Bull. Jpn. Soc. Fish. Oceanogr. 82(1), Page 26-35, 2018   Influence of DIN derived from ports and treated sewage effluent on nori (Pyropia) farms of the northeastern part of Harima Nada Kazuhiro Harada1†, Katsuyuki Abo2, Shusaku Kawasaki3, Fumihiro Takesako3 and Kazutaka Miyahara1 1 Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Akashi, Hyogo 674–0093, Japan 2 National Research Institute of Fisheries and Environment of Inland Sea, Japan Fisheries Research and Education Agency, 2–17–5 Maruishi, Hatsukaichi, Hiroshima 739–0452, Japan 3 Hyogo Prefectural Federation of Fisheries Co-operative Associations, Hyogo Nori Institute, Akashi, Hyogo 674–0093, Japan † E-mail: kazuhiro_harada@pref.hyogo.lg.jp Dynamics of dissolved inorganic nitrogen (DIN) in relation to the color of fresh nori (Pyropia) were examined around nori farms in the coastal waters of the northeastern part of Harima Nada (off the coast of Akashi City and Harima Town in Hyogo Prefecture). DIN concentration in surface water was higher inside the ports due to industrial effluent and rivers, and around the outfall of treated sewage effluent. Horizontal distribution of high DIN concentration in surface water extended in the east-west direction along the coastline. On the other hand, offshore concentrations were lower. The dynamics of salinity and NH4–N concentration suggest that during the ebb tide (eastward flow in this area), discharge from ports and treated sewage effluent in the western area can influence the coastal nori farms east of this study area. Also, the numerical simulation method results showed that DIN supplied from the treated sewage effluent flowed eastward during the ebb tide, and reached the coastal nori farms. The quality of fresh nori produced in the eastward coastal nori farms from this study area was better than that from the offshore area, presumably influenced by the nutrients discharged from the ports and the treated sewage effluent. Key words: Pyropia, DIN, water of ports, treated sewage effluent, industrial effluent, Nori culture