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Verbal·Information and Ideas·Command of Evidence

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In Arctic ecosystems, microbial methanogenesis accelerates as permafrost thaws, releasing stored organic carbon into the atmosphere as methane (${\mathrm{CH}}_4$). Biogeochemist Dr. Ksenia Romanova investigated the temperature sensitivity of methanogenic archaea by incubating two soil types—saturated thermokarst bog soil (representing degraded, collapsed permafrost) and intact upland mineral permafrost soil—across a thermal gradient ranging from $0^{\circ }\mathrm{C}$ to $20^{\circ }\mathrm{C}$. Romanova hypothesized that anoxic thermokarst soils possess active microbial consortia capable of exhibiting exponential increases in ${\mathrm{CH}}_4$ production as temperatures rise, whereas intact mineral soils display muted temperature responses.

Which choice best describes data from the graph that support Dr. Romanova’s hypothesis?

A

Methane emissions in intact mineral permafrost soil remained below $20{\mathrm{mg}\mathrm{CH}}_4/{\mathrm{m}}^2/\mathrm{day}$ across all temperatures, whereas emissions from thermokarst bog soil increased sharply to over $90{\mathrm{mg}\mathrm{CH}}_4/{\mathrm{m}}^2/\mathrm{day}$ at $20^{\circ }\mathrm{C}$.

B

Thermokarst bog soil produced lower methane flux than intact mineral permafrost soil at temperatures below $10^{\circ }\mathrm{C}$.

C

Both soil types exhibited linear decreases in methane production as the incubation temperature approached $20^{\circ }\mathrm{C}$.

D

Intact mineral permafrost soil showed an increase in methane flux that exceeded the flux of thermokarst bog soil at $15^{\circ }\mathrm{C}$.