The Replacement of Peridinium by Cyanobacteria in Lake Kinneret (Israel): A Commentary Review

The dynamics of N & P nutrient inputs and the 
consequent epilimnetic concentration during 1969-2018 in 
Lake Kinneret was studied. The consequences of their availability on algal 
composition were also studied. Two prominent periods were indicated: 1) 
Sufficient supply of N accompanied by Peridinium enhancement; 2) N deficiency 
and P sufficiency-induced Peridinium reduction and Cyanobacterium enhancement. 
The impact of Anthropocene conditions and dust deposition on N & P 
availability is evaluated.

study, algal uptake. Consequently phytoplankton dynamics is just one compartment within a complex interaction expressed as a final product entitled Total Nitrogen. Among Nitrogen forms the highest demands are due to Nitrates and Ammonium; therefore, temporal changes of Nitrogen stocks and Phytoplankton Biomass is essential.
Results shown in Figure 2 indicate a concentration decline of the highest nutritionally valued NH 4 and NO 3 during April months in 1969-2001 and obviously TN. Therefore, April is the maximum of the Peridinium bloomed biomass and the TN decline onwards is, therefore, the result of the temporal later decrease of its biomass. The temporal  changes of the concentration of TN, NO 3 and Organic Nitrogen (results are not presented) are similar: long-term decline. It is likely that sources of those nutrients are partially internal and supplemental Nitrogen demands for Peridinium are from external sources. The April data ( Figure 2) indicates the similarity of NH 4 and TP temporal change of concentrations: 1969-1985, increase and decline onwards. The temporal decline of negligible external inputs of NH 4 through Jordan River inflows are shown in Figure 8. The increase of Epilimnetic TP stock ( Figure 8) is probably originated not externally but internally via P mediated germinating Peridinium cysts. The cyst-mediated P supplied the demands for the bloom formation until 1985 when Peridinium density declined ( Figure 5). It has to be noted that simultaneous enhancement of Chlorophyta, Cyanophyta and Diatoms accompanied the elevation of Peridinium intensity ( Figure 5). The external supply of Phosphorus has also reduced significantly since the mid-1980's as a consequence of the removal of sewage (90%) and fish-pond waters (80%). The trend of increase of Epilimnetic concentration of TP was leveled off consequently. The Epilimnetic concentration Open Journal of Modern Hydrology The evaluation of Nutrient dynamics in the Epilimnion during September months   (Figure 4) indicates the long-term decline of TN, NO 3 and Organic Nitrogen (data not presented). September is Summer conditions, no rain flush of Nitrates, which were mostly removed in winter. The external supply of Phosphorus is carried out and even intensified by irrigation water in summer. That is because of P-bounded linkage to organic substance breakdown under soil dryness conditions. Internal supply of P is minimal during the existence of Stable stratification in Lake Kinneret. The impact of external input enhancement of NO 3 and TP as suggested to be carried out by the seasonal effect of precipitation-runoffs is presented in Figure 3. Nevertheless, the decline of TN during the January months ( Figure 3) affected Peridinium decline. The NO 3 increase in the January months (Figure 3) is just a short time case due to the early rain flushing of the free unbounded and highly available NO 3 in the Hula Peat soil stock. The decline of epilimnetic NH 4 concentration during the January months since the late 1970's is an additional support of Nitrogen reduction within the TN stock decline since the mid-1980's. The prominent dissipation of Epilimnetic Nitrogen stock ( Figure 4).

