16Hit1600
Information and IdeasVery hardChoosing a quotation that identifies a water source

Information and Ideas practice question

The Verdin River drains a high basin where nearly all precipitation falls as snow. Hydrologist Callum Ndiaye's team has gauged the river monthly since 2004 and compared the records with measurements made in the 1970s. Total annual discharge has changed little. Its timing has changed sharply: the spring peak now arrives about three weeks earlier, and the basin's snowpack is typically gone by mid-July. In August the Verdin still runs, at roughly two-thirds of its 1970s August volume. That August water is strikingly cold, 8 degrees Celsius on 30-degree afternoons, and it carries dissolved silica at four times the concentration found in the spring flood, a signature matching the deep bedrock aquifer beneath the basin.

Which quotation from the text best supports the claim that the water flowing in the Verdin in August has traveled through the basin's deep bedrock rather than reaching the river as that summer's surface runoff?

  1. A. "Total annual discharge has changed little."
  2. B. "the spring peak now arrives about three weeks earlier, and the basin's snowpack is typically gone by mid-July"
  3. C. "In August the Verdin still runs, at roughly two-thirds of its 1970s August volume."
  4. D. "That August water is strikingly cold, 8 degrees Celsius on 30-degree afternoons, and it carries dissolved silica at four times the concentration found in the spring flood, a signature matching the deep bedrock aquifer beneath the basin."Correct

Answer: D. "That August water is strikingly cold, 8 degrees Celsius on 30-degree afternoons, and it carries dissolved silica at four times the concentration found in the spring flood, a signature matching the deep bedrock aquifer beneath the basin."

The claim is about the source of the August water, and only choice D provides a positive identification: low temperature on hot afternoons and a silica concentration matching the deep bedrock aquifer are properties water acquires underground, not at the surface in August. Choice B is the error of treating the elimination of one alternative as identification of the source; with the snowpack gone, the water is not that summer's snowmelt, but this says nothing about bedrock as opposed to ponds, wetlands, soil water, or storage releases. Choice A concerns the annual water budget, which is compatible with any source for August flow. Choice C is the error of substituting evidence about quantity for evidence about origin: knowing August flow has declined to two-thirds of its former volume does not indicate where the remaining water comes from.

Why the other answers are wrong

A. "Total annual discharge has changed little."
This is about the total annual water budget, which is the same no matter where August's water comes from — it can't identify a source.
B. "the spring peak now arrives about three weeks earlier, and the basin's snowpack is typically gone by mid-July"
This rules out one source (that summer's snowmelt is gone) but doesn't point to bedrock specifically; the water could still be coming from ponds, wetlands, or soil storage. You need evidence that positively identifies the origin.
C. "In August the Verdin still runs, at roughly two-thirds of its 1970s August volume."
This tells you how much water is flowing in August, not where it comes from. The question asks about origin, so look for evidence about the water's properties instead.

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