Ecological assessment of the sources and effects of high turbid waters in the Fuji River watershed ―The Fuji River Conservation Group―

<p>The recent increase of turbidity in the Fuji River system has received a great concern because the huge amounts of suspended solids (SS) transported by the river may impact on biodiversity and fishery of the coastal waters of Suruga Bay. We conducted a field survey to identify the source and ecological impacts of turbid water occurring at the Hayakawa tributary and the downstream reach of the Fuji River system. Intensive monthly or biweekly sampling of river water and sediments in 26 study sites revealed that strong turbid flow of water tended to occur associated with heavy rainfall in the system. Moreover, one of the main sources of such strong turbidity was from the Amehata River watershed, a steep mountainous tributary of Hayakawa River. The almost all of SS transported from Amehata River was inorganic fraction, which was likely composed of rock-derived clay particles (< 2 μm). Our ecological survey revealed that there was no significant change in the abundance, biomass, species diversity and food webs of stream communities between SS-impacted and non-impacted study sites, even though careful interpretation for our data should be made due to the lack of historical comparisons. We organized a local workshop on river environment and management, as one of the activities of the present study, in order to improve the collaborative watershed governance that involves a large and diverse cast of stakeholders in the Fuji River system.</p>