Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Ezell, W. Andrew

Committee Member

Shepard, P. James

Committee Member

Hatten, A. Jeff

Committee Member

Fan, Zhaofei

Date of Degree

4-30-2011

Document Type

Dissertation - Open Access

Major

Forestry

Degree Name

Doctor of Philosophy (Ph.D)

College

College of Forest Resources

Department

Department of Forestry

Abstract

Headwater streams are considered to be the greatest contributor to nonpoint source and are a crucial part of overall watershed dynamics because they comprise more than 50-80% of stream networks and watershed land areas. This study addressed the influence of headwater areas (ephemeral and intermittent) on downstream hydrology and water quality following harvest as well as characteristics of vegetation communities within three first-order catchments in the Upper Gulf Coastal Plain of Mississippi. Four treatments representing a range of potential Best Management Practices (BMPs) for ephemeral drains were used: BMP1 - removal of all merchantable stems while leaving understory intact with minimum surface soil disturbance; BMP2 - same as BMP1 with the addition of logging debris to the drainage channel; No harvest - left uncut as a reference; Clearcut - total harvest with no BMPs applied. Harvested treatments caused the height of water table to increase up to 55 cm; however impacts of timber harvesting on peak discharge, storm discharge, and time of concentration were not consistent with water table response. Response time to stormflow was reduced significantly in harvested treatments (BMP2 and unrestricted harvest) as a result of decreased evapotranspiration and increased soil disturbance. Forest clearcutting in ephemeral drains caused intensive surface soil disturbance that resulted in substantial impacts to net soil erosion/deposition in both channel and hillslope positions and significantly increased total suspend sediment (TSS). There were no significant differences between two BMP and reference treatments in net soil erosion/deposition and TSS. Distinct vegetation communities between channel and hillslope positions in ephemeral-intermittent drains corresponded to water table gradients. Timber harvesting affected vegetation communities through direct and indirect disturbances. Four indicator species (V. blanda, L. glandulosa, A. gigantean, and P. acrostichoides) were identified as having a strong response to hydrologic gradients in ephemeral-intermittent drains.

URI

https://hdl.handle.net/11668/15085

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