[Influence of Land Use Structure and Spatial Pattern on Water Quality of Small and Medium-sized Rivers in Poyang Lake Basin].

To reveal the influence mechanism of land use structure and spatial pattern on water quality of small and medium-sized rivers, water samples were collected from 25 sampling points in three small and medium-sized rivers of the Poyang Lake Basin in January 2022 and July 2022. Bioenv analysis, the Mantel test, and variance partitioning analysis were used to quantify the effects of land use structure and spatial patterns on water quality at different spatial scales; generalized additive models were used to fit the relationship between water quality and different land use structures and spatial patterns; and a generalized linear model was used to construct segmented regression models and calculate the thresholds based on the stepwise recursive method. The results showed that:① the average interpretation rate of land use structure and spatial pattern on river water quality was 59.72% during the wet period and 48.95% during the dry period. The sub-basin and riparian 100 m scales were the key scales of land use structure and spatial pattern affecting water quality in small and medium-sized rivers, with an average explanation rate of 54.70% and 64.88%, respectively. The joint explanation of land use structure and spatial pattern was an important factor driving the change in river water quality, accounting for 66.90% of the total explanation. ② The impact of land use structure on the water quality of small and medium-sized rivers had a significant threshold effect. When the proportion of construction land was less than 2%, farmland was less than 8%, or forest land was more than 82% at the sub-basin scale and the proportion of construction land was less than 12%, farmland was less than 41%, or forest land was more than 49% at the riparian buffer scale, all could significantly improve water quality. ③ The effect of spatial pattern on water quality in small and medium-sized rivers also had a threshold effect but was weaker than that of land use structure. A patch shape value more than 28.77 or patch diversity more than 0.69 at the sub-basin scale and a patch shape value more than 2.99 or patch diversity more than 1.02 at the riparian buffer scale could improve water quality. The above results showed that strengthening the management of land use at the sub-basin and riparian 100 m scales and setting a reasonable threshold of land use structure and spatial pattern can effectively prevent water quality from deteriorating.

[Bisulfite Promoted Minute Fe2+-Activated Peroxydisulfate for Paracetamol Degradation].

Fe2+ has been commonly selected to activate peroxydisulfate(PDS) for sulfate radical(SO4-·) generation because of its eco-friendly, cost-effective, and high activity characteristics. However, Fe2+ can be rapidly oxidized to Fe3+ in the reaction, leading to poor utilization of iron for PDS activation. Further, a fairly high concentration of Fe2+ is generally required and may cause iron sludge production and secondary pollution. In this study, a minute Fe2+-activated PDS system induced by bisulfite(BS) was used to degrade paracetamol(APAP) in water. The results showed that the Fe2+-PDS system could be enhanced by the circulation of Fe2+-Fe3+ with the injection of BS and by keeping Fe2+ at a high concentration. Under the optimal conditions(PDS=0.6 mol·L-1; BS=0.4 mol·L-1; Fe2+=10 µmol·L-1; pH=4), 100% APAP(4 µmol·L-1) was removed within 180 s. The degradation rate of APAP increased with the increase in BS(0-0.6 mmol·L-1) and PDS(0.2-1.5 mmol·L-1) concentration, and a modest Fe2+ concentration could accelerate APAP removal. Co-existing substances inhibited the APAP removal and followed the order of HCO3->HPO42->Cl->NO3->humic acid(HA). Based on the quenching experiments and electron paramagnetic resonance spectroscopy test, SO4-· was shown to be the primary reactive species for APAP decomposition in the BS-Fe2+-PDS process. Three-dimensional fluorescence spectroscopy revealed that APAP intermediates had fluorescence characteristics. Moreover, five intermediates were identified, and the probable APAP degradation pathways were proposed. The removal efficiencies of APAP were lower in real waters than that in ultrapure water. Nevertheless, the removal effect was greatly improved after a prolonged reaction time. All results indicated that the BS-Fe2+-PDS system could be a promising method for organic pollutant treatment.

[Characteristics of Microplastic-derived Dissolved Organic Matter(MPDOM) and the Complexation Between MPDOM and Sulfadiazine/Cu2].

