Transcript: Finding a Secret Map to Erosion

Lucas Reusser, Ph.D. Candidate, Geology

Paul Bierman, Professor of Geology

Narr: On New Zealand's north island, the Waipaoa River drains into the sea. Upriver, things are not so pretty. More than a century of deforestation for farming has created some of the most dramatic erosion in the world. Here, raw gullies and collapsing hillsides dump tons of mud into headwaters, choking wildlife and vineyards downstream.

Lucas: People in New Zealand have been trying very hard to find a way to re-stabilize the hill slopes and try to mitigate some of these problems with sediment that they are having. And so that's where I come in.

Narr: For land managers looking to restore the Waipaoa Basin, or eroding landscapes anywhere, finding the source of sediment moving downstream is critical, but where exactly is the sediment coming from? Reusser and professor Paul Bierman have developed a new rapid method for pinpointing this pollution and tracking it downstream. The measure a rare form of the element Beryllium that forms high in the atmosphere. This isotope, Beryllium 10, falls to the earth and accumulates, sticking to sand and sediment. For Bierman and Reusser, the amount of Beryllium in their samples works like a secret map for navigating eroding landscapes.

Their results were published in the journal Geology and their work happens in one of the most specialized geology labs in the world.

Dr. Bierman This is the Cosmogenic Nuclide Extraction Lab and in this lab we removed small amounts of very rare isotopes from aliquot of quartz and other minerals. The purpose of that is to date landforms on earth's surface and to determine how quickly parts of earth's surface are eroding.

So, two things are new in this paper. Once thing is the analytic method that we used. We measured the Beryllium 10 that is adhered to outside of grains and we measured it in river sediments and that's only been done a couple times before and it's never been done with a mission to figure out where that sediment was coming from. The second piece that we've done was that we worked down a river network. So Luke started by collecting samples in the far steep headwaters and worked his way down he main channel of the river until it emptied into the ocean. What he's determined there is that there is a very predictable change in the number of Beryllium 10 atoms adhered to the sediment as you move downstream. What that change represents is input of sediment from a huge gully or landslide complex that basically has no Beryllium 10 and as the sediment is carried downstream the inputs from side channels and tributaries that have increasing amounts of Beryllium 10.

Lucas: This is actually an example of one of the samples from a river channel in the Waipaoa Basin that was collected and brought it back here and pulverized it and eventually measured the meteoric Beryllium 10 that's adhered to each one of these sediment grains.

Dr. Bierman We start with sediment, and for the work we did in the Waipaoa Basin we take that sediment back and we sieve it to a specific grain size, the kind of sand you would typically find on a beach, and we crush it to a fine powder. And after that we extract the Beryllium 10 by fluxing the powder, very little of it, half a gram in the presence of some very strong chemicals that break down the bonds that hold the minerals together. And then we take that fluxed material, we essentially have melted the rock, we put it in very pure water and only the Beryllium and the Potassium are soluble at that point and that lets us extract the Beryllium, we can remove the Potassium with other chemical treatments, and then we have basically pure Beryllium. We take that material out to Livermore Lab in CA where we measure the ratio of Beryllium 9 atoms to Beryllium 10 atoms. And because we know we've added a certain number of Beryllium 9 atoms, once we have that ratio and we know how much Beryllium 9 we've added, it's a simple multiplication to get how much Beryllium 10 was in our sample.

Lucas: So now we can come in and in an an accurate manner characterize what portions of the drainage basin are problematic and which ones aren't so problematic for land managers to target.

This research was funded in part by The National Science Foundation

Produced by University Communications at the University of Vermont
www.uvm.edu/uvmtoday

Photography: Paul Bierman and Lucas Reusser
Narration: Joshua Brown
Camera and editing: Megan Hack