Chemical, Physical, and Biological Characteristics of Urban Soils

Urban soils provide an array of ecosystem services to inhabitants of cities and towns. Urbanization affects soils and their capacity to provide ecosystem services directly through disturbance and management (e.g., irrigation) and indirectly through changes in the environment (e.g., heat island effect and pollution). Both direct and indirect effects contribute to form a mosaic of soil conditions. In the Baltimore Ecosystem Study (BES), we utilized the urban mosaic as a series of "natural experiments" to investigate and compare the direct and indirect effects of urbanization on soil chemical, physical, and biological properties at neighborhood, citywide, and metropolitan scales. In addition, we compared these results with those obtained from other metropolitan areas to assess the effects at regional and global scales and to assess the generality of these results. Our overall results suggest that surface soils of urban landscapes have properties that can vary widely, making it difficult to define or describe a typical "urban" soil or soil community. Specifically, we conclude that (i) urban effects on soils occur at multiple scales; (ii) management effects are greater than environment effects, although environmental effects are more widespread reaching beyond the boundary of most urban areas; (iii) urban landscapes are biologically active in pervious areas and have a high potential for carbon storage and nitrogen retention; (iv) the importance of urban and native factors depends on the property being measured; and (v) cross-city comparisons support in part the biotic homogenization and urban ecosystem convergence hypothesis.