Program

We have recognized river and submarine groundwater discharge (SGD) as important components of the hydrological cycle and chemical budgets in the coastal zone. While it is clear that many coastal systems are impacted by river and SGD, however, their variation in decadal time scale under climate change is largely unknown, particularly in complex coastal system influenced both by river and SGD. Toyama Bay (TB) is such an ideal study area, a semi-enclosed bay in the Sea of Japan at mid latitude zone, which receives huge amounts of nutrients from runoff and fresh SGD. In this study, we examine the inter-annual changes and possible driving force of river and SGD fluxes into Toyama Bay. The river basin near the TB, snowmelt runoff timing is sensitive to temperature change in winter. In this study, hydrographic parameters in the TB were measured monthly from 2005 to 2014. We constructed salt and water budget in the inner TB and calculated monthly fresh SGD flux. SGD peak occurred in spring and summer in recent decade, consistent with seasonal change of groundwater table. Fresh SGD flux decreased in recent three decades, consistent with snowfall reduction due to global warming. In contrast, river flux increased but associated TN and TP fluxes decreased from 1985 to 2013. River flux significantly increased in spring might be explained by that snowmelt season shifted early due to global warming.