Nanhu Lake Research Articles

Characterization and genomic analysis of phage vB_SmaP_c9-N, a novel Stenotrophomonas maltophilia podophage with antibiofilm activity.

Stenotrophomonas maltophilia strains are increasingly emerging as multidrug-resistant pathogens. Moreover, S. maltophilia commonly produces biofilms that enhance antibiotic resistance in bacteria. Phages are effective alternative drugs for treating S. maltophilia infections. In this study, the lytic phage vB_SmaP_c9-N (abbreviated as Φc9-N), which is specific for S. maltophilia, was isolated from Nanhu Lake, Wuhan, China. Electron microscopy observation revealed that Φc9-N is a podophage. Φc9-N is stable over a wide pH range, from pH 4 to 10, and its activity did not change after storage at 4°C for 2months. The latency period of Φc9-N is 5 min, and its outbreak period is 35min. Antibacterial tests showed that Φc9-N could effectively inhibit the growth of S. maltophilia c24. Moreover, the biofilm production of S. maltophilia c24 decreased when Φc9-N was administered either to the forming biofilm or to the mature biofilm. These results suggest that Φc9-N has application potential in clinical treatment. The genome of Φc9-N is a dsDNA of 43,170 bp with 55 putative unidirectional genes, 18 of which were assigned putative functions, while other genes encoded hypothetical proteins. Genome sequence comparisons and phylogenetic analysis indicated that Φc9-N represents a new species, and, together with the Stenotrophomonas phages BUCT700, BUCT703, BUCT598, and vB_SmaS_P15, can be included in the newly proposed genus "Maltovirus" in the family Autographiviridae.

Benthic primary production decreases internal phosphorus loading from lake sediments under light supplement

In aquatic ecosystems, light penetrating the sediment surface in shallow lakes may regulate the internal phosphorus (P) release through benthic primary production, which subsequently affects oxidation, pH levels, and alkaline phosphatase activity in the upper sediment. To study the effects of light exposure on the P dynamics at the sediment-water interface under eutrophic conditions, a two-month mesocosm experiment was conducted in twelve cement tanks (1000 L each). The tanks were equipped with Light-Emitting Diode (LED) lights, and surface sediments collected from eutrophic Lake Nanhu (China) were exposed to four different light intensities (0, 50, 100, 200 μmol m−2 s−1). The results revealed that: 1) Both the total phosphorus concentration and the phosphorus release flux from the sediment were lower in the light treatments (mean value, 0.59–0.71 mg L−1 and 0.00–0.01 mg m−2 d−1, respectively) than in the control treatment (0.77 mg L−1 and 0.01 mg m−2 d−1, respectively), indicating that light supplement could decrease the internal P release. 2) Benthic primary production promoted by light directly absorbed soluble reactive phosphorus and decreased the internal P release. The resulting improved production could also increase dissolved oxygen concentrations at the sediment-water interface, thus indirectly inhibiting internal P release. 3) The relative contributions of direct absorption and indirect inhibition on the internal P release ranged between 23% to 69% and 31% to 77% depending on the light intensity.

Irreversible community difference between bacterioplankton generalists and specialists in response to lake dredging.

Understanding response of bacterioplankton community responsible for maintaining ecological functions of aquatic ecosystems to environmental disturbance is an important subject. However, it remains largely unclear how bacterioplankton generalists and specialists respond to dredging disturbance. Illumina MiSeq sequencing and statistical analyses were used to evaluate landscape patterns, evolutionary potentials, environmental adaptability, and community assembly processes of generalists and specialists in response to dredging in eutrophic Lake Nanhu. The Proteobacteria and Actinobacteria dominated bacterioplankton communities of generalists and specialists, and abundances of Proteobacteria decreased and Actinobacteria increased after dredging. The generalists displayed higher phylogenetic distance, richness difference, speciation rate, extinction rate, and diversification rate as well as stronger environmental adaptation than that of specialists. In contrast, the specialists rather than generalists showed higher community diversity, taxonomic distance, and species replacement as well as closer phylogenetic clustering. Stochastic processes dominated community assemblies of generalists and specialists, and stochasticity exhibited a larger effect on community assembly of generalists rather than specialists. Our results emphasized that lake dredging could change landscape patterns of bacterioplankton generalists and specialists, whereas the short-term dredging conducted within one year was unable to reverse community difference between generalists and specialists. Our findings extend our understanding of how bacterioplankton generalists and specialists responding to dredging disturbance, and these findings might in turn call on long-term dredging for better ecological restoration of eutrophic lakes.

