RESPONSE OF SOIL PHOSPHORUS SORPTION CAPACITY TO URBAN OCCUPATION IN TROPICAL HUMID AND SEMIARID CLIMATE
Diffuse pollution, Urbanization, Phosphorus availability, Isotherms.
In natural ecosystems, the availability of phosphorus in soil varies mainly as a function of soil organic matter content, clay content and mineralogy, and pH between soils of different climatic conditions. The urban occupation of watersheds contributes to the accumulation of phosphorus in the soil to the extent that it exceeds its maximum sorption capacity and thus increases diffuse losses of phosphorus to water bodies. In urban ecosystems, excessive input of phosphorus into water bodies accelerates the process of eutrophication. To improve phosphorus management in watersheds, it is necessary to understand how sorption capacity varies between natural and urban soils. The hypothesis of this study is that in urban soils the phosphorus sorption capacity is reduced due to decreased clay content, increased pH and organic matter content compared to natural soils. Furthermore, we believe that urbanization reduces the natural variability expected among soils of different degrees of development present in humid and semiarid tropical environments regarding phosphorus sorption, generating soils with homogeneous phosphorus sorption characteristics among themselves when compared to natural soils. The objective of this study is to evaluate the availability and sorption capacity of phosphorus in natural and urban soils and to verify the factors that influence the variability in phosphorus sorption capacity among soils with different degrees of development. The soils of thirty-eight areas belonging to the humid and semiarid tropical region of the state of Rio Grande do Norte (nineteen in natural ecosystems and nineteen in urban ecosystems) will be physically and chemically characterized and evaluated for phosphorus sorption capacity. Langmuir and Freundlich isotherms will be obtained to establish the relationship between the amount of phosphorus sorbed and its equilibrium concentration. Principal Component Analysis will be performed in order to understand how phosphorus availability and sorption respond to urban occupation.