Riparian vegetation along ephemeral streams in arid and semi-arid environments and implications for the Clean Water Act
Date
2022-05
Authors
Manning, Aspen
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Abstract
The Clean Water Act protects water quality, but its jurisdiction is limited to traditionally navigable waters and those tributaries that have relatively permanent flow (i.e., perennial flow) or a significant nexus (i.e., they significantly affect water quality in downstream waterways). In the arid southwestern United States, most streams are intermittent (flowing seasonally) or ephemeral (flowing only in response to precipitation), therefore they do not meet the relatively permanent standard. Determining whether a given ephemeral stream has a significant nexus to a downstream waterway is complicated, especially in arid regions where geomorphic evidence of flow events can persist for long periods of time. Riparian vegetation is used in field-based jurisdictional determinations, however the riparian vegetation of ephemeral streams in arid and semi-arid regions is understudied. This dissertation contributes to the existing empirical data on the riparian vegetation of ephemeral streams in the southwestern United States by examining the longitudinal spatial patterns of riparian communities along six ephemeral streams in New Mexico and Arizona using remote sensing. Normalized Difference Vegetation Index (NDVI) was used to determine the size and cover of riparian vegetation, which was then correlated to topographic, climatic, geomorphic, and streamflow characteristics. Riparian vegetation responds much more strongly to topographic and climatic variables than to streamflow variables. These results indicate that the riparian vegetation of ephemeral streams responds to different environmental factors compared to riparian vegetation along intermittent or perennial rivers. The results presented here can inform Clean Water Act policies regarding ephemeral streams in the southwestern United States.
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Keywords
Riparian vegetation, Ephemeral streams, Clean Water Act, Connectivity
Citation
Manning, A. (2022). <i>Riparian vegetation along ephemeral streams in arid and semi-arid environments and implications for the Clean Water Act</i> (Unpublished dissertation). Texas State University, San Marcos, Texas.