Impacts of urbanization on carbon balance and human health risk: I. & II. Soil carbon dynamics under impervious surfaces and III. Water quality influences on a common West Nile virus vector.
Type of DegreePhD Dissertation
DepartmentForestry and Wildlife Science
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A significant increase in urbanization will be observed during the next fifty years. Global environmental changes cannot be addressed without a better understanding of biogeochemical cycles in urban areas. Thus, more insight into the effects of urbanization on (i) soil biogeochemical properties, and (ii) water quality and its interactions with public health including increasing population of urban mosquitoes, are of critical importance. In this research, the effects of soil sealing by urban impervious surfaces such as building, roads, sidewalks, and parking lots on soil carbon and nitrogen dynamics investigated. In a second study, the effects of urbanization and expansion of urban lawns on survival rates of mosquitos related to infection of West Nile virus was examined. In order to study the effects of urban impervious surfaces on soil carbon and nitrogen dynamics two separate approaches were required: 1) A field controlled study consisting of three different treatments (i) concrete slabs, (ii) mock-up of houses built on a crawl space and (iii) grassed (reference) plots. In this study, we found that the major cause of carbon loss beneath impervious surfaces was top soil removal . Soil carbon content decreased by 48.39 % (± 16.29 %) and 56.99 % (± 8.59 %) beneath the concrete and homes compared to reference plots at top 10 cm. The soil C beneath the concrete plots decreased over time while it fluctuated beneath the homes. The carbon loss to atmosphere beneath the homes at top 10 cm was the major mechanism of carbon loss following the initial disturbance. Moreover, nitrogen, microbial biomass, and net nitrogen mineralization rate were significantly lower beneath impervious surfaces compared to reference plots. However, accumulation of nitrate and phosphate beneath the impervious surfaces was evident. 2) A field chronosequence study was necessary to verify the result from the control study and shed light on true gain or loss of carbon beneath impervious surfaces over time. In this study, we quantified soil carbon (C), nitrogen (N), and influential parameters affecting them beneath homes built on a crawl space ranging from 11 to 114 years in age. The average soil C and N content in the top 10 cm were 61.86 % (± 4.42 %), and 65.77 % (± 5.65 %) respectively lower beneath the homes in comparison to urban lawns. The soil C and N loss beneath the homes revealed a quadratic correlation with age and maximum C loss occurring at approximately fifty years in age. Microbial biomass carbon (MBC), and nitrogen (MBN) were significantly lower beneath the homes compared to the urban lawns. The third chapter was to determine the effects of urbanization and formation of urban lawns on survival rates of mosquitoes using a laboratory microcosm approach. Abscised leaves from three common overstory tree species in the southeastern United States and turfgrass clippings were used to simulate potential backyard breeding habitats for Culex. Urban lawns also alter water quality which may be affected by the surrounding vegetation which serves as a source of organic matter. Abscised leaf treatments had significantly lower survival rates than grass treatments with maximum pupae development of 3.93 ± 2.29 % in the pine treatment and 1.92 ± 1.72 % adult development in the sweetgum treatment. Grass treatments developed 28.50 ± 5.75 % and 22.50 ± 4.79 % pupae and adult mosquitoes respectively, suggesting that urbanization and formation of urban lawns create a suitable habitat for growth of mosquitoes when water ponding exists.
- Dissertaion-Hamed Majidzadeh.pdf