ABSTRACT
As land surfaces are altered by urban development in ways that change topography and especially the partitioning of precipitation between infiltration and surface run-off, the hydrologic forcing factors that shape wetland structure and function will be altered (Brinson 1993; Bedford 1996). The channeling of urban stormwater runoff from impervious surfaces directly to streams results in rapid development of peak flows, and often at higher discharge levels, followed by more rapid recessions, decreases in base flow, larger discharge variations, changes in seasonal patterns, and alteration and deepening of channel morphology (Azous and Horner 2001; Paul and Meyer 2001; Groffman et al. 2003; Booth et al. 2004; Walsh et al. 2005). In addition, ditches, berms, and drainage for mosquito and flood control alter water tables and surface flow patterns (Ehrenfeld and Schneider 1991; Ehrenfeld et al. 2003) and create novel hydrologic regimes (Kentula et al. 2004). The effect of these hydrological alterations is to lower water tables, so that wetlands are dry for extended periods, and have ‘flashy,’ rapidly changing hydrographs (Figure 27.2). Furthermore, waste water and storm runoff inputs, from septic fields, road runoff, and leaking sewer pipes affect both stream flow and the loading of nutrients and pollutants (Bernhardt et al. 2008).
