Urbanization and agriculture increase exports and differentially alter elemental stoichiometry of dissolved organic matter (DOM) from tropical catchments

Björn Gücker; Ricky C S Silva; Daniel Graeber; José A F Monteiro; Iola G Boëchat

doi:10.1016/j.scitotenv.2016.01.158

Urbanization and agriculture increase exports and differentially alter elemental stoichiometry of dissolved organic matter (DOM) from tropical catchments

Sci Total Environ. 2016 Apr 15:550:785-792. doi: 10.1016/j.scitotenv.2016.01.158. Epub 2016 Feb 2.

Authors

Björn Gücker¹, Ricky C S Silva², Daniel Graeber³, José A F Monteiro², Iola G Boëchat²

Affiliations

¹ Applied Limnology Laboratory, Federal University of São João del-Rei, São João del-Rei, Brazil. Electronic address: guecker@ufsj.edu.br.
² Applied Limnology Laboratory, Federal University of São João del-Rei, São João del-Rei, Brazil.
³ Department of Bioscience, Aarhus University, Denmark.

PMID: 26849342
DOI: 10.1016/j.scitotenv.2016.01.158

Abstract

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 concentrations, catchment DOC exports, and DOM elemental stoichiometry in 20 tropical catchments at the Cerrado-Atlantic 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 concentrations, 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 catchments had the strongest effects on catchment DOM. Thus, urbanization may have alleviated N limitation of heterotrophic 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 concentrations, 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 DOM biogeochemistry in the investigated tropical catchments and should thus be important targets for management and mitigation efforts.

Keywords: Agriculture; Atlantic forest; Cerrado savanna; DOM export; Elemental stoichiometry; Land use; Neotropical catchments; Organic carbon; Pasture; Rivers; Streams; Urbanization.