title: Impacts of converting low-intensity pastureland to high-intensity bioenergy cropland on the water quality of tropical streams in Brazil.
abstract: In Brazil, the cultivation of bioenergy crops is expanding at an accelerated rate. Most of this expansion has occurred over low-intensity pasture and is considered sustainable because it does not involve deforestation of natural vegetation. However, the impacts on the water quality of headwater streams are poorly understood, especially with regard to the influence of land use patterns in the watershed. In this study, we investigated the effects of land-use conversion on the water quality of streams draining sugarcane fields and examined whether the preservation of forested areas at the top of the headwaters would help mitigate the negative impacts of intensive agriculture. Water samples were collected in two paired catchments in southeastern Brazil, which is one of the largest sugarcane production regions in the world. Our results show significant differences in the water quality of streams predominantly draining the pasture or the sugarcane field. Several parameters commonly used to indicate water quality, such as the concentrations of nitrate and suspended solids, were significantly higher in the sugarcane than in the pasture stream. Differences in water quality between the streams draining predominantly pasture or sugarcane fields were accentuated during the wet season. The preservation of forests surrounding the headwater streams was associated with overall better water quality conditions, such as lower nitrate concentrations and temperature of the stream water. We concluded that forest conservation in the headwater agricultural catchments is an important factor preventing water quality degradation in tropical streams. Therefore, we strongly recommend the preservation of robust riparian forests in the headwaters of tropical watersheds with intensive agriculture. More studies on the effects of best agricultural practices in bioenergy crops can greatly improve our capacity to prevent the degradation of water quality in the tropical waterways as intensive agriculture continues to expand in this region of the world.
authors.affiliation: Forest Hydrology Laboratory, Department of Forest Sciences, Luiz de Queiroz College of Agriculture, University of São Paulo. Av. Pádua Dias 11, CEP 13418-900 Piracicaba, SP, Brazil. Electronic address: rht.eco@usp.br.
authors.forename: Ricardo Hideo
authors.initials: RH
authors.lastname: Taniwaki
authors.affiliation: Forest Hydrology Laboratory, Department of Forest Sciences, Luiz de Queiroz College of Agriculture, University of São Paulo. Av. Pádua Dias 11, CEP 13418-900 Piracicaba, SP, Brazil. Electronic address: cccassiano@usp.br.
authors.forename: Carla Cristina
authors.initials: CC
authors.lastname: Cassiano
authors.affiliation: Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, P.O. Box 38, 20688 Solomons, MD, USA. Electronic address: filoso@umces.edu.
authors.forename: Solange
authors.initials: S
authors.lastname: Filoso
authors.affiliation: Forest Hydrology Laboratory, Department of Forest Sciences, Luiz de Queiroz College of Agriculture, University of São Paulo. Av. Pádua Dias 11, CEP 13418-900 Piracicaba, SP, Brazil. Electronic address: silvio.ferraz@usp.br.
authors.forename: Silvio Frosini de Barros
authors.initials: SFB
authors.lastname: Ferraz
authors.affiliation: Isotopic Ecology Laboratory, Centro de Energia Nuclear na Agricultura, University of São Paulo. Av. Centenário 303, CEP 13416-000 Piracicaba, SP, Brazil. Electronic address: pcamargo@cena.usp.br.
authors.forename: Plínio Barbosa de
authors.initials: PB
authors.lastname: Camargo
authors.affiliation: Isotopic Ecology Laboratory, Centro de Energia Nuclear na Agricultura, University of São Paulo. Av. Centenário 303, CEP 13416-000 Piracicaba, SP, Brazil. Electronic address: martinelli@cena.usp.br.
authors.forename: Luiz Antônio
authors.initials: LA
authors.lastname: Martinelli
mesh_terms: D000383:Agriculture; D056804:Biofuels; D001938:Brazil; D018556:Crops, Agricultural / Q000254:growth & development*; D045483:Rivers; D060753:Water Quality
chemical_list: D056804:Biofuels
keywords: Headwaters; Land-use change; Nitrate; Sugarcane; Suspended sediment