US EPA

8665410 

Book/Book Chapter 

Submarine Groundwater Discharge and its Influence on Primary Production in Japanese Coasts: Case Study in Obama Bay 

Honda, H; Sugimoto, Ryo; Kobayashi, S 

2018 

Global Environmental Studies 

101-115 

10.1007/978-981-10-7383-0_8 

WOS:000461947600009 

We report the relationship between submarine groundwater discharge (SGD) and primary production in the nearshore coast of Obama Bay, Japan, using three approaches. First, we conducted high-resolution mapping of Rn-222 and biogeochemical properties along the coast. The eastern part of the bay was strongly influenced by groundwater through several direct and indirect pathways. Lower delta N-15 values in seaweed collected from the eastern area were indicative of larger influences of groundwater. Second, we measured the vertical distributions of Rn-222, salinity, and chlorophyll-a (Chl-a) concentrations along two transects from onshore to offshore at two sites (Tomari and Kogasaki) located on the eastern coast of the bay. In Tomari, Chl-a concentrations were higher in the surface layer in the nearshore coastal area where Rn-222 and salinity showed higher and lower values, respectively, due to terrestrial spring water and SGD in the intertidal zone. In contrast, higher Rn-222 and Chl-a values were detected in the bottom layer in Kogasaki. This suggested that SGD was composed mainly of recirculated seawater discharge from the seafloor. Finally, temporal variations in multiple parameters related to SGD and phytoplankton production were recorded in Kogasaki in July and November. There was no clear relationship between tide and Rn-222 concentrations in either month, but pCO(2) and dissolved O-2 showed clear diurnal variations. The estimated O-2 production rate in July was higher than that in November. This seasonal difference may have been caused by differences in the SGD rate (7.1 cm d(-1) in July and 3.7 cm d(-1) in November). 

Submarine groundwater discharge; Rn-222; Nutrients; Primary production; Coastal seas