Function rather than structure of phytoplankton community reveals changes of water quality in an ecological restored lake.

Although phytoplankton is well known as robust bioindicators to aquatic environments, their indicating functions based on different community parameters remain to be understood. In order to filter effective bioindicators in aquatic ecosystems, four phytoplankton community parameters including species richness (SR), total biomass (SBP), functional groups (FGBP), and size-fractionated chlorophyll-a (SC) were demonstrated in a subtropical artificial lake with ecological restoration in South China. Our results indicated that all the above four parameters exhibited high sensitivity to environmental variations and illustrated distinct aspects of indicating functions to aquatic environments due to their individual biological characteristics. Based on FGBP, both spatial and temporal differences in phytoplankton community could be identified. SR and SBP only classified the spatial and temporal distributions, respectively, while SC could distinguish the sewage outfalls from other sites. In terms of ecological management, two parameters (SR and FGBP) could distinguish the restored waters from untreated environments as non-point source pollution, and another parameter SC could indicate the sewage outfalls as point source pollution. Therefore, the combination of the above two categories of phytoplankton community parameters could make the strongest indicating functions. Our study provided greater insight into indicating functions of phytoplankton community parameters in an ecological restored lake and enabled better managements in such artificial lakes.

Variation in the burden and chemical forms of thallium in non-detoxified tissues of tilapia fish (Oreochromis niloticus) from waterborne exposure.

Thallium (Tl) is highly toxic to aquatic ecosystems, but information about its concentration and distribution characteristics in different fish tissues is limited. In this study, juvenile tilapia (Oreochromis niloticus) were exposed to Tl solutions with different sub-lethal concentrations for 28 days, and the Tl concentrations and distribution patterns in the fish non-detoxified tissues (gills, muscle, and bone) were analyzed. The Tl chemical form fractions, Tl-ethanol, Tl-HCl, and Tl-residual, corresponding to easy, moderate, and difficult migration fraction, respectively, in the fish tissues were obtained by sequential extractant approach. The Tl concentrations of different fractions and total burden were determined using graphite furnace atomic absorption spectrophotometry. Exposure-concentration effect determined the Tl burden in the fish tissues. The average Tl-total concentration factors were 360, 447, and 593 in the bone, gills, and muscle, respectively, and the limited variation during the exposure period indicates that tilapia have a strong ability to self-regulate and achieve Tl homeostasis. However, Tl fractions varied in tissues, and the Tl-HCl fraction dominated in the gills (60.1%) and bone (59.0%), switchover Tl-ethanol fraction dominated in the muscle (68.3%). This study has shown that Tl can be easily taken up by fish during 28-days-period and largely distributed in non-detoxified tissues especially muscle, in which concurrent risks of high Tl-total burden and high levels of Tl in the form of easy migration fraction, posing possible risks to public health.

Potential of microplastics participate in selective bioaccumulation of low-ring polycyclic aromatic hydrocarbons depending on the biological habits of fishes.

Currently, although the cumulative effects of microplastics (MPs) and organic pollutants (OPs) in the environment and within organisms are being investigated, whether and how MPs participate in bioaccumulation of OPs based on a carrier effect is still unclear. In the present study, water and aquatic organisms were collected from the Pearl River. Polycyclic aromatic hydrocarbons (PAHs) and MPs were separated by solid phase extraction and were measured by gas chromatography mass spectrometry and Fourier transform infrared spectroscopy, respectively. Higher PAH concentrations at the river outlet and higher MPs abundance in the inner river were observed, indicating a mismatched distribution between PAHs and MPs. No correlation between MP abundance and PAH concentration in fishes was detected, implying that MPs exerted limited influence on PAH concentrations. Interestingly, bioconcentration factors of one major low-ring PAH (phenanthrene) in fishes showed a significant correlation with MPs abundance, implying that although MPs did not affect the variation in PAH concentrations, they potentially participated in selective bioaccumulation of PAHs. Moreover, significant correlations between MPs abundance and PAHs in fishes with different feeding and living habits were found, indicating that MPs' participation in PAH bioaccumulation was dependent on fish biology and life history. Furthermore, the health risk posed by PAHs in fishes at the river outlet surpassed the line of potential high risk, while the ecological risk posed by MPs at the inner river was in the danger category, indicating the ecological risks posed by PAHs and MPs are uneven along the Pearl River. These findings deepen our understanding of the underlying mechanism of MPs participating in selective bioaccumulation of low-ring PAHs in fishes based on fish biology and point out the present risks posed by these two pollutants in the Pearl River and its estuary, which contribute to aquatic environmental protection and fishery production in this region.

