Geographical location and water depth are important driving factors for the differences of suspended particulate organic matter (SPOM) in lake environment across nationwide scale: Evidences from n-alkane fingerprints

Recent trends in polycyclic aromatic hydrocarbons pollution distribution and counteracting bio-remediation strategies

Polycyclic aromatic hydrocarbons (PAHs) are distributed worldwide due to long-term anthropogenic pollution sources. PAHs are recalcitrant and highly persistent in the environment due to their inherent properties, such as heterocyclic aromatic ring structures, thermostability, and hydrophobicity. They are highly toxic, carcinogenic, immunotoxic, teratogenic, and mutagenic to various life systems. This review focuses on the unique data of PAH sources, exposure routes, detection techniques, and harmful effects on the environment and human health. This review provides a comprehensive and systematic compilation of eco-friendly biological treatment solutions for PAH remediation, such as microbial remediation approaches utilizing microbial cultures. In situ and Ex situ bioremediation of PAH methods, including composting land farming, biopiles, bioreactors bioaugmentation, and phytoremediation processes, are discussed in detail, as is a summary of the factors affecting and limiting PAH bioremediation. This review provides an overview of emerging technologies that use multi-process combinatorial treatment approaches and answers to generating value-added by-products during PAH remediation.

Polycyclic aromatic hydrocarbons (PAHs) in a sediment core from Lake Taihu and their associations with sedimentary organic matter

Sediment core is the recorder of polycyclic aromatic hydrocarbon (PAH) pollutions and the associated sedimentary organic matter (SOM), acting as crucial supports for pollution control and environmental management. Here, the sedimentary records of PAHs and SOM in the past century in Lake Taihu, China, were reconstructed from a 50-cm sediment core. On the one hand, the presence of PAHs ranged from 8.99 to 199.2 ng/g. Vertically, PAHs declined with the depth increased, and the sedimentation history of PAHs was divided into two stages with a discontinuity at 20 cm depth. In composition, PAHs in the sediment core were dominated by three-ring PAHs (44.6% ± 9.1%, mean ± standard deviation), and were followed by four-ring (27.0% ± 3.3%), and five-ring (12.1% ± 4.0%) PAHs. In toxicity assessment, the sedimentary records of benzo[a]pyrene-based toxic equivalency were well described by an exponential model with R-square of 0.95, and the environmental background toxic value was identified as 1.62 ng/g. On the other hand, different components of SOM were successfully identified by n-alkane markers (p < 0.01) and the variations of SOM were well explained (84.6%). A discontinuity of SOM was recognized at 22 cm depth. Association study showed that the sedimentary PAHs were associated with both anthropogenic and biogenic SOM (p < 0.05) with explained variances for most individual PAHs of 60%. It indicated the vertical distributions of PAHs were driven by sedimentary SOM. Therefore, environmental processes such as biogenic factors should attract more attentions as well as PAH emissions to reduce the impacts of PAHs.

Controlled and driving mechanism of the SPM variation of shallow Brackish Lakes in arid regions

Suspended particulate matter (SPM) in the brackish Ebinur Lake of arid northwest China profoundly affect its water quality and watershed habitat quality. However, the actual driving mechanisms of the Lake's SPM changes remain unclear. Therefore, the purpose of this study is to explore the controlling factors driving the variability of SPM in the Ebinur Lake. This study constructed month-by-month SPM maps of Ebinur Lake based on time-series remote-sensing imageries and SPM inversion model. Thirty-four factors that might influence SPM changes were extracted, and the Partial Least Squares Structural Equation Modeling (PLS-SEM), suitable for complex relationships and factor interactions, was applied to identify the relative influence of each factor quantitatively. The results showed: (1) a clear increasing trend of SPM concentration in Ebinur Lake from 2011 to 2020; (2) that SPM changes were influenced by external and internal factors, explaining 48.2 % and 46.9 % of the changes, respectively; (3) that, to the external factors, meteorological factors exerted the greatest influence on SPM (relative contribution of 38.9 %); that, to the internal factors, water salinity imposed the greatest influence on SPM (relative contribution of 43.3 %); (4) that, among the meteorological factors, the measured variable Alashankou wind speed expressed the most significant positive effect on SPM (weighting coefficient of 0.894), and sulfate generated the strongest positive effect on SPM (weighting coefficient of 0.791) among the water salinity factors. Hence, the quantitative identification of drivers of SPM changes in Ebinur Lake could provide a new perspective to investigate the driving mechanisms of lake water quality in arid areas and inform their sustainable restoration and management.

