PS 50-61
Microbial biochemistry of a transitioning terminal lake ecosystem; Walker Lake, NV
Walker Lake, a terminal lake located in western-central Nevada, has experienced substantial desiccative stress since the late 1800s. The anthropogenic decrease of the water level has caused this alkaline (pH ~9.4), monomictic lake to suffer detrimental increases in the concentrations of total dissolved solids and salinity, leading to the loss of native fish species. The shifts in the chemical composition of Walker Lake water will ultimately affect microbial and microalgal communities that drive major nutrient and energy cycles of the ecosystem. This study aims to characterize sediment and water column microbial populations of Walker Lake over an annual cycle and compare data thus obtained to analogous work performed several years prior. Characterizations and correlative analyses include: real-time measurement of major environmental variables, microbial community structure via molecular DNA-based techniques, a cultivation-based assessment of dominant microbial physiotypes, aqueous chemistry analyses, and stable-isotopic characterizations of sulfur cycle intermediates. Initial sampling for the current phase of this project occurred during an unanticipated (based on previous samplings) period of holomixis in September and also November of 2013.
Results/Conclusions
Dilution cultivations from November of 2013 showed similar abundances of microbial sub-populations throughout the water column; consistent with a mixed state. Higher abundances of anaerobic microbial physiotypes were observed in sediment samples. Microbial physiotypes, cultivated from sediment and the water column (0m, 10m, and 19m), included heterotrophs (106-109 cells/mL in water column (WC), 106-108 cells/mL in sediment (S)), nitrate reducers (101-104 cells/mL WC, 104-106 cells/mL S), iron reducers (101-104 cells/mL WC, 106-108 cells/mL S), manganese oxide reducers (0 cells/mL WC, 103-104 cells/mL S), nitrite oxidizers (104-105 cells/mL WC, 106-107 cells/mL S), nitrite reducers (0 cells/mL WC, 102-104 cells/mL S), sulfate reducers, and fermenters. Cultivations indicated significant populations of arsenate-reducing and arsenite-oxidizing microorganisms (103 and 108 cells/mL respectively in sediment), correlating with the high arsenic content (>1400 ppb). Whereas, Illumina DNA sequencing results had not been received before abstract submission, diverse populations of novel, alkaliphilic microorganisms were anticipated, based on prior results. This ongoing characterization of Walker Lake microbial biogeochemistry during a period of environmental transition provides a foundation to aid interpretation of future ecosystem shifts and serves as a benchmark against which to compare ecosystem recovery if lake levels can be restored.