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The importance of trophic interactions for determining the distributions, abundances, and taxonomic compositions of organisms in ecosystems has long been studied and debated. Here we test the effect of a trophic cascade on diatom (Asterionella formosa) blooms in subtropical, eutrophic Lake Taihu, China. A long-term data series (2005–2015) on planktivorous fish, zooplankton and diatoms has been analysed. Structural equation modelling is used to test our hypotheses about the influences of top-down and bottom-up forces on A. formosa. Since 2009, a spring bloom of A. formosa has occurred in the lake, coinciding with a reduction of Daphnia galeata biomass and of total cladoceran biomass following a marked increase in the stock of planktivorous fish (bighead carp and silver carp). Light, phosphorus (total and soluble reactive phosphate) and silica did not act as limiting factors for the growth of A. formosa. Structural equation modelling analysis showed that top-down effects of cladocerans on A. formosa biomass were more important than bottom-up effects (wind speed and soluble reactive phosphate). Although A. formosa was negatively correlated with total nitrogen, total with other inorganic nitrogen (NO 3 and NH 4) did not restrict the proliferation of diatom blooms after 2007. These results suggested that the substantial reduction of the Daphnia population caused a diatom bloom through a trophic cascade by planktivorous fish. Our study provides new insight into the effects of trophic interactions on diatom bloom formation in natural freshwater ecosystems.

Filter-feeding silver carp (Hypophthalmichthys molitrix) has been extensively used to control algae blooms in Chinese lakes. However, the benefit of stocking silver carp to restore eutrophic lakes remains controversial and the reasons for the different responses observed are unclear.In this study, we conducted an outdoor experiment to assess the impact of the biomass level of four silver carp (c. 0, 25, 50, and 100 g/m(3)) on phytoplankton through direct grazing and fish-mediated nutrient recycling, respectively. We used a nested design with nutrient-permeable chambers with or without fish placed inside ponds. In this way, the phytoplankton incubated outside the chambers was affected by both consumer grazing and nutrient recycling, whereas the phytoplankton inside the fish-free chambers was only affected by consumer-mediated nutrient recycling.Outside the chambers, the concentrations of total nitrogen, dissolved total nitrogen, and total phosphorus did not differ significantly among the treatments, whereas the dissolved total phosphorus level was significantly higher in the fishless treatment. The concentration of chlorophyll a (Chl a), phytoplankton biomass and the ratio of nanophytoplankton Chl a to total phytoplankton Chl a in the fish-present treatments were significantly higher than in the fishless treatment and the phytoplankton was dominated by small-sized species. While the zooplankton biomass and zooplankton:phytoplankton biomass ratio were significantly lower in the fish-present treatments, indicating a strong fish predation on zooplankton. As for the water inside the chambers, there was no significant difference among the four treatments for any of the measured variables except total phosphorus.Our results suggest that silver carp indirectly stimulated phytoplankton growth by reducing the zooplankton grazing rather than through nutrient recycling, and that fish grazing on phytoplankton could not compensate for the loss of grazing by zooplankton, leading to higher phytoplankton biomass when silver carp was present. The benefit of using filter-feeding fish as a biomanipulation tool to create clear water is therefore questionable unless control of nanophytoplankton can be achieved.

