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- All Subjects: Ecology
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Description
Constructed treatment wetlands (CTW) are being increasingly utilized in urbanized areas as a cost-effective and environmentally-friendly method for treating wastewater. CTWs can be especially useful for urban areas in aridland environments because they facilitate the reuse of water during water shortages. In my study, I determined the rates at which the aboveground and belowground emergent macrophytes sequestered nitrogen in a 42 ha aridland CTW in Phoenix, Arizona, USA. To do so, I measured foliar nitrogen content in aboveground and belowground biomass of three plant species groups (Typha latifolia + Typha domingensis, Schoenoplectus acutus + Schoenoplectus tabernaemontani, and Schoenoplectus californicus). Using these data, I calculated aboveground and belowground nitrogen budgets for the three species groups annually from 2011 to 2018.
Aboveground nitrogen content showed a maximum in 2011, decreasing until 2015, increasing again until 2017, and dropping in 2018; belowground nitrogen content showed the opposite temporal trend. Because foliar nitrogen content was assumed to be relatively constant over time, my data suggested that belowground nitrogen content increased between 2011 and 2015 and decreased between 2015 and 2017. Aboveground nitrogen content underwent fluctuations due to fluctuations in aboveground biomass. This occurred due to ‘thatching’, or events of widespread toppling of large macrophyte stands. The ratio of aboveground to belowground biomass can vary widely in the same CTW. My findings suggested that managing senesced aboveground plant material in CTWs may optimize the CTW’s ability to sequester nitrogen. Further research is needed to determine the best management strategies, as well as its possible implications.
Aboveground nitrogen content showed a maximum in 2011, decreasing until 2015, increasing again until 2017, and dropping in 2018; belowground nitrogen content showed the opposite temporal trend. Because foliar nitrogen content was assumed to be relatively constant over time, my data suggested that belowground nitrogen content increased between 2011 and 2015 and decreased between 2015 and 2017. Aboveground nitrogen content underwent fluctuations due to fluctuations in aboveground biomass. This occurred due to ‘thatching’, or events of widespread toppling of large macrophyte stands. The ratio of aboveground to belowground biomass can vary widely in the same CTW. My findings suggested that managing senesced aboveground plant material in CTWs may optimize the CTW’s ability to sequester nitrogen. Further research is needed to determine the best management strategies, as well as its possible implications.
ContributorsCrane, Austin Matthew (Author) / Childers, Daniel (Thesis director) / Sanchez, Christopher (Committee member) / School of Life Sciences (Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
In today's world, critical thinking and using a systems approach to problem solving are skills that are far too rare. In the age of information, the truth has become muddled by "fake news" and a constant barrage of exaggerations or blatant falsehoods. Without critical thinking skills, "many members of our society do not command the scientific literacy necessary to address important societal issues and concerns" (NCES 2012, p.11). Additionally, far too many people are incapable of thinking long term and understanding how their actions affect others. Because of this shortsightedness our world is facing one of its biggest ecological crises \u2014 global warming confounded by overpopulation and overconsumption. Now, more than ever, it is critical "for our young people to have a basic understanding of the relevant scientific ideas, technologies and ethical issues and powers of reasoning, to be prepared to face these issues" (Harlen et al., 2015). I believe that investigating innovative ways to teach ecology could be an important step to accomplishing this. Learning to think like a scientist forces people to rely on facts, follow similar protocols to deduce these facts, and be able to think critically about misleading events. More specifically, ecology education will allow people to develop those skills while also learning about team work, open-mindedness, and their environment. Ecology is defined as "the branch of biology that deals with the relations of organisms to one another and to their physical surroundings" (Dictionary.com, 2018). It is clear that this subcategory of science could act as a powerful introduction to the scientific world and how we relate to it. Its introduction at a young age has the potential to create a generation of conscientious and curious lifelong learners. In an attempt to support effective ways to teach ecology, I developed an educational unit and applied it in different educational contexts. My target audience was elementary aged students and I tested this unit with children in Phoenix Metropolitan Area afterschool programs. I taught core concepts of ecology \u2014 the water cycle, the sun's energy, plants and photosynthesis, and food webs \u2014in a sequence of lesson plans that build upon each other. Finally, I determined the appropriate age group and setting for these lesson plans through research and in-class observations. In this document, I explain the process I went through in developing my lesson plans, why I felt compelled to make them, and my experiences in implementing them.
