Oxidative stress responses of submerged macrophyte Vallisneria asiatica to different concentrations of cyanobacteria

In a 10-day aquarium experiment,this investigation examines macrophyte restoration in eutrophic Lake Taihu,the physiological effects of different plant biomass levels and of increasing natural cyanobacterial concentrations on a submerged macrophyte,Vallisneria asiatica. Cyanobacterial stress suppressed the superoxide dismutase(SOD) activity of the plant's leaves and induced the catalase(CAT) and peroxidase(POD) activities of its roots. The soluble protein content in V. asiatica decreased with an increase in natural cyanobacterial concentrations,whereas the malonaldehyde(MDA) increased significantly at chlorophylla(Chl a) concentrations of 222 and 262 μg/L in water. V. asiatica adapted to the stress caused by cyanobacterial concentrations by adjusting its antioxidant defense system to remove the excessive reactive oxygen species when the algal Chl a concentration was 109 μg/L. Additionally,high biomass of V. asiatica(2 222 g FW/m 2) can inhibit the reproduction of cyanobacteria more significantly than low biomass(1 111 g FW/m2). High biomass of V. asiatica increased the oxidative stress in an individual plant when the initial Chl a concentration in the water reached 222 and 262 μg/L,as expressed by the increased MDA in leaves,compared with low biomass of V. asiatica. This provides a basis for controlling cyanobacterial concentrations and V. asiatica biomass for the recovery of V. asiatica in eutrophic Lake Taihu.     

STUDY OF THE ECOLOGICAL RESTORATION OF AQUATIC MACROPHYTES IN A EUTROPHIC SHALLOW LAKE

mooUonONEutrophicationhasdri,andwillperhapsbethemostwidespreadtypeofenviron-rnentalpollutionofwaterbodis.MostUrbanorsuburbanshallowwaterbodishaveex-perientaladetalrnan-causedeutrophhationinevitablyresultinginovergroWthofphytoplanktonandotherdramaticlakeeresySteInchangessuchasthedeCineofmacrophytes.TheensuingdeteriorationofwaterqualitycaedseriousenvirorunentalanderenoAncprobbo,bousemostoftheselakes,asidefrombeingwatefbodiesforlargescalecoInmendalfisheryusuallysupplywaterforindustryandagrict…     

Seasonal dynamics of crustacean zooplankton community structure in Erhai Lake,a plateau lake,with reference to phytoplankton and environmental factors

The seasonal dynamics of a crustacean zooplankton community in Erhai Lake was investigated from May 2010 to April 2011. In total, 11 species were recorded, including six （6 genera） cladoceran and five （5 genera） copepod species. The crustacean zooplankton densities ranged from 24.3 to 155.4 ind./L. In winter and spring, the large-bodied cladoceran Daphnia galeata dominated the crustacean plankton community. In summer and autumn, when the colonial or filamentous algae dominated the phytoplankton communities, the small-bodied species （e.g. Bosminafatalis, Ceriodaphnia quadrangular, and Mesocyclops leuckarti） replaced the large-bodied ones. One-way ANOVA and redundancy analysis revealed that community structure was dependent upon total nitrogen, total phosphorus, water temperature, transparency, and the biomass of small algae. The variation in both phytoplankton structure and environmental variables were important factors in the seasonal succession of crustacean zooplankton structure in Erhai Lake.     

The lining responses for shallow mountain tunnels subjected to frost heaving

Mountain tunnels in cold regions are vulnerable to adverse effects of freezing action.Thus,it is necessary to identify the lining responses of shallow mountain ...     

ENERGY FLOW OF BELIAMYA AERUGINOSA IN A SHALLOW ALGAL LAKE, HOUHU LAKE （WUHAN, CHINA）

The energy budget ofBellamya earuginosa in a shallow algal lake, Houhu Lake (Wuhan, China) was investigated by the measurement of flesh production (32.8 kJ/(m²·a)), egestion (337.7 kJ/(m²·a)), metabolism (246.7 kJ/(m²·a)), and estimation of excretion (21.4kJ/(m²·a)). The net growth efficiency of the species is about 10.9%, which accords with the generally reported value for gastropods. In addition, the relationships between starvation respiration (R, mgO₂/(Ind·d)), body weight (Wd, mg in dry wt) and temperature (T, °C) were also determined. The regression equationR=0.044Wd ^0.537 e ^0.061T was obtained by the least square method, The measured SDA of the species is 26.51% of its gross metabolism. Project No. 3960019 and 39430101 supported by NSFC and also a granted for the East Lake Ecological Experimental Station, CAS, Wuhan.     

