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Welcome to the blog for the Oberlin College Geomorphology Research Group. We are a diverse team of students working with Amanda Henck Schmidt on geomorphology questions. This blog is an archive of our thoughts about our research, field work travel notes, and student research projects. Amanda's home page is here.

Monday, February 16, 2015

Soil Pits Winter Term 2015



Soil Pits Site Descriptions & Analyses

CH-014 (Basin 35)


 


  •   CH-014 was collected from a riverbank. The O/A horizon is an organic-rich silt loam about 15cm deep. The B1 horizon (15-35cm) is very clayey, possesses a weak structure, and is between 30-40% gravel. The B2 horizon is 50-60% gravel. The flatland approaching the bank appears to be a grassy field with a few scattered small trees. The field slopes sharply towards the bank. The levels of 137Cs and 210Pbex exhibit fairly typical exponential-type decay with depth. The amount of 210Pbex decreases more quickly than the amount of 137Cs.


CH-015 (Basin 35)
   

  • The soil comprising CH-015 is a uniform, coffee-brown color throughout the column. The O/A horizon is a dark clay loam that is high in organics and is about 35cm thick. The B horizon is gravelly silt clay with 40-50% gravel and weak structure. This soil pit is located in a farm field. The amount of 137Cs and 210Pbex both increase between the 0-5cm section and the 5-10cm section, and drop off dramatically with increased depth. This pattern suggests that this area has experienced a change in erosion rates.



CH-028 (Basin 35)
  
 

  • CH-028 was collected on the ridge crest of a young coniferous forest. The first 4cm of soil is a grey silt loam that could be a less-developed forest A-horizon but may also be an erosional layer. The B1 horizon is a yellowish-brown silty clay soil with a well-developed blocky structure. The B2 horizon is a dark brown, sticky clay and has a well developed blocky structure. The soil profile contains low concentrations of 137Cs and 210Pbex and we only observe these isotopes in the upper 10cm of the soil. This suggests that the area has experienced significant erosion.


CH-029 (Basin 35)

  

  • CH-029 was collected from a fallow agricultural field that was probably forest at one time. The A horizon extends for about 30cm and is an olive-brown silt loam that contains some roots. The B horizon extends for another 30cm and is a yellowish brown silty clay. The horizons are separated by a whitish carbonate accumulation. The relatively uniform levels of 137Cs and 210Pbex throughout the soil profile indicate that the soil has been mixed by a plow.


CH-030 (Basin 35)
    

  • CH-030 was collected at the edge of a young coniferous forest, off the ridge seat. The A horizon extends for 20cm and is a silty loam. The B horizon extends for over 30cm below the A horizon and is a brownish yellow sandy clay. This soil pit looks similar to the others, except that it contains a more weakly developed zone of carbonate accumulation (stage 2 carbonate development). The absence of 137Cs and 210Pb in the 10-15cm section suggests that the soil currently at the 15-20cm depth used to be at the surface, but new soil has been deposited on top of it.


CH-061 (Basin 49)
     
 

  •  CH-061 was collected from a cliff in a fairly vegetated area. The pit is composed of a deep, well developed tropical soil, overlain with a forest soil. The A horizon extends for 5cm and is a light silty sand. The B1 horizon extends for 25cm and is a sandy clay. The B2 horizon is clayey and demonstrates stage II carbonate accumulation. The soil profile exhibits a small amount of 137Cs and a comparatively much greater amount of 210Pbex.


CH-081 (Basin 11)
     

  •       CH-081 was collected from a relatively high elevation road cut on a moderate (10-15°) slope in an old forest. The A1 horizon extends for 37cm and is a deep, organic-rich silt loam of a very dark color. The A2 horizon extends for 23cm and is a dark, yellowish brown sandy silt The level of 137Cs in the upper 15 cm of the soil remains relatively uniform, but the amount of 210Pbex decreases in an exponential fashion.  


Additional Resources


    •   The authors provide information on how to estimate erosion rates using FRN observations in areas where 137Cs inventories may be low or nonexistent, relying on unsupported 210Pb measurements in soil cores to construct sediment budgets that differentiate between several main types of land use in the study area. This relates well to our project, especially since some of the soil pits do not have high concentrations of 137Cs.
  • Mabit, Benmansour, and Walling, 2008. “Comparative Advantages and Limitations of the Fallout Radionuclides 137Cs, 210Pbex, and 7Be for Assessing Soil Erosion and Sedimentation.” Journal of Environmental Radioactivity, 99(2008), pp. 1799-1807. <JER_2008.pdf>.
    • This paper provides a great review of the information we can gather from FRN distribution in the soil, and the limitations associated with potential findings. The authors discuss the implications of different concentrations of FRNs in soil columns and detail what type of erosion/deposition could have led to that distribution. This provides a detailed background on soil pits and what they can tell us about past and ongoing conditions.
  •   Walling and He, 1999. “Using Fallout Lead-210 Measurements to Estimate Soil Erosion on Cultivated Land.” Soil Science Society of America Journal, 63(1999), pp. 1404-1412.  
    • This paper focuses on using 210Pb to estimate rates of water-induced soil erosion on cultivated land. Soil cores showing the distribution of 210Pb in the soil are the investigative tool used. This relates well to the objectives of our project examining the effects of changes in land use on erosion rates. 
  •     Mabit et al, 2014. “Fallout 210Pb as a Soil and Sediment Tracer in Catchment Sediment Budget Investigations: A Review.” Earth-Science Reviews, 138(2014), pp. 335-351. http://www.sciencedirect.com/science/article/pii/S001282521400115 
    • Mabit et al. provide a full walkthrough of the applications of fallout 210Pb as a soil and sediment tracer, focusing on catchment sediment budget investigations. This review encompasses applications of 210Pb that are beyond the scope of our investigation, but it would be useful to go through and read the sections on soil pits. 

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