Big Picture

NY Times Science section:

The top image [sic] shows the state's southeastern region on Aug. 9. The bottom image was made on Sept. 4, after storm clouds cleared. The images, their colors artificially adjusted, show vegetated areas in bright green; flooded areas are darker.

It remains to be seen how Louisiana's wetlands will survive the storm. Scientists are only beginning to discern damage inflicted on them from high winds and waves, and from the presence of so much floodwater for so many days.

Much of the water is contaminated by spills from oil and gas installations and from vehicles trapped in the storm. Wetlands can cleanse water of pollutants up to a point, but even they can be overwhelmed.

According to the United States Geological Survey, Louisiana has lost an average of 34 square miles of wetland a year since the 1930's as efforts to control the Mississippi River kept its muddy waters out of the marshes, depriving them of needed infusions of sediment.