1Chapter 2 Origins and Fate of Inorganic Nitrogen from Land to Coastal Ocean on the Yucatan Peninsula, Mexico

Land use changes and poor wastewater management threaten valuable coastal resources by augmenting nutrient delivery to near-shore ecosystems. Oligotrophic, tropical systems are particularly vulnerable because relatively small changes in nutrient load can cause shifts in community composition and ecosystem function. In order to examine nutrient dynamics along a rapidly developing coastline, we characterized water chemistry in a series of cenotes and bays on the Caribbean coast of Mexico. We also measured the isotopic and tissue nutrient content of resident seagrasses and algae to examine possible nitrogen (N) sources and determine their influence on the nutrient status of primary producers in seagrass and coral reef ecosystems. Ranked water column NO3concentrations were significantly different in cenotes (NO3-, 62.6 ± 27.7 µM) vs. bays (NO3-, 2.8 ± 2.6 µM); however, NH4+ concentrations were not significantly different (NH4+, 0.8 ± 1.2 µM and

Abstract .......................................................................................................................................... 283 12.1 Introduction ..........................................................................................................................284 12.2 Methods ................................................................................................................................286