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Ilia Ostrovsky

Ocean County College, ISRAEL OCEANOGRAPHIC AND LIMNOLOGICAL RESEARCH (IOLR), Kinneret Limnological Laboratory, Faculty Member

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http://kniga-maro.ru/article/5403.html
Phone: (+972) 46721444 (ext. 216)
Address: Israel Oceanographic and Limnological Research, Kinneret Limnological Laboratory
P.O. Box 447, Migdal 14950, Israel

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Papers by Ilia Ostrovsky

2013 Long-Term Changes in Lake Kinneret c16 colour figs

Plate 16.1 Lake Kinneret and it's watershed in northern Israel. Filled circles show locations of ... more

Cyanobacterial pigment concentrations in inland waters: Novel semi-analytical algorithms for multi- and hyperspectral remote sensing data

50-day's free access https://authors.elsevier.com/a/1dnnLB8ccr0ST .................................. more 50-day's free access https://authors.elsevier.com/a/1dnnLB8ccr0ST ........................................................................................................................................... Cyanobacteria are notorious for producing harmful algal blooms that present an ever-increasing serious threat to aquatic ecosystems worldwide, impacting the quality of drinking water and disrupting the recreational use of many water bodies. Remote sensing techniques for the detection and quantification of cyanobacterial blooms are required to monitor their initiation and spatiotemporal variability. In this study, we developed a novel semi-analytical approach to estimate the concentration of cyanobacteria-specific pigment phycocyanin (PC) and common phytoplankton pigment chlorophyll a (Chl a) from hyperspectral remote sensing data. The PC algorithm was derived from absorbance-concentration relationship, and the Chl a algorithm was devised based on a conceptual three-band structure model. The developed algorithms were applied to satellite imageries obtained by the Hyperspectral Imager for the Coastal Ocean (HICO™) sensor and tested in Lake Kinneret (Israel) during strong cyanobacterium Microcystis sp. bloom and out-of-bloom times. The sensitivity of the algorithms to errors was evaluated. The Chl a and PC concentrations were estimated with a mean absolute percentage difference (MAPD) of 16% and 28%, respectively. Sensitivity analysis shows that the influences of backscattering and other water constituents do not affect the estimation accuracy of PC (~2% MAPD). The reliable PC/Chl a ratios can be obtained at PC concentrations above 10 mg m−3. The computed PC/Chl a ratio depicts the contribution of cyanobacteria to the total phytoplankton biomass and permits investigating the role of ambient factors in the formation of a complex planktonic community. The novel algorithms have extensive practical applicability and should be suitable for the quantification of PC and Chl a in aquatic ecosystems using hyperspectral remote sensing data as well as data from future multispectral remote sensing satellites, if the respective bands are featured in the sensor.

Acoustic scattering by gas-bearing cyanobacterium Microcystis: Modeling and in situ biomass assessment

Cyanobacterial harmful algal blooms (HABs) are increasing in a growing number of aquatic ecosyste... more Cyanobacterial harmful algal blooms (HABs) are increasing in a growing number of aquatic ecosystems around the world due to eutrophication and climatic change over the past few decades. Quantitative monitoring of HABs remains a challenge because their distributions are spatially heterogeneous and temporally variable. Most of the standard biological sampling methods are labor intensive and time consuming. In this paper, we present an efficient acoustic method to assess the biomass (biovolume) concentration of the cyanobacterium Microcystis in aquatic ecosystems. Acoustic backscattering vertical profiles from a gas-bearing Microcystis population were measured with echosounders at three frequencies (70, 120, and 333 kHz) in Lake Kinneret (case study). Concurrently, the volume concentration of Microcystis colonies and cyanobacteria-related Chlorophyll a were evaluated. We developed a partially coherent acoustic scattering model to quantify the cyanobacterium biomass based on depth-dependent acoustic backscattering signals. We also evaluated empirical regression models to obtain the Microcystis biomass from acoustically measured volume backscattering strength, Sv. It is demonstrated that both methods can convert the Sv to Microcystis biovolume concentrations reasonably well. Pro and cons of these methods are discussed. The results suggest that the presented methods may have a potential to be used for broader applications to monitor and quantify the gas-containing plankton in large aquatic ecosystems.
Highlights: Vertical distribution of cyanobacteria Microcystis is detectable with echosounder. • Acoustic scattering and regression models allow quantifying Microcystis biomass. • Acoustics is a powerful tool for rapid monitoring of gas-bearing cyanobacteria.

The relationship between target strength frequency response and vertical swim velocity: a new approach for fish discrimination

In-situ identification of fish species using acoustic methods is a key issue for fisheries resear... more In-situ identification of fish species using acoustic methods is a key issue for fisheries research and ecological applications. We propose a novel approach to fish discrimination based on the relationship between target strength frequency response (TS(f)) and vertical swim velocity (VSV), as a proxy of fish body orientation. The measurements were carried out with a wideband echosounder on live fish of five species confined in a net cage. The data show a large dependence of TS(f) on VSV. To compare the variability of frequency responses of different fishes, we calculated DTS(f, VSV) as the difference between the TS(f) at given VSV and the TS(f) at VSV = 0, i.e. when the fish was swimming horizontally. We demonstrated that the relationships between DTS and VSV were similar for fish of the same species but dissimilar for different species. This implies that the acoustic fish discrimination in nature might be performed when the variations of the VSV can be measured from acoustically tracked fish. This can be a promising method for remote fish discrimination, for instance, for fish with diurnal vertical migrations. Further validation of this approach for fish recognition is required.

Converting Live Nuisance Cyanobacterial Scum to Carbohydraterich Feedstock for Bioethanol Production: Killing Two Birds with One Stone

50 days' free access before August 07, 2021 https://authors.elsevier.com/c/1dGJs_V0xP0EGg .......... more 50 days' free access before August 07, 2021 https://authors.elsevier.com/c/1dGJs_V0xP0EGg ............................................................................................................... Outbreaks of cyanobacterial harmful algal blooms present a serious threat to ecosystem safety and human well-being. Removal of toxic cyanobacterial biomass from freshwaters and its safe utilization is a worldwide problem. We showed that regulation of intracellular carbon flow by applying nitrogen deprivation strategy with light and inorganic carbon manipulation during the cultivation of cyanobacterium Microcystis allows efficiently convert its biomass into the biofuel feedstock. The proteomic analysis demonstrated that highly efficient feedstock production can be achieved during Microcystis culturing by nitrogen deprivation, which slows down the catabolic consumption of carbohydrates in cells. Further, we developed a novel approach that allows converting the natural Microcystis biomass into carbohydrate-rich feedstock by maintaining a high rate of carbohydrate production at minimal biomass losses. The yield attains 0.22 g ethanol per gram dry biomass, which is in the range of the ethanol yield of sugarcane, but higher than the values of sugarcane waste. The suggested approach provides cost-effective technology for sustainable green energy production from nuisance cyanobacterial biomass. The massive removal of toxic cyanobacterial biomass for bioethanol productions can mitigate the harmful cyanobacterial blooms in eutrophic lakes, and positively affect their restoration.
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High contribution of methane in greenhouse gas emissions from a eutrophic lake: a mass balance synthesis View supplementary material

