Nitrogen runoff versus herring runs

A herring run in part of Westport, Mass., renews questions about nitrogen pollution's destructive effect on wetlands. 

Some observers believe that elevated nitrogen levels from lawns, farms and and golf courses discourage marsh grasses from putting down the deep roots that knit marshes  together since the runoff makes nitrogen excessively plentiful at surface levels. And they worry that the nitrogen fuels   the thick green algae that  can clog herring runs during warm weather and kill much life  by sucking up too much of the oxygen.