Quantifying the contributions of riverine vs. oceanic nitrogen to hypoxia in the East China Sea

Fabian Große, Katja Fennel, Haiyan Zhang, Arnaud Laurent

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

In the East China Sea, hypoxia (oxygen ≤ 62.5 mmol m−3) is frequently observed off the Changjiang (or Yangtze River) estuary covering up to about 15 000 km2. The Changjiang is a major contributor to hypoxia formation because it discharges large amounts of freshwater and nutrients into the region. However, modeling and observational studies have suggested that intrusions of nutrient-rich oceanic water from the Kuroshio Current also contribute to hypoxia formation. The relative contributions of riverine vs. oceanic nutrient sources to hypoxia have not been estimated before. Here, we combine a three-dimensional physical-biogeochemical model with an element-tracing method to quantify the relative contributions of nitrogen from different riverine and oceanic sources to hypoxia formation during 2008–2013. Our results suggest that the hypoxic region north of 30° N is dominated by Changjiang inputs, with its nitrogen loads supporting 74 % of oxygen consumption. South of 30° N, oceanic nitrogen sources become more important, supporting 39 % of oxygen consumption during the hypoxic season, but the Changjiang remains the main control on hypoxia formation also in this region. Model scenarios with reduced Changjiang nitrogen loads and reduced open-ocean oxygen levels suggest that nitrogen load reductions can significantly reduce hypoxia in the East China Sea and counteract a potential future decline in oxygen supply from the open ocean into the region.
Original languageEnglish
Article number2701-2020
Pages (from-to)2701–2714
Number of pages14
JournalBiogeosciences
Volume17
Issue number10
DOIs
Publication statusPublished - 19 May 2020

Keywords

  • oceanography
  • coastal biogeochemistry
  • numerical modelling

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