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In the United States, the EPA and the United States Geological Survey (USGS) are the principal federal agencies working with the CEC to define and map ecoregions. Ecoregions may be identified by similarities in geology , physiography , vegetation , climate , soils , land use , wildlife distributions, and hydrology .
The area of temporary hypoxic bottom water that occurs most summers off the coast of Louisiana in the Gulf of Mexico [58] is the largest recurring hypoxic zone in the United States. [59] It occurs only during the summer months of the year due to summer warming, regional circulation, wind mixing and high freshwater discharge. [ 60 ]
The exaerobic zone is found at the boundary of anoxic and hypoxic zones. Hypoxia can occur throughout the water column and also at high altitudes as well as near sediments on the bottom. It usually extends throughout 20–50% of the water column, but depends on the water depth and location of pycnoclines (rapid changes in water density with depth).
Scientists prepare to collect near-bottom water aboard the R/V Pelican to verify oxygen measurements used to determine the size of the Gulf of Mexico hypoxic zone. (NOAA/LUMCON/LSU) A "dead zone ...
A 'dead zone' off the Gulf coast is larger than NOAA predicted. The massive area poses danger to marine life, and recovery could take decades. A 'dead zone' is growing in the Gulf of Mexico.
"Level I" divides North America into 15 broad ecoregions. "Level II" subdivides the continent into 52 smaller ecoregions. "Level III" subdivides those regions again into 182 ecoregions. [1] [2] "Level IV" is a further subdivision of Level III ecoregions. Level IV mapping is still underway but is complete across most of the United States.
Sep. 14—Low-oxygen levels off the coast of Oregon and Washington state hit earlier than usual this spring and have lasted longer than any other hypoxic event recorded on the West Coast in the ...
Ecoregions of North America, featuring the 50 United States, the District of Columbia and the five inhabited territories. The following is a list of ecoregions in the United States as identified by the World Wide Fund for Nature (WWF). The United States is a megadiverse country with a high level of endemism across a wide variety of ecosystems.