Energy flow in Branchiura sowerbyi （Oligochaeta： tubificidae） in a shallow macrophyte-dominated lake, Biandantang Lake

The energy flow of Branchiura sowerbyi was studied for the first time in China in a shallow macrophytic lake, Biandantang Lake, Hubei Province. The energy flow was calculated from the measurement of flesh production (12.5241kJ/m^2a), egestion (517.7302kJ/m^2a), metabolism (38.3273 kJ/m^2a), and excretion (4.3798kJ/m^2a). The net growth efficiency of the species is about 22.7%, which accords well with the generally reported value for oligochaetes. In addition, the relationship between starvation respiration (R, mgO2/ind‘d), wet weight (Ww, mg) and temperature (T, ℃) were also measured, with the regression function being R=0.008 Ww^0.736 e^0.050T.     

Two new species of Sellaphora (Bacillariophyta) from a deep oligotrophic plateau lake, Lake Fuxian in subtropical China

We describe two new species of Sellaphora from Lake Fuxian, Yunnan Plateau, China. Based on both light and scanning electron microscopy, these species are described as S. yunnanensis sp. nov. and S. sinensis sp. nov. The primary features of S. yunnanensis are: elliptical to linear-elliptical valves with broadly rounded ends, straight filiform raphe, almost straight central endings and small, slightly expanding central pores, small central area, symmetrical or slightly asymmetrical central nodule. The primary features of S. sinensis are: elliptical valves, obtusely rounded ends, similar raphe and axial area, transapically less expanded central area, larger, elliptical central nodule. We compare these species to those of a similar shape and morphology.     

Contrasting patterns of free-living bacterioplankton diversity in macrophyte-dominated versus phytoplankton blooming regimes in Dianchi Lake,a shallow lake in China

Freshwater shallow lakes typically exhibit two alternative stable states under certain nutrient loadings:macrophyte-dominated and phytoplankton-dominated water regimes.An ecosystem regime shift from macrophytes to phytoplankton blooming typically reduces the number of species of invertebrates and fishes and results in the homogenization of communities in freshwater lakes.We investigated how microbial biodiversity has responded to a shift of the ecosystem regime in Dianchi Lake,which was previously fully covered with submerged macrophytes but currently harbors both ecological states.We observed marked divergence in the diversity and community composition of bacterioplankton between the two regimes.Although species richness,estimated as the number of operational taxonomic units and phylogenetic diversity(PD),was higher in the phytoplankton dominated ecosystem after this shift,the dissimilarity of bacterioplankton community across space decreased.This decrease in beta diversity was accompanied by loss of planktonic bacteria unique to the macrophyte-dominated ecosystem.Mantel tests between bacterioplankton community distances and Euclidian distance of environmental parameters indicated that this reduced bacterial community differentiation primarily reflected the loss of environmental niches,particularly in the macrophyte regime.The loss of this small-scale heterogeneity in bacterial communities should be considered when assessing long-term biodiversity changes in response to ecosystem regime conversions in freshwater lakes.     

Energy flow in Branchiura sowerbyi (Oligochaeta: tubificidae) in a shallow macrophyte-dominated lake, Biandantang Lake

The energy flow ofBranchiura sowerbyi was studied for the first time in China in a shallow macrophytic lake, Biandantang Lake, Hubei Province. The energy flow was calculated from the measurement of flesh production (12.5241kJ/m²a), egestion (517.7302kJ/m²a), metabolism (38.3273 kJ/m²a), and excretion (4.3798kJ/m²a). The net growth efficiency of the species is about 22.7%, which accords well with the generally reported value for oligochaetes. In addition, the relationship between starvation respiration (R, mgO₂/ind·d), wet weight (Ww, mg) and temperature (T, °C) were also measured, with the regression function beingR=0.008Ww^0.736 e^0.050T. Project supported by NSFC (30270278, 3960019), the foundation of the government of Hubei Province (No. 2000J109), and the foundation of Ecological Station, CAS in the Institute of Hydrobiology.     

