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Phosphorus availability and turnover in the Chesapeake Bay: Insights from nutrient stoichiometry and phosphate oxygen isotope ratios
Author(s) -
Li Jiying,
Bai Yuge,
Bear Kristi,
Joshi Sunendra,
Jaisi Deb
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003589
Subject(s) - environmental chemistry , nutrient , phosphorus , phosphate , biogeochemical cycle , photic zone , eutrophication , redfield ratio , bay , chemistry , remineralisation , salinity , environmental science , oceanography , phytoplankton , inorganic chemistry , geology , organic chemistry , fluoride
Understanding phosphorus (P) availability and its control on eutrophication in the Chesapeake Bay is complicated by variable sources and biogeochemical reactions transforming P forms. We investigated seasonal and spatial variability in P limitation and biological utilization in the Bay using nutrient stoichiometry (of both dissolved and particulate forms), phosphate oxygen isotope ratios, and alkaline phosphatase activity at three sites along the salinity gradient. We demonstrate that particulate nutrient ratios can be used as indicators of nutrient limitation in the Bay and suggest strong seasonal and spatial variability in P availability: the surface water is P limiting in spring, but this condition is alleviated in summer and in the deeper waters. Variability in P limitation is well reflected in the trends of phosphate oxygen isotope composition (δ 18 O P ), with values approaching isotopic equilibrium under P limiting conditions, suggesting rapid biological P turnover. Furthermore δ 18 O P values suggest multiple phosphate sources including remobilization of terrestrial inorganic P phases and remineralization of organic P and P from both sources is sufficiently cycled by microorganisms, suggested by the extensive equilibrium oxygen isotope exchange. Our results further suggest high P utilization in the deeper euphotic zone where nutrients are abundant, raising caution on studying nutrient availability and limitation only in the surface water.