Saccharomyces cerevisiae additions normalized hemocyte differential genes expression and regulated crayfish (Procambarus clarkii) oxidative damage under cadmium stress.

Because China produces the most crayfish in the world, safe solutions must be improved to mitigate the risks of ongoing heavy metal stressors accumulation. This study aimed to use Saccharomyces cerevisiae as a bioremediation agent to counteract the harmful effect of cadmium (Cd) on crayfish (Procambarus clarkia). Our study used three concentrations of S. cerevisiae on crayfish feed to assess their Cd toxicity remediation effect by measuring total antioxidant capacity (TAC) and the biomarkers related to oxidative stress like malondialdehyde (MDA), protein carbonyl derivates (PCO), and DNA-protein crosslink (DPC). A graphite furnace atomic absorption spectroscopy device was used to determine Cd contents in crayfish. Furthermore, the mRNA expression levels of lysozyme (LSZ), metallothionein (MT), and prophenoloxidase (proPO) were evaluated before and following the addition of S. cerevisiae. The results indicated that S. cerevisae at 5% supplemented in fundamental feed exhibited the best removal effect, and Cd removal rates at days 4th, 8th, 12th, and 21st were 12, 19, 29.7, and 66.45%, respectively, which were significantly higher than the basal diet of crayfish. The addition of S. cerevisiae increased TAC levels. On the other hand, it decreased MDA, PCO, and DPC, which had risen due to Cd exposure. Furthermore, it increased the expression of proPO, which was reduced by Cd exposure, and decreased the expression of LSZ and MT, acting in the opposite direction of Cd exposure alone. These findings demonstrated that feeding S. cerevisiae effectively reduces the Cd from crayfish and could be used to develop Cd-free crayfish-based foods.

Higher allochthonous organic carbon increases polycyclic aromatic hydrocarbon concentration whereas fossil fuel combustion alters the composition: Evidence from a eutrophic plateau lake in southwest China.

Understanding the source of polycyclic aromatic hydrocarbons (PAHs) is crucial for determining their structural, degradational, and burial characteristics in lake sediments. Here, we used a sediment core to determine the changing sources and burial characteristics of 16 PAHs from Dianchi Lake, southwest China. The ∑16PAH concentrations ranged from 105.10 to 1248.05 ng g-1 (448.97 ± 351.25 ng g-1), exhibiting a sharp increase since 1976. Our results showed that the depositional flux of PAHs has increased by approximately 3.72 times over the past 114 years (1895-2009). The C/N ratio, stable isotopes (δ13Corg and δ15N), and n-alkanes data all indicated that allochthonous contributors of organic carbon have substantially increased since the 1970s, playing an important role in the increase in sedimentary PAHs. Positive matrix factorization indicated that petrogenic sources, coal and biomass combustion, and traffic emissions were the main sources of PAHs. The relationships between PAHs from different sources and total organic carbon (TOC) varied with the sorption characteristics. The effect of TOC on the absorption of high-molecular-weight aromatic PAHs from fossil fuels was significant. A higher risk of lake eutrophication is accompanied by higher allochthonous organic matter imports, which might stimulate an increase in sedimentary PAHs through algal biomass blooms.

Anthropogenic Activities Generate High-Refractory Black Carbon along the Yangtze River Continuum.

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.

Spatiotemporal response of dissolved organic matter diversity to natural and anthropogenic forces along the whole mainstream of the Yangtze River.

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 δ13CDOC 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.

Sediment record in pollution, toxicity risk, and source assignment of polycyclic aromatic hydrocarbons (PAHs) in Erhai Lake, Southwest China.

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 Σ16PAHs, 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 Σ16PAHs and carPAHs concentrations in surface sediments were higher in the southern lake. The Σ16PAHs 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.

The influence of nutrients on the composition and quantity of buried organic carbon in a eutrophic plateau lake, Southwest China.

The regulation of lacustrine organic carbon (OC) burial by nutrient is an outstanding knowledge gap in the current understanding of lake carbon cycles. In this study, we determined how nutrients quantitatively correspond with OC burial using the parallel factor analysis (PARAFAC) method in Dianchi Lake, southwest China. Factors were classified into three types according to their historical sedimentation characteristics: the background factor (BF), response factor (RF), and contingency factor (CF). The BF represented the original OC input combination in the lake and was insensitive to nutrient changes. The RF represented the OC input combination that was induced or promoted by nutrient changes in the lake. The CF represented short-term discontinuous factors in sedimentary history, which may be related to unique historical events. The results indicate that changes in the total nitrogen (TN) to total phosphorus (TP) ratio correlated with changes in the BF contribution; whereas the quantity of OC was mainly correlated with TN. The >90% of OC buried in sediment was quantitatively simulated by BF and RF; the driving effect of RF on OC burial was approximately 13 times higher than that of BF. It was observed that a 1 mg kg-1 increase in TN led to approximately 2.2 units increase in RF contribution in Dianchi Lake, while the BF was insensitive to changes in TN. Thus, changes in lake nutrients may effectively change the composition and quantity of OC buried in lake sediment.

