Bacterioplankton Dynamics in the McMurdo Dry Valley Lakes, Antarctica: Production and Biomass Loss over Four Seasons

Abstract

Research of the microbial ecology of McMurdo Dry Valley lakes has concentrated primarily on phototrophs; relatively little is known about the heterotrophic bacterioplankton. Bacteria represent a substantial proportion of water column biomass in these lakes, comprising 30 to 60% of total microplankton biomass. Bacterial production and cell numbers were measured 3 to 5 times, within four Antarctic seasons (October to January), in Lakes Fryxell, Hoare, and Bonney. The winter-spring transition (September to October) was included during one year. Lake Fryxell was the most productive, but variable, lake, followed by Lakes Bonney and Hoare. Bacterial production ranged from 0 to 0.009 µg C ml-1 d-1; bacterial populations ranged from 3.2 x 10(4) to 4.4 x 10(7) cells ml-1. Bacterial production was always greatest just below the ice cover at the beginning of the season. A second maximum developed just above the chemocline of all the lakes, as the season progressed. Total bacterioplankton biomass in the lakes decreased as much as 88% between successive sampling dates in the summer, as evidenced by areal integration of bacterial populations; the largest decreases in biomass typically occurred in mid-December. A forward difference model of bacterial loss in the trophogenic zone and the entire water column of these lakes showed that loss rates in the summer reached 6.3 x 10(14) cells m-2 d-1 and 4.16 x 10(12) cells m-2 d-1, respectively. These results imply that bacteria may be a source of carbon to higher trophic levels in these lakes, through grazing.

Limnological conditions in Subglacial Lake Vostok, Antarctica

“…Thus, if our incubations had been conducted over a longer time frame, we would have expected such carbon-fed cells to eventually initiate the growth phase. The metabolic rates from the 10uC incubation were converted to the ambient lake temperature of 23uC (Wü est and Carmack 2000) with the Arrhenius equation and an energy of activation of 12,600 kcal mol 21 (empirically determined Q 10 of 2.3 from bacterial production in a permanently ice-covered Antarctic lake located in the McMurdo Dry Valleys; Takacs and Priscu 1998). With this correction, the respiration rate under ambient lake temperatures is estimated to be 0.013 6 0.0090 to 0.38 6 0.011 nmol glucose L 21 d 21 (or 0.0050 6 0.0030 to 0.15 6 0.0050 nmol C L 21 d 21 ), which is on the low end of the range reported by Karl et al (1999) for an accretion ice core from 3,603 m (0.32-0.50 6 0.43 nmol C L 21 d 21 at 23uC).…”

Ace Lake: three decades of research on a meromictic, Antarctic lake

“…Comparable rates of bacterial production occur in neighbouring saline lakes in the Vestfold Hills . However, as is the case for primary production, meromictic Ace Lake sustains higher bacterial production than the meromictic lakes of the Dry Valleys, where in Lake Bonney and Lake Fryxell summer rates were between 0 to 4.9 and 0 to 10 lg C L -1 day -1 , respectively (Takacs and Priscu 1998).…”

Elevated levels of dimethylated‐sulfur compounds in Lake Bonney, a poorly ventilated Antarctic lake

“…Lisle and Priscu (in press) recently observed the presence of aggregates in the water column of Lake Bonney that are the equivalent of marine snow, and they found that these aggregates were ''hot-spots'' for microbial and viral activity, as is the case with marine snow (Azam and Long 2001). It is worth noting that dissolved organic carbon (DOC) concentrations increase dramatically in the bottom waters of each lobe, reaching levels in excess of 20 mg L Ϫ1 (Takacs andPriscu 1995, 1998). Such an increase could result from the conversion of particulate organic carbon to DOC, as is proposed for DMS and DMSO d .…”

“…Such an increase could result from the conversion of particulate organic carbon to DOC, as is proposed for DMS and DMSO d . However, heterotrophic activity in the waters below the chemocline is very low to nonexistent (Takacs andPriscu 1995, 1998;Ward et al 2003), indicating that these conversions must be occurring very slowly. Wakeham et al (1987) found that anaerobic phototrophic bacteria were implicated in the cycling of DMS in a seasonally stratified coastal salt pond.…”