Bacterial Community Structure and the Prediction of Metabolic Function in Landscape Lake Water in Xi'an

The study of bacterial community diversity and metabolic function in lake water is of great significance to the healthy development of the urban landscape lake water environment. In this study, Hancheng Lake, Nanhu Lake, Xingqing Lake, and Taohuatan Lake were selected as the study area. Illumina Nova high-throughput sequencing technology was used to study the composition and structure of bacterial communities in four different types of lakes. The correlation between bacterial communities and environmental factors was analyzed using the RDA method. Tax4Fun was used to predict the metabolic function of bacterial communities. The results showed that the diversity of bacterial communities was different in different lakes. The α diversity of Taohuatan Lake was the highest, and that of Xingqing Lake was the lowest. The bacterial community structure of the same lake had a trend of aggregation. The dominant phyla of bacteria in the four lakes were similar, mainly Proteobacteria, Bacteroidetes, and Actinobacteria. The difference was only in the proportion of bacteria. Additionally, the distribution of bacterial communities at the genus level in the four lakes was quite different. The physical and chemical properties of lakes were significantly correlated with bacterial community, and the most critical factor was nitrogen and phosphorus nutrients(P<0.05). Tax4Fun function prediction showed that the metabolic function of bacterial communities in the four lakes was similar, and the relative abundance of amino acid metabolism and carbohydrate metabolism was the highest. In addition, the potential drug-resistant bacterial pollution and the possibility of human infectious diseases were higher. These results are helpful for understanding the current situation of bacteria in urban lakes in Xi'an and providing a theoretical basis for the management and sustainable development of urban lakes.

Microbial communities, resistance genes, and resistome risks in urban lakes of different trophic states: Internal links and external influences

Anthropogenic discharge of nutrients, metals, and antibiotics poses multiple threats to the health of aquatic ecosystems and humans, e.g., causing eutrophication, and introduction of resistance genes into human pathogens. The potential link between microbial communities, resistance genes, and eutrophication levels in urban lakes is complex and remains unclear, which is crucial for ecological and human health risk assessment. Here, five urban lakes of different trophic conditions were investigated to quantify their microbial diversity, and high-resolution profiles of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) were established. Metagenome and multivariance analyses indicated that the microbial structures, distribution of resistance genes and mobile genetic elements (MGEs), and virulence factor genes (VFGs) significantly differed between the lakes. The hypereutrophic lake Nanhu harbored the lowest microbial diversity but the highest level of resistance genes. Microbial communities and MGEs were identified as the main drivers in shaping the profiles of ARGs and MRGs, while external environmental factors played an indirect role in the changing resistance genes. Two members of Proteobacteria, Aestuariivirga and Limnohabitans were identified as predominant bacterial hosts of ARGs in most samples. In addition, the resistome risk scores were found positively correlated with water quality factors and negatively correlated with microbial diversity in the urban lakes. Our study provides novel insights into the link between microbial diversity, MGEs, and the potential dissemination risk of ARGs in urban lakes.

One-pot hydrothermal synthesis of MoS2 modified sludge biochar for efficient removal of tetracycline from water

