Riparian corridor vegetation structure and soil function along urban, suburban, and rural streams in Louisville, KY, USA.

Abstract

Stream riparian zones are ecotones between terrestrial and aquatic environments. Studying these areas in urban environments is important since they lie adjacent to stream water supplies. I conducted a study of riparian woody and groundcover vegetation along urban, suburban, and rural streams (land-use designations based on % impervious surface) to assess how cities are affecting plant community structure. I also studied riparian soil gas flux (carbon dioxide, methane, and nitrous oxide) in relation to water table depth and groundwater nutrient concentrations spanning a 10-month period (January to October, 2008). I found distinct woody and groundcover communities associated with proportion of impervious surface surrounding the research sites. These communities differed regarding diversity and proportion of native, exotic, and wetland species distributions. The most urban communities generally had lower species richness, more exotic species, and fewer wetland species when compared to rural areas. Urban areas also exhibited the highest streambanks and lowest water tables. Carbon dioxide gas flux rates were higher in urban areas, but methane and nitrous oxide fluxes did not respond uniformly to site differences as classified by proportion of impervious surface. Methane and nitrous oxide differences, in addition to seasonal variability, were more greatly affected by local site level differences in substrate and nutrient ratios as well as soil moisture