Date of Award


Document Type


Degree Name

Master of Science (MS)


Forest Resources

Committee Chair/Advisor

Dr. William Conner

Committee Member

Dr. Jamie Duberstein

Committee Member

Dr. Skip Van Bloem


Eutrophication is a major threat to mangroves, exposing these ecosystems to an excess surge of nutrients from either natural or human-influenced events. In addition to causing water quality issues, this phenomenon could alter some ecosystem processes, including tree physiology. In order to understand how increased nutrients affect mangrove water use on a whole forest scale, we fertilized red (Rhizophora mangle L.) and black (Avicennia germinans [L.] L.) mangrove plots with inorganic forms of nitrogen (N) and phosphorus (P). Sap flow data were collected over two growing seasons and one winter dry season and used to model outer sapwood water use. Comparisons were made between water use in trees fertilized with N or P vs. unfertilized “control” trees. We additionally tested the spatial and temporal efficacy of solid-form fertilization methodology in a tidally restricted site. Porewater data were collected from 0.5, 1.0, and 1.5 m from fertilization cores for 6.5 months and analyzed for inorganic nutrient concentrations. While the concentration of soil porewater P (PO4-) was higher at the P fertilized plot compared to the control, these concentrations decreased laterally from 0.5 m to 1.5 m from the P fertilization microsite, and there was no negative effect of time on nutrient concentration. N fertilization was successful in increasing porewater N (NH3+) concentrations compared to the control site over the course of our study. Our results indicate that N and P fertilization methods described in the literature are sufficient and effective for fertilizing a radius of at least 0.5 m over a 6-month interval. We did not find significant spatial effect of N fertilization in soil porewater NH3+ or NO3- concentrations, and temporal effects showed very slow rates of inorganic soil N buildup over the course of our study. Average daily maximum sap flow rates showed that neither N nor P fertilization caused an increase in average daily maximum rates of water transport through the outer black mangrove sapwood (5, 15mm) in the growing seasons. While daily shallow sapwood water use modeled in outer black mangrove sapwood (5, 15 mm) during the growing season was higher than that of red mangrove trees, we did not see a significant effect of fertilization on increased water use rates in either species. Since red and black mangroves did not respond to either N or P fertilization with increased water use patterns by sapwood depth (5, 15 mm), these species may be better equipped than assumed to face the challenges of excess nutrients at the individual tree scale, at least among trees that have received relatively high P loading rates from upstream agricultural sources over the previous decade.



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