What are the determinants of wastewater discharge reduction in China? Decomposition analysis by LMDI

Wastewater discharge reduction (WDR) is a key breakthrough point for China's environmental protection. Based on China's 30 provincial data from 2011 to 2017, this paper applied the logarithmic mean Divisia index (LMDI) method to clarify the determinants of WDR at national, regional, and provincial levels. Except for wastewater discharge factor, economic development, and total population, four innovative factors, total water application intensity, water environment cost, water treatment industry development level, and drainage infrastructure investment scale were first proposed in this study. The results indicated that from 2011 to 2017, at the national level, total water application intensity and water treatment industry development level were dominant contributors to WDR, while other factors all inhibited WDR. At the regional level, the results of wastewater discharge factor, economic development, and water environment cost were similar to the national level. The drainage infrastructure investment scale had a positive effect on WDR in Northeast and South China while having a negative effect on other regions. And except for Northeast China, the water treatment industry development level promoted WRD, while the total population inhibited WDR. Finally, the determinants of WDR at the provincial level were investigated. On this basis, targeted corresponding policies were provided in this paper.

Differences in the composition, source, and stability of suspended particulate matter and sediment organic matter in Hulun Lake, China

The occurrence, migration, transformation, and stability of sediment (SOM) and suspended particulate (SPOM) organic matters have important effects on the environmental behaviors of carbon, nitrogen, phosphorus, and other pollutants in a water environment. The content, composition, fluorescence characteristics, source, and stability of SOM and SPOM in Hulun Lake, a typical lake in cold and arid region of China, were compared by sequential extraction, three-dimensional fluorescence spectroscopy, parallel factor technique, carbon-nitrogen ratio, and stable carbon isotope. Contents of SOM and SPOM in north and west were higher than those in east and south. The average content of SPOM (24.70 ± 4.63 g/kg) was slightly higher than that of SOM (23.04 ± 10.27 g/kg), but the difference was not significant. Humin was the dominant component in SOM and SPOM, accounting for 73.7% and 61.2%, respectively. Humus was the main fluorescence component of water-extractable organic matter in SOM and SPOM, accounting for 79.9% and 70.4%, respectively, of the total fluorescence intensity. SOM and SPOM were derived from terrestrial sources with a relative contribution rate of about 70%. SPOM was more influenced by autochthonous sources and had a significantly lower humification degree and stability than SOM. Effects of climate changes on migration, transformation, stability, and bioavailability of organic matters and endogenous pollutants closely related to organic matters in lakes of cold and arid regions should be paid attention in the future.

Anthropogenic-driven chronological increase of sediment organic carbon burial in a river-lake system

Total organic carbon (TOC) in lake sediments from upstream catchments is deposited and buried in substrate, recording historical environmental changes. However, the linkage among natural variability, anthropogenic activity, and TOC burial for has not yet been clarified. This study examined the lake sediments of five 200-cm-deep dated depositional cores in west Dongting lake, China to quantify the magnitude, allocation, and amplitude of TOC burial. 44.47-59.36% of TOC burial flux was buried at 100-200 cm, suggesting lake sediments at deep layers stored considerable carbon. TOC burial rate (BR_TOC) decreased along the lake entrance to its body, which was explained by the geochemical differences. Since 1900, BR_TOC presented an increasing with a 4-7 times uptrend, showing three sedimentary stages with the increased human disturbance, such as deforestation, hydroelectric facilities. Moreover, the coefficient of variation of BR_TOC in the third stage was lower than that in the second stage for the implementation of watershed reforestation and reservoir construction. Our findings stressed that natural variations of lake sedimentation background induced the change of TOC burial among the depositional sites, and enhanced that anthropogenic perturbation drove its chronological increases. This research unveiled the linkage between TOC burial, natural variability, and human disturbance from the perspective of burial evolutions in a lacustrine sedimentary environment.

How reliable is chlorophyll-a as algae proxy in lake environments? New insights from the perspective of n-alkanes

Chlorophyll-a (Chl-a) has been employed as the "golden proxy" of algae biomass and algae cell densities in lake environments for many years. However, how reliable Chl-a is as algae proxy in lake environments needs further evaluation. Here, we take the eutrophic Lake Chaohu and 46 lakes and reservoirs across China as objects on temporal and spatial scales, respectively, to resolve this issue from the perspective of n-alkanes. Our results showed that Chl-a ranged from 10.5 to 735 μg∙L^-1 with a geometric mean of 92.4 μg∙L^-1 in Lake Chaohu. There were no statistically significant correlations between Chl-a and algae cell densities in all seasons (Pearson's correlation, p > 0.05), and also for macrophytes and terrestrial plants input (p > 0.05). It was related to the complex changes of environmental factors. By contrast, Chl-a ranged from 7.1 to 1608 μg∙L^-1 with a geometric mean of 125 μg∙L^-1 in nationwide lakes and reservoirs, and its occurrence was not only related to algae, but also associated with macrophytes and terrestrial plants (p < 0.05). In summary, Chl-a can be applied as an algae proxy, but its application is subject to certain restrictions. Besides, the multiple sources of Chl-a in lake environments may result in an overestimation of algae cell densities. Compared to Chl-a, biogenic n-heptadecane (bio C₁₇) could be regarded as a potential alternative. Hence, we compared the advantages and disadvantages of bio C₁₇ and Chl-a in the aspects of specificity, accuracy, sensitivity and applicability. We found that for most scenarios, their limitations could be surmounted by each other, but failed in some scenarios. Accordingly, an ensemble proxy system may be used for more reliable representation of algae in lake environments.

