We explored variations in inorganic soil nitrogen (N) concentrations across metropolitan Phoenix, Arizona, and the surrounding desert using a probability-based synoptic survey. Data were examined using spatial statistics on the entire region, as well as for the desert and urban sites separately. Concentrations of both NO 3-N and NH 4-N were markedly higher and more heterogeneous amongst urban compared to desert soils. Regional variation in soil NO 3-N concentration was best explained by latitude, land use history, population density, along with percent cover of impervious surfaces and lawn, whereas soil NH 4-N concentrations were related to only latitude and population density. Within the urban area, patterns in both soil NO 3-N and NH 4-N were best predicted by elevation, population density and type of irrigation in the surrounding neighborhood. Spatial autocorrelation of soil NO 3-N concentrations explained 49% of variation among desert sites but was absent between urban sites. We suggest that inorganic soil N concentrations are controlled by a number of 'local' or 'neighborhood' human-related drivers in the city, rather than factors related to an urban-rural gradient.
Bibliographical noteFunding Information:
We thank Steven S. Carroll for the sampling design; M. Myers, A. Budet, S. Paine, M. Clary, A. Stiles, L. Stabler, and S. Holland for field assistance; Salt River Project for the donation of helicopter time; Cities of Phoenix, Scottsdale and Tempe, Maricopa County Parks, Tonto National Forest, Arizona State Lands Department, Sky Harbor Airport and all the private property owners involved for giving us permission to access their land. This work was funded by National Science Foundation Grants # DEB-9714833 and DEB-0423704.
- CAP LTER
- Integrated inventory
- Soil NH -N
- Soil NO -N-N
- Spatial autocorrelation
- Urban ecosystem