Stratification, vertical mixing, and upward ammonium flux in hypersaline Mono Lake, California
Romero, José R.; Jellison, Robert; Melack, John M.
Archiv für Hydrobiologie Volume 142 Number 3 (1998), p. 283 - 315
published: Jul 7, 1998
ArtNo. ESP141014203006, Price: 29.00 €
The effects of freshwater inputs and wind on stratification, vertical mixing, and upward fluxes of ammonium were evaluated during 6-yr (1989-1994) of monomixis (one period of complete mixing a year) in hypersaline Mono Lake, California. Falling lake level (evaporation > freshwater inputs) during 5-yr led to unstable salinity (S) profiles (mixed-layer S > hypolimnetic S) over the period of strong thermal stratification (June-October). Profiles in October 1991 and 1994 indicate the occurrence of double diffusive salt fingering because of unstable salinity stratification. Stable salinity stratification persisted throughout the summer and delayed holomixis in 1993, the only year freshwater inputs were greater than evaporation. Biweekly to monthly eddy diffusivities (Kz<) at the thermocline were estimated with the flux-gradient heat method corrected for solar heating. June-September Kz averages ranged from 9.5 x 10-7 m2/s (SE = 4.8 x 10-7) during wet 1993 (0.4 m lake level rise) to 4.2 x 10-6 m2/s (SE = 1.9 x 10-6) during the 1989 drought (0.6 m lake level decrease). The Lake Number, an index of seiche-induced mixing below the mixed-layer, explained 68 % of the variance in April-September metalimnetic diffusivities. Over the 6-yr 50-90 % of the seasonal (April-September) upward flux of ammonium was used or converted within the metalimnion likely from algal uptake and nitrification.