Soil Properties In the Urban Core of New York City

Urban areas include several types of land use which can vary in the extent of soil disturbance and alteration of the original soil properties. Soils in small green spaces in the “inner city” are often neglected by soil scientists and soil survey. To characterize soil conditions in the urban core of the New York City, soil profiles from 27 vegetated sites in Manhattan were examined. Sites were evenly distributed across the island and included small landscaped courtyards, border strips, and cemeteries. Land use history was examined as part of site selection to avoid potential waste disposal areas.

Each pedon was classified to the series level based largely on parent material characteristics, particle size class, and degree of development. Soil samples from two depths at each site were analyzed to determine “urban background” levels of 46 polycyclic aromatic hydrocarbons (PAHs) and 23 metals. Some basic soil properties were measured, and selected samples were also examined for black carbon and clay mineralogy.

Almost half (44 percent) of the pedons were coarse-loamy and formed in human-transported materials with less than ten percent human artifacts. Slightly more than one quarter were sandy-skeletal and formed in fill with construction debris.

PAHs and metals were found at higher concentrations in Manhattan soils than in soils from rural areas of New York State. High molecular weight PAHs such as benzo(a)pyrene and the metals Pb, Hg, and Zn exceeded the current New York State Soil Cleanup Objectives for unrestricted use in both surface and subsurface horizons.

In contrast to the low base status soils (dystrudepts) naturally found in this area, more than 90 percent of the samples had greater than 60 percent base saturation. In addition, significant amounts of calcium carbonate and black carbon have been added to the reactive phase of many of these soils.