09:30 〜 09:45
[MIS11-03] Responses of phytoplankton biomass to river-borne nutrient flux in the coastal waters of Suruga Bay
キーワード：volcanic watershed、spring-fed river、biogeochemical flux、riverine nutrinets、phytoplankton、primary production
Riverine transports of biogeochemical elements from watersheds can be an important flux that supports the downstream and coastal food webs. Thus, numerous studies have been performed to identify the linkage between terrestrial and coastal ecosystems through nutrient flux from lands to the oceans. However, the spatial and temporal patterns of coastal phytoplankton responses to river-borne materials, as well as the effect of tectonic and volcanic activity on riverine biogeochemical flux, have yet to be fully understood.
Here we present our empirical studies conducted in a Japanese watershed to show that volcanic-rock lithology strongly influences the biogeochemical characteristics of river-borne nutrients and thereby influence primary productivity in the coastal ecosystem. We performed the field sampling campaigns covering the whole area of Kano River watershed, central Japan, to measure discharge, nutrient concentrations, and other physico-chemical variables. The spatial analyses showed that streams and rivers flowing through the lava flow area of the southern east slope of Mt.Fuji (i.e., Mishima Lava) contained high concentrations of basalt-derived minerals (P, Si, V, etc.) and exhibited a significant quantitative contribution to their downstream flux from the entire watershed. Moreover, our coastal-monitoring surveys and batch-culture experiments showed that coastal phytoplankton biomass was fueled by such riverine biogeochemical flux. Furthermore, the satellite ocean color data showed that the spatial and temporal patterns of surface chlorophyll-a concentration tended to respond to nutrient inputs following rainfall and terrestrial runoff events.
On the basis of the obtained results, we emphasize that riverine-nutrient input is critically important to phytoplankton dynamics in this coastal ecosystem. We further discuss the implications of these findings on food web dynamics in coastal ecosystems under changing climate with more frequent storm runoff events.
Here we present our empirical studies conducted in a Japanese watershed to show that volcanic-rock lithology strongly influences the biogeochemical characteristics of river-borne nutrients and thereby influence primary productivity in the coastal ecosystem. We performed the field sampling campaigns covering the whole area of Kano River watershed, central Japan, to measure discharge, nutrient concentrations, and other physico-chemical variables. The spatial analyses showed that streams and rivers flowing through the lava flow area of the southern east slope of Mt.Fuji (i.e., Mishima Lava) contained high concentrations of basalt-derived minerals (P, Si, V, etc.) and exhibited a significant quantitative contribution to their downstream flux from the entire watershed. Moreover, our coastal-monitoring surveys and batch-culture experiments showed that coastal phytoplankton biomass was fueled by such riverine biogeochemical flux. Furthermore, the satellite ocean color data showed that the spatial and temporal patterns of surface chlorophyll-a concentration tended to respond to nutrient inputs following rainfall and terrestrial runoff events.
On the basis of the obtained results, we emphasize that riverine-nutrient input is critically important to phytoplankton dynamics in this coastal ecosystem. We further discuss the implications of these findings on food web dynamics in coastal ecosystems under changing climate with more frequent storm runoff events.