ContributorsVotaw, Alexandra Lindsay (Author) / Larson, Kelli (Thesis director) / Herrmann, Lisa (Committee member) / York, Abigail (Committee member) / School of Art (Contributor) / The Design School (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Often, when thinking of cities we envision designed landscapes, where people regulate everything from water to weeds, ultimately resulting in an ecosystem decoupled from biophysical processes. It is unclear, however, what happens when the people regulating these extensively managed landscapes come under stress, whether from unexpected economic fluctuations or from changing climate norms. The overarching question of my dissertation research was: How does urban vegetation change in response to human behavior? To answer this question, I conducted multiscale research in an arid urban ecosystem as well as in a virtual desert city. I used a combination of long-term data and agent-based modeling to examine changes in vegetation across a range of measures influenced by biophysical, climate, institutional, and socioeconomic drivers. At the regional scale, total plant species diversity increased from 2000 to 2010, while species composition became increasingly homogeneous in urban and agricultural areas. At the residential scale, I investigated the effects of biophysical and socioeconomic drivers – the Great Recession of 2007-2010 in particular – on changing residential yard vegetation in Phoenix, AZ. Socioeconomic drivers affected plant composition and increasing richness, but the housing boom from 2000 through 2005 had a stronger influence on vegetation change than the subsequent recession. Surprisingly, annual plant species remained coupled to winter precipitation despite my expectation that their dynamics might be driven by socioeconomic fluctuations. In a modeling experiment, I examined the relative strength of psychological, social, and governance influences on large-scale urban land cover in a desert city. Model results suggested that social norms may be strong enough to lead to large-scale conversion to low water use residential landscaping, and governance may be unnecessary to catalyze residential landscape conversion under the pressure of extreme drought conditions. Overall, my dissertation research showed that urban vegetation is dynamic, even under the presumably stabilizing influence of human management activities. Increasing climate pressure, unexpected socioeconomic disturbances, growing urban populations, and shifting policies all contribute to urban vegetation dynamics. Incorporating these findings into planning policies will contribute to the sustainable management of urban ecosystems.
ContributorsRipplinger, Julie (Author) / Franklin, Janet (Thesis advisor) / Collins, Scott L. (Thesis advisor) / Anderies, John M (Committee member) / Childers, Daniel L. (Committee member) / York, Abigail (Committee member) / Arizona State University (Publisher)
Created2015
Description
This is a study of the plight of smallholder agriculture in Northwest Costa Rica. More specifically, this is the story of 689 rice farms, of an average size of 7.2 hectares and totaling just less than 5,300 hectares within the largest agricultural irrigation system in Central America. I was able to define the physical bounds of this study quite clearly, but one would be mistaken to think that this simplicity transfers to a search for rural development solutions in this case. Those solutions lie in the national and international politics that appear to have allowed a select few to pick winners and losers in Costa Rican agriculture in the face of global changes. In this research, I found that water scarcity among smallholder farms between 2006 and 2013 was the product of the adaptations of other, more powerful actors in 2002 to threats of Costa Rica's ratification of the Central American Free Trade Agreement. I demonstrate how the adaptations of these more powerful actors produced new risks for others, and how this ultimately prevented the rural development program from meeting its development goals. I reflect on my case study to draw conclusions about the different ways risks may emerge in rural development programs of this type. Then, I focus on the household level and show that determinants of successful adaptation to one type of global change risk may make farmers more vulnerable to other types, creating a "catch-22" among vulnerable farmers adapting to multiple global change risks. Finally, I define adaptation limits in smallholder rice farming in Northwest Costa Rica. I show that the abandonment of livelihood security and well-being, and of the unique "parcelaro" identities of rice farmers in this region define adaptation limits in this context.
ContributorsWarner, Benjamin (Author) / Childers, Daniel (Thesis advisor) / Eakin, Hallie (Committee member) / Abbott, Joshua (Committee member) / Wiek, Arnim (Committee member) / Arizona State University (Publisher)
Created2014
Description
Research shows that many water governance regimes are failing to guide social-ecological systems away from points, beyond which, damage to social and environmental well-being will be difficult to correct. This problem is apparent in regions that face water conflicts and climate threats. There remains a need to clarify what is it about governance that people need to change in water conflict prone regions, how to collectively go about doing that, and how research can actively support this. To address these needs, here I present a collaborative research project from the dry tropics of Guanacaste Province, Costa Rica. The project addressed the overarching questions: How can water be governed sustainably in water-contested and climate-threatened regions? And, how can people transition current water governance regimes toward more sustainable ones? In pursuit of these questions, a series of individual studies were performed with many partners and collaborators. These studies included: a participatory analysis and sustainability assessment of current water governance regimes; a case analysis and comparison of water conflicts; constructing alternative governance scenarios; and, developing governance transition strategies. Results highlight the need for water governance that addresses asymmetrical knowledge gaps especially concerning groundwater resources, reconciles disenfranchised groups, and supports local leaders. Yet, actions taken based on these initial results, despite some success influencing policy, found substantial challenges confronting them. In-depth conflict investigations, for example, found that deeply rooted issues such friction between opposing local-based and national institutions were key conflict drivers in the region. To begin addressing these issues, researchers and stakeholders then constructed a set of governing alternatives and devised governance transition strategies that could actively support people to achieve more sustainable alternatives and avoid less sustainable ones. These efforts yielded insight into the collective actions needed to implement more sustainable water governance regimes, including ways to overcoming barriers that drive harmful water conflicts. Actions based on these initial strategies yielded further opportunities, challenges, and lessons. Overall, the project addresses the research and policy gap between identifying what is sustainable water governance and understanding the strategies needed to implement it successfully in regions that experience water conflict and climate impacts.