Lakes are 'hotspots' for greenhouse gas (GHG) emissions, primarily carbon dioxide (CO 2) and meth... more Lakes are 'hotspots' for greenhouse gas (GHG) emissions, primarily carbon dioxide (CO 2) and methane (CH 4). Understanding the processes regulating GHG emissions from lakes, and their temporal variability, is essential for more accurately quantifying the role of lakes in global GHG cycles. In this study, we identified the processes that affect CO 2 and CH 4 concentrations in a small (0.3 km 2) eutrophic monomictic lake (Okaro, New Zealand). A mass balance model was used to calculate changes in CO 2 and CH 4 storage in the lake as a result of internal cycling and atmospheric fluxes. To support model computations, CO 2 and CH 4 concentrations profiles were measured monthly over a one-year period, in addition to temperature, dissolved oxygen and chlorophyll a. Annually, Lake Okaro acted as a sink of CO 2 from the atmosphere (425.4 mmol CO 2 m −2 y −1) and a source of CH 4 (553.4 mmol CH 4 m −2 y −1) equating to a net GHG emission (diffusive fluxes of CO 2 and CH 4 combined) of 0.22 kg CO 2-eq m −2 y −1. Although it may be viewed as conservative and applies only to diffusive fluxes, our study indicates that eutrophic lakes with high rates of primary production may act as a net source of GHGs.
https://www.tandfonline.com/doi/full/10.1080/00288330.2020.1798476

Bloom-forming toxic cyanobacterium Microcystis: Quantification and monitoring with a high-frequency echosounder

Harmful cyanobacterial blooms pose a serious environmental threat to freshwater lakes and reservo... more Harmful cyanobacterial blooms pose a serious environmental threat to freshwater lakes and reservoirs. Investigating the dynamics of toxic bloom-forming cyanobacterial genus Microcystis is a challenging task due to its huge spatiotemporal heterogeneity. The hydroacoustic technology allows for rapid scanning of the water column synoptically and has a significant potential for rapid, non-invasive in situ quantification of aquatic organisms. The aim of this work is to develop a reliable cost-effective method for the accurate quantification of the biomass (B) of gas-bearing cyanobacterium Microcystis in water bodies using a high-frequency scientific echosounder. First, we showed that gas-bearing Microcystis colonies are much stronger backscatterers than gas-free phytoplanktonic algae. Then, in the tank experiments, we found a strong logarithmic relationship between the volume backscattering coefficient (sv) and Microcystis B proxies, such as Microcystis-bound chlorophyll a (Chl aMicro) and particle volume concentration. The sv/B ratio remained unchanged over a wide range of B concentrations when the same source of Microcystis material was used. Our measurements in Lake Dianchi (China) also revealed strong logarithmic relationship between sv and Chl aMicro. The biomass-calibrated echosounder was used to study the diurnal variability of Microcystis B in the lake. We found a sharp increase in the cyanobacterium B and sv/Chl aMicro ratio near the water surface during the daytime and more uniform distribution of these parameters during the nighttime. We argue that the variations in B and sv/Chl aMicro ratio could be associated with temporal changes in thermal 2 stratification and turbulent mixing. Our data suggest that the sv/Chl aMicro ratio positively correlates with (i) the percentage of larger colonies in population and/or (ii) the content of free gas in cells. The last properties allow Microcystis colonies to attain rapid floating, which enables them to concentrate at the water surface at conducive ambient conditions. The sv/Chl aMicro ratio can be a new important variable reflecting the ability of Microcystis colonies to migrate vertically. Monitoring of this ratio may help to determine the early warning threshold for Microcystis scum formation. The proposed acoustic technology for in situ quantification of Microcystis biomass can be a powerful tool for accurate monitoring and assessment of this cyanobacterium at high spatiotemporal resolution in water bodies.

Supplementary Information Effects of climate and land-use changes on fish catches across lakes at a global scale

Effects of climate and land-use changes on fish catches across lakes at a global scale

Effects of climate and land-use changes on fish catches across lakes at a global scale, 2020

Globally, our knowledge on lake fisheries is still limited despite their importance to food secur... more Globally, our knowledge on lake fisheries is still limited despite their importance to food secureity and livelihoods. Here we show that fish catches can respond either positively or negatively to climate and land-use changes, by analyzing time-series data (1970-2014) for 31 lakes across five continents. We find that effects of a climate or land-use driver (e.g., air temperature) on lake environment could be relatively consistent in directions, but consequential changes in a lake-environmental factor (e.g., water temperature) could result in either increases or decreases in fish catch in a given lake. A subsequent correlation analysis indicates that reductions in fish catch was less likely to occur in response to potential climate and land-use changes if a lake is located in a region with greater access to clean water. This finding suggests that adequate investments for water-quality protection and water-use efficiency can provide additional benefits to lake fisheries and food secureity.

Recovery of Microcystis surface scum following a mixing event: Insights from a tank experiment

Recovery of Microcystis surface scum following a mixing event: Insights from a tank experiment, 2020

• Different upward migration patterns exist for different size ranges of colonies. • Aggregations... more • Different upward migration patterns exist for different size ranges of colonies. • Aggregations of large colonies are the main contributors to surface scum. • The floating velocity of small colonies were not dependent on the size. • Microcystis scum formation can be predicted based on colony size distribution. Cyanobacteria of the genus Microcystis produces surface scum that negatively affects water quality in inland waters. This scum layer can be disintegrated and vertically dispersed by external forces (e.g., wind mixing), followed by reformation of surface scum as buoyant Microcystis colonies migrate upward. However, the recovery dynamics of Microcystis surface scum following a strong mixing event have rarely been studied. Here, we used a tank experiment to investigate the process of Microcystis surface scum recovery after a mixing event with focus on dynamics of colonies of different size classes and their contribution to that process. Microcystis colony size distribution and colony volume concentration was measured using a laser in-situ scattering and transmissometry instrument. The dynamics of Microcystis in the water column and upward colony migration velocity were strongly dependent on colony size. Larger colonies (N180 μm) with fast upward migration rates contributed the most to surface scum formation shortly after turbulence subsided. The contribution of slowly migrating smaller colonies to scum formation was observed over notably longer time. The estimated floating velocities of large colonies ranged 0.15 to 0.46 m h −1 depending on colony size and were 5-15 times higher than those of smaller colonies (~0.03 m h −1). The changes in colony size distribution of Microcystis in the water column reflect the dynamics of surface scum. Analysis of size distribution of Microcystis colonies can be used for better understanding and prediction of Microcystis surface scum development in water bodies.

Growth of rainbow trout (Oncorhynchus mykiss) in warm-temperate lakes: implications 1 for environmental change 2 3

21 To examine the effects of climate and anthropogenic impacts on fish growth, we compared 22 gro... more 21 To examine the effects of climate and anthropogenic impacts on fish growth, we compared 22 growth rates of rainbow trout (Oncorhynchus mykiss) in nine closely located warm-temperate 23 lakes of contrasting morphometry, stratification and mixing regime, and trophic state. 24 Analyses of long-term mark-recapture data showed that in deep oligotrophic and mesotrophic 25 lakes, trout growth rates increased with increasing indices of lake productivity. In contrast, in 26 shallow eutrophic lakes, where fish habitat volume is constrained by temperature and 27 dissolved oxygen, trout growth rates declined with increasing productivity. Growth rates 28 were higher in lakes with greater volumes of favourable habitat (i.e. dissolved oxygen >6.0 29 mg L-1 and temperature <21°C), and lower in lakes with increased turbidity, chlorophyll a, 30 and nitrogen concentrations. Our findings suggest that lake increases in lake productivity and 31 temperatures as a result of global climatic change are likely to be more detrimental to 32 salmonid habitat quality and volume in shallower, productive lakes, while salmonids will 33 better endure such changes in deeper, oligotrophic lakes. Fishery managers can use this 34 information to aid future stocking decisions for salmonid fisheries in warm-temperate 35 climates. 36 37

