Phosphorus availability and turnover in the Chesapeake Bay: Insights from nutrient stoichiometry and phosphate oxygen isotope ratios

Jiying Li, Yuge Bai, Kristi Bear, Sunendra Joshi, Deb Jaisi

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

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 (δ18OP), with values approaching isotopic equilibrium under P limiting conditions, suggesting rapid biological P turnover. Furthermore δ18OP 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.

Original languageEnglish (US)
Pages (from-to)811-824
Number of pages14
JournalJournal of Geophysical Research: Biogeosciences
Volume122
Issue number4
DOIs
StatePublished - Apr 1 2017
Externally publishedYes

Bibliographical note

Funding Information:
We thank Debbie McKay, Kristen Heyer, Laura Fabian, and others at the Maryland Department of Natural Resources, Rick Younger, and the crew of R/V Kerhin for help with sample acquisition and sharing the shipboard data. We are very thankful to the Chesapeake Bay program for sharing the water column geochemistry data. We acknowledge Lisa Stout, Ha Vu, Nirman Dhakal, Mingjing Sun, Dengjun Wang, Hui Li, Qiang Li, and Balakrishna Avula for help processing unusually large volume of water samples. The work has been supported by grants from the U.S. Department of Agriculture (2015-67020 and 2016-08499) and National Science Foundation (1301765 and 1654642). All CBP data were obtained freely from the CBP Data Hub (http://www.chesapeakebay.net/data). Supporting data are included as three tables in a supporting information file; any additional data may be obtained from J.L. (e-mail: lijiying@udel.edu). We thank the two anonymous reviewers for comments that helped improved the manuscript.

Publisher Copyright:
©2017. American Geophysical Union. All Rights Reserved.

Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.

Keywords

  • Chesapeake Bay
  • isotopes
  • microbial turnover
  • phosphorus

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