ContributorsKuzdas, Christopher Paul (Author) / Wiek, Arnim (Thesis advisor) / Childers, Daniel (Thesis advisor) / Vignola, Raffaele (Committee member) / Eakin, Hallie (Committee member) / Basile, George (Committee member) / Arizona State University (Publisher)
Created2014
Description
Climate change will result not only in changes in the mean state of climate but also on changes in variability. However, most studies of the impact of climate change on ecosystems have focused on the effect of changes in the central tendency. The broadest objective of this thesis was to assess the effects of increased interannual precipitation variation on ecosystem functioning in grasslands. In order to address this objective, I used a combination of field experimentation and data synthesis. Precipitation manipulations on the field experiments were carried out using an automated rainfall manipulation system developed as part of this dissertation. Aboveground net primary production responses were monitored during five years. Increased precipitation coefficient of variation decreased primary production regardless of the effect of precipitation amount. Perennial-grass productivity significantly decreased while shrub productivity increased as a result of enhanced precipitation variance. Most interesting is that the effect of precipitation variability increased through time highlighting the existence of temporal lags in ecosystem response.
Further, I investigated the effect of precipitation variation on functional diversity on the same experiment and found a positive response of diversity to increased interannual precipitation variance. Functional evenness showed a similar response resulting from large changes in plant-functional type relative abundance including decreased grass and increased shrub cover while functional richness showed non-significant response. Increased functional diversity ameliorated the direct negative effects of precipitation variation on ecosystem ANPP but did not control ecosystem stability where indirect effects through the dominant plant-functional type determined ecosystem stability.
Analyses of 80 long-term data sets, where I aggregated annual productivity and precipitation data into five-year temporal windows, showed that precipitation variance had a significant effect on aboveground net primary production that is modulated by mean precipitation. Productivity increased with precipitation variation at sites where mean annual precipitation is less than 339 mm but decreased at sites where precipitation is higher than 339 mm. Mechanisms proposed to explain patterns include: differential ANPP response to precipitation among sites, contrasting legacy effects and soil water distribution.
Finally, increased precipitation variance may impact global grasslands affecting plant-functional types in different ways that may lead to state changes, increased erosion and decreased stability that can in turn limit the services provided by these valuable ecosystems.
Further, I investigated the effect of precipitation variation on functional diversity on the same experiment and found a positive response of diversity to increased interannual precipitation variance. Functional evenness showed a similar response resulting from large changes in plant-functional type relative abundance including decreased grass and increased shrub cover while functional richness showed non-significant response. Increased functional diversity ameliorated the direct negative effects of precipitation variation on ecosystem ANPP but did not control ecosystem stability where indirect effects through the dominant plant-functional type determined ecosystem stability.
Analyses of 80 long-term data sets, where I aggregated annual productivity and precipitation data into five-year temporal windows, showed that precipitation variance had a significant effect on aboveground net primary production that is modulated by mean precipitation. Productivity increased with precipitation variation at sites where mean annual precipitation is less than 339 mm but decreased at sites where precipitation is higher than 339 mm. Mechanisms proposed to explain patterns include: differential ANPP response to precipitation among sites, contrasting legacy effects and soil water distribution.
Finally, increased precipitation variance may impact global grasslands affecting plant-functional types in different ways that may lead to state changes, increased erosion and decreased stability that can in turn limit the services provided by these valuable ecosystems.
ContributorsGherardi Arbizu, Laureano (Author) / Sala, Osvaldo E. (Thesis advisor) / Childers, Daniel (Committee member) / Grimm, Nancy (Committee member) / Hall, Sharon (Committee member) / Wu, Jingle (Committee member) / Arizona State University (Publisher)
Created2014