Date of Award

2000

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Advisor

Donald Dean Adrian

Abstract

Water quality impairment in many water bodies in the state of Louisiana is attributed to agricultural nonpoint sources of pollution. Many of these use-impaired streams have also been hydromodified to facilitate agricultural development, deepening and straightening the channels to form "stretch lakes". This dissertation evaluated the unique, and previously uncharacterized and unquantified ricefield loadings and their impacts on these dystrophic waterbodies in order to provide the Louisiana Department of Environmental Quality (LDEQ) with assessments of stream impacts from implementing altered cropping practices known as "best management practices" (BMPs). In order to produce an assessment of rice BMPs, this dissertation developed several unique tools: (1) Development of the LA reaeration equation and measurement of dispersion. Dispersive mixing was found to be significant in these low velocity, hydromodified streams, requiring the use of a dynamic model and necessitating the development of measurement techniques, and the development of empirical equations so that reaeration may be tied to the depth and velocity profiles found in the "stretch lakes". (2) Determination of SOD and mechanism of deoxygenation. The stream was found to have a dissolved oxygen (DO) deficit that is sediment oxygen demand (SOD)-driven and the bottom anoxia was shown to be heavily impacted from agricultural nutrients, sediments and organic material. The SOD determined during calibration far exceeded those found in the literature; values of 4.0 g-O2/m2/day in the rice receiving streams were not uncommon. (3) Characterization and quantification of ricefield discharge BMP and sediment flux pollutant loads. Oxygen-demanding pollutant loads (carbonaceous biochemical oxygen demand, CBOD and nitrogenous, NBOD) were quantified for headwater, ricefield BUT discharges and resuspended sediment fluxes throughout an annual cycle. CBOD in the sediment flux was also estimated to be as great as 4.0 g-O2/m2/day during critical low-flow. (4) Development of a conversion algorithm from TOC to CBODu. Characterizing the sediment fluxes and rice discharge constituents required the use of long-term BOD data that is rarely available in datasets. A conversion algorithm from total organic carbon (TOC) was, thus, developed for use as a surrogate for ultimate CBOD (CBODu).

ISBN

9780599853546

Pages

195

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