Assessing spatiotemporal sources of biogenic and anthropogenic sedimentary organic matter from the mainstream Haihe River, China: Using n-alkanes as indicators

Sedimentary organic matter (SOM) plays an important role in the transportation and transformation of various pollutants and the carbon cycle in aquatic and terrestrial ecosystems, especially for seagoing rivers. However, few studies have focused on the sources and factors of SOM in rivers under the significant pressure of high urbanization and industrialization. In this study, we adopted the molecular markers of n-alkanes and their proxies in the mainstream Haihe River to reveal the spatiotemporal distributions and biogenic and anthropogenic sources of SOM. The concentrations of Σ₂₉n-alkanes, Σ_biogenicn-alkanes, and Σ_{anthropogenic}n-alkanes were 4985.6 (127.5-26,296.6), 1872.1 (38.1-9216.9), and 3113.5 (89.4-18,259.7) ng·g^-1 dw (dry weight), respectively. Hybrid sources of n-alkanes were found in this study. The composition distribution and proxies of n-alkanes showed that woody and herbaceous plants are the main sources of biogenic SOM, while incomplete fossil fuel burning and heavy oil emissions served as the main contributors to anthropogenic SOM in the mainstream Haihe River, especially through industrial activities. The average chain length of biogenic n-alkanes (ACL_bio) was verified to quantify the relative contributions of biogenic sources of SOM and proxies; the average chain length of anthropogenic n-alkanes (ACL_anthro), and the ratio of unit short‑carbon to unit long‑carbon anthropogenic n-alkanes (L/H) were verified to quantify the relative contributions of anthropogenic sources of SOM in the river system. Impacts from sedimentary geochemistry (such as total organic carbon (TOC) and grain size of sediments) on n-alkanes were explored, and the correlations of Σ₂₉n-alkanes with TOC and grain size of the river sediment indicated that terrestrial organic matter was the main source of SOM, while emissions from incomplete combustion and intensive manufacturer activities should also not be neglected.

Suspended particulate matter (SPM)-bound polycyclic aromatic hydrocarbons (PAHs) in lakes and reservoirs across a large geographical scale

Suspended particulate matter (SPM) plays a key role in the environmental fate of polycyclic aromatic hydrocarbons (PAHs) in lake environment. However, less is known about the occurrence, compositions and sources of SPM-bound PAHs as well as the correlations between SPM-bound PAHs and different suspended particulate organic matter (SPOM) on large geographical scale. In this study, we focused on the SPM-bound PAHs in 46 lakes and reservoirs across China to fill this gap. Our results showed that the concentrations of Σ₂₀ PAHs ranged from 334 to 38427 ng·g^-1 with a geometric mean (GM) of 3915 ng·g^-1. The occurrence of SPM-bound PAHs in this study was at a moderate level with large variations, which was associated with location and water depth according to linear discriminant analysis (LDA). Phenanthrene (Phe) was investigated as the overwhelming species with a GM of 1777 ng·g^-1, and was followed by fluoranthene (Fla), fluorene (Flu) and pyrene (Pyr) with GMs of 499 ng·g^-1, 276 ng·g^-1 and 184 ng·g^-1, respectively. The profiles of SPM-bound PAHs were primarily dominated by low-ring PAHs ranging from 56.0% to 97.1% (85.5% ± 7.7%, mean ± standard deviation). Four diagnostic ratios were applied for preliminary diagnoses, but inconsistent results were obtained in most samples. Ridge regression was applied to ascertain the potential influences of different SPOM on SPM-bound PAHs. The results revealed that the presence of SPM-bound PAHs was not only influenced by anthropogenic emissions, but also associated with biogenic organic matter. Our results provided a higher explanation than those just preliminarily estimated by total organic carbon (TOC). Nevertheless, there still exist over 50% of variance unexplained for most PAHs, and further study could focus more on the information of SPOM structures and potential local effects.