Spatial distribution and abundance of small fishes in Xiaosihai Lake, a shallow lake along the Changjiang(Yangtze) River, China

Spatial distribution and abundance of small fishes were studied in autumn 2007 in the Xiaosihai Lake, a shallow lake along the middle reach of the Changjiang (Yangtze) River. Based on the plant cover, the lake was divided into three major habitats: Myriophyllum spicatum habitat (MS habitat), Trapa bispinosa habitat (TB habitat), and non-vegetation habitat (NV habitat). A modified pop-net was used for quantitative sampling of small fishes in the three habitats, and the Zippin’s removal method was used for estimating densities of the small fishes. A total of 13 species belonging to 5 families were collected, with 11 species in MS habitat, 7 species in TB habitat, and 5 species in NV habitat. Habitat type had significant effect on the spatial distribution of small fishes. The Shannon-Wiener diversity index in the MS, TB and NV habitats were 1.28, 0.56 and 0.54, respectively. The total density and biomass of small fishes were significantly higher in the MS habitat (13.68 ind/m2 and 4.44 g/m2) than in the TB habitat (1.41 ind/m2 and 0.54 g/m2) and the NV habitat (1.08 ind/m2 and 0.40 g/m2), and were not significantly different between the TB habitat and the NV habitat. Water depth had no significant effect on spatial distribution of the small fishes. It was suggested that vegetation type played an important role in habitat selectivity of small fishes, and the presence of submersed vegetation should be of significance in the conservation of small fish diversity.     

A comparison between benthic gillnet and bottom trawl for assessing fish assemblages in a shallow eutrophic lake near the Changjiang River estuary

Two fishing methods including gillnetting and trawling to estimate attributes of fish assemblage were compared in Dianshan Lake from August 2009 to July 2010. Species composition dif fered significantly between the gears, with four significant contributors in gillnet catches and one in trawl catches. Trawling collected more proportions of benthic species by number and biomass than gillnetting. Size distribution was significantly influenced by fishing technique; gillnetting captured relatively less small-sized fishes and trawling captured less large-sized individuals. Trawling produced species richness closer to the one expected than gillnetting. On the whole, trawl catch was a quadratic polynomial function of gillnet catch and a significantly negative correlation was found between them, both of which varied as dif ferent polynomial functions of temperature. However, trawl and gillnet catches were significantly correlated only in one of five month groups. It is concluded that single-gear-based surveys can be misleading in assessments of attributes of fish assemblages, bottom trawling is a more ef fective gear for assessing fish diversity than benthic gillnetting, and using gillnet catches as an indicator of fish density depends on fishing season in the lake.     

Spatial distribution and abundance of small fishes in Xiaosihai Lake, a shallow lake along the Changjiang (Yangtze) River, China

Spatial distribution and abundance of small fishes were studied in autumn 2007 in the Xiaosihai Lake, a shallow lake along the middle reach of the Changjiang (Yangtze) River. Based on the plant cover, the lake was divided into three major habitats: Myriophyllum spicatum habitat (MS habitat), Trapa bispinosa habitat (TB habitat), and non-vegetation habitat (NV habitat). A modified pop-net was used for quantitative sampling of small fishes in the three habitats, and the Zippin’s removal method was used for estimating densities of the small fishes. A total of 13 species belonging to 5 families were collected, with 11 species in MS habitat, 7 species in TB habitat, and 5 species in NV habitat. Habitat type had significant effect on the spatial distribution of small fishes. The Shannon-Wiener diversity index in the MS, TB and NV habitats were 1.28, 0.56 and 0.54, respectively. The total density and biomass of small fishes were significantly higher in the MS habitat (13.68 ind/m² and 4.44 g/m²) than in the TB habitat (1.41 ind/m² and 0.54 g/m²) and the NV habitat (1.08 ind/m² and 0.40 g/m²), and were not significantly different between the TB habitat and the NV habitat. Water depth had no significant effect on spatial distribution of the small fishes. It was suggested that vegetation type played an important role in habitat selectivity of small fishes, and the presence of submersed vegetation should be of significance in the conservation of small fish diversity.     