Efficient removal of tetracycline (TC) has become a global challenge because the unsatisfactory removal rate of traditional sewage treatment technology. A carbon-based material (MoS2@SBC) was synthesized by one-pot hydrothermal method using municipal sludge as the feedstock to remove TC from water. Characterization analysis showed that MoS2@SBC had abundant functional groups (e.g., -OH, CO, SH) and large surface area. The maximum adsorption capacity of MoS2@SBC for TC could reach 229.2 mg/g at 298 K. Elovich model and Langmuir model better fitted the kinetics and isotherms data, respectively, which illustrated that chemisorption dominated the process of TC adsorption onto MoS2@SBC. Liquid film diffusion and intraparticle diffusion simultaneously controlled the adsorption process. The thermodynamics study described that adsorption was a spontaneous, endothermic and randomness increasing process. The ionic species/strength and solution pH were the critical factors affecting the adsorption process. The kinetics, isotherms and thermodynamics analysis, together with characterization results demonstrated that π-π conjugation, H-bonding, electrostatic interaction and pore filling were the main adsorption mechanisms. Additionally, the adsorption capacity of MoS2@SBC for TC in the actual waters (Yangtze River water and Nanhu Lake water) was inhibited. Furthermore, NaOH regeneration could maintain the sustainable adsorption performance of MoS2@SBC. This study developed a promising adsorbent for TC removal and provided a resource utilization approach for sludge.

Structural Characteristics of Zooplankton and Phytoplankton Communities and Its Relationship with Environmental Factors in Different Regions of Nanhu Lake in Jiaxing City

Nanhu Lake is a red tourist attraction in Jiaxing city and the birthplace of the "Red Boat Spirit."To identify the influence of environmental factors on the distribution of plankton communities after ecological restoration in different regions, the environmental factors and plankton community in areas A, B, C, D, and S of Nanhu Lake were investigated in January 2021 after the completion of the ecological restoration projects. The concentrations of total nitrogen(TN), dissolved total nitrogen (DTN), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), total phosphorus (TP), and dissolved total phosphorus (DTP) in the ecological restoration areas were significantly lower, and the content of dissolved oxygen (DO) was significantly higher (P<0.05) than those in the non-restoration area. The main phytoplankton species in the study area belonged to Cyanophyta and Bacillariophyta, and the main zooplankton species were protozoans and rotifers. The phytoplankton biomass in the restored area was lower than that in the unrestored area, and the number of phytoplankton and zooplankton species increased. Clustering and principal coordinate analysis results showed significant differences in plankton communities among the restoration areas (P<0.05), and plankton structures in regions A and B were similar. Redundancy analysis (RDA) showed that the main environmental factors affecting the distribution of phytoplankton communities were DO, NO3--N, pH, and water temperature (WT). The main driving factors of zooplankton community distribution were DO, NO3--N, NH4+-N, and TP. The results clarified the phytoplankton community characteristics and environmental correlation in different regions of Nanhu Lake, which can provide data support and reference for water ecological restoration of the lake.

Mobilization and geochemistry of nutrients in sediment evaluated by diffusive gradients in thin films: Significance for lake management

Investigation of in-situ mobilization of both nitrogen (N) and phosphate (PO43−) in sediment is important for lake management strategy. In this paper, diffusion gradients in thin films (DGT) and DGT induced flux in sediments (DIFS) model are newly designed for in-situ measurement of iron (Fe), PO43−, nitrate (NO3–N) and ammonium (NH4–N), and nutrients’ mobility in sediment in Lake Nanhu (China). According to DGT profiles together with physicochemical properties in sediment, (I) PO43− is released from (i) Fe-bound P plus loosely sorbed P in anoxic sediment and (ii) the loosely sorbed P in oxic sediment; (II) anoxic sediment inhibits nitrification and NO3–N release, but it favors denitrification and dissimilatory nitrate reduction to ammonium (DNRA), leading to NH4–N release; (III) Eh and organic matter are two key influence factors on mobility of PO43−, NO3–N and NH4–N. According to DIFS calculation, the dynamics of desorption and diffusion at two sites belong to (i) slow rate of resupply and (ii) fast resupply cases, respectively. Internal loadings are estimated to be 92.74 (PO43−), 268.1 (NH4–N) and −2466 kg a−1 (NO3–N), which reflects sediment mainly acts as a source for PO43− and NH4–N, and a sink for NO3–N in water. Based on sediment P release risk index (SPRRI), P release risks in lake sediments are estimated, ranging from light to relative high level. DGT and SPRRI aid choice of restoration methods for sediment, including sediment dredging, phytoremediation and in-situ inactivation.

