Urbanization and agriculture increase exports and differentially alter elemental stoichiometry of dissolved organic matter (DOM) from tropical catchments Björn Gücker a, ⁎, Ricky C.S. Silva a , Daniel Graeber b , José A.F. Monteiro a , Iola G. Boëchat a a Applied Limnology Laboratory, Federal University of São João del-Rei, São João del-Rei, Brazil b Department of Bioscience, Aarhus University, Denmark HIGHLIGHTS • We investigated land-use impact by comparing human-impacted with natu- ral catchments. • Pasture catchments had lower stream DOM concentration, with lower C:N and C:P. • Agricultural catchments had higher DOM export, with lower C:P. • Urban catchments had higher concen- tration and export, with lower C:N and higher C:P. • Urbanization exerted the strongest im- pacts and should be a management pri- ority. GRAPHICAL ABSTRACT abstract article info Article history: Received 11 August 2015 Received in revised form 24 January 2016 Accepted 24 January 2016 Available online xxxx Editor: D. Barcelo Many tropical biomes are threatened by rapid land-use change, but its catchment-wide biogeochemical effects are poorly understood. The few previous studies on DOM in tropical catchments suggest that deforestation and subsequent land use increase stream water dissolved organic carbon (DOC) concentrations, but consistent effects on DOM elemental stoichiometry have not yet been reported. Here, we studied stream water DOC concentra- tions, catchment DOC exports, and DOM elemental stoichiometry in 20 tropical catchments at the Cerrado–Atlan- tic rainforest transition, dominated by natural vegetation, pasture, intensive agriculture, and urban land cover. Streams draining pasture could be distinguished from those draining natural catchments by their lower DOC con- centrations, with lower DOM C:N and C:P ratios. Catchments with intensive agriculture had higher DOC exports and lower DOM C:P ratios than natural catchments. Finally, with the highest DOC concentrations and exports, as well as the highest DOM C:P and N:P ratios, but the lowest C:N ratios among all land-use types, urbanized catch- ments had the strongest effects on catchment DOM. Thus, urbanization may have alleviated N limitation of het- erotrophic DOM decomposition, but increased P limitation. Land use—especially urbanization—also affected the seasonality of catchment biogeochemistry. While natural catchments exhibited high DOC exports and concentra- tions, with high DOM C:P ratios in the rainy season only, urbanized catchments had high values in these variables throughout the year. Our results suggest that urbanization and pastoral land use exerted the strongest impacts on Keywords: DOM export Land use Pasture Agriculture Urbanization Organic carbon Elemental stoichiometry Science of the Total Environment 550 (2016) 785–792 ⁎ Corresponding author at: Applied Limnology Laboratory, Department of Geosciences, Campus Tancredo Neves, Federal University of São João del-Rei, 36307-352 São João del-Rei, Minas Gerais, Brazil. E-mail address: guecker@ufsj.edu.br (B. Gücker). http://dx.doi.org/10.1016/j.scitotenv.2016.01.158 0048-9697/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv