Inconsistent seasonal variation of antibiotics between surface water and groundwater in the Jianghan Plain: Risks and linkage to land uses.

Antibiotics are widely used in humans and animals, but their transformation from surface water to groundwater and the impact of land uses on them remain unclear. In this study, 14 antibiotics were systematically surveyed in a complex agricultural area in Central China. Results indicated that the selected antibiotic concentrations in surface waters were higher in winter (average: 32.7 ng/L) than in summer (average: 17.9 ng/L), while the seasonal variation in groundwaters showed an opposite trend (2.2 ng/L in dry winter vs. 8.0 ng/L in summer). Macrolides were the predominant antibiotics in this area, with a detected frequency of over 90%. A significant correlation between surface water and groundwater antibiotics was only observed in winter (R2 = 0.58). This study further confirmed the impact of land uses on these contaminants, with optimal buffer radii of 2500 m in winter and 500 m in summer. Risk assessment indicated that clarithromycin posed high risks in this area. Overall, this study identified the spatiotemporal variability of antibiotics in a typical agricultural area in Central China and revealed the impact of land uses on antibiotic pollution in aquatic environments.

Long-term succession characteristics and driving factors of zooplankton communities in a typical subtropical shallow lake, central China.

Zooplankton community could be affected by aquatic environment, land use patterns, and climate factors. However, few studies have evaluated the relative importance of these factors to the zooplankton community succession on a long-term scale. In this study, long-term data were used to analyze the succession characteristics and drivers of zooplankton communities in Honghu Lake, a large-scale shallow lake in central China. Results showed that zooplankton community structure changed greatly in 1959-2021. In general, the species number decreased, abundance and biomass increased, and the number and proportion of pollution tolerant species among dominant species increased during the past ~ 60 years. For the driving factors of zooplankton from 1992 to 2021, redundancy analysis showed that nutrients, wind speed, and aquaculture enclosure and pond were the main drivers of Protozoa and Rotifera, while phytoplankton abundance, wind speed, dissolved oxygen, and farmland were the main drivers of Cladocera and Copepoda. Generalized additive model showed that the aquatic environment had the highest direct explanation (mean is 60.2%) to zooplankton variation, followed by land use (mean is 35.6%) and climate factors (mean is 33.1%). Variance partitioning analysis showed that the effects of human activities (32.9-43.1%) associated with land use, water quality, and phytoplankton on the zooplankton succession are stronger than that of climate factors (19.9-29.2%). Additionally, lake eutrophication is an important factor for the decline in the richness index (p = 0.0017, r = - 0.8411) and Shannon index (p = 0.0301, r = - 0.8020) of zooplankton from 2019 to 2021. Our results highlighted that anthropogenic activity has stronger driving effects on zooplankton succession in the long term than climate changes in the lake. These findings can provide insights into zooplankton conservation in response to global climate change and complex anthropogenic actions.

Aboveground biomass estimation of wetland vegetation at the species level using unoccupied aerial vehicle RGB imagery.

Wetland vegetation biomass is an essential indicator of wetland health, and its estimation has become an active area of research. Zizania latifolia (Z. latifolia) is the dominant species of emergent vegetation in Honghu Wetland, and monitoring its aboveground biomass (AGB) can provide a scientific basis for the protection and restoration of this and other wetlands along the Yangtze River. This study aimed to develop a method for the AGB estimation of Z. latifolia in Honghu Wetland using high-resolution RGB imagery acquired from an unoccupied aerial vehicle (UAV). The spatial distribution of Z. latifolia was first extracted through an object-based classification method using the field survey data and UAV RGB imagery. Linear, quadratic, exponential and back propagation neural network (BPNN) models were constructed based on 17 vegetation indices calculated from RGB images to invert the AGB. The results showed that: (1) The visible vegetation indices were significantly correlated with the AGB of Z. latifolia. The absolute value of the correlation coefficient between the AGB and CIVE was 0.87, followed by ExG (0.866) and COM2 (0.837). (2) Among the linear, quadratic, and exponential models, the quadric model based on CIVE had the highest inversion accuracy, with a validation R2 of 0.37, RMSE and MAE of 853.76 g/m2 and 671.28 g/m2, respectively. (3) The BPNN model constructed with eight factors correlated with the AGB had the best inversion effect, with a validation R2 of 0.68, RMSE and MAE of 732.88 g/m2 and 583.18 g/m2, respectively. ​Compared to the quadratic model constructed by CIVE, the BPNN model achieved better results, with a reduction of 120.88 g/m2 in RMSE and 88.10 g/m2 in MAE. This study indicates that using UAV-based RGB images and the BPNN model provides an effective and accurate technique for the AGB estimation of dominant wetland species, making it possible to efficiently and dynamically monitor wetland vegetation cost-effectively.