Food Web Responses to a Cyanobacterial Bloom in a Freshwater Eutrophic Lake

The microbial food web is an important part in aquatic ecosystem, but studies on the microbial food web in freshwater ecosystem, especially in freshwater eutrophic lakes, still need further investigation. In the present study, using eutrophic Lake Nanhu as model, the community changes of phytoplankton, zooplankton, and bacteria between the bloom and non-bloom period were analyzed, and microzooplankton grazing experiments were also conducted to measure the grazing pressure and selectivity of microzooplankton on phytoplankton community. Phytoplankton community in Lake Nanhu was mainly dominated by Cyanophyta (49.44%), especially Anabaena circinalis and Microcystis flos-aquae, during bloom period. Rotifers were the main components of zooplankton in Lake Nanhu (44.15%), Brachionus calyciflorus and Moina macrocopa were the most dominant zooplankton in the non-bloom and bloom period, respectively. Bacteroidetes showed significantly higher mean proportion in bloom period than that in non-bloom period (p &lt; 0.001). The growth rates of phytoplankton ranged from −1.00 d−1 to 1.29 d−1, while grazing rates of microzooplankton ranged from −1.15 d−1 to 1.05 d−1. Results indicated that microzooplankton could respond quickly to the increase of phytoplankton during bloom period. Meanwhile, microzooplankton showed grazing preference on Cyanophyta and Cryptophyta during bloom period and non-bloom period, respectively. The microzooplankton grazing selectivity during bloom period might depend on phytoplankton community composition.

Experimental Study of Population Variations on the Morphology and Reproduction of &amp;lt;i&amp;gt;Daphnia galeata&amp;lt;/i&amp;gt; from Three Chinese Lakes

Environmental heterogeneity affected the genetic differentiation and phenotypic plasticity of Daphnia spp. populations in different lakes. However, the effect mechanism of lake population on the morphology and reproduction of Daphnia spp. was still unclear. This paper studied the differences of the morphology and reproduction of D. galeata populations from three Chinese lakes (CH: Lake Chaohu, NH: Lake Nanhu, EH: Lake Erhai), which the area size, nutrient levels, phytoplankton biomass and dominant fish were obviously various in the three lakes. The results showed that lake population affected significantly the morphology (helmet length and tail spine length) and reproduction (no. offspring at first reproduction per female-1) of D. galeata. Both helmet lengths and tail spine lengths of three D. galeata populations increased quickly within the first five instars, and afterwards showed various patterns. Multiple comparisons indicated that helmet lengths of NH population were significantly higher than those in EH and CH populations (P<0.001) whereas tail spine lengths of NH population were significantly smaller than those in EH (P=0.001) and CH (P=0.003) populations. The ratio of relative helmet length of CH population was significantly shorter than those of EH population (P<0.001) and NH population (P<0.001), and the ratio of relative tail spine length at first pregnancy of EH population was significantly longer than those of CH population (P<0.001) and NH population (P<0.001). Moreover, there is four juvenile instars in EH population whereas there are three juvenile instars in CH and NH populations. With the increase of adult instars, the number of offspring produced by D. galeata in all three populations displayed a similar pattern, which increased quickly at first, and then gradually decreased. Average maximum number of offspring at first reproduction (6.3±1.4 ind. per female-1) appeared in CH population, followed by EH (5.2±1.7 ind. per female-1) and NH (4.9±1.4 ind.•per female-1) populations. The innate rate of increase of CH population was relatively higher than those of EH and NH populations, but no significant differences among three populations were observed. Our results suggested that environmental heterogeneity could affect the reproduction and morphological plasticity of Daphnia spp. in different lakes.

