Short-term and seasonal variation in metabolic balance in Liverpool Bay
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Regions of freshwater influence (ROFIs) are dynamic areas within the coastal seas that experience cycles of stability driven by density gradients and the spring-neap tidal cycle. As a result, pulses of biological production may occur on a more frequent timescale than the classic seasonal cycle. Net community production (NCP) rates and chlorophyll a concentration are presented from a site within the ROFI of Liverpool Bay and compared to similar measurements made at a site outside the ROFI during 2009. The influence of water column stability on biological production in the ROFI was also investigated using high-frequency observations from a Cefas Smartbuoy. Both sites were autotrophic from spring to autumn before becoming heterotrophic over winter. NCP at the inshore site was estimated to range from 30.8 to 50.4 gC m−2 year−1. A linear relationship detected between chlorophyll a and NCP from both sites was used to estimate metabolic balance over 1 year at the ROFI site using high-resolution chlorophyll a concentrations from the Smartbuoy but was found to poorly replicate NCP rates compared to those derived from dissolved oxygen fluxes. There was no clear biological response to periods of stratification within the ROFI, and it is proposed that changes in light attenuation in the Liverpool Bay ROFI, driven not only by stratification but also by fluctuations in riverine sediment load, most likely play an important role in controlling phytoplankton growth in this region.
KeywordsAutotrophy Heterotrophy Stratification Liverpool Bay ROFI Oxygen
We would like to thank the captain and crew of RV Prince Madog as well as all research assistants on the cruises, Dr. Matthew Palmer and the PHiXT project at National Oceanography Centre Liverpool, and Sean Gaffney at British Oceanographic Data Centre. AP was supported by a Natural Environment Research Council Strategic Ocean Funding Initiative studentship (NE/F012632/1). CM would like to acknowledge a Royal Society Research Grant (RG080305). The Smartbuoy data was collected under a Department for Environment, Food and Rural Affairs funded programme (SLA25). We wish to thank Professor Stephen V. Smith and one anonymous reviewer for their valuable comments.
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