Soil-based treatments of mechanically collected cyanobacterial blooms from Lake Taihu: efficiencies and potential risks.

In China, mechanical collection of cyanoblooms followed by soil-based treatments has been widely used as emergency strategies in many eutrophicated freshwaters. This study was to evaluate both efficiencies and potential risks of typical soil-based technologies. Results from this study indicated that over 90% of cyanobacterial biomass and 96% of dissolved microcystins (MCs) could be restrained in soils via three-level systems, which were much better than single-level systems. High concentrations of MCs, ranged from 65 to 276 ng g⁻¹ and from 2.12 to 6.6 ng g⁻¹, were found in soils around treatment systems and croplands, respectively. In the soil solutions, MCs ranged from 0.35 to 2.0 µg L⁻¹, showing a potentially high leaching risk. In the samples from shallow groundwater near the treatment systems, MC concentrations were detected as high as 1.2 µg L⁻¹. Moreover, bioaccumulations of MCs varied between 22 and 365 µg kg⁻¹, and 19-222 µg kg⁻¹ were found in 13 kinds of crops and 7 kinds of wild grass, respectively. Our results indicated for the first time that current soil-based technologies were effective but could pose potential environmental, ecological, and public health risks. Further improvements of these technologies were also proposed based on our findings.

Effects of South-to-North Water Diversion Project Cascade Dams on Riparian Vegetation Along the Middle and Lower Reaches of the Hanjiang River, China.

The influence of the construction of dams for water diversion on the ecological environment has attracted recent widespread attention. Over time, dams have emerged as one of the most important factors affecting the vegetation along the riparian zones of rivers. To elucidate the effects of cascade dams on riparian vegetation along the middle and lower reaches of the Hanjiang River, we examined riparian vegetation types upstream and downstream from dams. A total of 14 sample sites and 131 quadrats perpendicular to the river were investigated in June 2019, and 14 sample sites and 134 quadrats were investigated in October 2019. The riparian vegetation was divided into 15 (in June) and 11 (in October) vegetation types by two-way indicator species analysis (TWINSPAN). Significant differences were found between the vegetation types upstream and downstream of dams. Redundancy analysis (RDA) showed that soil moisture content, distance from the water, altitude and soil total nitrogen (TN) were the main environmental factors affecting plants distributions, and soil moisture content was the main factor affecting the zonal distribution of vegetation. By analyzing the impact of cascade dams on the hydrological regime, we found that the construction of cascade dams led to the differentiation of vegetation types upstream and downstream of the dam, and the riparian habitats were fragmented by these dams. This study provides both an important reference for the protection of riparian vegetation and riparian ecosystems and a basis for the management and restoration of river ecosystems after the construction of cascade dams.

The Effects of Edaphic Factors on Riparian Plants in the Middle and Lower Reaches of the Hanjiang River, China.