Stronger environmental adaptation of rare rather than abundant bacterioplankton in response to dredging in eutrophic Lake Nanhu (Wuhan, China)

Deciphering responses of rare versus abundant bacterioplankton to environmental change, crucial for understanding and mitigating of cyanobacterial blooms, is an important but poorly investigated subject. Using MiSeq sequencing, we investigated the taxonomic and phylogenetic diversity of rare and abundant bacterioplankton in eutrophic Lake Nanhu before and after dredging. We estimated environmental breadths and phylogenetic signals of ecological preferences of rare and abundant bacterioplankton, and investigated community function and bacterioplankton assembly processes. Both taxonomic and phylogenic distances of rare and abundant bacterioplankton communities were significantly positively correlated with the dissimilarity of environmental factors. Threshold indicator taxa analysis and Blomberg's K statistic indicated that rare taxa held broader environmental thresholds and stronger phylogenetic signals for ecological traits than abundant taxa. Environmental adaptations of both rare and abundant taxa exhibited distinct changes after dredging. Higher functional redundancy occurred in the abundant compared to the rare bacterioplankton, with functions of rare bacterioplankton decreasing and for the abundant ones increasing after dredging. The null model revealed that dispersal limitation belonging to stochastic processes determined the abundant bacterioplankton community assembly, whereas variable selection belonging to deterministic processes drove the rare one. Rare bacterioplankton was more environmentally constrained than the abundant one. Dissolved oxygen was the decisive factor in determining the balance between stochasticity and determinism in both rare and abundant bacterioplankton. Our study extends our knowledge of environmental adaptation of rare versus abundant bacterioplankton to massive disturbing measures, i.e. dredging, and allows to estimate dredging performance for mitigating cyanobacterial blooms from a molecular ecology viewpoint.

The Influence of Human Interference on Zooplankton and Fungal Diversity in Poyang Lake Watershed in China

The Poyang water system in Jiangxi Province, China, is important for floodwater storage, diversity maintenance, and the economy of the Poyang Lake watershed. In recent years, pollution has destroyed the ecosystem and impacted human health and the related economy. The water quality of the Poyang Lake watershed and the impact of human interference must be assessed. Conventional analysis and high-throughput sequencing were used to evaluate the structure of both zooplankton and fungi in six sub-lakes of the Poyang Lake watershed under different anthropogenic influences. The sub-lakes included were Dahuchi Lake (in natural preserve, DHC), Shahu Lake (in natural reserve, SH), Nanhu Lake (out of natural preserve, NH), Zhelinhu Lake (artificial reservoir, ZLH), Sixiahu Lake (agricultural lake artificially isolated from Poyang Lake, SXH), and Qianhu Lake (urban lake, QH). The densities and biomass of the zooplankton in DHC, SH, NH were higher compared with those in SXH, ZLH and QH (p &lt; 0.05). Zooplankton distribution of SXH was the most strongly associated with total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chl a), while QH was highly associated with pH, conductivity (Cond), and water temperature (WT). For fungal diversity, a large number of beneficial fungi, Basidiomycota (phylum level) and Massarina (genus level) were obtained from DHC (55.3% and 27.5%, respectively), SH (54.4% and 28.9%, respectively), and NH (48.6% and 1.4%, respectively), while a large number of pathogenic Chytridiomycota (at phylum level) were identified from SXH (21.0%), ZLH (5.5%), and QH (7.5%). Manmade pollutants have impacted the natural hydrology and water quality and promoted variation between the zooplankton and fungi in the six sub-lakes, reducing the relative abundance of beneficial fungi and increasing the number of pathogens in the environment, which threatens human health and economic production. Understanding the diversity among the zooplankton and fungi in the six sub-lakes of the Poyang Lake watershed may help guide future water management practices.