Microplastic-derived dissolved organic matter(MPDOM) during the aging process could be complexed with organic pollutants, heavy metals, and other contaminants and thus affect their migration and transformation. In this study, two types of microplastics, polyethylene terephthalate(PET) and polystyrene(PS), were selected to investigate the spectral properties of MPDOM and their effect on the complexation between MPDOM and sulfadiazine(SDZ)/copper ion(Cu2+) using the fluorescence quenching method, various spectroscopic analysis techniques, and the Ryan-Weber quenching model. The results of UV-vis absorption spectroscopy analysis showed that the molecular weight of the two MPDOMs decreased; the aromaticity and humification increased; and the carboxyl, carbonyl, hydroxyl, and ester substituents on aromatic rings increased after aging. The fluorescence quenching process between MPDOM and SDZ/Cu2+ was static quenching. After quenching, the aromaticity and humification of the two MPDOMs were similar, and the molecular weights were comparable. Combined with three-dimensional fluorescence spectra and parallel factor analysis, two humic-like components and one protein-like component were identified. In addition, the protein-like components of MPDOM reacted preferentially with SDZ and were more sensitive to Cu2+. The results of the Ryan-Weber quenching model revealed that the binding ability of humic-like components to PET-DOM was higher in both SDZ and Cu2+ quenching systems, but the binding ability of MPDOM in the SDZ quenching system was generally stronger than that in the Cu2+ system.

[Community Composition, Symbiotic Patterns, and Influencing Factors of Planktonic Fungi in Urban Lakes of Nanchang].

To investigate the characteristics of planktonic fungal communities in Nanchang lakes and the mechanism of environmental stress on planktonic fungal communities, surface water samples were collected from seven major urban lakes evenly distributed in different county-level districts of Nanchang in the dry (February and December), normal (April and October), and wet (June and August) seasons, respectively. The environmental stressors such as WT, DO, NH4+-N, and NO3--N were measured; the characteristics of planktonic fungal communities were studied using high-throughput sequencing; the symbiotic patterns of planktonic fungal communities were elucidated using network analysis and other methods; and the environmental stressors affecting the structure and symbiotic patterns of planktonic fungal communities were revealed. The results showed that ① the planktonic fungal community composition in lakes of Nanchang varied significantly among seasons but not significantly among the lakes. WT, DO, pH, and NH4+-N were the significant environmental stressors affecting the planktonic fungal community composition. ② The dominant phyla of the planktonic fungal community were Chytridiomycota (9.55%-33.14%), Basidiomycota (0.48%-4.25%), and Ascomycota (1.29%-3.19%), and the sizes of the dominant phyla were in the following order:wet season>normal season>dry season. The relative abundance of Chytridiomycota was significantly higher in the wet season than that in the normal season and the dry season, the relative abundance of Basidiomycota was significantly lower in the dry season than that in the normal and wet seasons, and the difference in Ascomycota among seasons was not significant. ③ The stability size of the planktonic fungal community symbiosis network in lakes of Nanchang was in the following order:wet season>normal season>dry season. WT was the best environmental stressor affecting the planktonic fungal community symbiosis pattern. The study can provide theoretical basis for the comprehensive evaluation and management study of the lake and provide guidance for protecting the lake ecosystem in the middle and lower reaches of the Yangtze River.

[Bacterioplankton Communities and Assembly Mechanisms in Wet Season of Lakes, Nanchang].

Bacterioplankton communities play an important role in nutrient cycling and organic matter decomposition in urban lakes. Based on high-throughput sequencing, we analyzed the temporal (April, June, and August) and urban-suburban difference and assembly of bacterioplankton communities in lakes of Nanchang City. Our results showed that:① the dominant bacterioplankton communities in the lakes were Actinobacteria (41.60%), Proteobacteria (22.29%), Cyanobacteria (16.21%), and Bacteroidota (10.17%). ② There were significant differences in bacterial communities between April, June, and August but not between urban lakes and suburban lakes. The abundance of 10 bacteria, mainly Proteobacteria (April>June>August) and Cyanobacteria (June>August>April), was significantly different among the three months. There was a significant distance decay pattern in June, which was not seen in April and August. ③ The proportion of non-freshwater bacteria was significantly higher in June than that in April and August, but there were no significant differences between urban lakes and suburban lakes. ④ Deterministic processes dominated the assembly of bacterioplankton communities, whereas stochastic processes had a lower contribution. Water temperature (WT) was the environmental factor that best explained the changes in bacterioplankton communities in the lakes.

