, the results highlight the significant contributions of abundant and rare taxa to microbial interactions and vertical fluctuations of β-diversity, respectively. Overall, this work deepens our understanding of patterns of microbial interactions and vertical fluctuation in β-diversity in lake sediment columns, particularly in freshwater lake sediments from the Tibetan plateau., Competing Interests: The authors declare that the research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Zhu, Deng, Huang, Han, Chen, Zhang, Liu, Liu and Huang.)

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.)

Combustion-derived black carbon (BC) is an important component of sedimentary carbon pool. Due to different physicochemical properties, determining the source of char and soot is crucial for BC cycling, especially for nonhomologous char and soot in the Tibetan Plateau (TP). This study analyzed the sequestration and source of BC, char, and soot in the Dagze Co (inner TP) sediment core via the content and δ 13 C, revealing the biomass and fossil fuel driving on nonsynchronous char and soot and their response to local anthropogenic activities and atmospheric transmission. The results showed that BC concentration increased from 1.19 ± 0.35 mg g -1 (pre-1956) to 2.03 ± 1.05 mg g -1 (after 1956). The variation of char was similar to BC, while nonhomologous growth was detected in char and soot ( r = 0.29 and p > 0.05). The source apportionment showed that biomass burning for 71.52 ± 10.23% of char and promoted char sequestration. The contribution of fossil fuel combustion to soot (46.67 ± 14.07%) is much higher than char (28.48 ± 10.23%). Redundancy analysis confirmed that local anthropogenic activities significantly influenced BC burial and atmospheric transport from outside TP-regulated BC burial. The contribution of biomass and fossil fuels to nonsynchronous char and soot is conducive to understanding the anthropogenic effect on BC burial in the TP.

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 -1 and accounted for 10.9 ± 4.7% of the particulate organic carbon. The spatial-mean δ 13 C 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., (Copyright © 2022 Elsevier Ltd. 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.)

In this study, the sedimentary records, sources, and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in Dianchi Lake were analyzed. The concentrations of ΣPAH 16 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., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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.)