Dissolved carbon biogeochemistry and export in mangrove-dominated rivers of the Florida Everglades

David T Ho,Sara Ferrón,René M Price,Peter K Swart,Leticia Barbero,William T Anderson,Victor C Engel

doi:10.5194/bg-14-2543-2017

Abstract

Abstract. The Shark and Harney rivers, located on the southwest coast of Florida, USA, originate in the freshwater, karstic marshes of the Everglades and flow through the largest contiguous mangrove forest in North America. In November 2010 and 2011, dissolved carbon source–sink dynamics was examined in these rivers during SF6 tracer release experiments. Approximately 80 % of the total dissolved carbon flux out of the Shark and Harney rivers during these experiments was in the form of inorganic carbon, either via air–water CO2 exchange or longitudinal flux of dissolved inorganic carbon (DIC) to the coastal ocean. Between 42 and 48 % of the total mangrove-derived DIC flux into the rivers was emitted to the atmosphere, with the remaining being discharged to the coastal ocean. Dissolved organic carbon (DOC) represented ca. 10 % of the total mangrove-derived dissolved carbon flux from the forests to the rivers. The sum of mangrove-derived DIC and DOC export from the forest to these rivers was estimated to be at least 18.9 to 24.5 mmol m−2 d−1, a rate lower than other independent estimates from Shark River and from other mangrove forests. Results from these experiments also suggest that in Shark and Harney rivers, mangrove contribution to the estuarine flux of dissolved carbon to the ocean is less than 10 %.

Highlights

In many tropical and subtropical regions, mangrove forests are a typical feature surrounding estuaries (Twilley et al, 1992; Bouillon et al, 2008a)
Maximum pressure of CO2 (pCO2) values were observed at intermediate salinities, decreasing towards both end-members, while dissolved O2 (DO) showed the opposite pattern, with saturations ranging from 36 to 113 %
The patterns of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) along the salinity gradient followed the same trend as pCO2 and were clearly non-conservative (Fig. 3a–f)

Summary

Introduction

In many tropical and subtropical regions, mangrove forests are a typical feature surrounding estuaries (Twilley et al, 1992; Bouillon et al, 2008a). Mangroves are thought to play an important role in tropical and subtropical coastal biogeochemical cycling and the global coastal carbon budget, due to their high productivity and rapid cycling of organic and inorganic carbon (Twilley et al, 1992; Jennerjahn and Ittekkot, 2002; Dittmar et al, 2006). Bouillon et al (2008a) showed that over 50 % of the carbon fixed by mangroves through photosynthesis could not be accounted for by growth in biomass, accumulation in soils, and export of organic carbon, and suggested that a large fraction of this missing organic carbon may be mineralized to dissolved inorganic carbon (DIC) and either lost to the atmosphere or exported to the surrounding waters.

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