[Enrichments, Migrations, and Conversions of Heavy Metal in the Soil/Sediment-Plant System Towards the Lake in Typical Poyang Lake Wetland].

A large area of periodic water-level-fluctuating zone (WLFZ) in the Poyang Lake, regulated by a special hydrologic rhythm, was deposited with significant amounts of nutrients and pollutants. In this study, the WLFZ located in a typical estuarine wetland was chosen and sampling transects were arranged according to different vegetation types towards the lake. Soil/sediment and dominant plant (different tissues) samples were collected, and contents and enrichment levels of heavy metals (Cr, Ni, Cu, Zn, As, Cd, Sb, and Pb) in these samples were analyzed. The migrations and conversions of heavy metal in the soil/sediment-plant system were evaluated, and driving environmental factors were explored. The results indicated that the contents of heavy metal in the soil/sediment presented an obvious single-peak distribution towards the lake, that is, the seasonally flooded zone was identified as the main deposited zone of heavy metals. There was a high enrichment level of Cu, Pb, and Sb in the soil/sediment from the WLFZ, and significant Cu and Sb pollution was identified (EF>5). The results from the potential ecological risk evaluation (RI) indicated that the ecological risk of the seasonally flooded zone was significantly higher than that in the flooded and unflooded zones, being at a low ecological risk (70 ≤ RI<140). There was no obvious spatial distribution of heavy metal contents in the dominant plant towards the lake, whereas significant seasonal differences were detected. The levels of heavy metals in plants at the growth phase (April) were higher compared to those at the other sampling times. The tissue distributions of heavy metal content basically followed the sequence of soil/sediment>root ≥ above-ground part, except for in Cd and Sb. The Cd content in the roots was significantly higher than that in the sediment/soil, and the Sb concentration was not significantly different among the three tissues. The bio-enrichment coefficient (BAF) and transfer factor (TF) of heavy metal in the dominant plant towards the lake did not show an obvious spatial pattern, and BAF and TF of heavy metals in the Artemisia capillaris Thunb. was higher than those in other dominant plants. The RDA revealed that pH, organic matter, plant height, and Fe-Mn oxides were the key environmental factors driving the migrations of heavy metals in the soil/sediment-plant system. These results will provide scientific basis and theoretical support for the biodiversity conservation and heavy metal pollution prevention and management in wetlands of the Poyang Lake.

[Effect of Colloids in Sediment and Soil on Their Sorption Behavior of Chloramphenicol].

Natural colloids (NCs) are ubiquitous in sediments and soils, which could affect the environmental fate of antibiotics. Focusing on chloramphenicol (CAP), different sources of the sediments and soil samples were selected to research the sorption capacity of NCs with different relative molecular weights towards CAP, as well as the impactors, combined with a multi-method approach including cross-flow ultrafiltration, dynamic light scattering, UV-visible absorption spectroscopy, and three-dimensional excitation-emission matrix fluorescence spectroscopy. The results revealed that the low molecular weight (LMW) of NCs was associated with a low autochthonous origin and a higher humification degree. The high molecular weight (HMW) of NCs were mainly terrestrial sources, and the aromatic rings contained more oxygen-containing functional groups such as carboxyl, hydroxyl, and carbonyl groups. Four fluorescence components were identified using the parallel factor analysis model, and the humic-like substances were the primary fluorescent components. Moreover, based on batch experiments, the study investigated the sorption behavior of CAP by the different fractions of the solid samples. The results showed that the sorption processes of CAP were well fitted by the linear model and Freundlich model. The average sorption rate of CAP by the original solid samples and the solid samples with removed organic and inorganic carbon were 4.46%, 3.93%, and 6.61%, respectively, indicating that organic carbon played an important role in the sorption behavior of CAP. The results of the sorption experiments indicated that CAP was more easily adsorbed on the LMW NCs that had a high degree of humification and a more aliphatic chain on the aromatic rings. In addition, tryptophan-like protein substances in NCs showed the inhibiting effect on the sorption progress of CAP. Redundancy analysis indicated that the sorption of CAP by NCs in sediment and soil was mainly related to the source, aromatics, oxygen functional groups on aromatic rings, humification degree, and humic-like substances of NCs.

