Reading and Answering 9

Category: Applied Sciences


In this week’s assignment, we will explore the ecological half-life of cesium in brown trout and Arctic char — two different salmonid species inhabiting the same lake in Scandinavia. The lake was contaminated with cesium-134 and cesium-137, following the Chernobyl accident. The cesium-134 has largely decayed away due to its short physical half-life, but the longer lived cesium-137 (physical half-life 30 years) persists in the fish 12 years after the nuclear accident.

One point of potential confusion is that in this particular case, we are not measuring the biological half-life of cesium in individual fish. The original fish are long dead since fish from these species typically live <5 years. Rather, we are annually measuring the “steady state” level of cesium primarily in the descendants of the original fish over a 12-year period. In other words, the cesium-137 in the fish is at equilibrium with cesium in their environment. This is the unstated assumption that is implicit in the article you will read. What this means is the measurements in the fish are reflective of the radioactivity in the lake.  Thus, the “ecological half-life” is a feature of radioactivity turnover in the lake, not the fish. Keep this in mind when you read the following paper and answer this week’s questions.

“Chernobyl radioactivity persists in fish,” Nature 400: 417, 1999. Preview the document

Q1: Image that this lake has no sediment in it. All else being equal, how would that effect Q1 and Q2 of the two-component decay function?

Q2: What would be the ecological half-lives of cesium-137 be, as measure in brown trout and Arctic char, in this sediment-free lake? (Report a calculated ecological half-life value for each species.)

Q3: The author’s attribute the differences in radioactivity measurements between these two very similar salmonid species to differences in their ecological niches (i.e., they have different microenvironments within the lake). This probably was evident to them when they caught the fish. Based on the data, do you think the Arctic char they captured for measurements were caught closer to the bottom or the surface of the lake?  

[Note: You need no other information than what you’ve read in the two articles above, to answer these questions.]  

please try answering the questions from your own words and don’t just copy from the articles even citation doesn’t work. my professor want you to paraphrase not just copy from the article.

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