It is important to understand the interactions between soil and plant in riparian zones to ensure ecosystem function. The effects of edaphic factors on plant composition and species diversity were investigated in the middle and lower reaches of the Hanjiang River (MLHR), China. A total of 154 species of herbs were recorded, and vegetation was divided into 32 clusters according to a two-way indicator species analysis (TWINSPAN). Cynodon dactylon and Paspalum distichum were the most common clusters, accounting for 22.7% and 12.5% of total samples, respectively. Hydric and mesic species were dominant in the first and second transects, with mesophytes dominating the third and fourth transects. First transects situated were mainly composed of perennials and annuals, respectively. Perennials in second transects were present in 83% of sites, and perennials in the third and fourth transects were present in 86% of the sites. Margalef richness index (Dma), Simpson dominance diversity index (D), Shannon-Wiener diversity index (H) and Pielou evenness index (Jsw) were higher in the first transects in some sites. The redundancy analysis (RDA) results indicated that soil moisture content was the dominant factor affecting hydrophilic vegetation types, and total nitrogen (TN) and soil organic matter (SOM) were the most critical factors affecting plant life history types and species diversities in this area.

Impact of land use on shallow groundwater quality characteristics associated with human health risks in a typical agricultural area in Central China.

Groundwater pollution seriously threatens water resource safety due to high-intensity land use throughout the world. However, the relationship between groundwater pollution characteristics and land use in alluvial plains is still unclear. In this study, the effects of land use on shallow groundwater quality and human health risk were investigated via two sampling campaigns in a typical alluvial plain, namely, Jianghan Plain, China. Results show that the shallow groundwater in this area was polluted by nitrogen (with average concentrations of 5.12 mg/L in the dry season and 4.46 mg/L in the rainy season) and phosphorus (0.29 and 0.13 mg/L in the two seasons, respectively). The nutrient concentrations during the dry season were significantly higher than those during the rainy season (p < 0.05). Correlation analysis indicated that the concentration of nutrients was significantly positively correlated with cultivated land and negatively correlated with water and residence, suggesting that land use patterns can affect the groundwater quality. The best buffer where land use patterns affect the total N concentration was about 1000 m for cultivated land and water, while the optimal ranges for ammonium N were about 1000 and 2500 m for the areas, respectively. For the total phosphorus, a radius of 2000 m leads to the best fitting effect on both areas. Human health risk assessment showed that the total health risk indexes in about 75% of the samples were higher than 1, indicating the potential risk of the shallow groundwater in this area to human health. The results indicate that land use patterns will greatly affect the shallow groundwater quality. Thus, adjusting the land use pattern can improve the water quality and reduce health risks. Identification and selection of appropriate management solutions for the groundwater protection should be based on not only water quality problems but also surface land use patterns.

Distribution of antibiotic resistance genes in an agriculturally disturbed lake in China: Their links with microbial communities, antibiotics, and water quality.

In this study, six antibiotic resistance genes (ARGs), one mobile genetic element (int1), and their relation with microbial communities, antibiotics, and water quality were investigated in and around of an agriculturally disturbed lake, namely, Lake Honghu. The ARGs and int1 in the research area had a 100 % detection frequency in each sample during two sampling times. The ARGs were higher in the rivers and inlets than in Lake Honghu. Sul1 was the main ARG in this area. Antibiotics, nutrients, and dissolved oxygen were significantly, positively, and negatively correlated with nearly all of the ARGs, respectively. This finding suggests that reducing antibiotics and the eutrophication level could reduce the risk of ARGs. Microbial community shift had the most direct contribution to ARG variation. However, when the indirect effect was considered, environmental factors contributed 34 % to the ARGs' variance, the microbial community contributed 28 %, and their joint effect contributed 27 % to the ARG profiles. The abundance of Firmicutes, Gemmatimonadetes, Proteobacteria, etc. and their positive correlation with ARGs were significant, suggesting that these phyla probably carry ARGs. The study provides a systematic profile of ARG distribution and dissemination in a typical Chinese lake and new ideas to control this emerging contaminant in lakes.

[Status of Antibiotic Contamination and Ecological Risks Assessment of Several Typical Chinese Surface-Water Environments].

