Nutrients could be the next big problem for San Francisco Bay — or make that in the Bay, because they’re already here at levels high enough to have caused trouble elsewhere. But despite its excess nitrogen and phosphorus, the Bay has been free of harmful algal blooms and oxygen-depleted dead zones for decades. Indeed, we’ve been so sure of this immunity to nutrients that most wastewater treatment plants don’t even have to remove them before discharging into the Bay. Recent chinks in the Bay’s resistance to nutrients are now alerting us, however, to get ready in case there’s worse to come.