Soil health variations across an agricultural–urban gradient, Iowa, USA

Abstract

Although variations in ecosystem processes associated with rural–urban gradients have focused on heavily populated regions, few studies have been conducted in smaller, urban cluster regions. In this study, we collected soil samples from 45 urban and rural locations near Charles City, Iowa (population ~ 7500) for soil organic carbon (C), nitrogen (N), C/N ratios, and heavy metal analyses and evaluated patterns across land use and landscape conditions. In the urban soils, Pb and As values were higher, whereas mean Zr and Rb concentrations were higher in agricultural soils. C/N ratios were higher in urban clusters compared to agricultural land use. Differences in soil concentrations were more evident when landscape position was considered, with higher concentrations of nutrients and heavy metals measured in floodplains associated with both agricultural and urban cluster areas, respectively. Overall, we conclude that the degree of urbanization and industrial development within the Charles City urban cluster was sufficiently intense to differentiate the urban soils from the surrounding agricultural landscape. Our results extend the analysis of urbanization on soil health beyond typical mega-cities to include measurable impacts around smaller urban clusters which comprise ~ 10% of the U.S. population.