Effects of untreated or insufficiently treated wastewater discharges on the spatial and temporal variability of nitrous oxide (N2O) emissions from different streams in southeastern Brazil

Increasing atmospheric N2O concentrations is of great environmental concern due to the role of this gas in climate change and stratospheric ozone destruction. Nitrogen-enriched lotic water bodies are significant sources of N2O. However, N2O emissions from rivers and streams, particularly those that receive untreated or insufficiently treated wastewater discharge, are poorly understood, especially in Brazil. The present study investigated the effects of the discharge of untreated or insufficiently treated wastewater on the spatial-temporal variability of N2O emissions from different streams in Ilha Grande, located within the Abraao hydrographic system, in southeastern Brazil. Estimated N2O fluxes determined in Abraao streams and upstream of the urbanized stretch ranged from 18.4 and 96.5 mu g N m(-2) h(-1). Inside the urbanized stretch, estimated N2O fluxes ranged from 110 to 561 mu g N m(-2) h(-1) under non-limited dissolved oxygen (DO) conditions and 133 to 2,229 mu g N m(-2) h(-1) under hypoxic conditions (DO < 2 mg O-2 L-1). High spatial and temporal variability in N2O emissions were noted, with the highest emissions in Abraao urban areas. Therefore, the differences observed between N2O fluxes from the studied streams at Abraao seem to be associated with different lotic water body conditions, such as availability of reactive N and DO.