Identifier

etd-04102008-105208

Degree

Master of Science (MS)

Department

Renewable Natural Resources

Document Type

Thesis

Abstract

One of the dominant themes of stream water quality research has been the effect of nutrients and organic materials on eutrophication of coastal waters. Despite this prevalence in water quality research, few studies have been conducted on water quality changes in low-gradient watersheds under a humid, warm subtropical climate, such as those in the coastal plains of the Northern Gulf of Mexico. This study addresses: (1) the nutrient conditions in headwater streams of a low-gradient, subtropical watershed, especially as it relates to the suggested criteria by the Environtmental Protection Agency (EPA), (2) organic and inorganic carbon dynamics in the headwaters and how they affects nutrient concentrations, (3) dissolved oxygen (DO) conditions in the headwaters and its dependence on temperature, streamflow, and carbon, and (4) nutrient and carbon transport from the headwater catchment. Monthly in-stream measurements of DO, water temperature, pH and conductivity were conducted at 15 locations within the Flat Creek watershed, a 3rd-order watershed in central Louisiana over a 22-month period spanning December 2005 to September 2007. Monthly and storm event water samples were collected from these locations for chemical analyses of nitrogen, phosphorus, and carbon. The results reveal a seasonal trend of increased inorganic carbon in the dry, summer months, while increased organic carbon was found during the wet winter/early spring months. There was a wide range of monthly DO levels (0.4 to 9.0 mg L-1) with the lowest levels generally occurring from May to July, a period with decreased organic carbon and increased inorganic carbon. Localized conditions were more indicative of dissolved oxygen than stream order in the watershed. Nutrient levels, especially nitrate/nitrite (0.127-1.378 mg L-1) were not meeting EPA’s suggested criteria (P25 for nitrate/nitrite is 0.067 mg L-1). There were no spatial relationships in nitrogen, but there was an increasing trend in total phosphorus downstream until a reduction downstream of beaver dam impacted sites. Annually, the Flat Creek watershed exported 15.36 kg carbon ha-1, 0.0087 kg nitrate/nitrite ha-1, and 0.0022 kg phosphorus ha-1. Nutrient fluxes were largely affected by storm runoff and discharge and showed a decreasing trend with increasing drainage size. This study shows that in the forest-dominated landscape of central Louisiana, it may not be possible to reduce nutrient concentrations sufficiently to limit dissolved oxygen consumption, implying that existing water quality standards may not adequately address natural conditions.

Date

2008

Document Availability at the Time of Submission

Secure the entire work for patent and/or proprietary purposes for a period of one year. Student has submitted appropriate documentation which states: During this period the copyright owner also agrees not to exercise her/his ownership rights, including public use in works, without prior authorization from LSU. At the end of the one year period, either we or LSU may request an automatic extension for one additional year. At the end of the one year secure period (or its extension, if such is requested), the work will be released for access worldwide.

Committee Chair

Y. Jun Xu

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