Scientists worry about South Sound's low oxygen levels

The ongoing problem of chronic low oxygen in some parts of South Puget Sound is drawing closer scrutiny amid concerns that it could grow worse.

The state Department of Ecology has announced a $400,000 study aimed at better understanding why some parts of the South Sound suffer from low oxygen, particularly Budd Inlet near Olympia and Carr and Case inlets along the Key Peninsula.

There's little sign the problem has worsened over the past 15 years, said Andrew Kolosseus, an environmental specialist at Ecology. Previous studies have found oxygen levels that are unhealthful but not lethal. But the concern is that things might decline, as they have in Hood Canal to the west.

"That's what we're worried about," Kolosseus said.

Low oxygen levels are taking a major toll in Hood Canal. Fish die-offs have struck the narrow fjord three times in the past five years, with thousands of fish and other marine creatures suffocating. Part of the canal's southern end is now a virtual dead zone, with a thick layer of bacteria coating the floor of the canal.

In the new study, researchers hope to track down the cause of the low oxygen in the South Sound by studying water samples drawn from areas south of Tacoma as well as from rivers and sewage-treatment plants that feed into the Sound.

Scientists are particularly interested in finding the sources of nitrogen, which can cause large algae blooms. When the algae dies and sinks, it's consumed by bacteria, which use up oxygen in the water. That cycle is thought to be a major source of the low-oxygen problems in Hood Canal.

Nitrogen occurs naturally but also comes from human sources like leaking septic systems, sewage-treatment plants and fertilizer.

Low-oxygen water is also found around Whidbey Island to the north.

But this research will focus on South Puget Sound for now because the problem appears more widespread there, Kolosseus said.

Warren Cornwall: 206-464-2311 or wcornwall@seattletimes.com