The Ecological Outcome of Climate Change in Lake Kinneret—Thermal Pollution

Water quality deterioration as a result of pollution comprised of several aspects, among others: nutrient input loads, fishery management, hydrological budget, toxicity, watershed deforestation, soil exposure, and exotic invaders. Thermal pollution is mostly considered as the impact of power or nuclear Station effluent or the effect of exceptional thermal abrupt shock. The long-term influence of global warming consideration is not extensively studied. The long-term (1969-2001) effect of climate change (warming and precipitation decline) on the Lake Kinneret ecosystem is presented. Water and air Temperature, Heat Capacity and Thermal conductivity of water combined with reduced precipitation accompanied by lake water level decline are ana-lyzed. It was found that the temperature of surface water increased with WL decline and decreased in deep layers during high WL. Future management design is suggested.


Introduction
Water quality deterioration (pollution) in lakes is mostly considered through nutrient dynamics, particulate suspended solids and dissolved substances. Nutrient pollution trait is not restricted only to input enhancements. Nutrient pollution is quite often the outcome of water input reduction accompanied by their fluctuations resulting from diminished water exchange and a consequent elevation of nutrient availability. During the last 30 -40 decades, the impact of fish's feeding habits was intensively included within the significances of lake pollution.
Nevertheless, the study of climate change and Thermal pollution impact on aq-uatic ecosystems was less documented [1]. Thermal aspects were mostly aimed at the influence of power or nuclear Station effluents on the ambient fauna and flora. The study of the impact of natural and anthropogenic conditions on the quality and potential deterioration of Lake Kinneret waters has been widely explored and documented [2]. In these scientific documents, the role of thermal effect was poorly accessed. Consequently, climate change, (global warming) which was indicated recently, was not intensively considered. Also, awareness of the impact of anthropogenic constraints was not thoroughly considered. The present paper is an attempt to evaluate thermal fluctuations and their implications for water quality.
Heat capacity or thermal capacity is defined as the amount of heat energy that must be provided to an object (water mass) in order to raise its temperature by one unit.
Heat capacity is proportional to the water mass size. Heat capacity of a certain mass is divided by the weight or volume of the mass, yielding the specific heat capacity (or "specific heat"). The volumetric heat capacity value defines the heat capacity per volume as expressed in the following equations: ∆T = Temperature increase ∆Q = Additional Heat amount (in calories) where ∆Q is the amount of heat that must be added to the water mass in order to raise its temperature from T1 to T2 by 1˚C (Celsius).
The objective of this paper is enhancing awareness about global warm trend of climate change and its implication on freshwater ecosystem and the significance of minor signals.

Material and Methods
The lake water temperature data as measured at discrete depths, air temperature, and the Thermocline depths and Water Level (mbsl) in this paper are those collected in the central deepest sampling station (A) and were taken from the Lake Kinneret Data Base [3].
The Israeli Meteorological Service provided rainfall data collected in Dafna Station located in the Northern region of the Hula Valley (Kinneret Drainage Basin). The Plankton data was compiled from the Annual Reports [3] of the Kinneret Limnological Laboratory, IOLR. All data parameters were evaluated as Open Journal of Modern Hydrology periodical (annual and multi-annual) means of monthly averages. The analysis evaluated and given in this study is based on periodical characteristic measures of simple means. The time frame of 1969-2001 was divided into three periodical segments: 1969-1980; 1981-1990 and 1991-2001.

Statistical Methods
Statistical analyses used in this study were taken from STATA 9.1, Statistics-Data Analysis. The analyses used were: Simple linear predicted correlation and Fractional Polynomial (FP) predicted Regression and Simple Linear Regression (with r 2 and p, probability, values).

Results
Data provided in Table 1 indicates an obvious reduction of Bathymetric layer volumes (Serruya 1978: Chapter Bathymetry) and the increase of layer temperatures (ΔT) by 0.2˚C -0.4˚C between 1969-2001.
Data provided in Table 2 indicates a decline of Bathymetric layers Heat Capacity ("Heat Budget", or "Heat Balance") between 1969 and 2001. The whole lake capacity was reduced from 16,016 to 11,985 × 10 6 Kcal during 32 years. Moreover, a potential predictive decline is forecasted if the same thermal and Heat investment under low and high water level will result in a dissimilar water temperature.
Data shown in Figure  The data provided in Table 3  The data provided in Table 4 indicates the closely related changes in rain decline and air temperature increase.  The closely related dynamics of rain, air temperature and lake water level are shown in Table 5 Figure 9). The temporal changes of the Thermocline depth indicate a shallower measure until the mid-1980's by about 4 meters, which later on became deeper by 8 meters (Figure 10). Thermocline temperature change with relation to depth allocation indicates an increase of 1˚C along 8 meters deepening and 2˚C elevation below 23 m depth allocation ( Figure 11).

