Mapping Phytoplankton and Related Physical-Chemical Variables within the Duplin River Tidal Drainage in Georgia
Poster Number:
271
Presenter/Primary Author:
John Schalles In 2006 hyperspectral imagery of the Duplin River tidal watershed at Sapelo Island (Georgia Coastal Ecosystems), we documented striking spatial variation in phytoplankton chlorophyll patterns within the Duplin River and the tributary streams. These channels carry flood and eb tide flows (mean tidal range of 2.1 m) within the marsh drainage system. In subsequent studies to better document and understand the algal distribution patterns, longitudinal transects were conducted between 2009 and 2012 within tributary channels and the Duplin River using a multi-instrument YSI 6600 sonde and a dual Ocean Optics USB2000 spectroradiometer system. We measured chlorophyll fluorescence, turbidity, salinity, temperature, dissolved oxygen, and pH on both rising and falling tides. Water samples were collected to validate and supplement the sonde data, including laboratory measures of chlorophyll a concentration, total suspended matter, and CDOM. Our results indicate that chlorophyll a concentration can vary by more than an order of magnitude and generally increase on falling tides between the Duplin main channel and upper tributary channels. Fewer patterns were discernible during the better mixed conditions of flood tides. Oyxgen and pH correlated with chlorophyll patterns, time of day, and tidal stage. Temperature and salinity patterns may be indicators of groundwater inputs as well as strength of connection with the adjacent Doboy Sound and nearshore wates. Our data supports a hypothesis that the export of benthic diatoms from flooded saltmarsh substrates influences phytoplankon pigment patterns on the falling tide and contributes significant biomass to creek and river phytoplankton communities. In related work, we have begun to document and analyze spatial patterns in microbenthic algal communities in exposed creek bank muds.
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