Tidal controls on trace gas dynamics in a seagrass meadow of the Ria Formosa lagoon (southern Portugal)

E Bahlmann,W Michaelis,R Santos,I Weinberg,R Seifert,T Eckhardt,J V Lavrič

doi:10.5194/bg-12-1683-2015

E Bahlmann, W Michaelis + Show 5 more

Open Access

https://doi.org/10.5194/bg-12-1683-2015

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Abstract

Abstract. Coastal zones are important source regions for a variety of trace gases, including halocarbons and sulfur-bearing species. While salt marshes, macroalgae and phytoplankton communities have been intensively studied, little is known about trace gas fluxes in seagrass meadows. Here we report results of a newly developed dynamic flux chamber system that can be deployed in intertidal areas over full tidal cycles allowing for highly time-resolved measurements. The fluxes of CO2, methane (CH4) and a range of volatile organic compounds (VOCs) showed a complex dynamic mediated by tide and light. In contrast to most previous studies, our data indicate significantly enhanced fluxes during tidal immersion relative to periods of air exposure. Short emission peaks occurred with onset of the feeder current at the sampling site. We suggest an overall strong effect of advective transport processes to explain the elevated fluxes during tidal immersion. Many emission estimates from tidally influenced coastal areas still rely on measurements carried out during low tide only. Hence, our results may have significant implications for budgeting trace gases in coastal areas. This dynamic flux chamber system provides intensive time series data of community respiration (at night) and net community production (during the day) of shallow coastal systems.

Highlights

We observed a strong influence of the tidal cycle on fluxes of both gases, with more pronounced emission fluxes generally occurring during tidal inundation
Elevated fluxes during tidal immersion were observed for all non-CH4 volatile organic compounds (VOCs) studied here
We have presented flux measurements for a variety of trace gases in a tidally influenced seagrass bed (Z. noltii) using a newly developed dynamic flux chamber system that can be deployed over full tidal cycles

Summary

Introduction

Coastal zones are important sites for carbon turnover and hotspots for a variety of volatile organic compounds (VOCs), including halogenated compounds (Gschwend et al, 1985; Moore et al, 1995; Baker et al, 1999; Rhew et al, 2000; Christoph et al, 2002; Manley et al, 2006; Valtanen et al, 2009) and sulfur-bearing compounds (Dacey et al, 1987; Cooper et al, 1987a, b; De Mello et al, 1987; Turner et al, 1989; Leck and Rhode, 1990; Baker et al, 1992) but a minor source of hydrocarbons such as CH4 (Van der Nat and Middelburg, 2000; Middelburg et al, 2002) While coastal ecosystems, such as salt marshes, macroalgae and phytoplankton communities have been intensively studied, little is known about trace gas fluxes from seagrass meadows. The importance of this transport pathway has been shown for CH4 emissions from a variety of vegetation types

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