Marine “dead zones” detailed in interactive online map

Jan 24, 2011

Growing populations and increasing pollution are contributing to more and more “dead zones” in bays and oceans around the world.

Now there’s an interactive online map pinpointing more than 760 spots across the globe—including 22 in Washington – that either are dead zones or are in danger of becoming one.

What’s a “dead zone?”

It happens when excess nutrients in the water help trigger an algae bloom. Mindy Selman explains that when all the algae die, they sink to the bottom.

“And as they decompose, they suck up oxygen ... so there’s no oxygen in that area, and the crabs, the shrimp, the fish, they either flee the area, or they die.”

Selman is a researcher for the World Resources Institute, the Washington D.C.-based environmental think tank that, with the Virginia Institute of Marine Science, put the online map together.

It’s pretty cool. Check it out …

The areas marked in yellow are eutrophic. That means they’ve got too much nitrogen and other nutrients that feed algae blooms. Areas marked on the map in red are hypoxic. That means they’ve got low oxygen levels that can lead to fish kills.

How do those extra nutrients get in the water?

Basically, they come from human activities such as:

  • Agriculture – animal manure and crop fertilizers
  • Development – faulty septic systems
  • Landscaping – fertilizers on lawns and home gardens

The best-known dead zone in Washington happens in Hood Canal. Last September hundreds of fish and thousand of shrimp died when oxygen levels plummeted in the narrow, poorly-flushed waterway. Bigger fish kills happened there in 2006 and 2003.

Here’s what the 2006 event looked like …

According to the WRI online map – which uses data from a 2002 survey done by the state Department of Ecology, as well as other scientific studies – other low-oxygen zones in Puget Sound include:

  • West Point in Seattle -- Spills from a King County sewage treatment plant in 2008 and 2009 have contributed to poor water quality.
  • Budd Inlet in Olympia  -- Storm water runoff and pipe discharges have led to periods of low oxygen.
  • Penn Cove on Whidbey Island -- The Skagit River and aquaculture operations add nutrients that have triggered toxic algae blooms and low oxygen levels.
  • Bellingham Bay – The Nooksack River carries agricultural and urban storm water nutrients to the bay, which has had toxic algae blooms and low oxygen events.

So-called “non-point sources” of pollution – as opposed to industrial wastes being discharged from pipes – are now the biggest pollution problem in many places, including the Puget Sound. Experts say getting a handle on thousands of sources of pollution that come from everyday human activities remains a huge challenge.

Mindy Selman from the WRI says the group hopes the online map will be a good tool to raise awareness about the problem and help lead to changes in policy, law and people’s behavior.