Nitrogen pollution flowing out of Iowa to the Gulf of Mexico has grown by nearly 50 percent in the last two decades — despite $420 million spent by Iowa in water quality improvement projects, the Des Moines Register reports. A new University of Iowa study shows the state’s nitrogen contribution to the Gulf dead zone spiked 47 percent to 618 million pounds in 2016. This year, the state is marking the fifth anniversary of the Iowa Nutrient Reduction Strategy, designed to cut Iowa’s nitrogen and phosphorus contributions in the Gulf by 45 percent. “We appreciate all that is being done with nutrient management and conservation farming. Unfortunately, we’re just impacting too few acres with too few practices,” said Larry Weber, executive associate dean for UI’s College of Engineering.