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Isotopic fractionation of ammonium and nitrate during uptake by Skeletonema costatum : Implications for δ15N dynamics under bloom conditions
Author(s) -
Pennock Jonathan R.,
Velinsky David J.,
Ludlam John M.,
Sharp Jonathan H.,
Fogel Marilyn L.
Publication year - 1996
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1996.41.3.0451
Subject(s) - phytoplankton , fractionation , nitrate , biogeochemical cycle , ammonium , environmental chemistry , bloom , particulates , diatom , nitrogen , chemistry , algal bloom , nutrient , oceanography , botany , biology , geology , chromatography , organic chemistry
Isotopic fractionation of ammonium (NH 4 + ) and nitrate (NO 3 − ) during uptake by phytoplankton was examined in batch culture experiments with the diatom Skeletonema costatum under nitrogen‐enriched conditions (5–100 µ M). The fractionation factor ( ε ) for NO 3 − uptake by Skeletonema was −9.0±0.7‰ and was concentration‐independent. For NH 4 + , ε was more variable and dependent on ambient NH 4 + concentration. For NH 4 + concentration ranges of 100‐50, 50‐20, and 20‐5 µ M, ε was −24.6±5.5, −27.2±1.6, and −7.8±3.0‰. In these cultures, isotopic fractionation by phytoplankton caused variations in δ 15 N of up to 50‰ for NH 4 + , 12‰ for NO 3 − , and 25% for particulate N. Similar variability in the δ 15 N of both dissolved inorganic and particulate organic N pools should be expected during phytoplankton blooms in nature. As a result, phytoplankton‐mediated isotopic variability must be considered when isotopic data are used to examine biogeochemical and physical processing of organic matter in marine ecosystems, particularly when biosynthesis and loss processes are decoupled in either space or time during bloom conditions.