Bacterioplankton community indicators for seasonal variation in a fragmented subtropical river.

In this study, spatiotemporal investigations were conducted along five cascade dams in the main channel of the North River of China during 2019 to explore bacterioplankton community indicators of water environments in a fragmented, highly regulated river. Bacterioplankton communities were good bioindicators of temporal variation in river environments, especially when considering the bacterial class level. Specifically, the most dominant bacterial classes (Gammaproteobacteria, Oxyphotobacteria, and Actinobacteria) and sub-dominant bacterial classes (Bacteroidia, Betaproteobacteria, and Acidimicrobiia) exhibited obvious temporal variation. Rainfall, water temperature (WT), water transparency (SD), and pH were all highly associated with temporal variation. In contrast, bacterioplankton indicators of spatial variation were limited to individual dominant bacterial classes for individual study periods, while rainfall, total phosphorus (TP), and pH were also associated with spatial variation. Clustering of bacterioplankton community compositions revealed that temporal differences were much stronger than spatial differences, which is consistent with most environmental parameters exhibiting obvious temporal differences, but minimal spatial differences. A possible reason for these observations could be that river fragmentation caused by cascade dams weakened spatial differences in communities, with WT, rainfall, and river runoff playing key roles in these patterns. In conclusion, bacterioplankton communities were good bioindicators of water environments in the fragmented river ecosystem of this study and their temporal variation was more apparent than their spatial variation.

Connection between the Gut Microbiota of Largemouth Bass (Micropterus salmoides) and Microbiota of the Pond Culture Environment.

The vital role of the gut microbiota in fish growth, development, immunity, and health has been largely confirmed. However, the interaction between environmental microbiota and the gut microbiota of aquaculture species remains unclear. Therefore, we analyzed the gut microbiota of largemouth bass (Micropterus salmoides) collected from subtropical ponds in southern China, as well as the pond water and aquatic sediment microbiota, using high-throughput sequencing of the 16S rRNA gene. Our results demonstrated significant differences in the compositions of pond water, sediment, and the gut microbiota of largemouth bass. Moreover, these compositions changed throughout the culture period. Only approximately 1% of the bacterial species in the pond sediment and gut microbiota were exchanged. However, the bacterial proportion of the gut microbiota from pond water microbiota was approximately 7% in samples collected in June and August, which increased markedly to 73% in October. Similarly, the proportion of bacteria in the pond water microbiota from the gut microbiota was approximately 12% in June and August, which increased to 45% in October. The study findings provide basic information for understanding the interactions between environmental microbiota and the gut microbiota of cultured fish, which may contribute to improved pond culture practices for largemouth bass.

Occurrence, source identification, and ecological risk assessment of polycyclic aromatic hydrocarbons in sediments of the Pearl River Delta, China.

The pollution characteristics, sources, and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in surface sediment samples from the river networks and outlets of the Pearl River Delta (PRD) were investigated. The total PAH concentrations were in the range of 69.1-1297 ng g-1 in river networks and 56.6-617 ng g-1 in river outlets. The results of source identification showed that PAHs in sediments were mainly derived from combined sources of coke tar and liquid fossil fuel combustion, coal/wood combustion, and petroleum contamination. The ecological risks of PAHs were evaluated based on sediment quality guidelines (SQG), mean probable effects levels quotient values (PEL-Q), and the toxicity equivalence factor (TEQBaP) method. The ecological risks of PAHs in sediments were at moderate levels in the Pearl River Delta. Although no high risk was found, regular and continuous monitoring of PAHs in sediments needs to be performed.