Fish are an integral component of aquatic ecosystems and play important roles in maintaining ecosystem stability. However, fish have recently been under great threat due to the deterioration of aquatic environments and the loss of suitable habitats. Due to the intensification of global warming and water eutrophication, the frequency and duration of cyanobacteria blooms have been increasing. Cyanobacteria blooms are often accompanied by cyanotoxin and taste-and-odor substance productions which threaten fish survival and fishery economics. However, the ecological interaction between cyanobacteria and fish is multifaceted. Biomanipulation techniques using fish to regulate excessive cyanobacteria growth have achieved certain effects in the bioremediation of eutrophic water bodies. Therefore, a comprehensive assessment of the impacts of cyanobacteria blooms on freshwater fish populations and the control and driving effects of fish on cyanobacteria are necessary to protect freshwater ecosystems. This study systematically analyzes the effect of cyanobacteria blooms on freshwater fisheries, toxicological effects of harmful cyanobacteria on fish, and the ecological regulation of fish on cyanobacteria. Accordingly, we have proposed future research directions. More attention should be paid to the impacts of cyanobacteria blooms on the physiology, ecology, and behavior of fish, and other animal populations. It is necessary to further clarify whether fish miniaturization and a decline in fish species diversity are directly related to cyanobacteria blooms. Fish exposure to cyanobacteria blooms is a complex topic because aquatic animals are not only exposed to cyanotoxins but also to cyanobacterial cells and lysates which contain various compounds. Thus, the overall effect of complex cyanobacteria biomass or in situ cyanobacteria blooms on fish and the corresponding aquatic ecological risk assessment probably will be the focus of future aquatic research. Moreover, a comprehensive examination of the impact of taste-and-odor substances produced by cyanobacteria on fishery products is also required. Biomanipulation, including traditional and non-traditional techniques, is one of the effective tools to control cyanobacteria blooms. Biomanipulation for water environment restoration can be affected by several factors including geographical characteristics, lake and reservoir morphology, algal composition, stocking mode, and biological community structure. Therefore, the feasibility of implementing biomanipulation should depend on the environmental and biological characteristics of water bodies and specific practices during decision-making processes. Previous studies suggest that combining bivalve and filter-feeding fish may enhance the bioremediation effect of algae but their synergistic effects and effectiveness in natural lakes remain to be further verified. Therefore, this study aims to provide a scientific basis to assess the ecological risk of cyanobacteria blooms, protect freshwater fish, and improve aquatic environments.

Response of aquatic organisms to eutrophication have been well reported, while less studies are available for the recovery of eutrophic lakes following a reduction in the external loading, especially for systems where nitrogen is reduced but the phosphorus concentration is maintained high due to internal loading. Diatoms are nitrate (NO

Rapid expansion of juvenile fish after biomanipulation can delay the successful restoration of submerged macrophytes, leading to a turbid water status in subtropical shallow lakes. Aimed to test the effects of direct removal of juvenile crucian carp (Carassius carassius) on water quality and growth of two submerged macrophytes Vallisneria natans and Hydrilla verticillate, a short-term outdoor mesocosm experiment was conducted in the Taihu Laboratory for Lake Ecosystem Research (TLLER). The results indicated that the concentrations of TN, TP, suspended solids, and chlorophyll a decreased significantly with increasing removal density of juvenile crucian carp, thus resulting in a clear status of the water. Additionally, the mean relative growth rate of V. natans and H. verticillata in the low- and high-density removal treatments were higher than that in the controls. Moreover, the removal of juvenile crucian carp also significantly increased the stem length of V. natans, but no significant effect on that of H. verticillata. Meanwhile, the total number of V. natans and H. verticillata in the low- and high-density removal treatments was higher than that in the controls, but all of H. verticillata were lower than the initials. Our results indicated that removing juvenile crucian carp could improve the water quality, increasing relative growth rate, height, and reproduction of V. natans, and improving the survival rate of H. verticillata. The promotion of fish removal on the V. natans growth was greater than H. verticillata. The results also implied that it was necessary to continuously remove the juvenile benthivorous fish several times for restoring the submerged macrophytes in shallow lakes.

Biomanipulation by piscivore stocking has been widely used to combat eutrophication in north temperate lakes, but its applicability in warm lakes has not yet been well elucidated. Here, we used experimental mesocosms to test the effects of a native benthi-piscivore (snakehead, Channa argus Cantor) on water clarity under subtropical conditions where small omni-benthivorous fish like crucian carp (Carassius carassius L.) prevail. Our results showed that, despite of a great reduction of crucian carp biomass, snakehead stocking did not create a strong trophic cascade as neither (herbivorous) zooplankton biomass nor their grazing pressure, indicated by biomass ratio of (herbivorous) zooplankton to phytoplankton, changed significantly. Moreover, snakehead stocking significantly increased water non-algal turbidity as well as nutrient and chlorophyll-a concentrations, suggesting that these benthi-piscivores also disturbed sediments like crucian carp did. Our study showed that biomanipulation by stocking of snakehead does not facilitate clear-water state in warm shallow lakes, even on the short-term.

