rock enriched in Na+
and SO4
2- as compared to most
aquifer rock, or the entrainment of an end member
containing higher Na+
, SO4
2-, and methane. Previous
studies have also shown that the largest discharging spring
in Ash Meadows, Crystal Spring (also referred to as
Crystal Pool Spring), has a significantly higher carbon-14
value than any other spring [3] and that the three
southernmost springs in the discharge area (Big Spring
being the largest) have anomalous strontium isotopic
values (Table 1) [8, 14].
Prior to this study, almost nothing was known about
the indigenous microbial populations of any subsurface or
spring habitat in the Southern US Great Basin. DNAbased
(16S rRNA gene) assessments of microbial
diversity developed for this study show that Ash
Meadows spring waters contain exceptional bacterial
diversity at both shallow (species-level) and deep
(phylum-level) measures of genetic relatedness. Among
our bacterial gene libraries, with the exception of one
highly dominant betaproteobacterial lineage in Big Spring
(an inferred methanotroph, 46 of 72 library clones), very
few multiple occurrences were noted within or between