TN Standing Stock and Algal Biomass (Figure 5)
What is the relation between Epilimnetic Nitrogen standing stock load and the dynamics of Phytoplankton biomass? Results presented in Figure 5    partial exception is indicated about Diatoms density related to TN standing stock: the biomass decline is due to >1000 tons of TN while under <1000 tons of TN their biomass density increases with TN stock elevation. Contrary to the other algal groups, Peridinium biomass density is enhanced when Nitrogen standing stock is elevated. This case can be similarly expressed from an oppositional view: Peridinium biomass and TN are positively correlated while densities

TP Standing Stock and Algal Biomass (Figure 6)
Results shown in Figure 6 with regard to Algal Biomass and TP relations are similar to those with TN standing stock: the decline of the biomass of Chlorophyta   [8] [9]. The evaluation of dustfall impact on the Epilimnetic-bioavailable-P concentration requires an insight into the wind regime (velocity and direction) in the Kinneret region (Serruya, S. 1978 Wind information was published [3] as colored graphical charts from which it was possible to define the period and daytime of the occurrence of maximal gust velocity ranges ( Table 2): The periodical frame was defined between June and August and the daytiming-15:00-17:00, which is the typical Summer Westerly gusts.
Results in Table 1 and Table 2  drainage and agricultural developments that might cause P-rich dust matter inputs into the lake. Nevertheless, Zarka et al. [9] stated that the sources of P-rich dust particles are not necessarily cultivated fields, cattle farms or intensive pasture areas. Moreover, the effectiveness of P-rich dust carrier is probably not due to the westerly directions. It is, therefore, suggested that the Epilimnetic TP concentration seasonal dynamics ( Figure 1) is driven by internal sources (P-mediated Peridinium Cysts) and probably to a lesser extent by inputs of dustfall originated from Dolomite and Feldspar substances. If, as previously hypothesized, import of P to the Epilimnmion is mostly due to deposition of wind carrier dust, it should   Table 1, Table 2). Nevertheless, during these months the P concentration declines and increases from October ( Figure 1) through January by sedimentation of P-rich Dolomite or Feldspar dominated dust particles [9] from local substances in the vicinity. Partial support for this suggestion is given in Table 1 [

Batimetrical Distribution of Epilimnetical Nutrients (Figure 9)
Batimetrical distribution of Epilimnetic nutrients is shown in Figure 9.

Peridinium, TP and TN Seasonal Matching
The role of the combined impact of P and N on Kinneret algal assemblages and particularly Peridinium was documented previously [13] [14] [15]. Results shown in Figure 10 & Figure 11 define the seasonal onset and die-off of the Peridinium bloom with the respective response to epilimnetic stocks of TN and TP. The monthly fluctuations of the biomass density indicate an onset development from October to the April Maximum and die-off from April to the minimum in August-October. The peak of Epilimnetic TN stock is matching the maximum of the Peridinium biomass. The seasonal die-off of the Peridinium biomass is matched with the decline of the Epilimnetic TN stock. Contrary to those TN-Peridinium relations, the increase of epilimnetic TP stock is matched with high Peridinium density. It is likely that two different dynamic traits are indicated: the external import of Nitrogen enhances Peridinium growth rate and its elevation is indicated as supplemented algal cells contributing cyst-mediated Phosphorus to the Epilimnion. An indicated prediction suggests that the rate of TN stock Die-off (exponent value, Figure 12) is higher as the Nitrogen load is increased.

Conclusive Summary
This paper is an attempt at an evaluation of the dependant/independent paradigm Open Journal of Modern Hydrology     River waters [27]. Nevertheless, prior to the draining of Lake Hula and surrounded swamps, the chemical trait of the peat soil was reductive and Peridinium bloomed intensively, but presently soil conditions are oxidative and, therefore, limitation of Se is not doubtful. Several parameters are known as prominently demanded by Peridinium bloom production: the compounds produced via the Calcite precipitation process [27] DIC, and Se 4+ and others (Cuprum was also predicted). Nevertheless, it is insufficient to indicate short-term parameters as impact factor, while Nitrogen reduction was defined as a long-term condition that also influenced other Phytoplankters. The impact of N, P, C, and Se (including different Se forms) on the Peridinium growth rate was confirmed as sole or any mixed parameters, but only long-term deficiency effect as sole element of Nitrogen was documented. The advantageous novelty of the study is aimed at comprehensive presentation of long term record of data monitoring as a solid contribution for future management implementation.

Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.