Cyanobacterial blooms producing toxic metabolites occur frequently in freshwater, yet the environmental behaviors of complex cyanobacterial metabolites remain largely unknown. In this study, the seasonal and spatial variations of several classes of cyanotoxins (microcystins, cylindrospermopsins, saxitoxins) and taste-and-odor (T&O) compounds (β-cyclocitral, β-ionone, geosmin, 2-methylisoborneol) in Lake Taihu were simultaneously investigated for the first time. The total cyanotoxins were dominated by microcystins with concentrations highest in November (mean 2209 ng/L) and lowest in February (mean 48.7 ng/L). Cylindrospermopsins were abundant in May with the highest content of 622.8 ng/L. Saxitoxins only occurred in May (mean 19.2 ng/L) and November (mean 198.5 ng/L). Extracellular T&O compounds were most concentrated in August, the highest being extracellular β-cyclocitral (mean 240.6 ng/L) followed by 2-methylisoborneol (mean 146.6 ng/L). Environment variables play conflicting roles in modulating the dynamics of different groups of cyanotoxins and T&O compounds. Total phosphorus (TP), total nitrogen (TN), chlorophyll-a and cyanobacteria density were important factors affecting the variation of total microcystins, β-cyclocitral and β-ionone concentrations. In contrast, total cylindrospermopsins, 2-methylisoborneol and geosmin concentrations were significantly influenced by water temperature and TP. There was a significant and linear relationship between microcystins and β-cyclocitral/β-ionone, while cylindrospermopsins were positively correlated with 2-methylisoborneol and geosmin. The perceptible odors may be good indicators for the existence of cyanotoxins. Hazard quotients revealed that potential human health risks from microcystins were high in August and November. Meanwhile, the risks from cylindrospermopsins were at moderate levels. Cylindrospermopsins and saxitoxins were first identified in this lake, suggesting that diverse cyanotoxins might co-occur more commonly than previously thought. Hence, the risks from other cyanotoxins beyond microcystins shouldn't be ignored. This study also highlights that the necessity for further assessing the combination effects of these complex metabolites.

There have been many studies on the effects of eutrophication on beta diversity (β-diversity) of species assemblages. However, few studies have focused on the effects of nutrient reduction on β-diversity and community structure, and long-time series analyses are particularly scarce. We conducted a 19-year case study on the impacts of management intervention on the temporal β-diversity of aquatic grazers in a lake at the Yangtze River Basin. In our study, we compared the changes in temporal β-diversity as well as its two components, nestedness and turnover, and the synchrony of the rotifer community after management intervention. Our results showed that while the abundance of some sensitive species increased, there was no trend in species richness. Moreover, both the seasonality and interannual stabilities of rotifer assemblages increased. The species synchrony decreased in both spring and summer after management intervention. We also found that management intervention significantly reduced nutrient concentrations but not water clarity and phytoplankton abundance. The total nitrogen (TN): total phosphorous (TP) ratio was reduced after management intervention, causing an increase in the abundance of cyanobacteria that may contribute to the increase of rotifer synchrony in autumn. Our results imply that stable environmental fluctuations after management intervention may increase temporal β-diversity and stability of herbivorous assemblages. However, imbalanced changes in TN and TP after management intervention may weaken the top-down control of zooplankton on phytoplankton and slow down water clarity improvement.

