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Gideon Gal   Dr.  Institute, Department or Faculty Head 
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Gideon Gal published an article in April 2018.
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Michael Weber

231 shared publications

Avi Ostfeld

42 shared publications

Boris Kompare

42 shared publications

Elad Salomons

42 shared publications

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(1999 - 2018)
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Article 0 Reads 1 Citation A multi-lake comparative analysis of the General Lake Model (GLM): Stress-testing across a global observatory network Louise C. Bruce, Marieke A. Frassl, George B. Arhonditsis, G... Published: 01 April 2018
Environmental Modelling & Software, doi: 10.1016/j.envsoft.2017.11.016
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The modelling community has identified challenges for the integration and assessment of lake models due to the diversity of modelling approaches and lakes. In this study, we develop and assess a one-dimensional lake model and apply it to 32 lakes from a global observatory network. The data set included lakes over broad ranges in latitude, climatic zones, size, residence time, mixing regime and trophic level. Model performance was evaluated using several error assessment metrics, and a sensitivity analysis was conducted for nine parameters that governed the surface heat exchange and mixing efficiency. There was low correlation between input data uncertainty and model performance and predictions of temperature were less sensitive to model parameters than prediction of thermocline depth and Schmidt stability. The study provides guidance to where the general model approach and associated assumptions work, and cases where adjustments to model parameterisations and/or structure are required.
Article 1 Read 0 Citations The dynamics of freshwater phytoplankton stability in the Naroch Lakes (Belarus) T.M. Mikheyeva, A. Parparov, B.V. Adamovich, E.V. Lukyanova,... Published: 01 October 2017
Ecological Indicators, doi: 10.1016/j.ecolind.2017.05.054
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The phytoplankton community of the Belarus Lakes Naroch, Myastro and Batorino, which have a Trophic State Index of 42.3, 60.7 and 66.8, respectively, underwent drastic changes to their structure during the period between 1968 and 2012. Thanks to an extensive monitoring program, these changes were well-documented and were qualitatively interpreted as signs of the community destabilization. The main objective of this study was the quantification of the ecological stability of the phytoplankton community in the Naroch Lakes. The approach to the quantification of ecological stability was based on defining the stability index as an inverse of the Euclidean Distance between the current and the reference states of the algal community (EuD-approach). The stability of the phytoplankton community was characterized by two indices: a “combined” index (SI[Comb]), and a “total community” index (SI[TotB]). SI[Comb] was calculated based on the individual taxonomic group biomasses and thus characterizes the stability of a community structure. SI[TotB] was calculated based on the values of the total algal biomass. Analyses of the results of this study extended the plausibility of the EuD-approach for the quantification of lake phytoplankton stability and allowed us to identify the dynamics of the stability of the Naroch Lakes phytoplankton. For the Naroch Lakes, we observed relatively larger SI[TotB] values in comparison with the SI[Comb] values. The results enabled us to examine the relationship between the lake trophic status and the stability of the phytoplankton community.
Article 0 Reads 1 Citation Development and application of a sustainability index for a lake ecosystem Gideon Gal, Tamar Zohary Published: 23 June 2017
Hydrobiologia, doi: 10.1007/s10750-017-3269-1
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We modify an existing water quality index of Lake Kinneret to better match the objective of sustaining the ecosystem over time. The Kinneret Sustainability Index (KSI) provides a quantitative indication of how similar the current ecosystem is in relation to a reference state that managers are striving to achieve and sustain once accomplished. As Lake Kinneret is the only freshwater lake in Israel, it is vital to sustain the lake ecosystem over time. The KSI provides lake managers with a means for assessing the state of the lake. The KSI is based on nine ecosystem variables and provides information on each variable and the combined index. We present examples of application of the KSI to lake management and conduct a sensitivity analysis of the underlying assumptions demonstrating its robustness to the assumptions. While the index presented here is specific to Lake Kinneret, it is a general approach that can be readily applied to lakes worldwide and can assist, for example, in achievement of the required good status for European lakes.
