PARENT SESSION
Oral Session #37: River and Riparian Restoration II.
Presiding: J. Berg
Tuesday, August 6. 1:00 PM to 4:00 PM. Mohave Meeting Room, TCC.
Herbaceous plants as bioindicators of groundwater decline for the San Pedro River, Arizona.
Bagstad, Kenneth*,1, Stromberg, Juliet1, 1 Arizona State University, Tempe, AZ
ABSTRACT- Riparian ecosystems in the southwestern United States face increasing threats of dewatering for human use, potentially leading to losses of biodiversity and ecological function. Biotic integrity of riparian ecosystems is closely related to groundwater availability, especially in arid environments. In this study, we examined the herbaceous plant communities of eighteen sites spanning a gradient of groundwater depth and surface flow frequency along the San Pedro River in southeastern Arizona. Diversity, composition, and abundance of herbaceous plants were examined as potential bioindicators by comparing vegetation variables against hydrologic conditions at each site. Transect species richness declined 13-22% and beta diversity declined 18-26% as groundwater levels fell and wetland species were replaced by upland species. Streamside wetland indicator scores were 15-38% higher at drier sites, indicating terrestrialization of the plant community. Additionally, interruption of perennial flow led to extirpation of perennial wetland species (e.g., Typha, Juncus, Eleocharis). Percent cover (abundance) was 14% higher at wetter sites in the dry sampling season, but was not significantly higher in the wet season. Other abiotic factors, including geomorphology, rainfall, and light availability, also relate to species diversity levels. These factors further explain variation in the herbaceous community and provide a more detailed understanding of community structure. Results of this study can be used to develop monitoring protocol encompassing these and other bioindicators, or in modeling biotic effects of groundwater decline within reaches of the San Pedro watershed.
KEY WORDS: biotic integrity, riparian, groundwater decline, San Pedro River