To learn about the status of antibiotic contamination and their ecological risks in Chinese surface-water environments, the risk quotient (RQ) and joint risk quotient (RQSUM) methods were applied to assess the ecological risks of five typical surface-water environments in China during the flood season. The results showed that the main types of antibiotic contamination in the five regions were sulfamethoxazole (SMX), sulfamethazine (SM), erythromycin (ETM), roxithromycin (RTM), tetracycline (TC), oxytetracycline (OTC), norfloxacin (NOR), and ofloxacin (OFL). Among eight types of antibiotic contamination, sulfamethoxazole (SMX) and erythromycin (ETM) occupied a dominant position. The contribution rate of SMX in the Yangtze River Delta and Chaohu Basin was 91.1% and 98.5%, respectively. Meanwhile, the contribution rates of ETM in Jianghan Plain, Pearl River Delta, and Yellow River Delta were 94.4%, 81.8%, and 60%, respectively. Based on the joint risk quotients (RQSUM), the order of ecological risks in the research areas was:Jianghan Plain (20.204) > Yangtze River Delta (8.769) > Chaohu Basin (2.692) > Yellow River Delta (1.943) > Pearl River Delta (1.222).

Combined toxic effects and mechanisms of microsystin-LR and copper on Vallisneria Natans (Lour.) Hara seedlings.

Microcystin-LR (MCLR) and copper are commonly found in eutrophic water bodies because of eutrophic run-offs, cyanobacterial blooms, and copper algicide applications. However, the ecotoxicological risk of their combination remains unknown. This study investigated the effect of MCLR, Cu, and their mixture on the growth and physiological responses of Vallisneria natans. Results showed that the combined toxicity of them was concentration dependent. Synergistic effects were elicited at low concentrations of MCLR and Cu exposure (≤0.25+0.64mg/L). Additive or antagonistic effects were induced at higher concentrations. Single and combined exposures could induce oxidative stress, such as increased superoxide anion radical levels. To cope with oxidative stress, V. natans could activate their antioxidant defense systems, such as enhanced superoxide dismutase production and changes in peroxidase activities. Exposure to combined MCLR and Cu (even only with 0.005+0.041mg/L) adversely affected their antioxidant defense systems. As a consequence, malondialdehyde levels significantly increased. The interaction of MCLR and Cu could also significantly increase the bioaccumulations of MCLR and Cu. This increase could be accounted for their synergistic toxic effects on V. natans. Our results suggested that the exacerbated ecological hazard of MCLR and Cu with environmental concentrations may harm aquatic ecosystems.

Occurrence and ecological hazard assessment of selected antibiotics in the surface waters in and around Lake Honghu, China.

The occurrence and temporal-spatial distributions of 13 antibiotics (tetracyclines, sulfonamides, and fluoroquinolones) in the water of a high-intensity aquaculture lake, Honghu Lake, and its associated river network and ponds were investigated. Tetracycline, oxytetracycline, chlortetracycline, and sulfadiazine are the four dominant antibiotics in this region, with maximum and median concentrations of 1454.8 and 304.8ng/L, 2796.6 and 161.9ng/L, 1431.3 and 349.9ng/L, and 499.5 and 106.5ng/L, respectively. The median concentrations of the other nine antibiotics are lower than 57.1ng/L. The highest contaminated sites are located in the Four-lake main canal and its lake inlets. Antibiotic concentrations were higher in November than in May and the concentrations were strongly correlated with water temperature, dissolved oxygen, and nitrates according to redundancy analysis. The source analysis indicated that besides untreated domestic and husbandry sewage, the aquaculture in the lake and ponds is a main source of antibiotics in the study region. The environmental hazards posed by the selected antibiotics were assessed by using the methods of hazard quotient and mixture hazard quotient. The results suggested that tetracycline, oxytetracycline, sulfadiazine, and ciprofloxacin pose medium to high ecological hazard to algae in almost all of the water samples, and the high combination ecological hazards of antibiotics are mainly posed by the high individual hazard quotient of tetracycline in the study area.

Analysis of nutrient transport and ecological response in Honghu Lake, China by using a mathematical model.