Discussion
In previous studies on the thermal structural and temporal changes in Lake Kinneret the significance of heat capacity and its relevance to ecological features ware not widely considered. Changes in air temperature and Rainfall normally have a direct impact on lake characteristics [1] [5] [6]. Shifts in precipitation cause changes in water budget and hydraulic residence time as well as in water level, and consequently in total volume and Thermocline depth, resulting in Bathymetrical layer volumes and heat capacity differences. Air temperature elevation causes warmer lake surface waters which, in turn, increase stratification stability due to profoundly increased water density gradient. Reduction in bottom-up fluxed nutrient migration is possibly enhanced. A decline of rainfall could be the reason for longer residence time followed by nutrient accumulation, a well-known cause of pollution and water quality deterioration. Moreover,  [17]. It was documented that temperature elevation enhances metabolic activity accompanied by biomass density decline as a result of a higher loss of food energy (lower feeding efficiency). The environmental significance is the decline of biomass density when the temperature is increasing, while fish predation is enhanced simultaneously.
Apparent data provided in Table 2 and Table 6 indicates a paradoxical situation: water temperature is increasing while Heat Capacity declined during 1969-2001. The heat dynamical feature resulted from thermal pollution deterioration of water quality: Climate change expressed as dryness trend (rainfall reduction) resulted in a shrinking of water volume and although water temperature increased Heat capacity declined. Conclusively, the warming trend of air temperature induces water heating beside volume reduction, resulting in a decline of heat capacity. It is likely that, for the realistic estimation of the influence of global warming on lake ecosystem, a combined measure of the temperature and natural volume of water is required. The data provided in Table 3 shows   1˚C -6˚C by the end of the 21st century is predicted [8].
Three physical parameters of thermal water characteristics are considered: Temperature, Heat Capacity and Thermal conductivity. Thermal conductivity of air is 23.4 times lower than that of water. Therefore, atmospheric air heating is slower than heat transfer between Bathymetrical water layers, causing surface water to be warmer than the air temperature. The present study considers the long term of multi-annual periodical fluctuations. When water temperature declines, heat conductance and Capacity decline as well. Nevertheless, Heat capacity is respectively related to the mass size (volume of water); therefore, precipitation reduction followed by WL measure is significantly integrated. Climate Change expression in Lake Kinneret and its Watershed was air and water temperature elevation accompanied by precipitation decline. River discharges declined and lake WL dropped. Temperature increase, together with water volume shrinkage and reduced heat capacity, created a stronger steepness of the thermal gradient, which respectively enhanced conductance. The onwards development was simultaneous heating of the Kinneret water column and acceleration of biological activity, resulting in a trend of water quality deterioration. Appropriate management under those circumferences is shortening of water residence time by enhancement of exchange. Figures 1-3 indicate a higher temperature of the uppermost 0 -11 m layer under lower WL. On the contrary, in deep layers during high WL periods, the temperature was lower (Figure 2). Figure 3 indicates a positive relationship between the temperature of the air and surface waters when the air temperature is higher than 21.5˚C and surface temperature is >23.5.
Consequently, it is suggested that surface water is affected by air heating and probably Heat Conductance from deeper layers is significant. Figure 4 indicates that surface water heat fluctuates very little (±0.5˚C) under high WL (>211 mbsl). Under low WL (<211 mbsl) the temperature of surface water increases with WL decline (211 -214 mbsl). Conclusively, the thermal impact is related to air warming, precipitation decline and water warming.
Under low WL (<211 mbsl), the temperature of surface water increases with WL decline (211 -214 mbsl). The temperature of deeper layers during high WL decreased. A direct positive relationship between the temperature of the air and surface waters was indicated when the air temperature was higher than 21.5˚C with a surface temperature >23.5. Consequently, it is suggested that surface water is affected by air heating and partly also by upward Heat Conductivity from deeper layers. Conclusively, the thermal impact is related to air warming, precipitation decline and water warming. Because the outcome of warming lake water is an enhancement of the metabolic activity of the lake biota, the appropriate management design is shortening of water residence time by enhancement of water exchange. This study exemplifies that even minor thermal fluctuations might be a signal of ecological modification. The only thermal measure of degrees might be insignificance for a lake under water input reduction accompanied by WL and volume decline.