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- All Subjects: decision making
- Creators: White, Dave
Description
Over the past century in the southwestern United States human actions have altered hydrological processes that shape riparian ecosystems. One change, release of treated wastewater into waterways, has created perennial base flows and increased nutrient availability in ephemeral or intermittent channels. While there are benefits to utilizing treated wastewater for environmental flows, there are numerous unresolved ecohydrological issues regarding the efficacy of effluent to sustain groundwater-dependent riparian ecosystems. This research examined how nutrient-rich effluent, released into waterways with varying depths to groundwater, influences riparian plant community development. Statewide analysis of spatial and temporal patterns of effluent generation and release revealed that hydrogeomorphic setting significantly influences downstream riparian response. Approximately 70% of effluent released is into deep groundwater systems, which produced the lowest riparian development. A greenhouse study assessed how varying concentrations of nitrogen and phosphorus, emulating levels in effluent, influenced plant community response. With increasing nitrogen concentrations, vegetation emerging from riparian seed banks had greater biomass, reduced species richness, and greater abundance of nitrophilic species. The effluent-dominated Santa Cruz River in southern Arizona, with a shallow groundwater upper reach and deep groundwater lower reach, served as a study river while the San Pedro River provided a control. Analysis revealed that woody species richness and composition were similar between the two systems. Hydric pioneers (Populus fremontii, Salix gooddingii) were dominant at perennial sites on both rivers. Nitrophilic species (Conium maculatum, Polygonum lapathifolium) dominated herbaceous plant communities and plant heights were greatest in effluent-dominated reaches. Riparian vegetation declined with increasing downstream distance in the upper Santa Cruz, while patterns in the lower Santa Cruz were confounded by additional downstream agricultural input and a channelized floodplain. There were distinct longitudinal and lateral shifts toward more xeric species with increasing downstream distance and increasing lateral distance from the low-flow channel. Patterns in the upper and lower Santa Cruz reaches indicate that water availability drives riparian vegetation outcomes below treatment facilities. Ultimately, this research informs decision processes and increases adaptive capacity for water resources policy and management through the integration of ecological data in decision frameworks regarding the release of effluent for environmental flows.
ContributorsWhite, Margaret Susan (Author) / Stromberg, Juliet C. (Thesis advisor) / Fisher, Stuart G. (Committee member) / White, Dave (Committee member) / Holway, James (Committee member) / Wu, Jianguo (Committee member) / Arizona State University (Publisher)
Created2011
Description
In the United States, some 94 million people (29% of the US population) live in areas immediately adjacent to a coast. The global phenomenon of climate-induced environmental change is largely framed as a one-way cause-and-effect relationship, where individuals, communities, and populations inhabiting at-risk locations are either forced to relocate or do so of their own accord. Yet residents of such at-risk areas are increasingly actively choosing to remain, even as risk intensifies. Using a mixed-methods approach, this dissertation examines environmental perceptions, the internalization of risk, the influence of information sources, and how individuals residing in coastal locations process their migration decisions. Established migration and hazard frameworks and theory are poorly positioned to understand the environments’ role in migration decisions. From these perspectives, environmental factors are near exclusively framed as negative affective biophysical push factors. Migration frameworks also fail to adequately incorporate reasons for non-migration. This dissertation directly addresses both these gaps in understanding. This research utilizes data from across the Gulf Coast, with a focus on fieldwork from Terrebonne Parish, Louisiana, and a dataset of 123 surveys and 63 interviews across a diverse group of coastal residents. Residents perceive of their environment in much more robust terms than just the biophysical. A majority of terms incorporated social and cultural aspects of environment, and environmental meaning was expressed across a continuum of proximal (most important/close) to more distal (less important/distant) scales. Little support is found for the traditional idea that economic or natural-environmental factors are more influential in decisions to migrate away from ones’ home. In predicting migration intention, socially and environmentally derived variables improved migration model performance. This dissertation demonstrates that internalization of risk by coastal residents is not a straightforward relationship, but rather one mediated by; social-environmental factors, personal experience, sense of place, and trust, which in turn influences intention to migrate, move locally, or remain in place. Residents perceive of their environment far more broadly than current risk-management planning allows. Results provide coastal residents, as well as community leaders and emergency managers who perceive environment differently, new tools for productive engagement and future policy development within coastal landscapes.
ContributorsTill, Charlotte Emma (Author) / BurnSilver, Shauna (Thesis advisor) / Tsuda, Takeyuki (Committee member) / White, Dave (Committee member) / Arizona State University (Publisher)
Created2022