MEPS 312:85-100 (2006)  -  doi:10.3354/meps312085

Tidal resuspension of microphytobenthic chlorophyll a in a Nanaura mudflat, Saga, Ariake Sea, Japan: flood–ebb and spring–neap variations

Chul-Hwan Koh1, Jong Seong Khim1,*, Hiroyuki Araki2, Hiroyuki Yamanishi2, Hiroyuki Mogi2, Kenichi Koga3

1School of Earth and Environmental Sciences (Oceanography), Seoul National University, Seoul 151-742, South Korea
2Institute of Lowland Technology, and 3Faculty of Science and Engineering, Saga University, Saga 840-8502, Japan
*Corresponding author. Email:

ABSTRACT: The resuspension of microphytobenthic chlorophyll a (chl a) and suspended particulate matter (SPM) from the upper intertidal flat was studied at Nanaura, Ariake Sea, Japan, and a spatial comparison of chl a and SPM in the northern Ariake Sea is presented here. A 15 d time series of chl a and SPM records (measured at 15 cm above the bottom) revealed that resuspension was clearly associated with flood–ebb and spring–neap tidal characteristics, where significant resuspension was found during early flood, particularly in the high-energy period (viz. spring tide). The peaks of resuspended chl a and SPM during 28 tidal periods were observed to consistently occur shortly after the current velocity reached a maximum and when the threshold current velocity was found to be ca. 15 cm s–1. Much more highly fluctuating, irregular peaks of chl a and SPM were occasionally observed, these were attributable to high wind speeds, ≥3 m s–1. Computation of chl a and SPM fluxes showed clear spring–neap variation, and time-integrated fluxes denoted predominant offshore residual transport during the observation period. Benthic chl a measured in the surficial sediment (top 0.5 cm) during 13 exposure periods showed a decreasing trend from spring to neap tide, similar to spring–neap variations of chl a in the water column during the semi-lunar tidal period. The daily mean percentage of resuspended chl a in the water column relative to the amount of benthic chl a was estimated to be ca. 10 to 70% (mean = 33%), implying that a certain portion of the microphytobenthos is resuspended during high tide and partly contributes to the total biomass in the water column of the upper intertidal flat.

KEY WORDS: Microphytobenthos biomass · Resuspension · Benthic chlorophyll a · Suspended particulate matter · Tidal flats · Ariake Sea

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