Variability in nitrogen stable isotope ratios of macroalgae: consequences for the identification of nitrogen sources |
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| Authors: | María Julia Ochoa‐Izaguirre Martín F. Soto‐Jiménez |
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| Affiliation: | 1. Posgrado en Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Unidad Académica Mazatlán, Sinaloa, México;2. Facultad de Ciencias del Mar, Universidad Autónoma de Sinaloa, Sinaloa, México;3. Unidad Académica Mazatlán, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México (UAM‐ICMyL‐UNAM), Sinaloa, México |
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| Abstract: | In our research, we collected and analyzed numerous macroalgal specimens (738) for isotopic analysis sampled over a year at monthly intervals across 20 sites within the Urías lagoon complex, a typical subtropical coastal ecosystem located in the Gulf of California. We quantified and characterized (chemically and isotopically) the N loads received by Urías throughout a year. We studied the spatial‐temporal variation of the chemical forms and isotopic signals of the available N in the water column, and we monitored in situ different environmental variables and other hydrodynamic parameters. Multiple N sources (e.g., atmospheric, sewage, seafood processing, agriculture and aquaculture effluents) and biogeochemical reactions related to the N cycle (e.g., ammonia volatilization, nitrification and denitrification) co‐occurring across the ecosystem, result in a mixture of chemical species and isotopic compositions of available N in the water column. Increased variability was observed in the δ15N values of macroalgae (0.41‰–22.67‰). Based on our results, the variation in δ15N was best explained by spatio‐temporal changes in available N and not necessarily related to the N sources. The variability was also explained by the differences in macroalgal biology among functional groups, species and/or individuals. Although the δ15N‐macroalgae technique was a useful tool to identify N sources, its application in coastal ecosystems receiving multiple N sources, with changing environmental conditions influencing biogeochemical processes, and high diversity of ephemeral macroalgal species, could be less sensitive and have less predictive power. |
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| Keywords: | biogeochemical processes Eutrophication isotopic fractionation macroalgal metabolism δ 15N‐Macroalgal |
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