Chemistry of Urban, Suburban, and Rural Surface Waters

The chemistry of urban surface waters is influenced by natural biogeochemical processes that interact with the physical structures as well as the many activities and material inputs associated with dense human habitation. Concentrations of sediment, nitrogen, phosphorus, natural and novel organic compounds, metals, chloride, sulfate, calcium, magnesium, sodium, and potassium all change as the percentage of urbanized land increases. Unique urban chemistries result from many factors in the urban environment. They include high rates of watershed loading that increase with human activity and population density; more direct hydrologic pathways that route runoff and waste streams to surface waters via drainage systems and wastewater treatment plants; changes in the capacity of the landscape to retain and transform nutrient and organic matter inputs due to loss of vegetative cover and effective riparian zones; and alteration of streambed sediments, streambed form, and rates of bank erosion by increased peak flows. The conditions that create the uniquely urban biogeochemical cycles often lead to a degradation of water quality, but the extent of degradation can vary dramatically. Improvements in waste management, drainage systems, and stream restoration have been shown to reduce degradation or rehabilitate water quality in urban areas. The following is a review of available knowledge on global urban water chemistry and the chemical cycling in urban watersheds, which results in distinct urban biogeochemistry.