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Redox control of N:P ratios in aquatic ecosystems

Authors

  • T. M. QUAN,

    1. Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, USA
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  • P. G. FALKOWSKI

    1. Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, USA
    2. Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA
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Corresponding author: Tracy M. Quan. Tel.: 732-932-6555-243; fax: 732-932-4083; e-mail: quan@marine.rutgers.edu

ABSTRACT

The ratio of dissolved fixed inorganic nitrogen to soluble inorganic phosphate (N:P) in the ocean interior is relatively constant, averaging ~16 : 1 by atoms. In contrast, the ratio of these two elements spans more than six orders of magnitude in lakes and other aquatic environments. To understand the factors influencing N:P ratios in aquatic environments, we analyzed 111 observational datasets derived from 35 water bodies, ranging from small lakes to ocean basins. Our results reveal that N:P ratios are highly correlated with the concentration of dissolved O2 below ~100 µmol L−1. At higher concentrations of O2, N:P ratios are highly variable and not correlated with O2; however, the coefficient of variation in N:P ratios is strongly related to the size of the water body. Hence, classical Redfield ratios observed in the ocean are anomalous; this specific elemental stoichiometry emerges not only as a consequence of the elemental ratio of the sinking flux of organic matter, but also as a result of the size of the basins and their ventilation. We propose that the link between N:P ratios, basin size and oxygen levels, along with the previously determined relationship between sedimentary δ15N and oxygen, can be used to infer historical N:P ratios for any water body.

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