Lake ecosystems are exposed to a range of anthropogenic pressures, particularly eutrophication, and in some cases also stocking and/or overfishing of top-predator fish species, all factors that have implications for the food web structure and which could lead to dominance of nuisance cyanobacteria. Restoration of degraded lakes demands insight into the relative role of top-down for bottom-up regulating forces. While knowledge about these forces in temperate lakes is extensive, comparatively little is known of their role in subtropical lakes where the importance of herbivorous and benthic feeding fish is higher. Here, we analyzed a long-term monitoring data set on subtropical, shallow Lake Taihu, China, and applied random forests regression to examine how phytoplankton was related to environmental variables and biotic assemblages. Our results indicate that the biomass and density of phytoplankton increased with increasing biomass of benthivorous and zooplanktivorous fish and decreased with increases in ammonium concentrations, the nitrogen to phosphorus ratio, and zooplankton biomass, while the response to climate fluctuations and changes in the biomass of piscivores was weak. Effects of higher trophic levels explained as much of the variance in phytoplankton biomass as did nutrients and climatic factors. Moreover, the remarkably reduced ratio of zooplankton to phytoplankton biomass and the decline in cladoceran individual biomass emphasized the increasing importance of top-down control in regulating the phytoplankton following extensive stocking. Our findings offer insight into how fish management may be combined with catchment-level restoration measures to conserve and enhance water quality.

In outdoor mesocosms, we experimentally studied the effect of combining two native filter feeders, bighead carp (Aristichthys nobilis) and Asian clam (Corbicula fluminea), to control nuisance cyanobacterial blooms. Four treatments - clam-only, fish-only, combined and controls - were used. In combination, bighead carp (80 g m(-3)) and Asian clam (260 g m(-2)), had a remarkable controlling effect on phytoplankton biomass and improved water quality. By the end of the experiment, the chlorophyll a (Chl a) concentration of the combined group was below 5 mu g L-1 compared with 36 mu g L-1 in the clam-only treatments and 31 mu g L-1 in the controls, whereas Chl a in the fish-only group had increased to 211 mu g L-1. Large-sized algae (Microcystis sp.) dominated in the control group and the clam-only group, whereas small-sized algae (Actinastrum hantzschii and Clamydomonas globose) dominated in the fish-only group. The concentrations of total nitrogen (TN) and total phosphorus (TP) in the water column were significantly reduced by clam stocking, regardless of the presence of fish. A 24-h laboratory experiment was conducted to verify whether the excrements produced by clams filtering small-sized algae could be eaten by bighead carp. At the end of the experiment, the density of Scenedesmus obliquus had decreased significantly in the clam-presentmesocosms, and the gut fullness index of bighead carp was significantly higher in the clam-present mesocosms than when clams were absent. Our results show that, under the selected experimental conditions and densities, water clarity improved when bighead carp and Asian clam occurred together, whereas Chl a concentrations and algae biomass increased in the fish-only mesocosms; in the clam-only mesocosms no significant effectswere observed. We suggest that the combination of filter-feeding fish and clams may enhance water clarity and it may therefore potentially be a useful restoration tool. (C) 2020 Elsevier B.V. All rights reserved.

Transplantation of submerged macrophytes has been widely used to improve water quality in restoring shallow lakes in China. However, in some lakes, small omnivorous fish predominated the fish assemblages and fed mainly on submerged macrophytes. Despite significant research examining grazing selectivity in herbivorous fishes, macrophyte feeding preferences of small omnivorous fishes are poorly understood. We conducted a mesocosm experiment to examine the effects of a prolific small omnivorous bitterling fish Acheilognathus macropterus on the relative growth rate (RGR) and biomass of submerged macrophytes (Ceratophyllum demersum, Myriophyllum spicatum, Vallisneria denseserrulata, and Hydrilla verticillata). Our results showed that the presence of A. macropterus significantly increased nutrient concentrations (e.g. total nitrogen and total phosphorus). The RGR of C. demersum in the bitterling-present treatment was significantly lower than the controls, in the presence of other macrophyte species. Further, total biomass of the four species of macrophytes in the fish-present mesocosms was markedly lower than in the fish-absent treatment, suggesting considerable consumption of macrophytes by bitterling. Moreover, the percent biomass of V. denserrulata and H. verticillata were significantly enhanced by the presence of bitterling. Our findings suggest that A. macropterus may increase nutrient concentrations through excretion and reduce the biomass and RGR of certain submerged macrophytes which may shift macrophyte community structure via selective grazing.

