KOBE – Hyogo Prefecture, which is suffering from poor catches of some fish, has decided to allow greater quantities of nitrogen and phosphorus in wastewater discharged into the Seto Inland Sea, after deeming its water too clean for fish to live in, officials said Monday.
The prefecture plans to set what it sees as Japan’s first lower limit on substances affecting the marine environment, possibly within the year. The nonbinding standard includes keeping the minimum nitrogen amount at 0.2 milligrams per liter.
The prefecture also plans to ask local municipalities and companies to cooperate with its plan to introduce the new standards on domestic and industrial wastewater discharges, thought by some to be displacing water that contains the chemicals naturally with unnaturally clean releases.
“We want to release wastewater carefully by consulting research organizations and experts so that we don’t drastically change the marine environment,” said an official at the prefectural government.
The Seto Inland Sea frequently experienced red tides during Japan’s high economic growth period from the mid-1950s to the early 1970s as factory wastewater with abundant nitrogen and phosphorus flowed into the sea, causing increases in plankton.
Japan has since toughened environmental controls and introduced better waste-processing technologies. The central government has set the upper limit for nitrogen in the sea at 0.3 milligrams per liter for Hyogo. The actual amount stood at 0.17 mg in fiscal 2016. But as the chemicals declined, so did the plankton that fish feed on. Officials in the Hyogo Prefectural Government say the lack of plankton has led to recent poor catches of sand eel, a popular spring delicacy in the region.
This year, Hyogo’s fishing season for sand eel in March was terminated after three days due to seriously poor catches. The period used to extend into May.
Prefectures and municipalities located along the Seto Inland Sea have also been working to boost the amount of nitrogen and phosphorus in seawater.