Apparent relationships between anthropogenic factors and climate change indicators and POPs deposition in a lacustrine system

Sediment core records and impact factors of polycyclic aromatic hydrocarbons in Chinese lakes

Lake sediment is a natural sink for polycyclic aromatic hydrocarbons (PAHs). PAH sedimentation characteristics and their impact factors of Chinese lakes have mainly been qualitative assessed. However, quantitative impacts of PAH sedimentation from different factors have not been well analyzed. To fill this gap, we screened PAH sedimentation records from the literature, for 51 lakes in China and other regions of the world, to identify historical concentration variation and the impact factors of PAHs in different regions, in lake sediment. The results show that PAH concentrations in the sediment core in the selected Chinese lakes (478 ± 812 ng/g dry weight (dw)) were significantly lower than those in North America (5518 ± 6572 ng/g dw) and Europe (3817 ± 4033 ng/g dw). From 1900 to 2015, most of the lakes in China showed an increasing trend of PAH sedimentation concentrations, with the lakes in Southeastern China showed a decreasing trend of PAH concentration in the period of 2001-2015, which was later than the peak times shown in Western countries (1941-1970). The 2-3-ring PAHs were the main components in the sediment core of Chinese lakes, but the proportion to the total PAHs decreased from 72% in 1900-1940 to 55% in 2001-2015. Generalized additive modeling (GAM) was adopted to simulate the associations between PAH sedimentation records and the impact factors. There are large regional variations of economic and industrial development in China. The impact factors of PAH accumulation in the lake sediments differ in different regions. However, population and the consumption of coal, pesticides, and fertilizer were identified to be the most important impact factors influencing PAH sedimentation. The Chinese government needs to strengthen control measures on pollutant discharge to reduce the anthropogenic impact of PAH sedimentation in lakes.

Influence of temperature and precipitation on the fate of polycyclic aromatic hydrocarbons: simulation experiments on peat cores from a typical alpine peatland in Central China

The corresponding relationships between temperature, precipitation, and polycyclic aromatic hydrocarbon (PAH) concentration in a typical ombrotrophic peatland in Dajiuhu, Shennongjia, were quantitatively characterized by field sampling tests validated with simulation experiments. The PAH concentrations of peat cores in Dajiuhu peatland ranged from 262 to 977 ng·g^-1, with a mean value of 536 ± 284 ng·g^-1. PAHs were mainly composed of 2-3 ring PAHs, accounting for 31.7% ± 2.00% and 31.7% ± 5.00%, respectively. The concentration of PAHs in peat cores showed a significant decrease with increasing temperature, while the low molecular weight PAHs (LMW-PAHs) were more sensitive to temperature changes compared to the high molecular weight PAHs (HMW-PAHs). Besides, with the increase of quantity and velocity of leaching liquid, PAHs in peat were first transferred in the form of attached large-size particles and then gradually entered the aqueous phase. According to the IPCC projections of global warming, Dajiuhu peatland will release 956 ± 26.3 kg·°C^-1 PAHs into gas phase during 2030-2052, and a conservative projection based on local temperature trends showed that 459 ± 12.6 kg·°C^-1 PAHs will be released into gas phase by 2047 in Dajiuhu peatland. The projected release fluxes of PAHs in Dajiuhu peatland with precipitation volume and precipitation velocity are 381 ± 201 kg·100 mm^-1 and 1052 ± 167 kg·min·mL^-1, respectively, which are primarily from peat into particulate and aqueous phase.

Source apportionment of polycyclic aromatic hydrocarbons (PAHs) in a sediment core from Lake Dagze Co, Tibetan Plateau, China: Comparison of three receptor models

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.

Association between Lake Sediment Nutrients and Climate Change, Human Activities: A Time-Series Analysis

Climate change and human activities are closely linked with the nutrient accumulation in sediments, but the role of influence factors and the driving mechanisms are unclear. Here, by using the generalized additive model (GAM), we investigated the contributions and driving mechanisms of climate change and human activities on TON, TN, and TP accumulation in sediments of typical lakes in the Huai River basin (Nansi Lake and Hongze Lake) from 1988 to 2018. The impacts of factors, such as air temperature (AT), real GDP per capita (GDP), population density (PD), crop sown area (CSA), artificial impervious area (AIA), and domestic sewage discharge (DSD) were considered in this study. The results of the multivariate GAM showed that the sediment variables were significantly affected by climate change in Nansi Lake, but not in Hongze Lake. AT and DSD contributed the most to the variation of sediment TOC in Nansi Lake, while the most critical factors affecting TN and TP were AT, PD and DSD. PD and CSA showed strong ability to explain the change of TOC in Hongze Lake, while CSA and DSD showed strong ability to explain the variations of TN and TP. The results show that the selected optimal multivariate GAM can well quantify the effects of climate change and human activities on nutrient enrichment in lake sediments. Effective recommendations are provided for decision-makers in developing water quality management plans to prevent eutrophication outbreaks in lake waters by targeting and controlling key factors.