Induced polarization (IP) methods are effective approaches in exploration and environmental geophysics. In practice, the earth electrical conductivity shows anisotropy, which will also influence the IP response. However, only a few researches have studied this issue. In this paper, we modeled and analyzed the induced polarization response in the anisotropic conductive subsurface. The finite volume method (FVM) was used to model the 3D anisotropic resistivity model, and the maximum relative error for a vertical anisotropy two-layer model is below 1%. Then we calculated the TDIP response and FDIP response based on equivalent resistivity and Cole-Cole model respectively through taking account of anisotropic model parameters. Finally, we analyzed the IP response of a two-layer horizontal anisotropic model and a 3D cube model embedded in the horizontal anisotropic subsurface. The results suggest that anisotropy paradox phenomenon still exists in the IP forwarding modeling. Apparent IP parameters of the survey lines on the surface are different between two orthogonal directions. The anisotropy should be taken into account in practical TDIP and FDIP exploration.

Knowledge of occurrence and extent of quick clay is vital regional for hazard zonation and in detail for infrastructure projects. Quick clay poses a serious geohazard in Scandinavia and Canada (amongst others) as it practically liquefies at failure and thus leads to serious, retrogressive slides. To this end, geotechnical drillings and samples are analyzed, to indicate sensitive clay in an area. As quick clay has a higher resistivity than marine clays, geophysical methods looking at resistivity distribution provide a valuable tool in addition to geotechnical assessment. So far, this has mostly focused on electrical resistivity tomography (ERT) for detecting these subtle changes. Supporting a recent road development project close to Oslo AEM was suggested in order to link drill sites and fill the data gaps between them. Quick clay is not easily identified in the AEM data, but some possible occurrences agree well with the results from drillings. Especially where the sediment layer is thick, variations in electrical resistivity within this layer can be resolved. These subtle changes can be linked to quick-clay extend by comparison with borehole data and ground-based geophysical methods (ERT and IP). We discuss results from the combination of these methods and outline the possibilities and limitations of quick-clay mapping using AEM.

Audio frequency magnetotullric (AMT) is widely used in the exploration of mineral and underground water. Three-dimension (3D) AMT exploration makes the imaging of underground geological body or structure with the best precision and resolution. And it needs a lot of AMT acquisition units to carry out exploration. Current commercial AMT unit was suffered from high power consumption and low work efficiency for 3D AMT exploration. We design and realize a low power AMT acquisition network based on ZigBee, GPS and ARM based embedded control system. Each AMT acquisition unit is composed of power supply module, GPS module, ARM module, and data acquisition module. The power supply module is controlled by the GPIO of the ZigBee Pro module. Power supply for GPS module, ARM module, data acquisition module, and induction coils can be switched on or off remotely by ZigBee network. The GPS module offers clocks and timing signals for the data acquisition module. The ARM based embedded control module is composed of AT91RM9200, 1GB NAND flash, 64 MB NOR flash, WI-FI, Ethernet and 64 MB SDRAM. It controls the data acquisition, calibration, and self-testing in AMT exploration. The data acquisition module is composed of 4 channels for the signal conditioning of weak AMT signals, 4 channels 24-bit ADC, and 24-bit fixed DSP. The low power differential amplifiers and low power audio amplifiers are used for the amplifying and filtering of the input signals. All AMT acquisition units are configured as ZigBee routers to build a wireless sensor network in mountain area successfully. A notebook with ZigBee router is used to control the AMT acquisition network. Software is developed in notebook to monitor network, send control command, retrieve the status of each AMT acquisition unit, and control the data acquisition process. One hundred AMT acquisition units are made, and tested in Tibet. The tests were successful in most area, but it was difficult to build a ZigBee network in some area where the tough topology was faced.