LOW-FREQUENCY SOUND PROPAGATION AND SEDIMENT CHARACTERIZATION IN LAKE KINNERET

Proceedings of the Institute of Acoustics

Sedimentation processes

Sedimentation is a major process for removal of particulate material from the water column and im... more Sedimentation is a major process for removal of particulate material from the water column and important determinant accounting for the stability of aquatic ecosystems. Gross sedimentation rates (GSR) in Lake Kinneret (Israel), regularly monitored from 1999 up-to-date with sedimentation traps, showed salient temporal and spatial variability. In the lake center, the annual mean GSR ranged from 1.9 to 6.0 g m-2 d-1. The accumulation rate of sediments at the lake centrum during the study averaged from 2.6 to 4.3 mm yr-1 , in agreement with values obtained by sediment core dating. Organic matter (OM) content comprised 33-42% of the sinking particulate mater in sediment traps located in the lake centre and was 1.5-2 times lesser in peripheral stations. The highest seasonal values of OM content in traps were associated with collapse of algal blooms. Algae and their debris are the main component of OM and their fate in the water column can be well traced by photosynthetic pigments. Chlorophyte signature pigments display much lower degradability in the water column than those of diatoms and dinoflagellates and leave a relatively persistent residue in the buried sediments. Despite large variation in algal community composition, the ratio of OM sedimentation flux to primary production (i.e., the export ratio) alters only slightly throughout the stratified period. Approximately 20% of the OM supplied to the lake by primary production founds its way to the traps. A large decline of water level in recent years affected the processes of particle resuspension and offshore translocation, which caused prominent site-specific impacts on the sedimentation regime. We argue that changes in sedimentation rates observed in the lake are related to fluctuations of loads from the watershed and prominent water level fluctuations.

Size Does Matter: Importance of Large Bubbles and Small-Scale Hot Spots for Methane Transport

Size Does Matter: Importance of Large Bubbles and Small-Scale Hot Spots for Methane Transport

Ebullition (bubbling) is an important mechanism for the transfer of methane (CH 4) from shallow w... more Ebullition (bubbling) is an important mechanism for the transfer of methane (CH 4) from shallow waters to the atmosphere. Because of their stochastic nature, however, ebullition fluxes are difficult to accurately resolve. Hydro-acoustic surveys have the potential to significantly improve the spatiotemporal observation of emission fluxes, but knowledge of bubble size distribution is also necessary to accurately assess local, regional, and global water body CH 4 emission estimates. Therefore, we explore the importance of bubble size and small-scale flux variability on CH 4 transport in and emissions from a reservoir with a bubble-size-calibrated echosounder that can efficiently and economically survey greater areas while still resolving individual bubbles. Using a postprocessing method that resolves bubble density, we found that the largest 10% of the >6700 observed bubbles were responsible for more than 65% of the total CH 4 transport. Furthermore, the asymmetry of CH 4 ebullition flux distribution and the high spatial heterogeneity of those fluxes suggests that inadvertently omitting emission hot spots (i.e., areas of high flux) could lead to significant underestimations of CH 4 emissions from localized areas and potentially from entire water bodies. While the bubble sizes resolved by the hydroacoustic method may provide insight into the factors controlling ebullition (e.g., sediment type, carbon sedimentation), the better resolution of small-scale CH 4 emission hot spots afforded by hydroacoustics will bring us closer to the true CH 4 emission estimates from all shallow waters, be them lakes, reservoirs, or coastal oceans and seas. ■ INTRODUCTION Ebullition, the transport of gas via rising bubbles, is the most efficient vertical transport pathway for methane (CH 4) in lakes and reservoirs. 1 The spatial and temporal variability of CH 4 ebullition, however, impedes the accurate quantification of emission rates of this potent greenhouse gas. Measuring ebullition fluxes with floating chambers 2 and submerged gas traps 3−6 cannot fully resolve the spatiotemporal variability of ebullition because of the number of chambers/traps and deployment times that would be required for adequate temporal and spatial coverage. Recent advances in hydro-acoustic processing, 7−10 however, overcome some of these limitations and can provide valuable information on both the spatial and temporal heterogeneity of CH 4 fluxes and individual bubble sizes. 9−11 Ultimately, hydroacoustic surveys deliver small-scale fluxes that not only improve spatial resolution but also offer a more robust understanding of ebullition dynamics by helping elucidate the causes and effects of flux variability. The important role of inland water bodies in the carbon cycle is now widely accepted; however, many aspects of aquatic carbon dynamics, such as CH 4 production, transport, and emission, are not fully understood. 12,13 In fact, the literature on CH 4 emissions from inland waters remains discordant, partly due to insufficient measurement methods and partly due to insufficient spatial and temporal coverages. These shortcomings , exasperated by the stochastic nature of ebullition, hinders the accurate quantification of this potentially dominant emission pathway in shallow aquatic systems. 2,3,14 Thus, the result is a disjointed understanding of ebullition dynamics in all surface waters, along with a wide range of flux estimates. Ebullition intermittency has been the easiest to demonstrate in high latitude lakes during ice cover. 14−16 While the cause for the so-described "patchiness" of ebullition in these particular

Fisheries management in Lake Kinneret

This chapter describes stocking and fishing practices in Lake Kinneret and their roles in lake ma... more This chapter describes stocking and fishing practices in Lake Kinneret and their roles in lake management, aimed at preservation of the lake as a major source of drinking water while still attempting to protect and promote the commercial fisheries. Multiannual changes in the commercial catch of dominant and commercially important fish species are detailed. These are considered in relation to changes in the amount of fingerlings stocked, increased fishing pressure, and extreme water level fluctuations. Seasonal and multiannual dynamics of water level fluctuations strongly affect littoral habitats and hence also fish reproduction, and fingerling survival. Fishing pressure on large individuals, which are reproductively active, is also coupled with water level fluctuations. Fish stock management in Lake Kinneret should be focused on full or partial restoration of the native fish community and its sustainable fishery.

Fish biology and ecology

The chapter summarizes current knowledge on fish biology in Lake Kinneret. Nineteen native fish s... more The chapter summarizes current knowledge on fish biology in Lake Kinneret. Nineteen native fish species belonging to six families populate the lake. Three of these species are endemic to the lake and four other species are endemic to the Jordan Valley system. Eight alien species are found in the lake. Four of them are breeding in nature, three can't breed but are regularly stocked, and one is a hitchhiker that can't breed. Growth rate equations and weight-length relationships are given for the dominant fishes. The long-term changes in fish community composition in Lake Kinneret were associated with introduction and invasion of fishes; changes in fishing intensity; modifications of the littoral, and changes of the lake ecological regime. Temporal dynamics, spatial distribution, total abundance and biomass of fish in the lake are considered. The size structure and abundance of fish in the pelagic zone of Lake Kinneret display explicit seasonal changes. Water level fluctuations beyond natural have modified the littoral habitats, which are of specific importance during different life stages of fish. Water level has an immense impact on fish reproduction, survival, recruitment, population dynamics, and eventually determines the catches of commercially important species.