A two-dimensional (2D) water quality model was established to determine the response of water quality variables and submerged aquatic vegetation biomass to load reduction from watershed inflows and enclosure aquaculture in Honghu Lake in China. Results showed that the total nitrogen (TN) and total phosphorus (TP) loads from upstream discharge were the major external loads in the lake, accounting for 70% and 63% of the total loads, respectively. Scenario simulation results indicated that 93.2% of the lake area in summer (August) and 89.5% in autumn (November) could reach the protective targets (TN<1.0mg/L) under 50% reduction of inflow TN loads. Meanwhile, 58.7% of the lake area in summer and 63.1% in autumn could reach the protective targets (TP<0.05mg/L) under 50% reduction of aquaculture areas. The mass budget results of TN and TP showed that TP immobilisation was larger than TN immobilisation. The immobilisations for TN and TP from July to September were higher than those of other months under the combined impacts of increasing runoff during the wet period, phytoplankton bloom and water residence time. The 2D water quality model provided a relevant example for assessing the effects of runoff and aquaculture activities and served as scientific support for lake management to improve water quality in large shallow macrophytic lakes.

Effects of engineered application of Eichhornia crassipes on the benthic macroinvertebrate diversity in Lake Dianchi, an ultra-eutrophic lake in China.

An ecological engineering project with confined growth of 1.5 km(2) of Eichhornia crassipes was implemented to remove pollutants in Lake Dianchi. To assess the ecological effects of this project on benthic macroinvertebrate assemblages, a 1-year investigation at the areas inside and outside E. crassipes mats was conducted from May 2013 to May 2014. All the 10 sampling sites in the areas were grouped into two statistically significant clusters mainly corresponding to inside and outside E. crassipes mat areas (EMAs), by clustering analysis. E. crassipes reduced the densities of pollution indicator taxa (e.g., Oligochaeta and Chironomidae larvae); thus, the total densities of benthic macroinvertebrates at the area inside EMAs (mean 328.2 ind./m(2)) were slightly lower than that at the area outside EMAs (mean 505.6 ind./m(2)). Four functional feeding groups including 38 species of benthic macroinvertebrates were collected at the area inside EMAs, while only three functional feeding groups containing 17 species were collected at the area outside EMAs. The biodiversity indices (Shannon-Weiner, Margalef, Simpson, and Peilou indices) and K-dominance curves also showed higher diversity of benthic macroinvertebrates at the area inside EMAs than at the area outside EMAs. These results suggested that a certain scale of engineering application of E. crassipes was beneficial to benthic macroinvertebrate communities in the ultra-eutrophic Lake Dianchi and it could be used as a pioneer species in ultra-eutrophic lake for pollutant removal.

Effects of linear alkylbenzene sulfonate on the growth and toxin production of Microcystis aeruginosa isolated from Lake Dianchi.

The exogenous organic pollutant linear alkylbenzene sulfonate (LAS) pollution and Microcystis bloom are two common phenomena in eutrophic lakes, but the effects of LAS alone on Microcystis remain unclear. In the present study, we investigated the effects of LAS on the growth, photochemical efficiency, and microcystin production of Microcystis aeruginosa in the laboratory. Results showed that low LAS (≤10 mg/L) concentrations improved the growth of M. aeruginosa (12 days of exposure). High LAS (20 mg/L) concentrations inhibited the growth of M. aeruginosa on the first 8 days of exposure; afterward, growth progressed. After 12 days of exposure, the concentrations of chlorophyll a in algal cells were not significantly affected by any of LAS concentrations (0.05 to 20 mg/L) in the present study; by contrast, carotenoid and protein concentrations were significantly inhibited when LAS concentrations reached as high as 20 mg/L. After 6 and 12 days of exposure, low LAS (≤10 mg/L) concentrations enhanced the maximal photochemical efficiency (Fv/Fm) and the maximal electron transport rate (ETRmax) of M. aeruginosa. Furthermore, LAS increased the microcystin production of M. aeruginosa. Extracellular and intracellular microcystin contents were significantly increased after M. aeruginosa was exposed to high LAS concentrations. Our results indicated that LAS in eutrophic lakes may increase the risk of Microcystis bloom and microcystin production.