Urea is a dynamic pool of bioavailable nitrogen in coral reefs |
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Authors: | J B Crandall M A Teece |
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Institution: | (1) State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210, USA |
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Abstract: | Urea may be an important source of nitrogen in low nutrient coral reef environments because corals and other organisms can
assimilate it easily and it is found throughout ocean waters. We measured the distribution and concentrations of urea in seagrass
beds, areas of schooling fish, coral formations and bottom sediments in the Upper Florida Keys Reef Tract. The flux of urea
from bottom sediments was also measured. Ambient concentrations of urea in the offshore reefs were similar to the concentrations
of nitrate and ammonium. Seagrass beds, areas of schooling fish and coral formations had elevated concentrations of urea that
were up to eight times higher than nitrate in the system. Numerous ephemeral hotspots of urea that were 8–20 times the ambient
urea concentration existed in seagrass beds, areas of schooling fish, and above sediments. Coastal areas and inland canals
had high urea concentrations where urban runoff and septic effluents were prevalent, but there was no anthropogenic influence
in the offshore habitats. Urea concentrations above bottom sediments were not different from ambient concentrations and benthic
flux chamber incubations showed biological activity in carbonaceous sediments but no net urea production. The decrease in
urea concentrations from coasts and inland waterways to a consistent ambient concentration in the offshore reef system and
ephemeral hotspots of high urea concentration suggest that urea is a dynamic pool of bioavailable nitrogen in the reefs of
the Upper Florida Keys. |
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