Properties of sediment dissolved organic matter respond to eutrophication and interact with bacterial communities in a plateau lake.

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). δ13CDOC 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.

One-century sedimentary record, sources, and ecological risk of polycyclic aromatic hydrocarbons in Dianchi Lake, China.

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

Trends in the impact of socioeconomic developments on polycyclic aromatic hydrocarbon concentrations in Dianchi Lake.

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

Source analysis and influencing factors of historical changes in PAHs in the sediment core of Fuxian Lake, China.

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 Σ16PAH concentration fluctuated widely, with one or more maximum values. During 1971-2004, the Σ16PAH 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.

Source identification of particulate organic carbon using stable isotopes and n-alkanes: modeling and application.

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.

Disturbance mechanisms of lacustrine organic carbon burial: Case study of Cuopu Lake, Southwest China.

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 210Pbex 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.

Rapid photodegradation of terrestrial soil dissolved organic matter (DOM) with abundant humic-like substances under simulated ultraviolet radiation.

Solar ultraviolet (UV) radiation exhibits a significant degradation for dissolved organic matter (DOM) in natural water ecosystems. However, research on photodegradation process of terrestrial components (e.g., humic-like substances) of DOM are limited due to drastic water dilution and rapid degradation. Here, photochemical degradation of terrestrial soil DOM with abundant humic-like substances from different land use were investigated by utilizing spectral technologies. Simulated UV radiation caused obvious losses on concentration, component structures, and fluorescence characteristic of soil DOM samples. The correlations between absorption specific parameters (a280, SUVA254, and SR) and dissolved organic carbon (DOC) were especially pronounced (p < 0.05), which could be used as valid indicators to determine changes in DOM composition and molecular size during photobleaching process. The decreases of DOM fluorescence intensity were corresponded to first-order kinetic and half-life reactions. The greatest reduction on fluorescence intensity (31.56-81.97%) belonged to peak C (i.e., humic-like substances). Overall, DOM from forest and grass soil ecosystems was more easily photochemical degraded than anthropogenic soil DOM. Enhancive contribution of fresh DOM formed by photodegradation increased autochthonous characteristic and bioavailable nutrition by increasing biological index (BIX) values and ammonia nitrogen (NH4+-N) concentration. The slight microbial decomposition effects on DOM happened in unsterilized dark condition. Our findings provided insights for understanding the rapid photodegradation processes of composition and structure of terrestrial DOM. Graphical abstract.

[Distribution and Burial Characteristics of Nitrogen Forms in Sediment of Dianchi Lake During Last Century].

In order to analyze the composition, distribution and burial characteristics of nitrogen in sediments of Dianchi Lake in the last hundred years, 6 sediment cores were sampled in July 2014 to determine the contents of different nitrogen species and sedimentary age sequence. The integrated results demonstrated a high content of total nitrogen in sediments ranging from 1263.68-7155.17 mg·kg-1. The contents of nitrate nitrogen and ammonium nitrogen were low, which were 10.00-144.00 mg·kg-1and 9.20-146.50 mg·kg-1, respectively. Organic nitrogen was the main component in the sediments, ranging from 255.80 to 5644.25 mg·kg-1, composing a large average percentage of 91.26%. In addition, the nitrogen pollution of sediment in Dianchi Lake has reached a high level and is becoming serious since 1970s, which surged in the late 1990s. The spatial difference of total nitrogen was obvious, with comparably the most in the south, less in the north and least in the center. The average deposition rate was changing from 0.092 g·(cm2·a)-1 to 0.187 g·(cm2·a)-1 in the last 100 years and increased first, then declined, finally showed a slight upward trend over time. The burial rate of total nitrogen in sediment increased over time and almost grew up straightly after 1990,which decreased from the south to the north of Dianchi Lake in space. It was estimated that the reserves of total nitrogen, organic nitrogen, nitrate nitrogen, ammonium nitrogen in the sediment were 92139.15 t, 86745.62 t, 2464.16 t, 2929.37 t, respectively, from 1900 to 2014.