3:30 PM - 3:45 PM
[MIS14-07] Effects of Kanogawa River flooding on spatial and temporal dynamics of phytoplankton in the coastal waters of the Suruga Bay
Keywords:flooding events, riverine nutrients, phytoplankton, satellite data
Land-derived nutrients often influence the biodiversity and ecosystem functioning of coastal ecosystems. Therefore, many studies have been conducted to identify the effects of riverine nutrient transport on coastal primary productivity and trophic dynamics in the systems. Recent studies have increasingly identified that the biogeochemical flux associated with volcanic activity, such as volcanic ash deposition and lava flow, stimulated phytoplankton growth in the ocean. However, the effects of river-borne flux of volcanic nutrients on phytoplankton dynamics have rarely been identified. Our previous studies have revealed that river water from the quaternary volcanic area of the Kanogawa River watershed contains high concentrations of basalt-derived minerals (P, Si, V, etc.) and such “volcanic nutrient inputs” provided important nutrient subsidies to phytoplankton communities in the coastal waters of the Suruga Bay. Here we show that the spatial and temporal dynamics of phytoplankton growth in the Suruga Bay was strongly influenced by such riverine nutrient transport from the Kanogawa River watershed.
We constructed the hierarchical Bayesian model to describe the space-time data of satellite chl.a concentrations in the Suruga Bay (obtained from MODIS-Aqua) during the 2003-2020 period by using the explanatory variables, such as light (PAR), temperature (SST) and major river flow (Q). The model comparison approach revealed that the river flow (Q) variable greatly increased the predictive performance for explaining the space-time chl.a data, implying that fluvial nutrient transport may be crucial for phytoplankton dynamics. The detailed spatial data of satellite chl.a concentrations (G-COMC/SGLI) obtained for 56 flooding events during the 2018-2021 period showed that in the Uchiura Bay (the NE part of the Suruga Bay), CDOM concentration (a proxy of river water), as well as the specific growth rate of phytoplankton, increased non-linearly with the increase of flood magnitude of the Kanogawa River. Moreover, the spatial extent of such flood-induced high productive areas spread over the entire area of the Uchiura Bay.
The present study revealed that the river-borne flux of volcanic nutrients from the Kanogawa River may control the spatio-temporal pattern of coastal primary productivity of the Suruga Bay. Moreover, the flooding events drastically increase such ecosystem functioning associated with the increase of river peak flow (up to ~1,000 m3/s of discharge). These results suggest that the river flow management should consider not only flooding prevention on lands but the improvement of ecosystem functioning of the downstream coastal ecosystems.
This research was supported by the River Works Technology Research and Development Program from the Ministry of Land, Infrastructure, Transport and Tourism, Japan.
We constructed the hierarchical Bayesian model to describe the space-time data of satellite chl.a concentrations in the Suruga Bay (obtained from MODIS-Aqua) during the 2003-2020 period by using the explanatory variables, such as light (PAR), temperature (SST) and major river flow (Q). The model comparison approach revealed that the river flow (Q) variable greatly increased the predictive performance for explaining the space-time chl.a data, implying that fluvial nutrient transport may be crucial for phytoplankton dynamics. The detailed spatial data of satellite chl.a concentrations (G-COMC/SGLI) obtained for 56 flooding events during the 2018-2021 period showed that in the Uchiura Bay (the NE part of the Suruga Bay), CDOM concentration (a proxy of river water), as well as the specific growth rate of phytoplankton, increased non-linearly with the increase of flood magnitude of the Kanogawa River. Moreover, the spatial extent of such flood-induced high productive areas spread over the entire area of the Uchiura Bay.
The present study revealed that the river-borne flux of volcanic nutrients from the Kanogawa River may control the spatio-temporal pattern of coastal primary productivity of the Suruga Bay. Moreover, the flooding events drastically increase such ecosystem functioning associated with the increase of river peak flow (up to ~1,000 m3/s of discharge). These results suggest that the river flow management should consider not only flooding prevention on lands but the improvement of ecosystem functioning of the downstream coastal ecosystems.
This research was supported by the River Works Technology Research and Development Program from the Ministry of Land, Infrastructure, Transport and Tourism, Japan.