New paperSeptember 2026Environmental Science & TechnologyN

Urban nitrogen policy should follow pathways, not the calendar

Seasonal fertilizer bans are easy to write and easy to enforce. A new Viewpoint argues they are an imperfect proxy for how nitrogen actually leaves a neighborhood.

Cutaway of a Florida yard in the rain: a June-to-September fertilizer sign, a spreader, and a dog on the lawn; nitrogen moving as runoff into a storm drain and pipe, leaching through the soil, and seeping from a septic drainfield through groundwater, all reaching a bay with seagrass — From one yard, nitrogen reaches the bay several ways at once: runoff through the storm drain, leaching through the soil, and septic effluent through groundwater, each on its own schedule. A June–September fertilizer ban addresses only part of it. Illustration.

Many Florida communities restrict lawn fertilizer during the summer rainy season. In this Viewpoint I argue that a calendar rule like that is an imperfect proxy for nitrogen export, and that urban nitrogen policy should target what actually controls it: the sources of nitrogen, the chemical forms it takes, the pools where it is stored, and the hydrologic pathways that carry it to water.

The argument draws on a decade of urban stormwater research in the Tampa Bay region with former students and postdocs Yun-Ya Yang, Mary Lusk, and Jariani Jani. That work used nitrate isotopes to trace where stormwater nitrate came from, and characterized the organic nitrogen that nitrate measurements alone miss.

SourcesLawn fertilizer, septic systems, sewer leaks

FormsNitrate, ammonium, organic nitrogen

StorageSoils, ponds, shallow groundwater

PathwaysRunoff, pipes, infiltration

Urban nitrogen policy should follow pathways, not the calendar

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