Characterization of Microplastic Pollution of Sediments from Urban Lakes

In recent years, microplastics (MPs) in the environment has become a topic of increasing concern. In this study, typical urban lakes, such as Yushan Lake and Nanhu Lake in Maanshan City, were selected to study the physical morphology and spatial distribution characteristics of MPs in sediments in spring and summer and to explore the sources of MPs in the lakes. On average, MPs in sediments occurred with a content of (0.0284±0.0597) g·kg-1 and abundance of (278.9±529.1) n·kg-1 in spring, and (0.0317±0.0778) g·kg-1 and (277.1±395.6) n·kg-1 in summer, respectively. Using a paired sample T-test, it was found that there was no significant correlation difference between the content (N=22, t=-0.269, P=0.791) and the abundance (N=22, t=0.035, P=0.973) of MPs in the spring and summer sediments. Regarding shape, the MPs in the sediments in the study area were divided into three types:fiber, film, and particle, accounting for 52.9%, 28.9%, and 18.2%, respectively. Size-fraction analysis indicated MPs<1 mm made up the majority, accounting for 83.9% of the total number. It was found that the MPs were mainly polyethylene (PE) and polypropylene (PP) polymers with seriously weathered surfaces. The sediments, which were adjacent either to land with a large stream of people and vehicles or to areas with frequent watersports, had notably high abundance of MPs, revealing the close correlation between the spatial distribution of MPs in lake sediments and human activities. It is thought that atmospheric precipitation (fiber), stormwater, washing of clothes (fiber), degradation of large plastics in the lake, and fishing activities (fishing nets, foam) are the main sources of MPs in lake sediments.

Dredging mitigates cyanobacterial bloom in eutrophic Lake Nanhu: Shifts in associations between the bacterioplankton community and sediment biogeochemistry

Cyanobacterial blooms are a worldwide environmental problem, which is partly attributed to their access to excessive nitrogen (N) and phosphorus (P). Preventing the blooms by reducing N and P from internal inputs is viewed as a challenge. To evaluate the effects of dredging on cyanobacterial abundances and bacterioplankton communities, water and sediment samples were collected from eutrophic Lake Nanhu (Wuhan, China) before dredging (2017) and after dredging (2018). After dredging, significant decreases were observed for sediment nutrients (e.g., C, N, and P sources); C-, N-, P-, and S-cycling-related enzyme activity; N- and P-cycling-related gene abundance; microbial abundance; and dramatic changes were observed in the composition of the sediment microbial community. The release rates of nutrient including nitrogen, phosphorus, and organic matter decreased after dredging, and sediment biogeochemistry was closely correlated to nutrient release rates. Additionally, our observations and analyses indicated that the abundance and diversity of the bacterioplankton community decreased significantly, the composition and interaction of the bacterioplankton community dramatically changed, and the bacterioplankton community function (e.g., N, P-cycling-related enzymes and proteins) down regulated after dredging. Water and sediment physicochemical factors explained 72.28% variation in bacterioplankton community composition, and these physicochemical factors were significantly correlated with diversity, composition, and function of bacterioplankton community. Our findings emphasized that cyanobacterial blooms in freshwater ecosystems were closely correlated with noncyanobacterial bacterioplankton that were largely conserved at the phylum level, with Proteobacteria, Actinobacteria, and Bacteroidetes as the main taxa. To our knowledge, this is the first report clarifying the mechanism of cyanobacterial blooms mitigation by dredging, via changing the association between the bacterioplankton community and sediment biogeochemistry. Our findings are of significance and indicate that dredging is effective for mitigating cyanobacterial blooms.

Succession of sulfur bacteria during decomposition of cyanobacterial bloom biomass in the shallow Lake Nanhu: An ex situ mesocosm study

Previous studies of the dynamics of sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) have focused on deep stratified lakes. The objective of this study is to present an in-depth investigation of the structure and dynamics of sulfur bacteria (including SRB and SOB) in the water column of shallow freshwater lakes. A cyanobacterial bloom biomass (CBB)-amended mesocosm experiment was conducted in this study, in which water was taken from a shallow eutrophic lake with sulfate levels near 40 mg L−1. Illumina sequencing was used to investigate SRB and SOB species involved in CBB decomposition and the effects of the increases in sulfate input on the water column microbial community structure. The accumulation of dissolved sulfide (∑H2S) produced by SRB during CBB decomposition stimulated the growth of SOB, and ∑H2S was then oxidized back to sulfate by SOB in the water column. Chlorobaculum sequences (the main SOB species in the study) were significantly influenced by increases in sulfate input, with relative abundance increasing approximately four-fold in treatments amended with 40 mg L−1 sulfate (referred to as 40S) when compared to the treatment without additional sulfate addition (referred to as CU). Additionally, an increase in SOB number was observed from day 26–37, concurrent with the decrease in SRB number, indicating the succession of sulfur bacteria. These findings suggest that biological sulfur oxidation and succession of sulfur bacteria occur in the water column during CBB decomposition in shallow freshwater ecosystems, and the increases in sulfate input stimulate microbial sulfur oxidation.

