Forest Operations Impact on Forest Soil and Water on Poorly Drained Organic Soil Watersheds in North Carolina.

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Title: Forest Operations Impact on Forest Soil and Water on Poorly Drained Organic Soil Watersheds in North Carolina.
Author: Grace, Johnny McFero III
Advisors: Dr. R. Wayne Skaggs, Committee Chair
Abstract: A 3-year study was conducted to evaluate the effect of thinning a drained loblolly pine (Pinus taeda L.) plantation and harvesting a mature natural (primarily hardwood) watershed on the hydrology and soil hydraulic properties of poorly drained organic soils in the Tidewater region of eastern North Carolina. Harvesting increased bulk density and decreased saturated hydraulic conductivity (ksat), drainable porosity, and saturated water content in the natural watershed. Thinning also decreased ksat and drainable porosity; however, bulk density was not influenced. Mean event outflow increased from 22.0 mm on the control to 47.3 mm on the harvested watershed. Similarly, event peak flow and number of flow days from the harvested watershed were more than 100 percent greater than observed on the control. Mean daily outflow doubled and peak flow rates increased 40 percent on the thinned watershed in relation to the control. These differences in hydrologic behavior are primarily attributed to the harvesting and thinning operation which resulted in reduced ET. Phosphorus increased following harvesting the natural watersheds and thinning the plantation watersheds. Nitrate-nitrogen load increased from 6.35 kg/ha*yr during the calibration period to 36.0 kg/ha*yr during the period following harvesting, an increase four times greater than observed on the control watershed. However, nitrate-nitrogen loads were not significantly impacted by the thinning operation in this study. Sediment load increased following treatment for both the harvesting and thinning treatment. Observed increases in nutrient load occurred following harvesting and thinning; however increased load was primarily associated with increases in outflow rather than elevated nutrient concentrations. The DRAINMOD hydrologic water management model predicted total outflows were within 30 mm and 20 mm of measured flows for the 3-year period (2000-2002) for WS2 (control) and WS5 (thinned), respectively. The difference in daily average outflows over the period was 0.04 mm for WS2 and -0.02 mm for WS5. DRAINMOD accurately predicted daily water table depths over the 3-year period to within 10 cm for WS2 and 5 cm for WS5. Long-term (50 years) average outflow was 21.8 cm for the unthinned condition and 34.7 cm for the thinned condition over the 50-year simulation (1951-2000).
Date: 2004-12-09
Degree: PhD
Discipline: Biological and Agricultural Engineering

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