The physical regime and the respective biogeochemical processes in the lower water mass of Lake Kinneret

Abstract

Physical measurements made in Lake Kinneret, during the stratified period, indicate that the lower water mass (LWM) consists of two layers: a turbulent benthic boundary layer (BBL) and a hypolimnetic layer overlying the BBL. The water in the LWM moves in response to vertical mode one seiching of the metalimnion; this movement is accentuated near the perimeter of the metalimnion due to shoaling of the seiche and breaking of internal waves. The motion associated with this phenomena induce a well mixed benthic boundary layer (BBL) adjacent to the lake bottom. The BBL and hypolimnion were distinguished chemically because transport of solutes between these water bodies was very small. Compared to the hypolimnion, the BBL was characterized by more intensive biomineralisation processes as indicated by the faster depletion of DO and NO3, by higher levels of NH4,H2S, and soluble reactive phosphorus (SRP) and by lower pH values. SRP levels in the hypolimnion were particularly low, suggesting that phosphorus was either preferentially removed by sedimentation from the hypolimnion, or it was not released from particles. As a result NH4 over SRP ratios in the hypolimnion were significantly higher than in the BBL and diffusional fluxes of both nutrients from the LWM to the trophogenic epipelagic water, should therefore be characterized by relatively high N/P ratios.