Constraining nitrogen sources to a seagrass-dominated coastal embayment by using an isotope mass balance approach

Douglas G. Russell, Adam J. Kessler, Wei Wen Wong, Dick Van Oevelen, Perran L.M. Cook

Research output: Contribution to journalArticleResearchpeer-review

1 Citation (Scopus)

Abstract

Nitrogen (N) is often the key nutrient limiting primary production in coastal waters. Quantifying sources and sinks of N is therefore critical to understanding the factors that underpin the productivity of coastal ecosystems. Constraining nitrogen inputs can be difficult for some terms such as N fixation and marine exchange as a consequence of uncertainties associated with scaling and stochasticity. To help overcome these issues, we undertook a N budget incorporating an isotope and mass balance to constrain N sources in a large oligotrophic coastal embayment (Western Port, Australia). The total N input to Western Port was calculated to be 1400 Mg N year-1, which is remarkably consistent with previous estimates of sedimentation rates within the system. Catchment inputs, N fixation, marine sources and atmospheric deposition comprised 44, 28, 28 and 13% of N inputs respectively. Retention of marine-derived N equated to 3 and 10% of total N and NOx flushed through the system from the marine end-member. The relatively high contribution of N fixation compared with previous studies was most likely to be due to the high proportion of nutrient-limited intertidal sediments where N is mediated by seagrasses and sediment cyanobacteria.

Original languageEnglish
Pages (from-to)701-709
Number of pages9
JournalMarine and Freshwater Research
Volume73
Issue number5
DOIs
Publication statusPublished - May 2022

Keywords

  • N
  • denitrification
  • isotope
  • nitrogen
  • nitrogen budget
  • nitrogen fixation
  • seagrass
  • tidal flat

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