Article 0 Reads 0 Citations Predicting the impact of Lake Biomanipulation based on food-web modeling—Lake Kinneret as a case study E. Ofir, J.J. Heymans, J. Shapiro, M. Goren, E. Spanier, G. ... Published: 01 March 2017
Ecological Modelling, doi: 10.1016/j.ecolmodel.2016.12.019
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Biomanipulation is a tool decision makers use to achieve desirable management goals. In lakes, one of the most common goals is the improvement of water quality, an objective that can be achieved mainly by reducing the amount of phytoplankton in the water. Although it is a very clear goal that is achievable by using actions that affect the phytoplankton biomass, experience shows that primary biomanipulation goals are rarely achieved. A biomanipulation program was conducted in Lake Kinneret over a 12-year period with the goal of improving water quality by reducing the population of the dominant fish species in the lake. However, the biomanipulation failed to achieve the goal and the program was stopped. We used Ecopath with Ecosim (EwE) scenarios to examine the effect of biomanipulation on the ecosystem. The results of these scenarios show that biomanipulation actions, such as those used in the lake, indeed fail to improve water quality; furthermore, they will actually increase the amount of phytoplankton in the water and decrease water quality. The development of the method described in the present article provides managers with the means to evaluate the effect of biomanipulation on an ecosystem. This method enables researches to conduct a pre-action analysis of the planned measures and examine whether the goal can be achieved, saving money and time and preventing damage to the ecosystem.
Article 0 Reads 1 Citation Detecting changes to the functioning of a lake ecosystem following a regime shift based on static food-web models E. Ofir, G. Gal, M. Goren, J. Shapiro, E. Spanier Published: 01 January 2016
Ecological Modelling, doi: 10.1016/j.ecolmodel.2015.08.026
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Highlights•We analyze changes to a lake ecosystem by comparing two mass balance models.•The differences between the two models highlight the effect of a tipping point.•Using this method we establish management recommendations.•This approach can be applicable to all aquatic ecosystems. AbstractEcosystem management requires a large base of knowledge regarding the main factors of the components in the system, the relationship between them and their relationships with the external forces that affect ecosystem behavior. In many cases, this knowledge is not always available. Therefore, analyzing previous events and determining the effects they had on the ecosystem can provide insights regarding the factors that caused the changes and their continuing effect on the ecosystem. This task is not simple, due to a large variability of factors in the ecosystem and the difficulty in identifying them. Based on the Ecopath approach, we developed a means for analyzing the Lake Kinneret ecosystem by comparing two mass balance models representing two very different periods. The first model is based on the period of 1990–1993, prior to a regime shift that occurred in the ecosystem and the second model is based on 2006–2010, a period characterized by unstable behavior in the ecosystem. Examining the differences between the two models allowed us to map changes in the ecosystem and to identify the changes and the ecosystem components affected by the regime shift. Using the results we demonstrate the potential of providing management recommendations regarding Lake Kinneret's ecosystem and fishery.
BOOK-CHAPTER 0 Reads 1 Citation Protozoa (Unicellular Zooplankton): Ciliates and Flagellates Ora Hadas, Nehama Malinsky-Rushansky, Gideon Gal Published: 01 January 2014
Lake Kinneret, doi: 10.1007/978-94-017-8944-8_14
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Heterotrophic and mixotrophic protozoa have been recognized as important constituents of aquatic microbial food webs since the 1990s. Much less is known about the ecosystem roles of these organisms than about bacteria and archaea. Several pioneering studies in Lake Kinneret made in the 1980s clearly indicated that heterotrophic and mixotrophic ciliates and flagellates were of great significance in the mineralization of organic matter and cycling of carbon, nitrogen, and phosphorus. Modeling studies suggested that the protozoa, especially ciliates, appeared to be a critical food source for copepods. However, only after many years there was renewed research on protozoa as drivers of carbon flux and nutrient cycling. Routine monitoring of the lake ciliate populations was begun in 2006.