POST-FLOOD NUTRIENT DISTRIBUTION PHENOMENA IN COASTAL WATERS OFF RIVER MOUTH

High discharge caused by river flood can affect the water quality of downstream river, and coastal area where this river releasing its water. To investigate the effect of river flood on nutrient distribution, two field measurements were conducted, i.e November 2, 2001, July 20, 2002, representing usual condition and after flood condition respectively. Research site is coastal area of the Abukuma River mouth, Japan with eight sampling stations. The results show that the river flood affected water quality by increasing the concentration of suspended solid and nutrient. River mouth waters contain remarkably high concentration of nitrogen (4.4 mg/L) after river flood. Nitrogen and phosphorus were distributed as the function of distance to the river mouth in usual condition. However, condition after river flood show that nutrient had been brought far to the offshore, indicated by the higher concentration in stations located far from the river mouth. For nitrogen path, nitrification process was likely to be occurred in surface layer of coastal area, whereas detritus decomposition occurred in bottom layer. Settling process in coastal waters appeared dominant in phosphorus path after the flood. Keywords: River flood, nutrient distribution, open coastal water