An important part of the McMurdo Long Term Ecological Research (LTER) is monitoring of spatial and temporal patterns, and processes that control net primary production (carbon dynamics) in perennial ice-covered lakes. One of the primary losses of carbon fixed by phytoplankton is through respiration, directly by the phytoplankton themselves and secondarily through the metabolic contributions of heterotrophic organisms such as bacterioplankton and protozoa. The coupling of low metabolic activity and supersaturated gases in the water column prohibits a direct measurement of respiration. Therefore, we measure the respiratory electron transport system (ETS) activity which drives oxidative phosphorylation, and hence oxygen consumption in all aerobic organisms (Packard 1985). This data set addresses this core area of research and estimates a community-wide respiration rate at specific depths in McMurdo Dry Valley lakes (Hoare, Fryxell and Bonney).
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Lake water samples were collected at specific depths with a five-liter Niskin bottle during normal LTER limnological sampling. Sub-samples were decanted into three-1 L Nalgene bottles (2-light and 1-amber), two-500 mL amber Nalgene bottles, three-150 mL borosilicate glass bottles, two-20 mL scintillation vials, and one-30 mL serum vial. The two-one liter clear Nalgene bottles were used for the ETS experiment. Depending on the lake and depth at which each analysis was performed, 1000-2000 mL of lake water was filtered through a Whatman 47 mm GF/F filter. The filter was folded in half (organic material inside), placed in a glassine envelope, and stored at 0 degrees Celsius until analysis (<30 min). In an ice bath, the filter was combined with 3 mL of homogenization buffer and homogenized for 90 seconds with a glass/teflon tissue grinder. The mixture was decanted into a cone centrifuge tube; it was centrifuged in the cold for 3 minutes, vortexed for 30 seconds, and centrifuged for another 15 minutes. 0.5 mL of the extract was pipetted supernatant into three 1-cm quartz cuvettes (2 replicate, 1 control) and placed in an ice bath. The control sample was boiled for 10 minutes and cooled in an ice bath. 1.5 mL of substrate solution and 0.5 mL of INT solution was added to each cuvette, vortexed for 30 seconds, and incubated at 1-4C for one hour. The reaction was terminated in the cuvette with 0.5 mL of termination solution.
The absorbance was measured at 490 nm with a spectrophotometer. Light absorption by the sample idirectly proportional to the moles of electrons transferred through the electron transport system (ETS). Community ETS (umol O2 L-1 hr-1) was calculated using the following equation:
ETS = (AbsR - AbsC) a * b c * t
where AbsR is the average absorbance of the replicate samples, AbsC is the absorbance of the control sample, a is ratio of the volume of homogenization buffer to the volume of lake water filtered, b is the ratio of the final volume of reaction mixture in each cuvette to the volume of extract supernatant, c is the extinction coefficient for formazan (31.8 Abs cm-1 umol O2-1), and t is the incubation period.
Community ETS was adjusted to ambient lake temperature using the Arrhenius equation:
ETSadj = ETS * e^(Ea (( 1 / (CI + 273 K)) - ( 1 / (CA + 273 K))) / R )
where Ea is the energy of activation (15,000 cal mol-1, Q10 = 2.66), CI is the incubation temperature (C), CA is the ambient lake water temperature at specific depth, and R is a gas constant (1.987 cal mol-1 K-1).
A first order relationship exists between ETS activity and respiratory capacity in aquatic microorganisms (e.g., Kenner and Ahmed 1975, Christiansen et al. 1980). Our studies have revealed that 44% and 56% of measured ETS activity is from bacterioplankton and phytoplankton, respectively, in Lake Bonney (Takacs and Priscu, unpublished data). Using these relationships, in concert with published respiration:ETS ratios (Packard 1985), we derived a community respiration:ETS ratio of 0.61 for the water column of Lake Bonney. Individual respiration:ETS ratios for bacteria and phytoplankton were computed as 0.513 and 0.097, respectively.
In 2016, metadata was enhanced and completed for data preservation and export (San Gil)
Data from this table was submitted to INSTAAR by John Priscu's team at Montana State University. The raw data files listed under 'file name' are the names of the original files submitted, which are stored in the /data1/data/lakes/lakebio/ directory on INSTAAR's Unix system. The 1993/94 and 1994/95 datasets are Microsoft Excel version 6.0 files, and the1995/96, 1996/97 and 1997/98 datasets are ascii text files. Upon arrival at INSTAAR, the data manager fine-tuned the location codes and limno runs to match those provided in the "locations, dates, codes for lake chemistry, biology samples" file. The file was imported into Microsoft Access on INSTAAR's Unix system, and can currently be found there. The file was then exported in ascii, comma delimited text and MS-DOS text (table layout) to present on the MCM LTER web site. Both of these files are linked to this web page above. Information for the metadata was obtained from the Metaets9697.rtf and Metaets9798.rtf files. The files were called up using Microsoft Word version 6.0. Text from these files was used to create this page in html format.