Theses and Dissertations

Date of Award


Document Type


Degree Name

Master of Science (MS)


Ocean, Coastal, and Earth Sciences

First Advisor

Dr. Alejandro Fierro

Second Advisor

Dr. Edward Proffitt

Third Advisor

Dr. Andrew McDonald


Nutrient over-enrichment is a global threat to coastal and marine environments. Yet, system-specific attributes of estuarine and coastal ecosystems may result in large differences in their sensitivity and susceptibility to such threat. In tropical latitudes, plant species adapted to low-nutrient habitats generally have nutrient-conservation mechanisms that acquire, use, and internally recycle nutrients efficiently. Thus, a major challenge for managers and decision makers is to develop a predictive and holistic understanding of how nutrient loading alters ecosystem functions and therefore ecosystem services. The objective of the present research is to document short and long-term effects of persistent nutrient enrichment on black mangrove (Avicennia germinans) shrubs and understory vegetation in South Texas coast. I hypothesized that the recurrent addition of nutrients will result in noticeable changes in growth patterns and nutrition of black mangroves, as well as ground cover and species composition of associated saltmarsh vegetation. We established a long-term experiment where supplementation of Nitrogen (N), Phosphorous (P), N+P, and Iron (Fe) occurred periodically to document effects on height, basal diameter (BD), leaf area index (LAI), canopy biovolume, and nutrient resorption efficiency of 40 black mangrove shrubs. Foliar nitrogen contents of green and senescent leaves were analyzed to obtain nutrient resorption efficiency. In addition, measurements of chlorophyll and saltmarsh vegetation cover were periodically recorded. After 24 months of enrichment, all nutrient treatments have promoted growth relative to the control of these dwarf mangroves and altered vegetation structure in various degrees. Specifically, NP enrichment has altered primary growth (height) and secondary growth (basal diameter) as well as canopy biovolume. Nitrogen and P resorption efficiencies were not significantly different, but both increased with +N, +P and +NP treatments compared to controls. Additions of NP and P caused a significant increase in Batis maritima and A. germinans area cover. Chlorophyll contents were significantly higher in +N relative to controls. The outcomes of this study improve understanding of estuarine plant responses to coastal nutrient enrichment that may be necessary for improving adaptive management, predicting resilience and enhancing outcomes of coastal wetlands restoration.


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