Big Soda Lake (Nevada). 1. Pelagic bacterial heterotrophy and biomass1

Abstract

Bacterial activities and abundance were measured seasonally in the water column of meromictic Big Soda Lake which is divided into three chemically distinct zones: aerobic mixolimnion, anaerobic mixolimnion, and anaerobic monimolimnion. Bacterial abundance ranged between 5 and 52 x 10h cells ml-', with highest biomass at the interfaces between these zones: 2-4 mg C liter' in the photosynthetic bacterial layer (oxycline) and 0.8-2.0 mg C liter' in the chemocline. Bacterial cell size and morphology also varied with depth: small coccoid cells were dominant in the aerobic mixolimnion, whereas the monimolimnion had a more diverse population that included cocci, rods, and large filaments. Heterotrophic activity was measured by [methyl-3H]thymidine incorporation and [14C]glutamate uptake. Highest uptake rates were at or just below the photosynthetic bacterial layer and were attributable to small (< 1 pm) heterotrophs rather than the larger photosynthetic bacteria. These high rates of heterotrophic uptake were apparently linked with fermentation; rates of other mineralization processes (e.g. sulfate reduction, methanogenesis, denitrification) in the anoxic mixolimnion were insignificant. Heterotrophic activity in the highly reduced monimolimnion was generally much lower than elsewhere in the water column. Therefore, although the monimolimnion contained most of the bacterial abundance and biomass (-60%), most of the cells there were inactive.

Depth Distribution of Microbial Diversity in Mono Lake, a Meromictic Soda Lake in California

“…In general, more chain-forming colonies and more large spirochetes were present in the monimolimnion. This finding is consistent with previously reported findings for other soda lakes (15,73). Casamayor et al (9), in a study of meromictic Lake Vilar, Spain, found that shifts in the distributions of closely related sequences reflected the distributions and ecological properties of the organisms possessing the sequences.…”

Bacterial secondary production in oxic and anoxic freshwaters

“…In agrcemcnt with other observations (Love11 and Konopka 1985;McDonough et al 1986;and Zehr et al 1987), we found that bacterial production often peaked midway through the anoxic hypolimnion rather than in the deepest, most reduced, depths. Similarly, in some of the lakes bacterial production in the deepest depths peaked during early anoxia but declined over time throughout summer (Fig.…”

“…For example, in Lake Ogelthorpe (McDonough ct al. 1986), Big Soda Lake (Zehr et al 1987), and Paul Lake (Pace and Cole 1994), the highest rates of bacterial production were observed just as oxygen concentrations became undetectable; bacterial production declined deeper into the more reduced hypolimnion. In Mirror Lake, Ochs et al (1995) found bacterial production in anoxic water to be -10 times higher than that in the epilimnion during summer stratification.…”

Spatial and Temporal Patterns in the Microbial Diversity of a Meromictic Soda Lake in Washington State

“…In agreement with previously reported findings for other meromictic soda lakes (24,74), an important outcome of our clone library analysis is the shift in the qualitative and quantitative compositions of the bacterial assemblage across the mixolimnion, the chemocline, and the 4. Dendrogram (constructed by the unweighted-pair group method with arithmetic means) of the pairwise nonparametric estimates of community structure similarity () between Soap Lake samples obtained from the mixolimnion (5m), the chemocline (20m), the monimolimnion (23m), and sediments (mixsed and monsed).…”