**4.5 Residence time (RT) prolongation**

Residence Time prolongation (Water exchange reduction) affected also Nitrogen and Phosphorus dynamics (**Figures 9**–**11**). The process of Peridinium decline and Cyanobacteria enhancement was also supported by RT prolongation. The climate change initiated a linkage of chain events. Discharge decline and water scarcity (dryness) resulted WL decrease, RT prolongation and nutrient supply reduction accompanied by the modification of algal community structure. Normally, the higher the discharge is the faster is the increase of the WL and the shorter is the RT. and vice versa. The decline of discharge and Nitrogen input was accompanied by decline of epilimnetic TN stock and decrease of TN/TP mass ratio. Optimal Ecosystem management is aimed at protecting sustainability and the operation tool is through hydrological control: desirable ranges of pumping, WL fluctuations, nutrient dynamics preventing water quality deterioration resulting adequate water quality. Before 2010 the majority of domestic water supply originated from Lake Kinneret but essential climate change condition constrains created the need for the construction of alternative water source - Desalinization. The decline of discharge and insufficient Nitrogen input caused the phytoplankton community change. The newly created ecosystem structure enforced management adaptation for sustainability protection. When water budget is positive accompanied by appropriate withdraw (pumping and/or open Dam options) RT become shorter and water exchange is high. Decline of Nitrogen availability accompanied by Phosphorus enhancement caused the decline of TN/TP mass ratio [23, 35]. Hydrological management of Lake Kinneret is creating a dilemma for future implementation: Water supply is done by desalinization, salinity and Microcystis are enhanced as supported by close dams that enhance RT prolongation and water quality deterioration. It is therefore likely that recently, WL regime is not the management key factors and other parameters should step forward on the scale of priorities such as: salinity, nutrients and toxic Cyanobacteria biomass. For example, during heavy rain a partial open of the Dam is recommended to remove salt, phosphorus and Cyanobacteria biomass while water supply is not critical.
