With Isaac bearing down on New Orleans, the city finds itself at a delicate moment in its rebuilding since Hurricane Katrina struck seven years ago. Private and government investment is fueling the push to overhaul some of the city’s troubled but culturally rich neighborhoods near the French Quarter, where poor families are being replaced as wealthier ones move in. While the city’s in a boom and even gentrifying, some question whether it will wither the roots that grew the city’s distinctive identity. The number of whites, although smaller than before Katrina, has grown as an overall percentage from 28 percent to 33 percent of the city’s population. The city has its first white mayor since the 1970s, while the City Council now has a majority of white members. On the flip side, blacks say there’s danger that their community will be diminished in a city that owes deep cultural and economic debts to its Afro-Caribbean roots. Since the storm the African-American community has shrunk by about 118,500 people, dropping from about 68 percent of the population to about 60 percent.