At least 1.4 million seagulls feed at landfills in North America. Aside from the nuisance they pose, a study finds their nutrient-rich feces may threaten the health of nearby waters. The study estimates North American gulls deposit 240 tons of nitrogen and 39 tons of phosphorus into nearby lakes and reservoirs each year, fertilizing algae and weeds and costing local governments about $100 million in nutrient offset costs.