Vallisneria natans decomposition rates and associated macroinvertebrates, microbes and microalgae along a vertical depth gradient in an urban lake (Nanhu Lake, China)

ABSTRACTKnowledge on aquatic macrophyte decomposition has well developed, yet the decomposition and associated biotic factors along a vertical gradient in waters remain less examined. Here, we used Vallianeria natans leaves to investigate the decomposition rate and associated decomposers and microalgae at different vertical depths, by placing V. natans leaves into litterbags (0.5 and 5 mm meshes) and incubating them at the air–water interface (AW), sediment-water (SW) interface, and 10 cm (B10) or 20 cm (B20) burial in sediment over 60 days in a littoral zone of lake. Decomposition rates decreased with increased depths in each mesh size, with significant differences among and between AW (0.028 d−1), SW (0.022 d−1), B10 (0.014 d−1) and B20 (0.011 d−1) treatments in 0.5 mm litterbags and no significant difference between B10 (0.027 d−1) and B20 (0.025 d−1) in 5 mm litterbags. The average contribution of macroinvertebrates to biomass loss was highest in B20 (44.66%), lowest in AW (22.66%) and midst in both SW (25.35%) and B10 (38.78%), and was much less than that of both microbes and microalgae at each location. We show the importance of macroinvertebrates, microbes and microalgae in mediating macrophyte decomposition rate in response to different vertical locations in freshwaters.

Responses of decomposition rate and nutrient release of floating-leaved and submerged aquatic macrophytes to vertical locations in an urban lake (Nanhu Lake, China)

ABSTRACTA leaf-bag field experiment was conducted to investigate the decomposition and release of nutrients from leaves of two aquatic macrophytes (floating-leaved Trapa bispinosa and submerged Vallisneria natans) deposited in the four vertical locations (i.e. air-water interface, AW; sediment-water interface, SW; buried at a depth of 10 cm, B10; buried at a depth of 20 cm, B20) of littoral zone in Nanhu Lake, China, for 60 days from July to August 2015. Leaf initial quality significantly influenced mass loss and nutrient release except TN (total nitrogen) remaining. Compared to V. natans, T. bispinosa leaves decomposed faster under the same treatments. The decomposition was greatly affected by both leaf chemical quality and the location of deposition. With the increasing depth of vertical locations, leaf biomass loss and nutrient release of both T. bispinosa and V. natans decreased. In addition, initial N:P ratio and cellulose were the major determinants for decomposition in AW and SW treatments while total phenol in B10 and B20. Our results suggest that the combined effect of leaf chemical quality and burial could mediate macrophyte mass loss and release of nutrients and carbon, which in turn can influence organic matter accumulation and nutrient cycling in shallow freshwater lakes.

Effects of macrophyte cultivation on community structure of rotifer in small lakes.

To understand the effects of macrophyte growth on water environment and rotifer community structure, monthly survey lasted for one year from October 2015 to September 2016 was conducted in Lake Minghu and Lake Nanhu at Jinan University in Guangzhou. There was no macrophyte cultivation in Lake Minghu. A kind of macrophyte Hydrilla verticillata grows from March-October in Lake Nanhu and grows vigorously in June-September. In this study, 50 species belonging to 23 gene-ra of rotifer, were recorded in the two lakes. 32 species were found in Lake Minghu and 39 species in Lake Nanhu, respectively. The dominant species in Lake Minghu were Polyarthra vulgaris, Trichocerca pusilla and Liliferotrocha subtilis. The dominant species in Lake Nanhu were Keratella cochlearis, Colurella adriatica and Lecane (Monostyla) bulla. The highest abundance of rotifers in Lake Minghu was at 3790 ind·L-1 in October 2015, and the lowest at 854 ind·L-1 in March 2016. The highest abundance of rotifers in Lake Nanhu was at 3555 ind·L-1 in November 2015, and the lowest at 977 ind·L-1 in January 2016. Results from the ANOSIM (one-way) test revealed that the community structure of rotifers was significantly different between Lake Minghu and Lake Nanhu. The largest contribution rate of the difference between the two lakes was made by Keratella cochlearis and Polyarthra vulgaris. RDA analysis showed that total phosphorus, chlorophyll a, and water temperature had significant impacts on the community structure of rotifer in Lake Minghu. During the period with luxuriant macrophyte in Lake Nanhu, the rotifer community structure was most influenced by total phosphorus, water temperature, chlorophyll a and water depth, dominated by benthic species Squatinella mutica, Colurella adriatica and Lecane bulla. During the period with sparse macrophyte, the community was mainly influenced by total nitrogen and transparency, dominanted by planktonic species Polyarthra vulgaris and Trichocerca similis. During the period with no macrophyte, communities were mainly influenced by pH and dissolved oxygen, and also dominated by planktonic ones Polyarthra vulgaris and Anuraeopsis fissa. Macrophyte could effectively absorb nutrients in water, inhibit growth of phytoplankton, improve water quality, increase spatial heterogeneity, support more species of rotifer, and maintain a stable aquatic ecosystem.

