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- All Subjects: Stream Ecology
- All Subjects: Algae
- Creators: Elser, James J
- Creators: Hartnett, Hilairy
I surveyed four Sonoran desert stream sites, and found significant relationships between flow permanence and plant and butterfly species richness and abundance, as well as strong relationships between plant and butterfly abundance and between plant and butterfly species richness. Most notably, my results pointed to hosted butterflies as a break-out category of butterflies which may more clearly delineate ecological relationships between butterfly and plant abundance and diversity along Sonoran Desert streams; this can inform conservation decisions. Managing for hosted (resident) butterflies will necessarily entail managing for the presence of surface water, nectar forage, varying levels of canopy cover, and plant, nectar plant, and host plant diversity since the relationships between hosted butterfly species richness and/or abundance and all of these variables were significant, both statistically and ecologically.
Humans have dramatically increased phosphorus (P) availability in terrestrial and aquatic ecosystems. As P is often a limiting nutrient of primary production, changes in its availability can have dramatic effects on ecosystem processes. I examined the effects of calcium carbonate (CaCO3) deposition, which can lower P concentrations via coprecipitation of phosphate, on P availability in two systems: streams in the Huachuca Mountains, Arizona, and a stream, Río Mesquites, in Cuatro Ciénegas, México. Calcium carbonate forms as travertine in the former and within the microbialites of the latter. Despite these differences, CaCO3 deposition led to lowered P availability in both systems. By analyzing a three-year dataset of water chemistry from the Huachuca Mountain streams, I determined that P concentrations were negatively related to CaCO3 deposition rates. I also discovered that CaCO3 was positively correlated with nitrogen concentrations, suggesting that the stoichiometric effect of CaCO3 deposition on nutrient availability is due not only to coprecipitation of phosphate, but also to P-related constraints on biotic nitrogen uptake. Building from these observations, bioassays of nutrient limitation of periphyton growth suggest that P limitation is more prevalent in streams with active CaCO3 deposition than those without. Furthermore, when I experimentally reduced rates of CaCO3 deposition within one of the streams by partial light-exclusion, areal P uptake lengths decreased, periphyton P content and growth increased, and periphyton nutrient limitation by P decreased. In Río Mesquites, CaCO3 deposition was also associated with P limitation of microbial growth. There, I investigated the consequences of reductions in CaCO3 deposition with several methods. Calcium removal led to increased concentrations of P in the microbial biomass while light reductions decreased microbial biomass and chemical inhibition had no effect. These results suggest that CaCO3 deposition in microbialites does limit biological uptake of P, that photoautotrophs play an important role in nutrient acquisition, and, combined with other experimental observations, that sulfate reduction may support CaCO3 deposition in the microbialite communities of Río Mesquites. Overall, my results suggest that the effects of CaCO3 deposition on P availability are general and this process should be considered when managing nutrient flows across aquatic ecosystems.
During 2013 and 2014, vegetation and herpetofauna were monitored at 21 riparian locations along the Virgin River via trapping and visual encounter surveys. Study sites were divided into four stand types based on density and percent cover of dominant trees (Tamarix, Prosopis, Populus, and Salix) and presence of restoration activities: Tam, Tam-Pros, Tam-Pop/Sal, and Restored Tam-Pop/Sal. Restoration activities consisted of mechanical removal of non-native trees, transplanting native trees, and introduction of water flow. All sites were affected by biological control. I predicted that herpetofauna abundance would vary between stand types and that herpetofauna abundance would be greatest in Restored Tam-Pop/Sal sites due to increased habitat openness and variation following restoration efforts.
Results from trapping indicated that Restored Tam-Pop/Sal sites had three times more total lizard and eight times more Sceloporus uniformis captures than other stand types. Anaxyrus woodhousii abundance was greatest in Tam-Pop/Sal and Restored Tam-Pop/Sal sites. Visual encounter surveys indicated that herpetofauna abundance was greatest in the Restored Tam-Pop/Sal site compared to the adjacent Unrestored Tam-Pop/Sal site. Habitat variables were reduced to six components using a principle component analysis and significant differences were detected among stand types. Restored Tam-Pop/Sal sites were most similar to Tam-Pop/Sal sites. S. uniformis were positively associated with large woody debris and high densities of Populus, Salix, and large diameter Prosopis.
Restored Tam-Pop/Sal sites likely supported higher abundances of herpetofauna, as these areas exhibited greater habitat heterogeneity. Restoration activities created a mosaic habitat by reducing canopy cover and increasing native tree density and surface water. Natural resource managers should consider implementing additional restoration efforts following biological control when attempting to restore riparian areas dominated by Tamarix and other non-native trees.
Phosphorus (P) is a limiting nutrient in ecosystems and is mainly used as fertilizer to grow food. The demand for P is increasing due to the need for increased food supply to support a growing population. However, P is obtained from phosphate rock, a finite resource that takes millions of years to form. These phosphate rock deposits are found in only a few countries. This uneven distribution of phosphate rock leads to a potential imbalance in socio-economic systems, generating food security pressure due to unaffordability of P fertilizer. Thus, the first P-sustainability concern is a stable supply of affordable P fertilizer for agriculture. In addition, improper management of P from field to fork leaves an open end in the global P cycle that results in widespread water pollution. This eutrophication leads to toxic algal blooms and hypoxic “dead zones”. Thus, the second P-sustainability concern involves P pollution from agriculture and cities. This thesis focuses on P flows in a city (Macau as a case study) and on potential strategies for improvements of sustainable P management in city and agriculture. Chapter 2 showed a P-substance-flow analysis for Macau from 1998-2016. Macau is a city with a unique economy build on tourism. The major P flows into Macau were from food, detergent, and sand (for land reclamation). P recovery from wastewater treatment could enhance Macau’s overall P sustainability if the recovered P could be directed towards replacing mined P used to produce food. Chapters 3 and 4 tested a combination of P sustainability management tactics including recycling P from cities and enhancing P-use efficiency (PUE) in agriculture. Algae and biosolids were used as recycled-P fertilizers, and genetically transformed lettuce was used as the a PUE-enhanced crop. This P sustainable system was compared to the conventional agricultural system using commercial fertilizer and the wild type lettuce. Chapters 3 and 4 showed that trying to combine a PUE-enhancement strategy with P recycling did not work well, although organic fertilizers like algae and biosolids may be more beneficial as part of longer-term agricultural practices. This would be a good area for future research.