FIG. 3.
Ex situ assays of As(III) oxidation by a microbial mat from the yellow S0 zone in Dragon Spring. Symbols: ○, total dissolved As in transect site 2 mat assays showing no appreciable change in total dissolved As concentrations during these assays; ⋄, dissolved H2S measured in assays containing transect site 2 filter-sterilized water with mat material collected from transect site 2; ▵, As(V) formation in assays containing mat material from transect site 2 suspended in spring water from transect site 2; •, As(V) formation in assays containing mat material from transect site 2 suspended in filter-sterilized spring water collected from transect site 5; ▴, As(V) formation in assays containing mat material from transect site 5 in filter-sterilized spring water collected from transect site 5; ▪, As(V) concentration in heat-killed mat material from transect site 2 suspended in filter-sterilized spring water from transect site 5. Data are from one representative field trip experiment, with symbols representing the average of duplicate assays at each time point for each treatment and error bars (where visible) representing the range of the duplicate assays. H2S concentrations were lower than those shown in Fig. 2A because volatile losses occurred during the filter sterilization of spring water.