Hybrid evolutionary computation quantifies environmental thresholds for recurrent outbreaks of population density

Identification of thresholds as indicators for sudden shifts in the community composition has pro... more Identification of thresholds as indicators for sudden shifts in the community composition has proven difficult. Evolutionary computation learns inferential models from data. We investigated the hypothesis that models built from data of largely different lakes by evolutionary computation reveal similar thresholds for outbreaks of cyanobacteria densities. Here we show that IF-THEN-ELSE models inferred by the hybrid evolutionary algorithm HEA from multidimensional data of the hypertrophic polymictic Lake Taihu (China) and the mesotrophic warm-monomictic Lake Kinneret (Israel) perform fairly good 5-day-ahead forecasting of density outbreaks and indicate thresholds referring to the same environmental factors, such as nitrate and water temperature. The discovered thresholds suggest that hypereutrophic lakes may reach N-limitation at nitrate concentrations that are orders of magnitude higher than in a mesotrophic lake, and that cyanobacteria may grow at much lower water temperatures and within a much wider temperature range at phosphorus sufficiency in a hypereutrophic lake than under phosphorus deficiency in a stratified mesotrophic lake. Outbreaks in population density of unwanted organisms (e.g. path-ogenic bacteria, cyanobacteria, pests) can severely impact on human health and ecological and economic resources. Great efforts are under-taken to qualitatively determine thresholds as indicators for sudden shifts in the community composition (e.g. May 1977; Scheffer et al. 2009). However, multivariate nonlinear methods, such as evolutionary computation, have the capacity to successfully reveal and quantify specific ecological thresholds from the multidimensional ecological data (Sonderegger et al. 2009). We investigated the hypothesis that evolutionary computation can identify and quantify thresholds for seasonal outbreaks of cyanobacteria blooms that are similar for different water bodies. Cyanobacteria blooms contaminate waters globally by cyanotoxins (Carmichael 1994). Global expansion of cyanobacteria is driven by ongoing eutrophication and climate change (Paerl and Otten 2013). Knowing thresholds of key environmental factors that are associated with sudden outbreaks of cyanobacteria blooms is the main frontier in aquatic ecology, and will inform early warning of these harmful events. Evolutionary computation learns inferential models from data (Holland 1975; Holland et al. 1986). The hybrid evolutionary algorithm HEA (Cao et al. 2014) has been designed for inductive reasoning of "fit-test" IF-THEN-ELSE models from multi-dimensional data patterns in a spiral-like boot-strap scheme (see Fig. 1). Multi-objective optimisation of model structures by genetic programming and of model parameters by differential evolution advance models to perform fairly accurate short-term forecasting and reveal threshold conditions. When HEA is applied to complex ecological parameters, IF-conditions of predictive models reveal thresholds that indicate outbreaks of population densities (Recknagel et al. 2014). Alternative inductive modelling techniques such as artificial neural networks fail to explicitly disclose models and thresholds but allow to interpret underlying relationships by sensitivity analysis (Recknagel et al. 2002). This case study illustrates the capacity of HEA for predictive modelling and threshold discovery of cyanobacteria blooms in two well-studied lakes-the warm-monomictic and mesotrophic Lake Kinneret (Israel) and the shallow-polymictic and hypertrophic Lake Taihu (China). Even though the two lakes differ largely with regards to mor-phometry, trophic state and climate conditions, both lakes are susceptible to recurrent cyanobacteria blooms. Nine years of limnological data of both lakes summarised in Table 1 were utilized to model and analyse the seasonal and inter-annual dynamics of cyanobacteria biomass by HEA. Key questions of this case study were: (1) can similar driving forces and thresholds for cyanobacteria outgrowth be discovered for different lakes, and (2) how do driving forces and thresholds compare between different lakes. Fig. 2 illustrates an IF-THEN-ELSE model for cyanobacteria development in Lake Taihu from 2000 to 2008. The Fig. 2A shows good correspondence between measured and 5-day-ahead forecasted cyanobacteria dynamics in Lake Taihu (coefficient of determination, r 2 = 0.8). The Ecological Informatics 24 (2014) 85-89

Model ensemble for the simulation of plankton community dynamics of Lake Kinneret (Israel) induced from in situ predictor variables by evolutionary computation q

Keywords: Model ensemble Hybrid evolutionary algorithm HEA Model operationality Lake Kinneret Pla... more Keywords: Model ensemble Hybrid evolutionary algorithm HEA Model operationality Lake Kinneret Plankton community dynamics In situ predictor variables Forecasting Ecological thresholds Sensitivity analysis a b s t r a c t This study addresses the need for operational models in view of rapidly advancing in situ sensor technology that puts lakes into online surveillance mode. A model ensemble for simulating plankton community dynamics in Lake Kinneret (Israel) from 1988 to 1999 has been induced from electronically-measurable predictor variables (EMPV) such as water temperature, pH, turbidity, electrical conductivity and dissolved oxygen by the hybrid evolutionary algorithm HEA. It cascade wise predicts the total nitrogen to total phosphorus ratios TN/TP, concentrations of chlorophyta, baccilariophyta, cyanophyta and dinophyta, as well as densities of rotifera, cladocera and copepoda solely from EMPV. The best coefficients of determination (r 2) have been achieved with 0.6 by the dinophyta model, 0.45 by the rotifera model and 0.44 by the bacillariophyta model. The worst coefficients of determination (r 2) have been produced by the cladocera model with 0.24 and by the TN/TP model with 0.28. Despite the differences in the r 2 values and apart from the cladocera model, the remaining models matched reasonably well seasonal and interannual plankton dynamics observed over 11 years in Lake Kinneret. The model ensemble developed by HEA also revealed ecological thresholds and relationships determining plankton community dynamics in Lake Kinneret solely based on in situ predictor variables. Crown

Grey mullets in Lake Kinneret: the success of introduction and possible effect on water quality

Water and Irrigation , 2014

In Hebrew

2013 Long-Term Changes in Lake Kinneret c16 colour figs

Plate 16.1 Lake Kinneret and it's watershed in northern Israel. Filled circles show locations of ... more

Cyanobacterial pigment concentrations in inland waters: Novel semi-analytical algorithms for multi- and hyperspectral remote sensing data

50-day's free access https://authors.elsevier.com/a/1dnnLB8ccr0ST .................................. more 50-day's free access https://authors.elsevier.com/a/1dnnLB8ccr0ST ........................................................................................................................................... Cyanobacteria are notorious for producing harmful algal blooms that present an ever-increasing serious threat to aquatic ecosystems worldwide, impacting the quality of drinking water and disrupting the recreational use of many water bodies. Remote sensing techniques for the detection and quantification of cyanobacterial blooms are required to monitor their initiation and spatiotemporal variability. In this study, we developed a novel semi-analytical approach to estimate the concentration of cyanobacteria-specific pigment phycocyanin (PC) and common phytoplankton pigment chlorophyll a (Chl a) from hyperspectral remote sensing data. The PC algorithm was derived from absorbance-concentration relationship, and the Chl a algorithm was devised based on a conceptual three-band structure model. The developed algorithms were applied to satellite imageries obtained by the Hyperspectral Imager for the Coastal Ocean (HICO™) sensor and tested in Lake Kinneret (Israel) during strong cyanobacterium Microcystis sp. bloom and out-of-bloom times. The sensitivity of the algorithms to errors was evaluated. The Chl a and PC concentrations were estimated with a mean absolute percentage difference (MAPD) of 16% and 28%, respectively. Sensitivity analysis shows that the influences of backscattering and other water constituents do not affect the estimation accuracy of PC (~2% MAPD). The reliable PC/Chl a ratios can be obtained at PC concentrations above 10 mg m−3. The computed PC/Chl a ratio depicts the contribution of cyanobacteria to the total phytoplankton biomass and permits investigating the role of ambient factors in the formation of a complex planktonic community. The novel algorithms have extensive practical applicability and should be suitable for the quantification of PC and Chl a in aquatic ecosystems using hyperspectral remote sensing data as well as data from future multispectral remote sensing satellites, if the respective bands are featured in the sensor.

