Influence of Submarine Groundwater Discharge on Primary Productivity in the Semi-Enclosed Bay in Japan

Abstract:

In recent years, a number of studies have shown that submarine groundwater discharge is an alternative nutrient pathway and can drive primary production in coastal seas. However, very little is known about an exact relationship between input of groundwater and response of primary production. To clarify the relationship, we conducted the field survey in the semi-enclosed coastal bay in Japan (Obama Bay). There are abundant amounts of groundwater resources in the basin. Firstly, we conducted ²²²Rn continuous measurement along the coast in March 2013 to obtain the spatial difference of groundwater impact. As a result, ²²²Rn activity clearly showed that groundwater discharge concentrates in the western part of the bay head. We thus conducted in-situ measurements of primary productivity using stable ¹³C tracer method and environmental parameters (ex. ²²²Rn activity, light intensity, temperature and nutrient concentrations) at 6 stations within the western bay head in July and August 2013. Primary productivity within the western bay head changed from 11.0 to 49.5 µg C L^-1 hr^-1 in July and from 9.3 to 32.4 µg C L^-1 hr^-1 in August. Moreover, there was significant relationship between primary productivity and ²²²Rn concentration in both months. Although light intensity and water temperature were different in each station and month, concentrations of nutrients limited primary productivity. These results showed that nutrient supply from SGD would affect crucial impact on primary productivity in Obama Bay.