Residual Distribution and Risk Assessment of Polychlorinated Biphenyls in Surface Sediments of the Pearl River Delta, South China.

We analyzed residual PCBs in surface sediments at 19 sites in the Pearl River Delta in the wet and dry seasons. Seven indicative PCB congeners (PCB28, PCB52, PCB101, PCB118, PCB153, PCB138 and PCB180) were detected in the surface sediments, among which the detection rate and mass concentrations of PCB52 were the highest. Total concentrations of the seven PCBs ranged from 19.8 to 111 µg/kg, with an average of 48.2 µg/kg. For the spatial distribution, the sum of the seven PCB (∑PCB) concentrations for the stations that were located in the city region of the Pearl River Delta were significantly higher than the ∑PCB concentrations for the eight outlets of the Pearl River Delta (p < 0.05). According to the US National Oceanic and Atmospheric Administration ERL and ERM guideline concentrations, the PCB concentrations may occasionally lead to adverse effects, especially in the dry season.

[Community structure of planktonic rotifers in the Pearl River Delta].

Four ecological investigations were carried out on planktonic rotifers in Pearl River Delta in 2012. The community structure, including spatial and temporal patterns of species composition, dominant species, biomass and biodiversity, was investigated. The correlation between the community structure of rotifers and the environmental factors was discussed. Moreover, the aggregation structures of rotifers were analyzed. A total of 53 rotifer species were found. Dominant species changed markedly with season and space. Polyarthra trigla had higher dominance. In terms of seasonal changes, the density and biomass were higher in dry season than in wet season, while the biodiversity and evenness indices were vice versa. The biomass and biodiversity of rotifers showed highly significant differences among seasons. In terms of spatial distribution, the average density and the average biomass showed an increase from the southwest to the northeast. The highest density and biomass were recorded in Shiqiao. The biodiversity and evenness indices had an opposite spatial distribution, with the highest values being recorded in Qingqi. The rotifer density was significantly different among the investigated sites, while the biomass and biodiversity were not significantly different. Correlation analysis demonstrated a highly significant positive correlation between rotifer density and biomass, as well as between biodiversity and evenness indices, and a highly negative correlation between biodiversity and biomass. The biodiversity and evenness indices both decreased markedly with the increase of biomass. Principal component analysis indicated that the rotifer density was closely correlated with environment factors, such as water temperature, pH, dissolved oxy- gen, chlorophyll a content, total phosphorus, and total nitrogen, in different seasons. Aggregation analysis based on rotifer density revealed five aggregation structures in the investigated sites, indicating significant differences in water quality among the investigated sites.

Distribution of heavy metals in sediments of the Pearl River Estuary, southern China: implications for sources and historical changes.

The distribution of heavy metals (Pb, Zn, Cd and As) in sediments of the Pearl River Estuary was investigated. The spatial distribution of heavy metals displayed a decreasing pattern from the turbidity maxima to both upstream and downstream of the estuary, which suggested that suspended sediments played an important role in the trace metal distribution in the Pearl River Estuary. In addition, metal concentrations were higher in the west part of the estuary which received most of the pollutants from the Pearl River. In the sediment cores, fluxes of heavy metals were consistent with a predominant anthropogenic input in the period 1970-1990. From the mid-1990s to the 2000s, there was a significant decline in heavy metal pollution. The observed decline has shown the result of pollution control in the Pearl River Delta. However, it is noteworthy that the metal concentrations in the most recent sediment still remained considerably high. Taken together, the enrichment of heavy metals in sediments was largely controlled by anthropogenic pollution.