[A-HW24] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW24-P11] Island-scale spatial variation in the coastal environmental factors: Case study in the Seto Inland Sea, western Japan

*Nhat Hong Nguyen¹, Mitsuyo Saito¹, Mayuko Hamada², Shin-ichi Onodera³, Takuya Akinaga¹, Aiping Zhu⁴ (1.Graduate School of Environmental and Life Science, Okayama University, 2.Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan, 3.Graduate School of Advanced Science and Engineering, Hiroshima University, Japan , 4.Anhui Normal University, China)

Keywords:salinity, nutrients, chlorophyll-a, Radon (222Rn), Island-scale

Coastal areas are important habitats for a variety of ecosystems for providing a feeding ground, nutrient cycle, aquaculture, and so on. Coastal system processes are the interaction of complex and coupled physical and biochemical which are influenced by ocean, land, and atmosphere at spatial and temporal scales. Coastal biodiversity can be affected by geographical factors or by environmental factors (water temperature, salinity, nutrient, etc) that limit or enhance species communities or select locally adapted species. Here, this study aims to analyze the spatial characteristics of environmental factors in the coastal area involved in ecosystems. Our target area is the coastal Ikuchijima Island, which is an island in the Seto Inland Sea, western Japan, and locates in the northwestern region of Hiuchi-Nada. In this study, the spatial variation of physical and biological parameters (salinity, temperature, nutrients, and chlorophyll-a) in the coastal area was observed on an island scale. Also, radon (²²²Rn) measurement was conducted to investigate the dynamics of submarine groundwater discharge (SGD). The result showed that surface salinity ranged from 29.9 to 30.8 with a mean value of 30.5. The concentrations of nutrients in coastal water showed in a wide range, varying between 0.01and 0.09 mgL^-1 for dissolved inorganic nitrogen (DIN), 0.03 and 0.09 mgL^-1 for dissolved inorganic phosphorus (DIP), and 0.48 and 0.90 mgL^-1 for dissolved inorganic silica (DSi). The concentration of nutrients was negatively correlated with that of salinity at all sampling stations. The concentrations of chlorophyll-a, an indicator of phytoplankton biomass, ranged from 0.70 to 1.06 µgL^-1. The higher values of chlorophyll-a were along the western shoreline and outermost eastern shoreline. These findings provide useful baseline information on the environmental characteristics that may be used for the future investigation of coastal ecosystems.