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GEOL151 Fall 2016: Lab for Week #6 A Soil Chronosequence on the Huntington River Terraces

Overview This week, we will examine a sequence of river terraces along the Huntington River in the town of Huntington (Figs. 1 and 2). These terraces were formed by progressive river incision that began after the Last Glacial Period and extended into modern times. Since the four terraces represent a wide span of ages, the soils on the terraces therefore represent a spectrum of different degrees of development. A sequence of closely-related soils of different age, such as the terrace soils preserved in Huntington, is referred to as a soil chronosequence. You will work in groups to dig four soil pits, one on each terrace (Fig. 2), where you will assess and describe horizons, texture, color, and other notable features. Our goal is to use these pits to make inferences about how soils develop over time. Gear Be forewarned; you will get dirty! Wear work clothes and close-toed shoes that you don’t mind covering in mud. Work gloves may also be helpful for protecting your hands. In addition, each of the four groups will need the following items for digging and describing the pits:

Large tarp Two shovels Small trowel Munsell color book Measuring tape Notebooks and pencils

Field Plan On each of the four terraces (Fig. 2), a group will dig a soil pit that is at least a meter in all three dimensions. The goal is to dig through the soil and into the parent material below. Try to make your pit walls as vertical and smooth as possible for easy observation (smoothing the walls with the side of a trowel will help). We will employ low-impact soil pitting techniques, which means that topsoil and sod should be carefully removed (and later replaced) and all the soil should be placed on a tarp so that it can be neatly put back into the pit. Once the pit is dug, stretch a tape measure from top to bottom along the wall you choose to use for observation, with “0” being at the ground surface. Then, working as a group, describe the pit carefully using the list of observation points on the following page. Create a detailed log of the horizons you see and their characteristics. Augment your log with sketches and/or photos, remembering that you will need to create a profile for each of the four pits based off of your notes and those of your peers. Make sure that at least one member of your group takes neat, detailed notes that can be shared with the rest of the class.

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After each group has constructed their pit, the class as a whole will take a systematic tour of all four pits, moving from the highest terrace to the lowest. Make sure your group is ready to give a short (five-minute) presentation about your pit, its horizons, and what interpretations you think you can make from it. As we leave each site, the hole should be filled and the sod replaced. Ideally, there should be no sign that a pit was ever dug there! Soil Pit Observations As you observe the soil exposed in your pit…

1. Take some observations about the overall geomorphic setting of your pit 2. Delineate and describe the O, A, E, B, and C horizons (if they exist) 3. Measure the thickness of each horizon 4. Describe any evidence of bioturbation 5. Describe the color of each horizon using the Munsell system 6. Describe the texture of each horizon (sandy, silty, clay or percentage mixture) 7. Make observations about the sorting of grain sizes within each horizon 8. Describe the location and appearance of organic materials 9. Look for rust-colored stains or any other noteworthy features you can find 10. Describe the contacts between adjacent horizons (i.e. sharp or gradational)

Then, as you observe your own pit and also other groups’ pits, contemplate the following:

1. What is the relative elevation of the terrace on which the pit is dug? 2. What is the relative age of the soil? 3. What was the parent material of the soil? 4. How well-developed is the soil? 5. Do the soil horizons you see tell you anything about the soil’s development? 6. How does the soil compare to the soils exposed in other pits? 7. How does relative soil age appear to control soil development?

Data Sharing We will be working as a group to conduct this field investigation; accordingly, sharing data in a timely fashion is critical. Each group must email Paul (pbierman@uvm.edu) a neat, detailed set of notes about their pit as well as an accompanying sketch by 5:00PM on Thursday 10/6 (i.e. the day following the field trip). Your notes and sketch should be easy to read and must include depths. Paul will upload them to the class website. You will need to use the notes/sketches from all four pits as you compile your final field report.

Field Report Present your data and interpretations in a detailed, professional field report focused on how soils develop over time and the processes that govern this development. Refer to the “How to Prepare a Successful Field Report” handout for more ideas on organization, content, and presentation.

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Along with your report, you should include four detailed soil logs (one for each pit) that you create on your own. These logs should each be large enough to easily read, with a sketch on one side and concise descriptions on the other. Although you will have notes from your own and other groups’ pits, you will need to make choices about what information is most important and how to most effectively visualize and describe each soil. I will provide a Powerpoint template that you can download from the class website, although you are also welcome to create these logs by hand or in a different computer program of your choosing. Regardless, they should be neat, visually pleasing, and standardized between the four so that it is easy for your reader to compare between the different soils. As will be the case with many of our investigations, there is no “right” answer. I am looking for you to present your data clearly, then make logical, supported interpretations. You may work together to develop ideas; however, each student must turn in his/her own field report and soil logs. These reports are due at the beginning of the lab period on Wednesday next week (10/12).

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Figure 1. Satellite image of the Huntington River terraces and surrounding area.

Terrace sequence location: 44.347562°N, -72.990963°E Elevation: 168 m

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Figure 2. Satellite image of the Huntington River terraces. The four terrace ages span >10,000 years; we will dig pits and investigate soil development on all four.