As we noted in earlier blogs ( http://gideonstrumpet.info/?p=242 ) there is a movement on, seeking to breach hydroelectric power generating dams in the Pacific Northwest in order to make life easier for salmon as they migrate upstream to reproduce.
Now, another part of the country is being heard from. There is now a move afoot to breach dams and levees in Louisiana. It seems that those dams — and there are some 8000 of them in the drainage basin of the Mississippi River — are impeding the flow of sediment that is necessary to replenish the Mississippi Delta marshes. But there is a potential problem with breaching those dams. The sediment trapped by them contains agricultural chemicals and other pollutants that may worsen the deteriorating water quality of the Mississippi. On the third hand, so to speak, if that nutrient-rich sediment makes it into the Louisiana marshes, it might stimulate plant growth, and that would contribute to marsh health.
So it looks like one of those situations in which nobody really knows what to do. Read all about it in Cornelia Dean, Dams Are Thwarting Louisiana Marsh Restoration, Study Says, N.Y. Times, June 29, 2009, at p. A13.