気仙沼湾流入河川における森か ら海までの水質形成

摘要

Understanding the factors controlling the flux and dynamics of riverine nutrients including dissolved nitrogen(N), phosphorus(P), and iron(Fe)from land to sea is necessary for elucidating the recovery processes of primary production in the coastal area, which had been attacked by the Great East Japan Earthquake and following tsunami. We examined the spatial distribution of nutrient concentrations in four rivers draining into the Kesennuma and Moune Bay to understand the impact of the disaster on river water quality. The spatial patterns of total N, P, and dissolved Fe concentration along the rivers suggest that their main sources may be agricultural fields and urban areas, and the impact of the land disturbances caused by tsunami may be negligible as for river quality. In Nishi-moune river, however, newly created salt marsh by tsunami attack and ground subsidence in coastal area changed the nutrient components and concentrations; that is, a remarkable decrease in nitrate, and slightly increase in ammonium, phosphorus, and dissolved organic carbon concentrations after passing through the salt marsh. This means that the relationship between forest and sea can be changed after the eqrthquake in this region. In addition, recent reconstruction of urban areas near the coastal area can also change the water chemistry. In fact, ammonium concentration is increasing at the mouth of the Ohkawa river since March 2013. It is necessary to continue to monitor river water quality for assessing the nutrient dynamics of coastal ecosystems.