Sulfate (SO42−) Decline Supported Lake Kinneret (Israel) Invasion of N2-Fixing Cyanobacterium Aphanizomenon ovalisporum

Abstract

Since 1990, the Lake Kinneret trophic status has shifted from phosphorus to nitrogen limitation. In the summer of 1994, an outbreak of N2 fixing cyanobacterium Aphanizomenon ovalisporum invaded the epilimnion of Lake Kinneret. Since then, sporadic densities of harmful cyanobacteria (HFCB) reappeared in the lake together with other toxic non-N2 fixing cyanobacteria. This predicted ecological modification developed because of a worldwide well-known background condition of descent N/P mass ratio. Reevaluation of the lake and its watershed ecosystems data exposed additional potential support of the process reduction of the epilimnetic sulfate (SO42−) concentration. Climate condition changes resulted in sulfate input reduction and its potential competitive interaction with molybdenum (MoO42−) enhanced the HFCB growth rate. The working hypothesis was the reevaluated incorporation of long-term records including rainfall, river discharge, depth of ground water table in the Hula valley peat soil, total moisture capabilities, and Kinneret epilimnion sulfate concentration. Results justify conclusive inference in Lake Kinneret of the following: sufficient phosphorus, insufficient nitrogen, and sulfate decline availabilities induced the HFCB outbreak in the summer of 1994.