Graduate Thesis Or Dissertation

 

Maritime windstorm influence on soil process in a temperate rainforest Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/k3569649c

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  • Maritime cyclonic windstorms cause widespread disturbance to forested ecosystems in southeast Alaska. The consequence of this disturbance process on the movement, storage, and quality of soil carbon, forest hydrology and streamwater chemistry was studied along a windthrow disturbance sequence. Soil profiles were described and the thickness of the major organic and mineral horizons were measured every 5 m along transects in 3 catchments with contrasting disturbance histories. A of these horizons were randomly selected and sampled to determine the quantity and quality of carbon present. Mineral soil samples were physically fractionated based on particle density. Total C and N, natural abundance δ¹⁵N, δ¹³C isotopes, and solid state ¹³C NMR were used to compare soil organic carbon pools in catchments with contrasting disturbance histories. An event-based sampling scheme was then used to compare hydrochemical properties of each catchment. Six storms were sampled over 14 months, representing a range of rainfall and soil moisture conditions. Streamfiow was measured, and water samples were collected every 4 hours during storm events from each catchment. Evidence for two distinct pathways for mineral soil carbon accumulation was found; 1) mineral and organic particle mixing by windthrow, 2) soil water transport of mobile organic carbon (MOC) to mineral soil horizons. MOC accumulated in mineral horizons principally through adsorption to mineral particles, and the extent of strong chemical association (adsorption) with mineral particles increased in older, thicker illuvial horizons. Forested catchments which experienced more intense soil mixing from windthrow were depleted in strongly humified soil carbon pools, and an overall increase in quality of soil carbon toward a partially decomposed particulate form was observed. Streamfiow on more-disturbed catchments peaked 4 to 12 hours later than in less disturbed catchments. During summer months, streamwater temperatures in more disturbed watersheds were cooler than air temperatures and less-disturbed catchments. Streams in more-disturbed catchments had higher pH, alkalinity and base cation concentrations than streams in less-disturbed catchments. These results suggest that catastrophic windtbrow disturbance smoothes hydrograph response to storms, and increases the chemical interaction of rainwater with mineral soil horizons by increasing rainwater infiltration and storage in deeper soil profiles. The changes in concentration and characteristics of organic carbon in mineral soil which result from soil mixing disturbances (windthrow, landslides) can strongly influence the hydrology, chemical properties of catchments, and the rate of nutrient cycling.
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