[thedoc]

Disruption of the nitrogen cycle can wreak havoc on ocean ecosystems for which oxygen is in short supply. Robin Fulweiler explores the formation of 'dead zones' in part II of The Nitrogen Story.

Read the article then tell us what you think...

[CliffordK]

As the human population continues to grow, there is more and more pressure on farming production, and thus more fertilizer.  There are agricultural practices that can minimize crop runoff...  but, it can be expensive, and potentially not as productive as the current practices.  And, of course, some "better" practices might be more labor intensive.

Flooding?
Perhaps that is part of the problem, inundating farmland that ordinarily would not have nitrogen runoff.  This might be hard to prevent, except by choosing crops in flood zones that would require less added nitrogen, and perhaps stabilize the soil and trap sediments.

One of the problems with coastal "dead zones" is that the coastal areas are also a host for numerous types of aquatic life.  I.E.  the small fish, corals, and etc do better living in shallow water, than in the open ocean.  And, thus a dead zone can be devastating to the fisheries.

The waves naturally aerate the sea.  Is there a way to enhance this process?  Could it be as simple as adding rocky outcroppings to the beaches?  Or perhaps building aeration pumps driven by underwater currents.

[yor_on]

It's serious.

Oceanic Dead Zones Continue to Spread (2008 Scientific American)

And "in the summer, northerly summer winds work together with the Earth's rotation to push oxygenated surface water offshore; this coastal water is replaced by low-oxygen but nutrient-rich waters from the depths of the continental shelf in a process known as upwelling. (See illustration.) Once this nutrient-rich water reaches the ocean's sunlit layers, it fertilizes blooms of phytoplankton. Resulting phytoplankton blooms feed the food chain and thereby help make the Pacific Northwest one of the nation's most productive fisheries. But the decomposition of unconsumed, sunken phytoplankton promotes the formation of deep pools of low-oxygen water.

Periods of upwelling-favorable northerly winds may be interrupted by relatively short periods of southerly winds during the summer and by longer periods during the fall. These southerly winds work together with the Earth's rotation to drive oxygenated surface waters back towards the shore and to drive low-oxygen bottom waters away from the shore in a process known as downwelling.  Periods of strong downwelling have traditionally occurred frequently enough to flush the low-oxygen pools from the continental shelf, and thereby prevent them from expanding all the way to the shore.

LEAVING NORMAL
But underwater surveys conducted by the research team of waters off the Pacific Northwest have identified the following new phenomenon:

    Pools of low-oxygen water have expanded from the continental shelf to near-shore waters off Oregon and Washington every summer since 2002; the close proximity of these dead zones to the shore had never been reported before that year.

    Coastal dead zones have been more hypoxic than the low-oxygen pools located on the continental shelf, with some coastal areas periodically completely stripped of their oxygen.

    Areas of hypoxia that have seasonally dotted the Pacific Northwest coast, "have been connected to one another by a ribbon of low-oxygen water that runs along the coastal sea floor," says Barth. So far, the most hypoxic year for the Pacific Northwest was 2006, when the research team discovered a dead zone off Newport, Oregon that sprawled over almost 1,200 square miles, and pressed so close to the shore that "a baseball hit from Highway 101 during the summer could land in it," says Barth. Covering up to 80 percent of the water column and lasting for an unusually long time (four months), "this dead zone transformed a teeming habitat into a fish-free zone that was carpeted with dead crabs, worms, severely stressed anemones and sea stars, and what looked like potentially noxious bacterial mats," says Barth." Is Climate Change Suffocating Our Seas?