The natural cycles of carbon (C), nitrogen (N), phosphorus (P) and water have been disturbed substantially by human activities. Urbanizing coastal drainage basins and large river deltas are located at the interface of freshwater and coastal components of the larger earth system and the process of urbanization is increasingly affecting these cycles. We take coastal water pollution as an example to illustrate this. To ensure sustainable development of urban-dominated water systems, future research challenges must include studies of the effects of the urbanization process on biogeochemical cycles that firstly, account for feedbacks and tipping points at the global scale; secondly, link to the Sustainability Development Goals; and finally, link to other forms of pollution. Urban coastal systems are of particular interest when exploring human–water–nutrient cycle interactions, and effective solutions for environmental and health problems associated with these interactions.
- reactive nitrogen