Drinking water treatment residue recycled to synchronously control the pollution of polycyclic aromatic hydrocarbons and phosphorus in sediment from aquatic ecosystems

Great efforts have long been made to control sediment pollution from persistent organic pollutants and phosphorus for aquatic ecosystem restoration. This study proposed a novel recycling of drinking water treatment residue (DWTR) to synchronously control sediment polycyclic aromatic hydrocarbons (PAHs) and phosphorus pollution based on a 350-day incubation test. The results suggested that DWTR addition reduced approximately 88%- 96% of potential bioavailable PAHs and 76% of mobile phosphorus in sediment. The dominant mechanisms for both reductions by DWTR were immobilization, mainly through increasing sediment amorphous aluminum and iron. The tendency of enhanced PAHs degradation by DWTR was also observed, especially for high molecular weight PAHs (e.g., chrysene, indeno(1, 2, 3-cd)pyrene, and benzo(g, hi)perylene), which decreased by approximately 21.1%- 22.0% of the total. Additionally, accompanying a clear increase in the connections of microbial cooccurrence networks, the variations in bioavailable PAHs, amorphous aluminum and iron, and other properties (e.g., pH, nitrogen, and organic matter) significantly (p < 0.01) enhanced Flavobacterium enrichment, although the enrichment of many other microbes potentially related to PAHs degradation (e.g., C1-B045) decreased after DWTR addition. Therefore, DWTR could promote the construction of a "PAHs immobilization with microbial augmentation" system while immobilizing phosphorus in sediment, indicating the high feasibility of controlling multiple sediment pollution.

Modern lake sedimentary record of PAHs and OCPs in a typical karst wetland, south China: Response to human activities and environmental changes

The sedimentary history of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) over the past 140 years in a lake sediment core from Huixian karst wetland was reconstructed. The total PAHs and OCPs concentrations ranged from 40.0 to 210 ng g^-1 and 0.98 to 31.4 ng g^-1, respectively. The vertical distribution of PAHs and OCPs in different stages was great consistent with the history of regional socio-economic development and the usage of OCPs. As the indicators of socio-economic development, gross domestic product (GDP), population, energy consumption, highway mileage, and private vehicles correlated with the PAHs concentrations, indicating the impact of human activities on PAHs levels. The PAHs and OCPs concentrations were also affected by environmental changes in the wetland, as reconstructed by total organic carbon (TOC), sand, silt, clay, quartz, and calcite in sediments. Redundancy analysis (RDA) results showed TOC was the dominant factor to explain the concentrations of PAHs and OCPs with the explanation of 86.7% and 43.5%, respectively. In addition, TOC content had significantly positive correlation with PAHs (0.96, p < 0.01) and OCPs (0.78, p < 0.01). In particular, the significantly positive correlation (p < 0.05) between calcite and PAHs and OCPs inferred that karstification might play an important role in the migration of PAHs and OCPs in the karst area. Therefore, the lake in Huixian wetland tended to be a sink more than a source of PAHs and OCPs influenced by the increasing TOC content and karstification under climate warming.

Stage-, sex- and tissue-related changes in H2O2, glutathione concentration, and glutathione-dependent enzymes activity in Aiolopus thalassinus (Orthoptera: Acrididae) from heavy metal polluted areas

This study is part of a large project carried out at the Cairo University, Egypt, and focused on assessing physiological and biochemical changes in Aiolopus thalassinus under the influence of environmental pollution with heavy metals (Pb, Cd, Cu, and Zn). The study aimed to investigate parameters related to maintaining redox balance, with particular emphasis on stage-, sex- and tissue-dependent differences in H₂O₂ and glutathione (GSH) levels and activity of selected enzymes involved in GSH metabolism. A noticeable increase in the concentration of H₂O₂ was found, especially in the gut of 5th instar nymphs and females from the highly polluted site. An increase in GSH concentration was significant, especially in the gut of adult A. thalassinus from the high polluted site. However, recycling of reduced form of glutathione in the gut by glutathione reductase (GR) was relevant only for females from the high polluted site. Nymphs and females generally showed higher glutathione S-transferase (GST) activity, especially in the gut. These stage- and sex-related differences can result from different growth dynamic and various reproductive functions of nymphs and both sexes. The digestive track is in direct contact with xenobiotics consumed with food. Nymphs are characterized by vigorous growth, they feed intensively, and their development processes are associated with substantial oxygen consumption. Also, maintaining the antioxidant system at a high level can be more important for females than males due to egg production over a long period. It appears that de novo GSH synthesis is a favorable and cost-effective adaptation mechanism for A. thalassinus living in the high polluted site.