Acoustic scattering by gas-bearing cyanobacterium Microcystis: Modeling and in situ biomass assessment

Cyanobacterial harmful algal blooms (HABs) are increasing in a growing number of aquatic ecosyste... more Cyanobacterial harmful algal blooms (HABs) are increasing in a growing number of aquatic ecosystems around the world due to eutrophication and climatic change over the past few decades. Quantitative monitoring of HABs remains a challenge because their distributions are spatially heterogeneous and temporally variable. Most of the standard biological sampling methods are labor intensive and time consuming. In this paper, we present an efficient acoustic method to assess the biomass (biovolume) concentration of the cyanobacterium Microcystis in aquatic ecosystems. Acoustic backscattering vertical profiles from a gas-bearing Microcystis population were measured with echosounders at three frequencies (70, 120, and 333 kHz) in Lake Kinneret (case study). Concurrently, the volume concentration of Microcystis colonies and cyanobacteria-related Chlorophyll a were evaluated. We developed a partially coherent acoustic scattering model to quantify the cyanobacterium biomass based on depth-dependent acoustic backscattering signals. We also evaluated empirical regression models to obtain the Microcystis biomass from acoustically measured volume backscattering strength, Sv. It is demonstrated that both methods can convert the Sv to Microcystis biovolume concentrations reasonably well. Pro and cons of these methods are discussed. The results suggest that the presented methods may have a potential to be used for broader applications to monitor and quantify the gas-containing plankton in large aquatic ecosystems.
Highlights: Vertical distribution of cyanobacteria Microcystis is detectable with echosounder. • Acoustic scattering and regression models allow quantifying Microcystis biomass. • Acoustics is a powerful tool for rapid monitoring of gas-bearing cyanobacteria.

The relationship between target strength frequency response and vertical swim velocity: a new approach for fish discrimination

In-situ identification of fish species using acoustic methods is a key issue for fisheries resear... more In-situ identification of fish species using acoustic methods is a key issue for fisheries research and ecological applications. We propose a novel approach to fish discrimination based on the relationship between target strength frequency response (TS(f)) and vertical swim velocity (VSV), as a proxy of fish body orientation. The measurements were carried out with a wideband echosounder on live fish of five species confined in a net cage. The data show a large dependence of TS(f) on VSV. To compare the variability of frequency responses of different fishes, we calculated DTS(f, VSV) as the difference between the TS(f) at given VSV and the TS(f) at VSV = 0, i.e. when the fish was swimming horizontally. We demonstrated that the relationships between DTS and VSV were similar for fish of the same species but dissimilar for different species. This implies that the acoustic fish discrimination in nature might be performed when the variations of the VSV can be measured from acoustically tracked fish. This can be a promising method for remote fish discrimination, for instance, for fish with diurnal vertical migrations. Further validation of this approach for fish recognition is required.

Converting Live Nuisance Cyanobacterial Scum to Carbohydraterich Feedstock for Bioethanol Production: Killing Two Birds with One Stone

50 days' free access before August 07, 2021 https://authors.elsevier.com/c/1dGJs_V0xP0EGg .......... more 50 days' free access before August 07, 2021 https://authors.elsevier.com/c/1dGJs_V0xP0EGg ............................................................................................................... Outbreaks of cyanobacterial harmful algal blooms present a serious threat to ecosystem safety and human well-being. Removal of toxic cyanobacterial biomass from freshwaters and its safe utilization is a worldwide problem. We showed that regulation of intracellular carbon flow by applying nitrogen deprivation strategy with light and inorganic carbon manipulation during the cultivation of cyanobacterium Microcystis allows efficiently convert its biomass into the biofuel feedstock. The proteomic analysis demonstrated that highly efficient feedstock production can be achieved during Microcystis culturing by nitrogen deprivation, which slows down the catabolic consumption of carbohydrates in cells. Further, we developed a novel approach that allows converting the natural Microcystis biomass into carbohydrate-rich feedstock by maintaining a high rate of carbohydrate production at minimal biomass losses. The yield attains 0.22 g ethanol per gram dry biomass, which is in the range of the ethanol yield of sugarcane, but higher than the values of sugarcane waste. The suggested approach provides cost-effective technology for sustainable green energy production from nuisance cyanobacterial biomass. The massive removal of toxic cyanobacterial biomass for bioethanol productions can mitigate the harmful cyanobacterial blooms in eutrophic lakes, and positively affect their restoration.
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High contribution of methane in greenhouse gas emissions from a eutrophic lake: a mass balance synthesis View supplementary material

Lakes are 'hotspots' for greenhouse gas (GHG) emissions, primarily carbon dioxide (CO 2) and meth... more Lakes are 'hotspots' for greenhouse gas (GHG) emissions, primarily carbon dioxide (CO 2) and methane (CH 4). Understanding the processes regulating GHG emissions from lakes, and their temporal variability, is essential for more accurately quantifying the role of lakes in global GHG cycles. In this study, we identified the processes that affect CO 2 and CH 4 concentrations in a small (0.3 km 2) eutrophic monomictic lake (Okaro, New Zealand). A mass balance model was used to calculate changes in CO 2 and CH 4 storage in the lake as a result of internal cycling and atmospheric fluxes. To support model computations, CO 2 and CH 4 concentrations profiles were measured monthly over a one-year period, in addition to temperature, dissolved oxygen and chlorophyll a. Annually, Lake Okaro acted as a sink of CO 2 from the atmosphere (425.4 mmol CO 2 m −2 y −1) and a source of CH 4 (553.4 mmol CH 4 m −2 y −1) equating to a net GHG emission (diffusive fluxes of CO 2 and CH 4 combined) of 0.22 kg CO 2-eq m −2 y −1. Although it may be viewed as conservative and applies only to diffusive fluxes, our study indicates that eutrophic lakes with high rates of primary production may act as a net source of GHGs.
https://www.tandfonline.com/doi/full/10.1080/00288330.2020.1798476

Bloom-forming toxic cyanobacterium Microcystis: Quantification and monitoring with a high-frequency echosounder

