Hydrophobicity of Cindery Typic Cryorthents Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9p290d688

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  • The hydrophobicity of soils of the Deschutes National Forest was studied. The soils are Cindery Typic Cryorthents, formed in cinders and ash from Mt. Mazama. Ponderosa pine is the dominant overstory vegetation. Of particular interest was the effect of prescribed burning on hydrophobicity. Fire has been shown to cause a normally hydrophilic soil to become hydrophobic. This non-wettability reduces water infiltration into the soil. As a result, the potential for erosion increases and less water is available for plant growth. The objectives of the study were to determine (1) whether or not prescribed burning causes the formation of a water repellent layer, (2) which variables affect the hydrophobicity of the soil following burning, (3) the horizontal and vertical extent of the hydrophobic layer, and (4) how long the hydrophobicity persists in the soil. Critical Surface Tension (CST) was measured to characterize hydrophobicity. A site burned 25 June 1982 and a site burned 15 September 1982 were sampled to meet objectives (1), (2), and (3). Objective (4) was met by sampling six additional sites where the time since burning ranged from 9 to 51 months. The presence of pre-burn hydrophobicity, believed to be caused by fungal products, complicated determining the effects of burning on the hydrophobicity of the soil. Pre-burn hydrophobicity was more extensive on the site which was sampled in September than the site sampled in June. Ninety-six % of the sampling points were hydrophobic during September and 42% during June. Two possible reasons were postulated for this difference. First, the amount of hydrophobicity due to the presence of fungal hyphae may vary seasonally; fungal products may accumulate during summer and then leach out of the profile with fall rains and spring snowmelt. Second, avoiding fungal pockets may not have been as successful when September sampling occurred as in June. Soil infected with fungal hyphae was avoided when CST was measured, because the fungal pockets did not form a continuous layer parallel to the surface. Fungal pockets were avoided by observing the light color of the dry fungal soil and the presence of hyphae. The soil had a light color because the water content was low. The soil was drier in September than in June. Distinguishing between fungal and non-fungal soil based on color differences was relatively easy in June, because the non-fungal soil was moist. However, the color difference between fungal and non-fungal soil was not as distinct during September sampling. The difference in color due to water content between fungal and non-fungal soil was small. As a result, the effort to avoid fungal caused water repellent areas was not as successful. More of the sampling points were hydrophobic in September. The June burn caused an increase in the hydrophobicity of the soil. The increase was greatest at the 2-3 cm depth. The hydrophobicity of the soil following burning in the June burn was explained by the degree of litter combustion. Hydrophobicity was produced where complete combustion occurred but not with incomplete combustion of the litter. Pre-burn hydrophobicity of the soil sampled in June occurred more often in the upper 2 cm than at the lower depths. Pre-burn hydrophobicity occurred at 42.5% of the sampling points. Post-burn hydrophobicity occurred randomly at all depths and occurred at 60.5% of the sampling points. On the site burned in September, most sampling points were hydrophobic before burning because of the presence of fungal products. Hydrophobicity decreased in the upper 2 cm of the soil. It was postulated that the hydrophobic fungal products were volatilized by the high temperatures of the prescribed burn and diffused deeper into the soil where they then condensed. The hydrophobicity of the soil following burning in the September burn was correlated with hydrophobicity of the soil be fore burning. Soil was found to be hydrophobic after burning if it was hydrophobic before burning. Measurements of litter depth, water content, and degree of combustion did not explain the variation in post-burn hydrophobicity of the soil at either site. Pre-burn hydrophobicity of the soil sampled in September occurred more near the surface than deeper in the soil. Pre-burn hydrophobicity was found at 96% of the sampling points. Post-burn hydrophobicity was not quite as extensive; 92% of the sampling points were hydrophobic. Post-burn hydrophobicity occurred deeper in the soil than pre-burn hydrophobicity in September, but the difference between depths was not significant. The percentage of hydrophobic sampling points decreased as time since burning increased. The relationship was significant at the 95% confidence level.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2013-08-01T18:48:51Z (GMT) No. of bitstreams: 1 EvansLynnB1983.pdf: 779980 bytes, checksum: bcf9e3f023907d4ec1ad11344150db0f (MD5)
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2013-08-05T18:52:11Z (GMT) No. of bitstreams: 1 EvansLynnB1983.pdf: 779980 bytes, checksum: bcf9e3f023907d4ec1ad11344150db0f (MD5)
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