New insights into spatiotemporal source apportionment of n-alkanes under mixed scenario: A pilot study on Lake Chaohu, China

N-alkanes are ideal molecular markers for the source apportionment of organic matter. However, the estimation of both biogenic and anthropogenic sources under mixed scenario using n-alkanes and their related proxies still remains an issue. In this study, we investigated spatiotemporal variations of n-alkanes in suspended particulate matter of Lake Chaohu for their source apportionment. Overall, Σ₂₉ n-alkanes ranged from 324.1 to 113685 ng·L^-1. C₁₇H₃₆ was the most abundant homologue and was followed by C₁₈, C₂₇ and C₂₉ homologues. Carbon preference indexes (CPIs) in most samples (at least 85%) were < 3, indicating mixed sources of n-alkanes in Lake Chaohu. Therefore, biogenic and anthropogenic n-alkanes were separated by subtraction to avoid potential bias. Our results showed Σ biogenic and Σ anthropogenic n-alkanes ranged from 14.8 to 3531.6 ng·L^-1 and 257.6 to 4938.5 ng·L^-1, respectively. For biogenic n-alkanes, their carbon-chain distributions posed a preponderant peak at C₁₇, indicating algae were the main contributors to biogenic n-alkanes in Lake Chaohu. Biogenic average chain length (ACL_bio) was developed to quantify the contributions of different biogenic sources. We recommended ACL_bio < 21 for algae dominance and ACL_bio > 26 for terrestrial plant dominance. For anthropogenic n-alkanes, their carbon-chain distribution presented obviously spatiotemporal variations. The sources of anthropogenic n-alkanes in summer and winter were typical dominances of light petroleum and incomplete fossil fuel burning/heavy oil emission, respectively. New developed proxies, anthropogenic average chain length (ACL_anthro) and the ratio of unit short- to long-carbon anthropogenic n-alkanes (L/H), are effective for quantifying the relative contributions of different anthropogenic sources. We recommend log₁₀L/H > 0.5 and ACL_anthro < 20.5 for light petroleum input dominance, log₁₀L/H < -0.5 and ACL_anthro > 26.5 for incomplete fossil fuel burning at high temperature/heavy oil emission dominance.

Spatiotemporal toxicity assessment of suspended particulate matter (SPM)-bound polycyclic aromatic hydrocarbons (PAHs) in Lake Chaohu, China: Application of a source-based quantitative method

The spatiotemporal associations between the emissions and environmental toxicities of polycyclic aromatic hydrocarbons (PAHs) in lake still remain an issue. Here, we focused on the suspended particulate matter (SPM)-bound PAHs in Lake Chaohu, China to quantitatively estimate their spatiotemporal toxicities from different sources. A source-based quantitative method, positive matrix factorization (PMF)-benzo[a]pyrene-based toxic equivalency (TEQ_BaP) model, was applied. Firstly, we investigated the spatiotemporal characteristics of SPM-bound PAHs. The concentrations of Σ₂₁ PAHs ranged from 1646 to 19267 ng·g^-1. Low-ring PAHs were found to have the highest fractions. T-distributed stochastic neighbor embedding (t-SNE)-partitioning around medoid (PAM) technic revealed significantly spatiotemporal variation characteristics of SPM-bound PAHs in Lake Chaohu. Season, location (west or east lake zone), and sample classification (estuary or lake) together governed the patterns. Then, their potential sources were apportioned. Our results found that diagnostic ratios did not work perfectly. However, 3 factors were separated by PMF model. Unburned petroleum (F1), biomass, coal and gasoline combustion (F2), and diesel, straw combustion (F3) were the main sources of PAHs, accounting for 36.16%, 48.96% and 14.88%, respectively. The patterns of the source profiles were season-dependent. Finally, the toxicity of SPM-bound PAHs from different sources were predicted by PMF-TEQ_BaP model, and the model predictions were satisfactorily acceptable. Overall, predicted Σ₁₉ TEQ_BaP of SPM-bound PAHs in Lake Chaohu ranged from 20.8 to 947.9 ng·g^-1. Benzo[e]pyrene (BeP), benzo[a]pyrene (BaP) and benzo[b]fluoranthene (BbF) were the main toxic species. Temporally, PAH toxicity posed significantly seasonal differences. F3 had primary contributions to Σ₁₉ TEQ_BaP. Cutting the diesel consumption and using cleaner energy substitutes were suggested to reduce the PAH toxicity in Lake Chaohu. Overall, we expected this study could give new insights into the spatiotemporal associations between the sources and toxicities of SPM-bound PAHs in lake ecosystem.