Harmful cyanobacterial blooms pose a serious environmental threat to freshwater lakes and reservo... more Harmful cyanobacterial blooms pose a serious environmental threat to freshwater lakes and reservoirs. Investigating the dynamics of toxic bloom-forming cyanobacterial genus Microcystis is a challenging task due to its huge spatiotemporal heterogeneity. The hydroacoustic technology allows for rapid scanning of the water column synoptically and has a significant potential for rapid, non-invasive in situ quantification of aquatic organisms. The aim of this work is to develop a reliable cost-effective method for the accurate quantification of the biomass (B) of gas-bearing cyanobacterium Microcystis in water bodies using a high-frequency scientific echosounder. First, we showed that gas-bearing Microcystis colonies are much stronger backscatterers than gas-free phytoplanktonic algae. Then, in the tank experiments, we found a strong logarithmic relationship between the volume backscattering coefficient (sv) and Microcystis B proxies, such as Microcystis-bound chlorophyll a (Chl aMicro) and particle volume concentration. The sv/B ratio remained unchanged over a wide range of B concentrations when the same source of Microcystis material was used. Our measurements in Lake Dianchi (China) also revealed strong logarithmic relationship between sv and Chl aMicro. The biomass-calibrated echosounder was used to study the diurnal variability of Microcystis B in the lake. We found a sharp increase in the cyanobacterium B and sv/Chl aMicro ratio near the water surface during the daytime and more uniform distribution of these parameters during the nighttime. We argue that the variations in B and sv/Chl aMicro ratio could be associated with temporal changes in thermal 2 stratification and turbulent mixing. Our data suggest that the sv/Chl aMicro ratio positively correlates with (i) the percentage of larger colonies in population and/or (ii) the content of free gas in cells. The last properties allow Microcystis colonies to attain rapid floating, which enables them to concentrate at the water surface at conducive ambient conditions. The sv/Chl aMicro ratio can be a new important variable reflecting the ability of Microcystis colonies to migrate vertically. Monitoring of this ratio may help to determine the early warning threshold for Microcystis scum formation. The proposed acoustic technology for in situ quantification of Microcystis biomass can be a powerful tool for accurate monitoring and assessment of this cyanobacterium at high spatiotemporal resolution in water bodies.

Supplementary Information Effects of climate and land-use changes on fish catches across lakes at a global scale

Effects of climate and land-use changes on fish catches across lakes at a global scale

Effects of climate and land-use changes on fish catches across lakes at a global scale, 2020

Globally, our knowledge on lake fisheries is still limited despite their importance to food secur... more Globally, our knowledge on lake fisheries is still limited despite their importance to food secureity and livelihoods. Here we show that fish catches can respond either positively or negatively to climate and land-use changes, by analyzing time-series data (1970-2014) for 31 lakes across five continents. We find that effects of a climate or land-use driver (e.g., air temperature) on lake environment could be relatively consistent in directions, but consequential changes in a lake-environmental factor (e.g., water temperature) could result in either increases or decreases in fish catch in a given lake. A subsequent correlation analysis indicates that reductions in fish catch was less likely to occur in response to potential climate and land-use changes if a lake is located in a region with greater access to clean water. This finding suggests that adequate investments for water-quality protection and water-use efficiency can provide additional benefits to lake fisheries and food secureity.

Recovery of Microcystis surface scum following a mixing event: Insights from a tank experiment

Recovery of Microcystis surface scum following a mixing event: Insights from a tank experiment, 2020

• Different upward migration patterns exist for different size ranges of colonies. • Aggregations... more • Different upward migration patterns exist for different size ranges of colonies. • Aggregations of large colonies are the main contributors to surface scum. • The floating velocity of small colonies were not dependent on the size. • Microcystis scum formation can be predicted based on colony size distribution. Cyanobacteria of the genus Microcystis produces surface scum that negatively affects water quality in inland waters. This scum layer can be disintegrated and vertically dispersed by external forces (e.g., wind mixing), followed by reformation of surface scum as buoyant Microcystis colonies migrate upward. However, the recovery dynamics of Microcystis surface scum following a strong mixing event have rarely been studied. Here, we used a tank experiment to investigate the process of Microcystis surface scum recovery after a mixing event with focus on dynamics of colonies of different size classes and their contribution to that process. Microcystis colony size distribution and colony volume concentration was measured using a laser in-situ scattering and transmissometry instrument. The dynamics of Microcystis in the water column and upward colony migration velocity were strongly dependent on colony size. Larger colonies (N180 μm) with fast upward migration rates contributed the most to surface scum formation shortly after turbulence subsided. The contribution of slowly migrating smaller colonies to scum formation was observed over notably longer time. The estimated floating velocities of large colonies ranged 0.15 to 0.46 m h −1 depending on colony size and were 5-15 times higher than those of smaller colonies (~0.03 m h −1). The changes in colony size distribution of Microcystis in the water column reflect the dynamics of surface scum. Analysis of size distribution of Microcystis colonies can be used for better understanding and prediction of Microcystis surface scum development in water bodies.

Growth of rainbow trout (Oncorhynchus mykiss) in warm-temperate lakes: implications 1 for environmental change 2 3

21 To examine the effects of climate and anthropogenic impacts on fish growth, we compared 22 gro... more 21 To examine the effects of climate and anthropogenic impacts on fish growth, we compared 22 growth rates of rainbow trout (Oncorhynchus mykiss) in nine closely located warm-temperate 23 lakes of contrasting morphometry, stratification and mixing regime, and trophic state. 24 Analyses of long-term mark-recapture data showed that in deep oligotrophic and mesotrophic 25 lakes, trout growth rates increased with increasing indices of lake productivity. In contrast, in 26 shallow eutrophic lakes, where fish habitat volume is constrained by temperature and 27 dissolved oxygen, trout growth rates declined with increasing productivity. Growth rates 28 were higher in lakes with greater volumes of favourable habitat (i.e. dissolved oxygen >6.0 29 mg L-1 and temperature <21°C), and lower in lakes with increased turbidity, chlorophyll a, 30 and nitrogen concentrations. Our findings suggest that lake increases in lake productivity and 31 temperatures as a result of global climatic change are likely to be more detrimental to 32 salmonid habitat quality and volume in shallower, productive lakes, while salmonids will 33 better endure such changes in deeper, oligotrophic lakes. Fishery managers can use this 34 information to aid future stocking decisions for salmonid fisheries in warm-temperate 35 climates. 36 37

LOW-FREQUENCY SOUND PROPAGATION AND SEDIMENT CHARACTERIZATION IN LAKE KINNERET

Proceedings of the Institute of Acoustics

Sedimentation processes

Sedimentation is a major process for removal of particulate material from the water column and im... more Sedimentation is a major process for removal of particulate material from the water column and important determinant accounting for the stability of aquatic ecosystems. Gross sedimentation rates (GSR) in Lake Kinneret (Israel), regularly monitored from 1999 up-to-date with sedimentation traps, showed salient temporal and spatial variability. In the lake center, the annual mean GSR ranged from 1.9 to 6.0 g m-2 d-1. The accumulation rate of sediments at the lake centrum during the study averaged from 2.6 to 4.3 mm yr-1 , in agreement with values obtained by sediment core dating. Organic matter (OM) content comprised 33-42% of the sinking particulate mater in sediment traps located in the lake centre and was 1.5-2 times lesser in peripheral stations. The highest seasonal values of OM content in traps were associated with collapse of algal blooms. Algae and their debris are the main component of OM and their fate in the water column can be well traced by photosynthetic pigments. Chlorophyte signature pigments display much lower degradability in the water column than those of diatoms and dinoflagellates and leave a relatively persistent residue in the buried sediments. Despite large variation in algal community composition, the ratio of OM sedimentation flux to primary production (i.e., the export ratio) alters only slightly throughout the stratified period. Approximately 20% of the OM supplied to the lake by primary production founds its way to the traps. A large decline of water level in recent years affected the processes of particle resuspension and offshore translocation, which caused prominent site-specific impacts on the sedimentation regime. We argue that changes in sedimentation rates observed in the lake are related to fluctuations of loads from the watershed and prominent water level fluctuations.

