Contrasting nitrogen and phosphorus budgets in urban watersheds and implications for managing urban water pollution

Urban waters remain widely impaired by excess nutrients, despite substantial management efforts. We present a comparison of urban watershed nitrogen (N) and phosphorus (P) budgets. Household actions of lawn fertilization and pet ownership were responsible for the majority of watershed N and P inputs, respectively. N and P exhibited contrasting dynamics within watersheds. Watersheds exported most or all P inputs via stormwater runoff, likely contributing to surface water degradation. High apparent N retention likely resulted from unmeasured watershed N losses to the atmosphere and groundwater. These contrasting dynamics suggest that N management should emphasize reducing watershed inputs, whereas P management should focus on reducing watershed P inputs and transport from vegetated landscapes to streets and storm drains.

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