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In June - August 2008, the cyanobacterial bloom and chlorophycean bloom broke out one after the other in the Xiangxi Bay of Three Gorges Reservoir. Based on the weekly monitoring in summer in the Bay, and by using cluster analysis and discriminant analysis, the spatiotemporal dynamics and related affecting factors of the two blooms were studied. Each of the blooms could be divided into non-bloom group, transitional group, and bloom group. The two blooms had different uptake levels of dissolved Si (DSi), NO3--N + NO2--N, and PO43--P. Cyanobacterial bloom had lower DSi concentration and lower TN/TP, DSi/TN and DSi/TP ratios than chlorophycean bloom. The discriminant factors of cyanobacterial bloom were Chl a, TN and PO43--P, while those of chlorophycean bloom were Chl a and DSi. Better discriminant results were obtained when dividing each bloom into non-bloom group and bloom group. The critical value of Chl a for cyanobacterial bloom and chlorophycean bloom was 40 and 20 μg × L-1, respectively. [ABSTRACT FROM AUTHOR]

The dynamics of total suspended solids (TSS) in Xiangxi Bay of Three Gorges Reservoir (TGR) during the period of spring algal bloom were weekly investigated. The results showed that the TSS in the Bay ranged from 0.66 to 134.92 mg · L-1, with a median of 6.80 mg · L-1, and tended to be increased from headwater to down-lake zones. The spatial pattern of non-volatile suspended solids (NVSS) was similar to that of TSS, while volatile suspended solids (VSS) showed obviously different pattern from TSS and followed the spatial pattern of chlorophyll a. Regression analysis indicated that in the mid-zone of the Bay, chlorophyll a was significantly related to TSS and VSS, and explained 66.7%-96.7% and 58.9%-85.5% of the variance in TSS and VSS, respectively. In the headwater and down-lake zones, there were no significant relationships between chlorophyll a and TSS (including NVSS and VSS). The TSS in mid-lake had more close relationship with VSS than with NVSS, while that in headwater and down-lake had more close relationship with NVSS than with VSS, implying that the mid-lake of Xiangxi Bay was a more autochthonous system than the headwater and down-lake where allochthonous influences were the more determinant factors. [ABSTRACT FROM AUTHOR]

The synthesis of polycyclic aromatic hydrocarbon (PAH) data allows us to quantify and gain insights into the spatiotemporal dynamics of PAH contamination in marine bays. Here, a data synthesis framework was developed to understand data-driven insights into the spatiotemporal levels, compositional profiles, and potential sources of PAHs in water and sediment of marine bays. PAHs were detected in 69 bays worldwide, with contamination hotspots located in Asian bays. PAH concentrations in pre-2000 were significantly lower than those in the 2000s and post-2010, while the dominant species in water and sediment were 2-3 ring and 4-6 ring PAHs, respectively. The composition patterns of PAHs included 2-3 ring, 3-5 ring, and 4-5 ring dominant categories, but no significant distance decay relationship was found in the composition similarity due to international energy trade. Temporal dynamic patterns of concentrations included Descending-, Ascending-, and Inverted V-type, whereas over longer time spans, the pattern is more similar to the Inverted V-type owing to the reductions in emission intensity. PAHs were derived from both petrogenic and pyrolytic sources, with combustion from both coal and petroleum being the dominant source. These data-driven discoveries provide quantitative insights into the spatiotemporal patterns in the concentration and composition of PAHs, contributing to the mitigation of PAH contamination.

Global patterns in soil microbiomes are driven by non-linear environmental thresholds. Fertilization is known to shape the soil microbiome of terrestrial ecosystems worldwide. Yet, whether fertilization influences global thresholds in soil microbiomes remains virtually unknown. Here, utilizing optimized machine learning models with Shapley additive explanations on a dataset of 10,907 soil samples from 24 countries, we discovered that the microbial community response to fertilization is highly dependent on environmental contexts. Furthermore, the interactions among nitrogen (N) addition, pH, and mean annual temperature contribute to non-linear patterns in soil bacterial diversity. Specifically, we observed positive responses within a soil pH range of 5.2-6.6, with the influence of higher temperature (>15°C) on bacterial diversity being positive within this pH range but reversed in more acidic or alkaline soils. Additionally, we revealed the threshold effect of soil organic carbon and total nitrogen, demonstrating how temperature and N addition amount interacted with microbial communities within specific edaphic concentration ranges. Our findings underscore how complex environmental interactions control soil bacterial diversity under fertilization., (© 2024 John Wiley & Sons Ltd.)

Based on the survey data of eight kinds of heavy metals in the Xiangshan Bay watershed during the flood season, the pollution status of heavy metals in water was analyzed. The potential ecological risks of heavy metals were evaluated based on the single factor pollution index ( P i ), the Nemero comprehensive pollution index ( P n ), and the heavy metal pollution index (HPI). Based on the correlation between land-use types and heavy metal concentrations, the sources of heavy metals were analyzed. The results show that the average concentration of heavy metals is in the order Fe > Mn > Zn > Cu > As > Cr > Pb > Cd. All heavy metal concentrations, except those of Mn and Fe, conform to the class I surface water environment quality standard. The risk level of heavy metals is low, and there is no pollution, but some contamination. Agricultural non-point source pollution is the main factor in the contamination of heavy metals. Overall, the heavy metals in the region have not reached the risk threshold. To reasonably avoid the risk of heavy metal pollution in the urban development process, it is important to strengthen the supervision of pollution sources based on agricultural non-point sources.

The spatiotemporal distribution of total nitrogen (TN) and total phosphorus (TP) in sediments of Xiangxi Bay, Three Gorges Reservoir was investigated from October 2004 to July 2006, with related affecting factors analyzed. The TN and TP concentrations in the sediments were higher in the middle stretch but lower in the two edges of the Bay. The maximum value of TN concentration (1.08 mg x g(-1)) appeared in the middle part of the Bay, and the minimum (0.89 mg x g(-1)) occurred at the adjacent areas to the river mouth; while the maximum value of TP concentration (1.07 mg x g(-1)) appeared in the middle, and the minimum (0.80 mg x g(-1)) was in the edges of the Bay. The TN concentration decreased in the sequence of autumn-winter-spring, but increased from spring to summer dramatically; while the seasonal variation of TP concentration was not very significant, with the maximum occurred in spring. Significant inter-annual variations were observed in the TN and TP concentrations. The spatial distributions of TN and TP concentrations were mainly affected by the sedimentation of suspended matter. In the regions where sedimentation rate was high, the TN and TP concentrations were also very high. The seasonal fluctuation of TN concentration was mainly affected by river discharge, while that of TP concentration was mainly affected by point source pollution.