Urban Land Use Effects on Soil Characteristics in the City of Baltimore
R.V. Pouyat, I. Yesilonis, and J. Russell-Anelli
As land is converted to urban uses, direct and indirect factors can affect soil characteristics. Direct effects include physical disturbances, burial or coverage of soil by fill material and impervious surfaces, and soil management inputs (e.g., fertilization and irrigation). Indirect effects include a rise in air temperature due to the heat island effect and contamination from various pollutants (e.g., heavy metals). Both effects result in a “mosaic” of soil conditions. For example, heavy metal accumulations will vary spatially due to human activities and atmospheric deposition patterns. To characterize soils in urban landscapes, we have sampled 125 0.1 acre plots stratified by land-use type in Baltimore City. Within each plot we collected a 0-10 cm depth composite sample for chemical analyses and three 0-5 cm depth undisturbed cores for bulk density analysis. A comparison of land-use/cover types showed that forest cover had 34% higher soil organic matter concentrations (g kg-1) than the high and medium land-use types, respectively. Forests had the lowest average soil pH (5.2) while transportation and high density residential land-uses had the highest pH of the land-use types (6.4 and 6.3, respectively). We suspect that management inputs of lime (Ca) in residential areas and road maintenance and concrete along transportation corridors can explain the relatively high soil pH measurements in these land-use types. Commercial, institutional, industrial, and high density residential land-use types had up to 17% higher bulk densities than medium density residential and forest land-use/cover types, respectively. The higher bulk densities most likely resulted from physical impacts resulting from human activity. Bulk density was inversely correlated with organic matter concentration (P < 0.0001, r = - 0.52). Calcium and sodium concentrations were extremely high across all land-use types and were highly correlated to each other within the forest cover type (P < 0.0001, r = 0.79). Of the heavy metals measured maximum and mean concentrations of Cr, Ni, Cu, Zn, and Pb were particularly high. These data suggest that soil characteristics are both directly and indirectly modified by urban environments and urban land uses.
Keywords: urban soil, heavy metals, urban

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