We realized a 2D/3D multi-frequency FDIP instrument system based on ZigBee wireless network and GPS to improve the data quality and efficiency of 2D/3D IP survey for engineering, environment and mineral exploration problems. The instrument is composed of a multi-function transmitter and more than 50 receivers. The transmitter is synchronized with GPS and can transmit more than 30 user defined waveforms and pseudo-random waveforms with frequencies range from 1/256 Hz to 128 Hz for field and laboratory usage. All receivers are identical with the ability to make the measurement of current injected into the earth and the potential difference between two electrodes. Each receiver is composed of 4 signal channels, DSP subsystem, GPS subsystem, and embedded computer subsystem. The DSP subsystem receives digital signal from four 24-bit A/D converters and carries out a sequence of filtering and calculation to reduce noise and interference inside the digital signal to improve signal to noise ratio (SNR). The GPS subsystem generates clock signal and synchronization signal for A/D conversion. This ensures all receivers doing data acquisition simultaneously. Therefore, the injected current and potential differences are measured at same time. This is the key for additional SNR improvement in IP survey. The embedded computer subsystem is the brain of the receiver. It is composed of wired network, WI-FI, ZigBee, ARM SOC, SDRAM, NOR flash, and NAND flash. A PC with a ZigBee adapter is used to control the data acquisition and monitors the data quality through ZigBee network. A lot of tests showed that more than 50 receivers can be controlled in the field with short latency. Therefore 196 voltage measurements and 1 current measurement can be made at a single acquisition. This improves the data quality and efficiency of 2D/3D IP survey significantly.

This paper presents an intelligent secondary battery test system based on a 24-bit high-resolution ADC ADS1211. We adopt ultra-high precision voltage reference AD780 and 24-bit ADC ADS1211 to ensure high-precision measurement. The system utilizes a micro-controller to intelligently set the parameters of channel state control circuit, switch charge-discharge mode, switch voltage and current feedback, control voltage and current sampling, test internal resistance of a battery cell, measure the ambient temperature, etc. This system achieves the functions of testing rechargeable battery, including constant current charge, constant voltage charge, constant current discharge and static performance, and the high precision measurement of secondary battery parameters. Furthermore, based on the test result we can analysis the comprehensive performance of the secondary battery and achieve a reasonable battery match to play the best performance. The main characteristics of the system are simple circuit, low cost, multi-function and high precision.

Geophysical exploration in productive mine is a challenging problem. There are many sources to produce strong electromagnetic interference to prevent the qualified data acquisition of IP, MT, AMT, TEM, and CSAMT exploration. Chinese Bureau of Geological Survey organized a geophysical data acquisition in productive mine applying different geophysical instruments and different geophysical methods, such as IP, CSAMT, and TEM. Because of strong EM interference, no instrument or method can satisfy the data quality requirement of geophysical exploration. Baiying (Silver) mine in Gansu province of northwest of China is a productive mine. Geophysical exploration with time domain induced polarization (TDIP) method cannot get good quality data when the spacing between current electrode and potential electrode is large because of the strong EM interference. To solve above problem, we carried out a testing to evaluate technologies needed for good quality data acquisition. We acquired a lot of data when the current injection was off to get the detailed characteristic of EM interference. Distributed high precision data acquisition station, spread spectrum technology, GPS synchronization, correlation detection, strong injected current, robust processing, frequency domain IP (FDIP), and longtime data acquisition are adopted to improve the data quality of IP exploration with the depth of exploration as about 1000m. We find that 30A of injected current is enough when above technologies are adopted, and the time of data acquisition is about 120s. If 8A of injected current is applied, the time of data acquisition for good quality data will be 1800s or more. At last, we carried out a 2D FIP exploration with minim potential electrode spacing as 20m, maxim current electrode spacing as 5200m, maxim injected current as 30A. The overall data quality is satisfactory, and the average measurement error of apparent resistivity is 0.3%.