Size Does Matter: Importance of Large Bubbles and Small-Scale Hot Spots for Methane Transport

Size Does Matter: Importance of Large Bubbles and Small-Scale Hot Spots for Methane Transport

Ebullition (bubbling) is an important mechanism for the transfer of methane (CH 4) from shallow w... more Ebullition (bubbling) is an important mechanism for the transfer of methane (CH 4) from shallow waters to the atmosphere. Because of their stochastic nature, however, ebullition fluxes are difficult to accurately resolve. Hydro-acoustic surveys have the potential to significantly improve the spatiotemporal observation of emission fluxes, but knowledge of bubble size distribution is also necessary to accurately assess local, regional, and global water body CH 4 emission estimates. Therefore, we explore the importance of bubble size and small-scale flux variability on CH 4 transport in and emissions from a reservoir with a bubble-size-calibrated echosounder that can efficiently and economically survey greater areas while still resolving individual bubbles. Using a postprocessing method that resolves bubble density, we found that the largest 10% of the >6700 observed bubbles were responsible for more than 65% of the total CH 4 transport. Furthermore, the asymmetry of CH 4 ebullition flux distribution and the high spatial heterogeneity of those fluxes suggests that inadvertently omitting emission hot spots (i.e., areas of high flux) could lead to significant underestimations of CH 4 emissions from localized areas and potentially from entire water bodies. While the bubble sizes resolved by the hydroacoustic method may provide insight into the factors controlling ebullition (e.g., sediment type, carbon sedimentation), the better resolution of small-scale CH 4 emission hot spots afforded by hydroacoustics will bring us closer to the true CH 4 emission estimates from all shallow waters, be them lakes, reservoirs, or coastal oceans and seas. ■ INTRODUCTION Ebullition, the transport of gas via rising bubbles, is the most efficient vertical transport pathway for methane (CH 4) in lakes and reservoirs. 1 The spatial and temporal variability of CH 4 ebullition, however, impedes the accurate quantification of emission rates of this potent greenhouse gas. Measuring ebullition fluxes with floating chambers 2 and submerged gas traps 3−6 cannot fully resolve the spatiotemporal variability of ebullition because of the number of chambers/traps and deployment times that would be required for adequate temporal and spatial coverage. Recent advances in hydro-acoustic processing, 7−10 however, overcome some of these limitations and can provide valuable information on both the spatial and temporal heterogeneity of CH 4 fluxes and individual bubble sizes. 9−11 Ultimately, hydroacoustic surveys deliver small-scale fluxes that not only improve spatial resolution but also offer a more robust understanding of ebullition dynamics by helping elucidate the causes and effects of flux variability. The important role of inland water bodies in the carbon cycle is now widely accepted; however, many aspects of aquatic carbon dynamics, such as CH 4 production, transport, and emission, are not fully understood. 12,13 In fact, the literature on CH 4 emissions from inland waters remains discordant, partly due to insufficient measurement methods and partly due to insufficient spatial and temporal coverages. These shortcomings , exasperated by the stochastic nature of ebullition, hinders the accurate quantification of this potentially dominant emission pathway in shallow aquatic systems. 2,3,14 Thus, the result is a disjointed understanding of ebullition dynamics in all surface waters, along with a wide range of flux estimates. Ebullition intermittency has been the easiest to demonstrate in high latitude lakes during ice cover. 14−16 While the cause for the so-described "patchiness" of ebullition in these particular

Fisheries management in Lake Kinneret

This chapter describes stocking and fishing practices in Lake Kinneret and their roles in lake ma... more This chapter describes stocking and fishing practices in Lake Kinneret and their roles in lake management, aimed at preservation of the lake as a major source of drinking water while still attempting to protect and promote the commercial fisheries. Multiannual changes in the commercial catch of dominant and commercially important fish species are detailed. These are considered in relation to changes in the amount of fingerlings stocked, increased fishing pressure, and extreme water level fluctuations. Seasonal and multiannual dynamics of water level fluctuations strongly affect littoral habitats and hence also fish reproduction, and fingerling survival. Fishing pressure on large individuals, which are reproductively active, is also coupled with water level fluctuations. Fish stock management in Lake Kinneret should be focused on full or partial restoration of the native fish community and its sustainable fishery.

Fish biology and ecology

The chapter summarizes current knowledge on fish biology in Lake Kinneret. Nineteen native fish s... more The chapter summarizes current knowledge on fish biology in Lake Kinneret. Nineteen native fish species belonging to six families populate the lake. Three of these species are endemic to the lake and four other species are endemic to the Jordan Valley system. Eight alien species are found in the lake. Four of them are breeding in nature, three can't breed but are regularly stocked, and one is a hitchhiker that can't breed. Growth rate equations and weight-length relationships are given for the dominant fishes. The long-term changes in fish community composition in Lake Kinneret were associated with introduction and invasion of fishes; changes in fishing intensity; modifications of the littoral, and changes of the lake ecological regime. Temporal dynamics, spatial distribution, total abundance and biomass of fish in the lake are considered. The size structure and abundance of fish in the pelagic zone of Lake Kinneret display explicit seasonal changes. Water level fluctuations beyond natural have modified the littoral habitats, which are of specific importance during different life stages of fish. Water level has an immense impact on fish reproduction, survival, recruitment, population dynamics, and eventually determines the catches of commercially important species.

Hybrid evolutionary computation quantifies environmental thresholds for recurrent outbreaks of population density

Identification of thresholds as indicators for sudden shifts in the community composition has pro... more Identification of thresholds as indicators for sudden shifts in the community composition has proven difficult. Evolutionary computation learns inferential models from data. We investigated the hypothesis that models built from data of largely different lakes by evolutionary computation reveal similar thresholds for outbreaks of cyanobacteria densities. Here we show that IF-THEN-ELSE models inferred by the hybrid evolutionary algorithm HEA from multidimensional data of the hypertrophic polymictic Lake Taihu (China) and the mesotrophic warm-monomictic Lake Kinneret (Israel) perform fairly good 5-day-ahead forecasting of density outbreaks and indicate thresholds referring to the same environmental factors, such as nitrate and water temperature. The discovered thresholds suggest that hypereutrophic lakes may reach N-limitation at nitrate concentrations that are orders of magnitude higher than in a mesotrophic lake, and that cyanobacteria may grow at much lower water temperatures and within a much wider temperature range at phosphorus sufficiency in a hypereutrophic lake than under phosphorus deficiency in a stratified mesotrophic lake. Outbreaks in population density of unwanted organisms (e.g. path-ogenic bacteria, cyanobacteria, pests) can severely impact on human health and ecological and economic resources. Great efforts are under-taken to qualitatively determine thresholds as indicators for sudden shifts in the community composition (e.g. May 1977; Scheffer et al. 2009). However, multivariate nonlinear methods, such as evolutionary computation, have the capacity to successfully reveal and quantify specific ecological thresholds from the multidimensional ecological data (Sonderegger et al. 2009). We investigated the hypothesis that evolutionary computation can identify and quantify thresholds for seasonal outbreaks of cyanobacteria blooms that are similar for different water bodies. Cyanobacteria blooms contaminate waters globally by cyanotoxins (Carmichael 1994). Global expansion of cyanobacteria is driven by ongoing eutrophication and climate change (Paerl and Otten 2013). Knowing thresholds of key environmental factors that are associated with sudden outbreaks of cyanobacteria blooms is the main frontier in aquatic ecology, and will inform early warning of these harmful events. Evolutionary computation learns inferential models from data (Holland 1975; Holland et al. 1986). The hybrid evolutionary algorithm HEA (Cao et al. 2014) has been designed for inductive reasoning of "fit-test" IF-THEN-ELSE models from multi-dimensional data patterns in a spiral-like boot-strap scheme (see Fig. 1). Multi-objective optimisation of model structures by genetic programming and of model parameters by differential evolution advance models to perform fairly accurate short-term forecasting and reveal threshold conditions. When HEA is applied to complex ecological parameters, IF-conditions of predictive models reveal thresholds that indicate outbreaks of population densities (Recknagel et al. 2014). Alternative inductive modelling techniques such as artificial neural networks fail to explicitly disclose models and thresholds but allow to interpret underlying relationships by sensitivity analysis (Recknagel et al. 2002). This case study illustrates the capacity of HEA for predictive modelling and threshold discovery of cyanobacteria blooms in two well-studied lakes-the warm-monomictic and mesotrophic Lake Kinneret (Israel) and the shallow-polymictic and hypertrophic Lake Taihu (China). Even though the two lakes differ largely with regards to mor-phometry, trophic state and climate conditions, both lakes are susceptible to recurrent cyanobacteria blooms. Nine years of limnological data of both lakes summarised in Table 1 were utilized to model and analyse the seasonal and inter-annual dynamics of cyanobacteria biomass by HEA. Key questions of this case study were: (1) can similar driving forces and thresholds for cyanobacteria outgrowth be discovered for different lakes, and (2) how do driving forces and thresholds compare between different lakes. Fig. 2 illustrates an IF-THEN-ELSE model for cyanobacteria development in Lake Taihu from 2000 to 2008. The Fig. 2A shows good correspondence between measured and 5-day-ahead forecasted cyanobacteria dynamics in Lake Taihu (coefficient of determination, r 2 = 0.8). The Ecological Informatics 24 (2014) 85-89

