Journal
MARINE POLLUTION BULLETIN
Volume 62, Issue 4, Pages 770-785Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.marpolbul.2011.01.005
Keywords
Groundwater discharge; Coral reef; Radon; Nutrients; Phytoplankton; Salinity
Funding
- JSPS (The Japan Society for the Promotion of Science)
- APN (Asia-Pacific Network) [ARCP2006-08NMY-Nadaoka]
- JST (Japan Science and Technology Agency)/JICA (Japan International Cooperation Agency)
- University of the Philippines
- [17206052]
- [18254003]
- [20246081]
- [21254002]
- [20121007]
- Grants-in-Aid for Scientific Research [20246081] Funding Source: KAKEN
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Radon (Rn-222) measurements were conducted in Shiraho Reef (Okinawa, Japan) to investigate nearshore submarine groundwater discharge (SGD(nearshore)) dynamics. Estimated average groundwater flux was 2-3 cm/h (maximum 7-8 cm/h). End-member radon concentration and gas transfer coefficient were identified as major factors influencing flux estimation accuracy. For the 7-km long reef, SGD(nearshore) was 0.39-0.58 m(3)/s, less than 30% of Todoroki River's baseflow discharge. SGD(nearshore) was spatially and temporally variable, reflecting the strong influence of subsurface geology, tidal pumping, groundwater recharge, and hydraulic gradient. SGD(nearshore) elevated nearshore nitrate concentrations (0.8-2.2 mg/l) to half of Todoroki River's baseflow NO3--N (2-4 mg/L). This increased nearshore Chl-a from 0.5-2 mu g/l compared to the typically low Chl-a (<0.1-0.4 mu g/l) in the moat. Diatoms and cyanobacteria concentrations exhibited an increasing trend. However, the percentage contributions of diatoms and cyanobacteria significantly decreased and increased, respectively. SGD may significantly induce the proliferation of cyanobacteria in nearshore reef areas. (C) 2011 Elsevier Ltd. All rights reserved.
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