Effects of micro-, meio- and macroinvertebrates associated with burial on the decomposition of an aquatic macrophyte (Vallisneria natans) in a eutrophic shallow lake in China

Aquatic invertebrates play an important role in plant decomposition. However, little information is available regarding the relative importance of micro-, meio- and macroinvertebrates in this process, particularly their role in the decomposition of buried organic matter. To investigate the role of these invertebrates in the decomposition of the aquatic macrophyte Vallisneria natans, leaves of V. natans were placed in litterbags with four different mesh sizes (0.025, 0.042, 0.5 and 5mm) and the bags were either incubated at the sediment–water (SW) interface or buried at a depth of 10cm (B10) for 60 days in Lake Nanhu, China, in July 2015. Increased mesh size significantly increased the loss of plant mass. The decomposition rate ranged from 0.0173 to 0.0467day–1 in the SW treatment, and from 0.0083 to 0.0280day–1 in the B10 treatment. Excluding microinvertebrates, burial significantly affected microbial respiration and invertebrate abundance. Increased mesh size increased invertebrate abundance and richness, but did not significantly affect microbial respiration in either treatment. The average contribution of micro-, meio- and macroinvertebrates and microbes to plant mass loss in the SW treatment was 23.1, 13.5, 7.0 and 56.5% respectively, compared with 19.7, 24.5, 12.3 and 43.5% respectively in the B10 treatment. The results of this study reveal the important but underestimated role of micro- and meioinvertebrates in macrophyte decomposition.

Antibiotic resistance genes in surface water of eutrophic urban lakes are related to heavy metals, antibiotics, lake morphology and anthropic impact.

Urban lakes are impacted by heavy human activities and represent potential reservoirs for antibiotic resistance genes. In this study, six urban lakes in Wuhan, central China were selected to analyze the distribution of sulfonamide resistance (sul) genes, tetracycline resistance (tet) genes and quinolone resistance (qnr) genes and their relationship with heavy metals, antibiotics, lake morphology and anthropic impact. sul1 and sul2 were detected in all six lakes and dominated the types of antibiotic resistance genes, which accounted for 86.28-97.79% of the total antibiotic resistance gene abundance. For eight tested tet genes, antibiotic efflux pumps (tetA, tetB, tetC, and tetG) genes were all observed in six lakes and had higher relative abundance than ribosomal protection protein genes (tetM and tetQ). For 4 plasmid mediated quinolone resistance genes, only qnrD is found in all six lakes. The class I integron (intI1) is also found to be a very important media for antibiotic resistance gene propagation in urban lakes. The results of redundancy analysis and variation partitioning analysis showed that antibiotic and co-selection with heavy metals were the major factors driving the propagation of antibiotic resistance genes in six urban lakes. The heavily eutrophic Nanhu Lake and Shahu Lake which located in a high density building area with heavy human activities had the higher relative abundance of total antibiotic resistance genes. Our study could provide a useful reference for antibiotic resistance gene abundance in urban lakes with high anthropic impact.