When archives are missing, deciphering the effects of public policies and climate variability on the Brazilian semi-arid region using sediment core studies

The northeastern region of Brazil is the most densely populated and biodiverse semi-arid regions of the planet. Effects of the natural climate variability and colonization on the landscape have been described since the beginning of the 16th century but little is known about their effects on natural resources. Climate projections predict temperatures above 40 °C and an increase in the number and duration of droughts at the end of the 21st century with strong societal impacts. Here, we analyze the influence of public policies, human activities and natural climate variability on the environment over the last 60 years. Our study is based on sedimentological and environmental reconstructions from two sediment cores collected in two dam lakes on the river Acaraú in the State of Ceará. Multiproxy analyses of both cores (inorganic geochemistry, pollen, charcoal, remote sensing) at an annual resolution showed that 1) at interannual scale composition and distribution of the dry forest (known as Caatinga) were not affected by the alternance of drought and high moisture episodes; 2) at decadal scale human activities such as agriculture were reflected by changes in vegetation cover and fishery by progressive changes in lake trophic status; 3) public policies were able to promote changes in the landscape e.g., land colonization with the regression of the dry forest and irrigation plan able to amplify the deforestation and change the floristic composition. Thanks to paleo-science approach, our environmental diagnosis should help future decision-making and provide guidelines for preservation of resources and wellbeing of the inhabitants.

Legacy per- and polyfluoroalkyl substances (PFASs) and alternatives (short-chain analogues, F-53B, GenX and FC-98) in residential soils of China: Present implications of replacing legacy PFASs

With the worldwide regulation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), the alternatives (short chain analogues and emerging per- and polyfluoroalkyl substances, PFASs) have gradually attracted global attention. This study analysed the replacing of legacy PFASs in China using PFASs data from residential soils, which might be good environmental indicators of their present usage. The total concentrations of 21 PFASs ranged from 244 to 13564 pg/g, and PFOA was the dominant compound among the studied PFASs, with a concentration of 354 ± 439 pg/g. Serious PFASs pollution in residential soils mainly occurred in Eastern Coastal China as a result of locally developed industry and economies. Weak but significant correlations were found between PFASs and environmental and socioeconomic factors, suggesting that various factors determine PFASs contamination in residential soils. The concentration and detection frequency (DF) of short-chain analogues (C < 8) (375 ± 509 pg/g and 100%), and F-53B (216 ± 306 pg/g and 98.9%) were higher than those for PFOS (193 ± 502 pg/g and 85.4%), indicating that these compounds have been widely used as PFOS alternatives and their consumption has already exceeded that of PFOS in China. In addition, GenX (the PFOA alternative) had a concentration and DF of 19.1 ± 104 pg/g and 40.5%, respectively. These values were much lower than those for PFOA (354 ± 439 pg/g and 96.6%), indicating GenX consumption is still limited at the national scale of China, despite its use as a PFOA replacement. Moreover, the low concentration and DF of FC-98 (2.31 ± 11.1 pg/g and 27.0%) indicate that its consumption might be negligible. Our study demonstrated that short chain analogues and emerging alternatives have become the dominant PFAS pollutants in Chinese residential soils, and further studies need to be conducted to understand their toxicity and environmental risks.

Characteristics of Internal Ammonium Loading from Long-Term Polluted Sediments by Rural Domestic Wastewater

Given long-term decentralized and centralized rural domestic wastewater (RDW) discharge, nitrogen is continuously depositing in sediments. RDW discharge is assumed to be an important source of ammonium in surface water; however, the effect of long-term RDW discharge on nitrogen pollution in sediments remains unknown. Batch incubations were conducted to investigate the characteristics of internal ammonium loading from long-term polluted sediments by RDW discharge. Four sediments were demonstrated to be heavily polluted by long-term RDW discharge, with total nitrogen (TN) values of 5350, 8080, 2730, and 2000 mg·kg^-1, respectively. The internal ammonium release from sediment was a slow and long process, and the risk of ammonium release from sediment during the dry season was significantly greater than that during the wet season. Though all selected sediments were heavily polluted by long-term RDW discharge, the relative contribution of internal ammonium loading from sediments was generally lower than that of external pollution. Hence, dredging is not suggested for RDW-polluted sediments except in response to an emergency. The excessive ammonium in the selected catchment was mainly from untreated and centralized black water in RDW. Centralized black waters in rural communities are highlighted to be separately treated or reused to maintain ammonium content at a safe level.