[Effects of Landscape Structures on Bacterioplankton Communities at Multi-spatial Scales in the Yuanhe River].

The aim of this study was to examine the relationships between land use and bacterioplankton communities at different spatial scales and the mechanisms underlying the effects of land use on bacterioplankton communities. Here, surface water samples were collected in 14 tributaries of the Yuanhe River in August 2019 (wet season) and January 2020 (dry season), and high-throughput sequencing technology was used to determine the characteristics of the bacterioplankton communities. Statistical methods such as Bioenv and variance partitioning analysis (VPA) were used to explore the relationships among landscape structure (i.e., landscape compositions and landscape configurations), water chemistry, and bacterioplankton communities. Furthermore, metacommunity theory was employed to explain the mechanisms by which land use and water chemistry affect bacterial communities. The results showed that:① in general, the effects of landscape configuration on bacterial communities were weak, whereas the effects of landscape composition on bacterial communities were significant and greater at the buffer scale than that at the sub-basin scale. ② There was no distinct distance-decay pattern for the effects of landscape composition on bacterial communities from the near-distance (100 m) to the long-distance (1000 m) buffer zones, with the maximal effects occurring in the 500 m circular buffer (wet season) and 300 m riparian buffer (dry season), respectively. ③ Land use influenced the bacterioplankton communities both directly through exogenous inputs (i.e., "mass effect" process) and indirectly by affecting water chemistry (i.e., "species sorting" process). VPA showed that the total explanation of bacterial community variations by water chemistry and the intersection of water chemistry and land use (13.5% in the wet season and 11.7% in the dry season) was higher than that of land use alone (2.7% in the wet season and 6.9% in the dry season). These results suggest that mass effects and species sorting jointly shaped bacterial community assembly but that the effects of species sorting outweighed those of mass effects. This study revealed the variability of landscape structure at different spatial scales on bacterial communities, and its results will help to determine the optimal spatial scale affecting bacterial communities and provide a reference basis for watershed land-use management.

[Spectral Characteristics of Dissolved Organic Matter in Sediments from Poyang Lake].

At present, there are few studies on the spectral characteristics of dissolved organic matter (DOM) in the sediments of the Poyang Lake basin. Therefore, excitation-emission matrix spectroscopy (EEMs) technology and ultraviolet-visible spectra combined with the parallel factor analysis (PARAFAC) were applied to investigate the fluorescent components and sources of DOM in sediments from Poyang Lake. The results showed that the DOM in sediments originated from both terrestrial and autochthonous sources with a high humification. Compared with the sub-lakes, the DOM from the main lake was characterized with a higher concentration of colored DOM, larger particle size, and higher aromaticity and humification degree. In addition, four fluorescence components of DOM in sediments were identified by the PARAFAC model, including three humic-like components (C1, C2, and C4) and one protein-like component (C3). The fluorescence intensity of the humic substances in the sub-lakes was higher than those in the main lake. Furthermore, the percentage of fluorescence abundance of C1 was the highest both in the sub-lakes (42%) and main lake (46%). The spatial distribution of the fluorescence intensity of the four components gradually increased from west to east, and the peak values were observed in the Duchang and Nanji Wetland. This may be related to the death of a large number of plants due to the rise in the water level during the wet season and human activities. Principal component analysis showed that although there were no significant differences in the four fluorescent components between the sub-lakes and the main lake, the humification degree of DOM in the sub-lakes was slightly higher than that in the main lake.