Electronic Theses and Dissertations

Identifier

753

Date

2012

Date of Award

11-30-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biology

Committee Chair

S. Reza Pezeshki

Committee Member

Corinna A. Ethington

Committee Member

Daniel Larsen

Committee Member

Takuya Nakazato

Abstract

Upstream water management affects downstream ecology, especially the wetland plants and soil. The primary goal of this dissertation was to quantify the dynamic responses of plants and soil to variable hydrologic inputs. Measurements were taken at different spatial scales, which were in the greenhouse, constructed drainage ditches, and bottomland hardwood forests. Wetland plants grown in greenhouse conditions were exposed to variable hydrology and aqueous nitrogen fertilization treatments. The study species was rice cutgrass, Leersia oryzoides. Individual plants were able to modify physiological responses, elemental tissue concentrations, and biomass allocation in order to withstand environmental stress. The plants grown in partially flooded conditions had the highest biomass measurements of the leaf, stem, and root components. Continuously flooded plants had the lowest rhizome biomass. A field study of L. oryzoides was conducted utilizing constructed drainage ditches. This species exhibited seasonal differences in internal allocation of nitrogen, phosphorus, and biomass. Higher concentrations of both nitrogen and phosphorus were measured in the shoots during spring and summer months. During the autumn and winter seasons, the roots had increased concentrations of both nitrogen and phosphorus. Following three months of growth, plants allocated more biomass to roots than to shoots with the highest total biomass measured in the autumn. Additional field studies evaluated landscape level effects in the Mississippi River floodplain following hydrological restoration to secondary channel complexes. Sites were established both upstream and downstream of the restoration project. The sites consisted of bottomland hardwood forests, both historically and presently dominated by black willow, Salix nigra. Soil nutrient concentrations had the greatest reduction at the site nearest the hydrological input compared to the downstream site. The restored hydrology enhanced the aboveground net primary productivity of the trees, including stem growth and leaf litter production. Data generated by these studies provide results that support the use of vegetated buffers in the aquatic/terrestrial transition zone to immobilize nutrients. Continued monitoring of vegetated drainage ditches and restored channel hydrology in the Mississippi River Basin is necessary in order to enhance the effectiveness of planning and managing projects directed toward improving nutrient cycling and water quality.

Comments

Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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