Water Science & Technology Vol 65 No 11 pp 1994–2002 © IWA Publishing 2012 doi:10.2166/wst.2012.099

Impacts of nutrients and related environmental factors on distribution and size structure of Noctiluca scintillans populations of the Eutrophic Tha Chin Estuary, Thailand

Wansiri Chuenniyom, Charumas Meksumpun and Shettapong Meksumpun

This study aimed to analyze the impacts of nutrients and related aquatic factors on changes in the Noctiluca population of the Tha Chin estuary, a nutrient-rich estuary located in the inner Gulf of Thailand. Field surveys were carried out at 30 stations during November 2009 to August 2010. The results indicated high levels of dissolved inorganic nitrogen (DIN; 13.89–46.99 μmol/L) and PO₄³⁻-P (0.20–3.05 μmol/L) where the Noctiluca red tide occurred, particularly during the high-loading period. Dense populations were usually found in the outer part of the estuary with comparatively high salinity (25–29 psu). The highest Noctiluca density was 72,333 cells L⁻¹ and the cell diameters ranged between 360 and 460 μm. Proportions of small-sized cells (P_s; less than 300 μm) varied over time. In this study, P_s showed a positive correlation with levels of PO₄³⁻-P, while the total population density was significantly affected by levels of NH₄⁺-N and DIN (p < 0.05). Overall, PO₄³⁻-P influenced the development of the Noctiluca red tide, with the limitation of PO₄³⁻-P levels to below 1 μmol/L suggested for controlling Noctiluca red tide outbreaks at their origin. To support environmental conservation and maintain sustainable production in the estuary, the levels of PO₄³⁻-P should be considered for the further effective development of water quality standards in estuarine zones.

Keywords: abundance and size structure; dissolved inorganic nitrogens; Noctiluca red tide; orthophosphate phosphorus; Tha Chin estuary

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