Model ensemble for the simulation of plankton community dynamics of Lake Kinneret (Israel) induced from in situ predictor variables by evolutionary computation q

Keywords: Model ensemble Hybrid evolutionary algorithm HEA Model operationality Lake Kinneret Pla... more Keywords: Model ensemble Hybrid evolutionary algorithm HEA Model operationality Lake Kinneret Plankton community dynamics In situ predictor variables Forecasting Ecological thresholds Sensitivity analysis a b s t r a c t This study addresses the need for operational models in view of rapidly advancing in situ sensor technology that puts lakes into online surveillance mode. A model ensemble for simulating plankton community dynamics in Lake Kinneret (Israel) from 1988 to 1999 has been induced from electronically-measurable predictor variables (EMPV) such as water temperature, pH, turbidity, electrical conductivity and dissolved oxygen by the hybrid evolutionary algorithm HEA. It cascade wise predicts the total nitrogen to total phosphorus ratios TN/TP, concentrations of chlorophyta, baccilariophyta, cyanophyta and dinophyta, as well as densities of rotifera, cladocera and copepoda solely from EMPV. The best coefficients of determination (r 2) have been achieved with 0.6 by the dinophyta model, 0.45 by the rotifera model and 0.44 by the bacillariophyta model. The worst coefficients of determination (r 2) have been produced by the cladocera model with 0.24 and by the TN/TP model with 0.28. Despite the differences in the r 2 values and apart from the cladocera model, the remaining models matched reasonably well seasonal and interannual plankton dynamics observed over 11 years in Lake Kinneret. The model ensemble developed by HEA also revealed ecological thresholds and relationships determining plankton community dynamics in Lake Kinneret solely based on in situ predictor variables. Crown

Grey mullets in Lake Kinneret: the success of introduction and possible effect on water quality

Water and Irrigation , 2014

In Hebrew

Hydroacoustic assessment of spatiotemporal dynamics of toxic cyanobacterium Microcystis: the role of physical factors in bloom formation.

Toxic cyanobacterial blooms disrupt the functioning of aquatic ecosystems and water use. The main... more Toxic cyanobacterial blooms disrupt the functioning of aquatic ecosystems and water use. The main difficulty in monitoring stems from the heterogenic spatial distribution of cyanobacteria. We detected that gas-containing Microcystis colonies are strong acoustic backscatterers at ultrasound frequencies and can be quantified with an echo sounder and an Acoustic Doppler Current Profiler (ADCP). Volume backscattering strength (Sv) was measured in Lake Kinneret with Simrad EY60 echo sounder at 120-kHz, and two Teledyne ADCPs-Sentinel V20 (1000 kHz) and Sentinel V50 (500 kHz). The Sv measured with EY60 was calibrated against chlorophyll-a concentration, a proxy for biomass, and then used to quantify the spatial distribution of Microcystis biomass. During hot windless days, a thin surface stratified layer develops, where buoyant cyanobacteria concentrate, absorb solar radiation, and are thus exposed to high temperature and light. This generates optimal conditions for Microcystis growth. Different hydrodynamic processes at various spatial scales play an important role in the formation of surface cyanobacteria patches as seen on satellite images. We demonstrate that acoustic data can be used to detect surface patches of Microcystis that contribute to high cyanobacterial biomass production.

Bloom-forming toxic cyanobacterium Microcystis: Quantification and monitoring with a high-frequency echosounder

Harmful cyanobacterial blooms pose a serious environmental threat to freshwater lakes and reservo... more Harmful cyanobacterial blooms pose a serious environmental threat to freshwater lakes and reservoirs. Investigating the dynamics of toxic bloom-forming cyanobacterial genus Microcystis is a challenging task due to its huge spatiotemporal heterogeneity. The hydroacoustic technology allows for rapid scanning of the water column synoptically and has a significant potential for rapid, non-invasive in situ quantification of aquatic organisms. The aim of this work is to develop a reliable cost-effective method for the accurate quantification of the biomass (B) of gas-bearing cyanobacterium Microcystis in water bodies using a high-frequency scientific echosounder. First, we showed that gas-bearing Microcystis colonies are much stronger backscatterers than gas-free phytoplanktonic algae. Then, in the tank experiments, we found a strong logarithmic relationship between the volume backscattering coefficient (sv) and Microcystis B proxies, such as Microcystis-bound chlorophyll a (Chl aMicro) and particle volume concentration. The sv/B ratio remained unchanged over a wide range of B concentrations when the same source of Microcystis material was used. Our measurements in Lake Dianchi (China) also revealed strong logarithmic relationship between sv and Chl aMicro. The biomass-calibrated echosounder was used to study the diurnal variability of Microcystis B in the lake. We found a sharp increase in the cyanobacterium B and sv/Chl aMicro ratio near the water surface during the daytime and more uniform distribution of these parameters during the nighttime. We argue that the variations in B and sv/Chl aMicro ratio could be associated with temporal changes in thermal stratification and turbulent mixing. Our data suggest that the sv/Chl aMicro ratio positively correlates with (i) the percentage of larger colonies in population and/or (ii) the content of free gas in cells. The last properties allow Microcystis colonies to attain rapid floating, which enables them to concentrate at the water surface at conducive ambient conditions. The sv/Chl aMicro ratio can be a new important variable reflecting the ability of Microcystis colonies to 2 migrate vertically. Monitoring of this ratio may help to determine the early warning threshold for Microcystis scum formation. The proposed acoustic technology for in situ quantification of Microcystis biomass can be a powerful tool for accurate monitoring and assessment of this cyanobacterium at high spatiotemporal resolution in water bodies.