Quantitative aspects of the nitrogen cycle

Abstract

This chapter discusses the quantitative aspects of the nitrogen cycle in Lake Kinneret including its sources and sinks. A thorough discussion is devoted to the internal flux of NH4+ from the lower water mass (LWM) to the epilimnion during the stratified period. Also, it is shown that most nitrogen removal from this lake occurs by emitting N2(g) through a combined process of presumably dissimilatory nitrate reduction to nitrite (DNRN) which is followed by anaerobic ammonium oxidation (anammox). In these processes, NO3 locked in the LWM at the onset of stratification is claimed to be converted to NO2 through DNRN heterotrophic activity, while the NH4+ is contributed through degradation of organic matter settling from the epilimnion, thus facilitating the occurrence of anammox. Both biotic processes which occur in the sub-oxic LWM account for the removal of approximately 70% of the annual riverine N inflows to this lake. This leaves only about one third of the N introduced from riverine sources to be used in the following annual cycle.