Stocks and dynamics of particulate and dissolved organic matter in a large,shallow eutrophic lake(Taihu,China) with dense cyanobacterial blooms

Cyanobacterial blooms occur in eutrophic lakes worldwide, and greatly impair these ecosystems. To explore influences of cyanobacterial blooms on dynamics of both particulate organic matter(POM) and dissolved organic matter(DOM), which are at the base of the food chain, an investigation was conducted from December 2014 to November 2015 that included various stages of the seasonal cyanobacterial blooms(dominated by M icrocystis) in a large-shallow eutrophic Chinese lake(Taihu Lake). Data from eight sites of the lake are compiled into a representative seasonal cycle to assess general patterns of POM and DOM dynamics. Compared to December, 5-fold and 3.5-fold increases were observed in July for particulate organic carbon(POC, 3.05–15.37 mg/L) and dissolved organic carbon(DOC, 5.48–19.25 mg/L), respectively, with chlorophyll a(Chl a) concentrations varying from 8.2 to 97.7 μg/L. Approximately 40% to 76% of total organic carbon was partitioned into DOC. All C, N, and P in POM and DOC were significantly correlated with Chl a. POC:Chl a ratios were low, whereas proportions of the estimated phytoplankton-derived organic matter in total POM were high during bloom seasons. These results suggested that contributions of cyanobacterial blooms to POM and DOC varied seasonally. Seasonal average C:P ratios in POM and DOM varied from 79 to 187 and 299 to 2 175, respectively. Both peaked in July and then sharply decreased. Redundancy analysis revealed that Chl a explained most of the variations of C:N:P ratios in POM, whereas temperature was the most explanatory factor for DOM. These findings suggest that dense cyanobacterial blooms caused both C-rich POM and DOM, thereby providing clues for understanding their influence on ecosystems.     

Efficiency of phosphorus accumulation by plankton,periphyton developed on submerged artificial substrata and metaphyton: in-situ observation in two shallow ponds

Phosphorus overenrichment of shallow ponds prevailing in wetlands leads to their eutrophication causing the collapse of those vulnerable habitats. The potential of phosphorus accumulation by periphyton developed on artificial substrata has been investigated in two shallow ponds(Bara?ka and ?iroki Rit) in northwest Serbia and compared to the same ability of plankton and metaphyton. The periphyton substrate carrier has been submerged from May to October. Both continuously(CS) and monthly developed(MS) periphyton were sampled. Autotrophic component of all investigated communities has been qualitatively assessed. Maximum accumulation of only 14.7 mg TP/m~2 was recorded in three-month exposed periphyton CS. MS exposed from July to August reached maximal 12.7 mg TP/m~2. Plankton community that was characterized by more diverse and abundantly developed algal component was more effective in phosphorus accumulation(0.7 mg/g dry weight) in comparison with dominantly inorganic and diatom-dominated periphyton in Bara?ka. Unstable conditions caused by recent revitalization(dredging organic matter and mud from pond basin—redigging) as well as rapid desiccation of ?iroki Rit disabled making an unambiguous conclusion about the efficiency of phosphorus accumulation among different communities, but suggested slight potential of phosphorus harvesting by metaphyton in this pond. Due to the shorter exposure time that brings the reduced risk of unpredictable changes in the ecosystem, as well as the considerable amount of accumulated phosphorus, large-scale application of one-month exposed periphyton developed on artificial substrates would be more advisable for phosphorus harvesting in nutrient affected shallow ponds.     

Periphyton response to nitrogen and phosphorus enrichment in a eutrophic shallow aquatic ecosystem

We examined changes in biomass and species dominance of periphyton in response to nitrogen (N) and phosphorus (P) enrichment in 12 mesocosms representing eutrophic aquatic ecosystems. The 100-L mesocosms consisted of lake water and pond sediment, and N and P were applied weekly. Periphyton samples were taken to assess the biomass (as estimated by the concentration of chlorophyll a (chl a)) and to determine which species were dominant. The mean periphyton biomass (chl a) in the P-enriched treatment did not differ from that in the control group, but increased with N enrichment. Compared with that in the control group, the chl a concentration increased with N+P enrichment in the early stages of the experiment, but decreased in the later stages. The decline in periphyton biomass at the later stages of the experiment was due to limited light availability, which resulted from the increased phytoplankton density in the experiment. The nutrient enrichment treatments resulted in changes in the dominant algal species in the periphyton, suggesting that various algal species showed different responses to different nutrients. The results of this study have implications for nutrient management in aquatic ecosystems.     

