Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

First Advisor

John W. Day

Abstract

The significance of nitrogen transformations in mangrove sediments to the exchange of nitrogen in mangrove forests and influence on aquatic primary productivity was studied between 1990-1992 in Terminos Lagoon, Mexico. Fluxes of dissolved inorganic and organic nitrogen, particulate nitrogen (PN), and total suspended sediments (TSS) were measured in a fringe mangrove forest using the flume technique. There was a net import of NH$\sb{4}\sp{+}$ and NO$\sb{2}\sp{-}$ + NO$\sb{3}\sp{-}$ from the creek and basin forest, while particulate (PN) and dissolved organic nitrogen were exported to the creek and basin forest. There was a net import of TSS to the fringe forest from both the creek and basin forests. Rates of direct and coupled denitrification were measured using $\sp{15}$N isotope techniques in intact sediment cores from fringe, basin, and riverine mangroves. The highest direct rates were measured in the riverine mangrove (221 $\mu$mol m$\sp{-2}$ h$\sp{-1}$) followed by the fringe mangrove (9.4 $\mu$mol m$\sp{-2}$ h$\sp{-1}$); while rates in the basin mangrove ranged from 1.9 to 4.5 $\mu$mol m$\sp{-2}$ h$\sp{-1}$. Direct denitrification rates in sediment cores from the fringe mangrove enriched with 100 $\mu$mol $\sp{15}$N-KNO$\sb{3}\sp{-}$ were $<$0.7 and from 4.5 to 7.7 $\mu$mol m$\sp{-2}$ h$\sp{-1}$ in cores enriched with 200 $\mu$mol. The lack of $\sp{15}$N production in cores from the fringe, basin, and riverine mangroves amended with $\le$200 $\mu$mol $\sp{15}$NH$\sb{4}\sp{+}$/core and the high recovery of $\sp{15}$N in the sediment indicate that coupled nitrification-denitrification was not an important nitrogen transformation. Most of the applied $\sp{15}$N was recovered as particulate nitrogen in the sediment. Primary production in a tidal creek bordered by mangrove forest and in open waters of Terminos Lagoon was stimulated more than 50% throughout the year by additions of standing surface water (1 and 5 mL) from inside a fringe mangrove forest. This study supports the evidence that (1) mangroves are efficient at recycling and retaining nitrogen throughout several processes that reduce export and (2) mangroves are nitrogen transformers importing dissolved inorganic nitrogen and exporting organic nitrogen which could increase primary productivity in adjacent coastal waters.

Pages

170

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