Theses and Dissertations

Date of Award


Document Type


Degree Name

Master of Science (MS)


Ocean, Coastal, and Earth Sciences

First Advisor

Dr. John A. Breier

Second Advisor

Dr. David Hicks

Third Advisor

Dr. Christopher Gabler


Time-scaling of estuarine inorganic nitrogen cycling contains many assumptions due to biogeochemical interactions. Nitrogen, often a limiting factor for primary production, is transformed and utilized by many estuarine organisms. Inorganic nitrogen is especially high in porewater. High nutrient pore water, contained within the interstitial spaces of sediment, has been assumed to influx high concentrations of inorganic nutrients into surface waters during resuspension events. These short-term resuspension events rapidly introducing high concentration of nutrients into the water column. In order to determine the internal time scale of inorganic nitrogen cycling, a box-model nutrient budget, horizontal in situ transects, and vertical nutrient profiles were utilized to examine inorganic nitrogen availability and temporal cycling within the Lower Laguna Madre estuary. The nitrogen budget was created to estimate the nitrogen residence time for the lagoon as a whole. The nitrogen budget suggests that the residence time for nitrogen in the Lower Laguna Madre system for approximately one year. In contrast, on the time scale of the horizontal transects and vertical profiles revealed rapid rates of nitrogen utilization in approximately six hours. Inorganic nitrate steadily declined below the detection limit of the senor, while dissolved oxygen began to increase to supersaturated concentrations up to 150 % saturation. An inverse correlation between dissolved nitrate and dissolved oxygen was shown (r2=0.821, p < 0.05), reinforcing the idea that nitrogen is the limiting factor for primary production. These observations indicate rapid internal cycling of nitrogen despite a significant longer overall residence time through the estuary. Utilizing the difference between the results of the nitrogen budget and the field study is important for: understanding time cycling for freshwater influx of nutrients in estuaries, overcoming assumptions in biogeochemical modeling, and representing complex but often subtle biogeochemical interactions within a system.


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