Physiological changes of submerged macrophytes in response to a floating filamentous green algae bloom in clear-water conditions

The aim of this study was to evaluate the physiological responses of a submerged macrophyte to a floating fi lamentous green algal bloom in clear-water conditions.Elodea nuttallii was grown with floating Cladophora sp.at four diff erent levels(0,control;140,280,560 g FW/m ~2)in an outdoor experimental system,and its photosynthetic and antioxidant systems were evaluated.The presence of floating Cladophora sp.signifi cantly changed the water environment by decreasing light intensity and increasing dissolved oxygen and the pH value.The photosynthetic parameters of E.nuttallii(e.g.?F/F _m~￠,F _v/F _m,total chlorophyll)were higher in the presence of floating Cladophora sp.than in the control at the beginning of experiment.Because of the increasing dissolved oxygen concentration and pH value,the values of these indicators decreased(except for photosynthetic pigments)during the experiment.Compared with E.nuttallii in the control,E.nuttallii growing in the presence of floating Cladophora sp.showed higher malondialdehyde content,catalase activity,and peroxidase activity.The biomass of E.nuttallii was decreased by about 30% in the presence of high biomasses of floating Cladophora sp.(280 and 560 g FW/m ~2).These results suggest that floating Cladophora had complex eff ects on the biomass of E.nuttallii and that changes in water quality resulting from floating Cladophora sp.may be more important than its direct shading eff ect.     

Spatial distribution and filtering efficiency of Daphnia in a deep subtropical reservoir

Studies of Daphnia distribution and function could help people manage and protect water quality.We investigated how spatial distribution and filtering efficiency of Daphnia in the transition and lacustrine zones of the Nanwan Reservoir(China).Samplings were conducted seasonally for 2 years from six sites in the reservoir.Daphnia abundance and biomass were significantly higher in the lacustrine zone than in the transition zone.Similar composition and biomass of edible phytoplankton were found in the two zones,suggesting that food quantity could not explain high Daphnia distribution in the lacustrine zone.The variations of water velocity and food quality could help explaining Daphnia patchy distribution in the reservoir.On the one hand,rapid water velocity can cause the Daphnia decrement in the transition zone.On the other hand,the ratio of particulate organic carbon(POC)to chlorophyll a(chl a)concentration was significantly higher in the transition zone,indicating more allochthonous material constituted the food source for Daphnia.The lower quality food likely suppressed Daphnia development in the transition zone.A linear regression between Daphnia abundance and Secchi depth(SD)may suggest a cause-effect relationship where increased filtering efficiency was responsible for increased water clarity to some extent.     

OSL chronology of a Palaeolithic site in a humid subtropical mountainous area of southeast China

The timing of Palaeolithic human activities in South China is still controversial because of the lack of a reliable chronology of archaeological sites. The Longdengshan Palaeolithic site(LPS), located close to the Wuyi Mountain of South China, represents the first discovered and scientifically excavated Middle Palaeolithic site in the Fujian Province. This site is of considerable significance for studying the diffusion and cultural connotation of early Homo sapiens in southern China. In this study, we present optically stimulated luminescence(OSL) ages obtained from medium-grained quartz collected at the LPS. The single-aliquot regenerative-dose measurements of red soil deposits collected at the same site yielded internally and stratigraphically consistent ages and similar errors, indicating a potential ability of the technique, and also reflecting the influence of various sedimentary facies on the test results. Our results indicate that the 38-63 μm quartz grains were generally partially-bleached and had large values of over-dispersion in the palaeo-reticulated laterites of west Fujian. Some samples yielded unsatisfactory results, suggesting that the degree of bleaching of diluvial and alluvial deposits should be properly assessed before dating. We did not detect any enrichment/depletion of U, Th and radioactive disequilibrium. The effect of chemical weathering on the dose rate estimation was negligible. Therefore, we used a central age model and the maximum age model to calculate the age of two samples, respectively, and the minimum age model to calculate the ages of the rest of the samples. The OSL ages of the samples ranged from 27.09 ± 2.30 ka to 54.65 ± 7.39 ka for the 38-63 μm quartz size fraction, and roughly corresponded to the Marine Isotope Stage 3. In addition, three ages out of five are based on the calculation of minimum ages in this research, which needs to be further verified by other dating methods.     

OBSERVATION OF A SHALLOW WATER INTERNAL OSCILLATION EVENT

At a shallow water station (6 m in depth), an internal oscillation event which consisted of one or two wave-like features, with a period of 3 h and a height of 1.5 m, was observed. The velocities within the water column were modified by the event during the flood phase of the tide ; a multilayered velocity structure and intense shear were generated. Further investigations are required to understand fully the mechanism for the formation of such an event.