NITROGEN

Urbanization Effects on Forest Nitrogen Cycling in Brazil’s Atlantic Montane Forest

Forests within and around urban areas provide multiple environmental benefits to urban residents. Of crucial importance, montane forests maintain water quality by reducing erosion and sediment inputs to streams and by retaining nutrients and pollutants deposited from the atmosphere, such as nitrogen, in vegetation and in soils.  Given their role in protecting urban drinking water supplies and aquatic ecosystems, montane forests around the world are being targeted for conservation and restoration. However, as urban areas continue to expand, so do nitrogen emissions and deposition, with potentially negative effects on soils and streams. 

In this study, we investigated the effects of nitrogen deposition on nitrogen cycling in Atlantic montane forests in southeastern Brazil.  Although more than 85% of this ecosystem has been cleared, streams draining Atlantic montane forests still supply drinking water to millions of urban residents in São Paulo and Rio de Janeiro metropolitan areas.  In this study, nitrogen inputs, soil nitrogen availability, and indices of soil leaching losses were measured in forests in and around Rio de Janeiro: (1) on an island 100 km west of Rio de Janeiro; (2) in the coastal city of Rio de Janeiro; and (3) in a protected area 40 km inland from Rio de Janeiro.

Contrary to expectation, we found that the protected national forest inland of Rio de Janeiro received nearly two times more nitrogen than both the urban and island forests, highlighting the vulnerability of protected areas to urban air pollution.  Several indicators showed, however, that nitrate losses from the urban and downwind forests were similar and far higher than those measured at the island forest.  This finding suggests that chronic exposure to nitrogen pollution from urban areas decreases the capacity of forests to retain nitrate, which is likely to end up in surface waters.  Overall, findings from the study show that forests closer to urban areas––under higher levels of N pollution––exhibit clear alterations in N cycling.

This project contributed to the development of new international collaborations (U.S., Mexico, Brazil) and broadened participation in science by involving students and technicians from underrepresented groups.  Specifically, the grant supported the professional development of three early career female Hispanic scientists and provided field and laboratory training for four women (one Ph.D., one M.Sc., one undergraduate, and one technician) as well as one Hispanic UNT graduate.

Collaborators: Kathleen Weathers (Cary Institute of Ecosystem Studies), Yareni Perroni (Universidad de Veracruz), William Zamboni de Mello and Patricia Alexandre de Souza (Universidade Federal Fluminense),  and Felipe García-Oliva (Universidad Nacional Autónoma de México).

Funded by the NSF Office of International Science and Engineering.