Assessment of Submarine Groundwater Discharge (SGD) as a Source of Dissolved Radium and Nutrients to Moorea (French Polynesia) Coastal Waters
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- 作者：Karen L. Knee ; Elizabeth D. Crook ; James L. Hench…
- 关键词：Submarine groundwater discharge ; Volcanic islands ; Moorea ; Nutrients ; Radium
- 刊名：Estuaries and Coasts
- 出版年：2016
- 出版时间：November 2016
- 年：2016
- 卷：39
- 期：6
- 页码：1651-1668
- 全文大小：1,788 KB
- 刊物类别：Earth and Environmental Science
- 刊物主题：Environment
Environment
Ecology
Geosciences
Environmental Management
Nature Conservation - 出版者：Springer New York
- ISSN：1559-2731
- 卷排序：39
文摘
Previous work has documented large fluxes of freshwater and nutrients from submarine groundwater discharge (SGD) into the coastal waters of a few volcanic oceanic islands. However, on the majority of such islands, including Moorea (French Polynesia), SGD has not been studied. In this study, we used radium (Ra) isotopes and salinity to investigate SGD and associated nutrient inputs at five coastal sites and Paopao Bay on the north shore of Moorea. Ra activities were highest in coastal groundwater, intermediate in coastal ocean surface water, and lowest in offshore surface water, indicating that high-Ra groundwater was discharging into the coastal ocean. On average, groundwater nitrate and nitrite (N + N), phosphate, ammonium, and silica concentrations were 12, 21, 29, and 33 times greater, respectively, than those in coastal ocean surface water, suggesting that groundwater discharge could be an important source of nutrients to the coastal ocean. Ra and salinity mass balances indicated that most or all SGD at these sites was saline and likely originated from a deeper, unsampled layer of Ra-enriched recirculated seawater. This high-salinity SGD may be less affected by terrestrial nutrient sources, such as fertilizer, sewage, and animal waste, compared to meteoric groundwater; however, nutrient-salinity trends indicate it may still have much higher concentrations of nitrate and phosphate than coastal receiving waters. Coastal ocean nutrient concentrations were virtually identical to those measured offshore, suggesting that nutrient subsidies from SGD are efficiently utilized.