Nutrient distribution in a shallow subtropical lagoon, south Brazil, subjected to seasonal hypoxic and anoxic events

Authors

  • Georgia de Barros Universidade Federal de Santa Catarina
  • Alessandra Larissa D'Oliveira Fonseca Louisiana State University
  • Alex Cabral dos Santos Universidade Federal de Santa Catarina
  • Maria Luiza Schmitz Fontes University of Technology Sydney
  • Alejandro Rodolfo Donnangelo Varela Universidade Federal de Santa Catarina
  • Davide Franco Università Degli Studi Di Venezia

DOI:

https://doi.org/10.1590/s1679-87592017101206502

Keywords:

Eutrophication, Stratification, Dead zones, Mineralization

Abstract

The Conceição Lagoon, located in south Brazil, is a semi-enclosed coastal ecosystem that has seasonal hypoxic and anoxic conditions in its vertically stratified central region, characterized as a site of retention and mineralization of organic matter. This study investigates water column dynamics in the central region of the Conceição Lagoon (CCL) and its relation to physical and chemical variables, in order to understand the hypoxic and anoxic events. Surface, halocline and bottom waters were evaluated at three sampling sites along the CCL. The samples were collected in triplicate during the summer, fall and winter of 2014. Hypoxic and/or anoxic events occurred in the summer (1/21) at the halocline (3 m) and bottom (4 m) waters, and in the fall (2/5) in the bottom water (4.5 m). Positive values of apparent oxygen utilization showed mineralization processes in the halocline and bottom waters. The lowest vertical stratification index was recorded in August (southern winter), which was associated with wind speed (14.7 m.s-1) and direction (southern quadrant). Nutrient concentrations were higher in winter, related to increasing of water mixing. This was the first study to evaluate the dynamics of hypoxic and anoxic events in the CCL and how nutrients respond to the physical structure of the water column.

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Published

2017-06-01

Issue

Section

Original Article

How to Cite

Nutrient distribution in a shallow subtropical lagoon, south Brazil, subjected to seasonal hypoxic and anoxic events. (2017). Brazilian Journal of Oceanography, 65(2), 116-127. https://doi.org/10.1590/s1679-87592017101206502