UVM Theses and Dissertations
Format:
Print
Author:
Fitzgerald, Evan P.
Dept./Program:
Rubenstein School of Environment and Natural Resources
Year:
2007
Degree:
M.S.
Abstract:
The Impervious Cover Model (ICM) was developed to explain the general response of biotic and abiotic characteristics of stream ecosystems to urban impacts over a range of physiographic regions. Much research has shown that a stream ecosystem response can be detected when the total impervious area (TIA) is at or above 10% of the watershed area, however limited research has focused on the impacts of urbanization at different spatial and temporal scales. This study explores these impacts by testing: (1) the effect of TIA on geomorphic stability, physical habitat conditions, and biotic communities at three different spatial scales, (2) the differences between urban and rural downstream hydraulic geometry (DHG) regressions, and (3) the response of biotic communities to different stages of urban channel evolution.
The physical and biotic conditions of stream reaches from 16 small watersheds in northwestern Vermont were assessed and analyzed for a response to TIA at multiple spatial scales. Separate analyses were performed for high and low-gradient stream types, and reach selection criteria minimized the influence of human impacts to channel boundary conditions (e.g., bank armoring) to ensure a robust test of the ICM for upslope TIA alone. Response of geomorphic stability and sensitive macroinvertebrates to TIA was nonlinear and significant (P <0.001), decreasing rapidly at 5% TIA. The effect of TIA on stream condition interacts significantly with drainage area and channel slope (P <0.05). DHG regressions developed for urban and rural watersheds show a significant scale-dependent response (p = 0.001) of channel width to urbanization.
Analysis of macroinvertebrate data from reaches in different stages of channel evolution indicates that stable reaches support greater EPT richness (p <0.005) and overall species richness (p <0.01) than unstable reaches. Results of ICM analyses and DHG regressions demonstrate that streams in Vermont may be more sensitive than those in other regions of the country in their response to urbanization, and that the response is scale-dependent. Results also indicate that some recovery of biotic communities may be possible following natural channel restabilization.
The results have important implications for land use planners in urbanizing watersheds and stream restoration professionals intending to use DHG regressions for channel restoration designs. Failure to recognize scale-dependent differences in the response of channel geometry to urbanization could lead to improper channel restoration designs and project failure.
The physical and biotic conditions of stream reaches from 16 small watersheds in northwestern Vermont were assessed and analyzed for a response to TIA at multiple spatial scales. Separate analyses were performed for high and low-gradient stream types, and reach selection criteria minimized the influence of human impacts to channel boundary conditions (e.g., bank armoring) to ensure a robust test of the ICM for upslope TIA alone. Response of geomorphic stability and sensitive macroinvertebrates to TIA was nonlinear and significant (P <0.001), decreasing rapidly at 5% TIA. The effect of TIA on stream condition interacts significantly with drainage area and channel slope (P <0.05). DHG regressions developed for urban and rural watersheds show a significant scale-dependent response (p = 0.001) of channel width to urbanization.
Analysis of macroinvertebrate data from reaches in different stages of channel evolution indicates that stable reaches support greater EPT richness (p <0.005) and overall species richness (p <0.01) than unstable reaches. Results of ICM analyses and DHG regressions demonstrate that streams in Vermont may be more sensitive than those in other regions of the country in their response to urbanization, and that the response is scale-dependent. Results also indicate that some recovery of biotic communities may be possible following natural channel restabilization.
The results have important implications for land use planners in urbanizing watersheds and stream restoration professionals intending to use DHG regressions for channel restoration designs. Failure to recognize scale-dependent differences in the response of channel geometry to urbanization could lead to improper channel restoration designs and project failure.