Intertidal regions changing coastal alkalinity: The Wadden Sea‐North Sea tidally coupled bioreactor

Yoana G Voynova,Andrew L King,Wilhelm Petersen,Martina Gehrung,Steffen Aßmann

doi:10.1002/lno.11103

Yoana G Voynova, Andrew L King + Show 3 more

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https://doi.org/10.1002/lno.11103

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Abstract

AbstractIn this study, we successfully implemented a total alkalinity (TA) analyzer in a flow‐through setup, in combination with a FerryBox. The high‐frequency (10 min) measurements along our ship's route revealed that in coastal systems, where carbon fluxes are dynamic, TA can differ significantly (by up to 100 μmol kg−1) between the nearshore and adjacent coastal regions. Even though this study could not account for the net yearly TA production in the coastal region, it demonstrated that there was a seasonal increase in TA of 100–150 μmol kg−1 in coastal waters of the North Sea, equivalent to TA production of 11.7–26.8 mmol m−2 d−1 during the spring and summer months. This seasonal change could not be accounted for by riverine contributions, but instead was probably related to seasonal organic matter production and processing in coastal and nearshore regions. Bottom sediments and the tidally coupled biogeochemical reactor between coastal (North Sea) and nearshore (Wadden Sea) regions are mediating this TA change, and the ~ 4 months lag between the seasonal increase in alkalinity and the peak organic matter production could be explained by the supply of (labile) organic matter and its temperature‐dependent remineralization via both aerobic and anaerobic pathways.

Highlights

IntroductionIntertidal regions changing coastal alkalinity coupling between the benthic and pelagic communities via tidal circulation (Postma 1981; Anschutz et al 2009; Beck and Brumsack 2012; Voynova et al 2015)
This suggests that, even though the absolute value of the total alkalinity (TA) may be slightly offset, TA concentration changes within the North Sea regions were captured by the HydroFIA TA
Even though this study could not account for the sources of net alkalinity production in the coastal region, it demonstrated that there was a seasonal TA change of 100–150 μmol kg−1

Summary

Introduction

Intertidal regions changing coastal alkalinity coupling between the benthic and pelagic communities via tidal circulation (Postma 1981; Anschutz et al 2009; Beck and Brumsack 2012; Voynova et al 2015) This coupling could provide remineralized nutrients and TA to surface waters, continually sustaining primary production when other nutrient sources become scarce (Santos et al 2014). We present the first long-term high-resolution (10 min sampling interval) time series of surface-water TA measured via a state-of-the-art analyzer, the CONTROS HydroFIA TA, combined with a FerryBox aboard a moving platform This sampling setup enabled seasonal and regional TA observations over a large coastal region (> 300 km), and this study links these observations to potential TA sources or sinks. This study aims to improve our understanding of the use of state-of-the-art TA analyzers, and of the variability and sources of TA in coastal environments

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