Increasing atmospheric CO2 concentrations associated with climate change will likely influence a wide variety of ecosystems. Terrestrial research has examined the effects of increasing CO2 concentrations on the functionality of plant systems; with studies ranging in scale from the short-term responses of individual leaves, to long-term ecological responses of complete forests. While terrestrial plants have received much attention, studies on the responses of marine plants (seagrasses) to increased CO2(aq) concentrations remain relatively sparse, with most research limited to small-scale, ex situ experimentation. Furthermore, few studies have attempted to address similarities between terrestrial and seagrass responses to increases in CO2(aq). The goals of this dissertation are to expand the scope of marine climate change research, and examine how the tropical seagrass, Thalassia testudinum responds to increasing CO2(aq) concentrations over multiple spatial and temporal scales. Manipulative laboratory and field experimentation reveal that, similar to terrestrial plants, seagrasses strongly respond to increases in CO2(aq) concentrations. Using a novel field technique, in situ field manipulations show that over short time scales, seagrasses respond to elevated CO2(aq) by increasing leaf photosynthetic rates and the production of soluble carbohydrates. Declines in leaf nutrient (nitrogen and phosphorus) content were additionally detected, paralleling responses from terrestrial systems. Over long time scales, seagrasses increase total above- and belowground biomass with elevated CO2(aq), suggesting that, similar to terrestrial research, pervasive increases in atmospheric and oceanic CO2(aq) concentrations stand to influence the productivity and functionality of these systems. Furthermore, field experiments reveal that seagrass epiphytes, which comprise an important component of seagrass ecosystems, additionally respond to increased CO2(aq) with strong declines in calcified taxa and increases in fleshy taxa. Together, this work demonstrates that increasing CO2(aq) concentrations will alter the functionality of seagrass ecosystems by increasing plant productivity and shifting the composition of the epiphyte community. These results have implications for future rates of carbon storage and sediment production within these widely distributed systems.

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abstract / Biological Sciences / Doctoral / Doctor of Philosophy

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Lakes near Sudbury, Ontario, experienced widespread acidification and metal-contamination beginning in the late-19th century. These stressors caused extreme damage to regional aquatic systems and their catchments, with aquatic biota experiencing reduced species richness and, in some cases, extirpations. Emission control measures markedly improved pH, however biotic recovery continues to lag water quality improvements, prompting investigation into mechanisms leading to this phenomenon. Due to the lack of long-term monitoring data, I use paleolimnological approaches to examine temporal trends in cladoceran zooplankton, from pre-impact conditions, through the period of acidification/metal contamination, and following the implementation of emission controls. I assess the degree of biotic recovery that has taken place in these lakes, and review the mechanisms that continue to structure cladoceran assemblages. Lakes closest to Sudbury recorded increases of ~15-65% relative abundance of Chydorus brevilabris, concurrent with the late-1800s industrial development. The relative abundance of C. brevilabris remains elevated above pre-impact levels in two Sudbury lakes; however, in Middle Lake, which was neutralized with calcium carbonate, declines in C. brevilabris (to ~pre-impact levels) occurred following neutralization. Conversely, lakes located ~60 km southwest of Sudbury, in Killarney Provincial Park, experienced muted assemblage change, with minor (< ~5%) increases in grazers (e.g., Daphnia spp., Holopedium glacialis) occurring within the past ~40 years. Lakes in Sudbury and Killarney acidified to pH < ~5, however those in Sudbury additionally received high inputs of nickel and copper, which have toxic effects on aquatic organisms, including some Cladocera. Contamination with these metals may have been a primary driver of cladoceran assemblage change. Elevated metal concentrations likely continue to structure the cladoceran assemblages in the Sudbury lakes. In addition, many of the lakes contain altered food webs (e.g., large populations of yellow perch) as a legacy of the acid and metal contamination, acting as a potential barrier to recovery. Finally, warming air temperatures over the past ~40 years, which I link to increases in primary production, may alter the composition of cladoceran species found in these lakes, and therefore prevent a return to pre-impact conditions. / Thesis (Master, Biology) -- Queen's University, 2014-04-28 12:26:39.903

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AN ABSTRACT OF THE THESIS OF Nicole K. Jensen, for the Masters of Science degree in Forestry, presented on April 3, 2012, at Southern Illinois University Carbondale. TITLE: TREE-RING CHEMISTRY AND GROWTH RESPONSE TO EXPERIMENTAL WATERSHED ACIDIFICATION MAJOR PROFESSOR: Dr. Eric Holzmueller Forest ecosystems in the eastern United States are threatened by acid deposition rates that have increased dramatically since industrialization. We utilized two watersheds at the Fernow Experimental Forest in West Virginia to examine long-term effects of acidification on ecological processes. One watershed has been treated with ammonium sulfate (approximately twice the ambient deposition rate) since 1989 to simulate acid deposition while the other served as a control. Prior to treatment both watersheds were similar in age and species composition. Ten dominant overstory Prunus serotina and Liriodendron tulipifiera trees were selected and cored from each watershed to measure bolewood concentrations of elements essential for growth over time. In addition, changes in tree species basal area were analyzed utilizing 50 long-term growth plots established in 1990. Results of this experiment show lower calcium and magnesium concentration and increased acidic cation concentration in the treated watershed for both species indicating a negative treatment effect. These results were similar to that of a previous study conducted at the Fernow with periods of significant differences in cation concentrations between the treated and control watershed. Growth response, measured through relative growth rates of cored trees and changes in basal area from growth plots, was not as conclusive, but it did appear that treatment may be having a negative affect for both species during the last measurement of the growth plots. These results indicate a need for further research to understand the impact of long-term acidification so that sustainable forest management practices in areas affected by acid deposition may be developed.

In recognition of the widespread deterioration of the natural environment, and the continual emergence of sudden catastrophic environmental changes resulting from complex interactions of theretofore apparently disparate phenomena, this research presents a complex systems approach to the modelling of such environmental catastrophes. Recognizing contemporary views of complexity and evolution, this research presents a dynamic complex systems model which displays emergent characteristics which can be directly related to the modelled phenomena - linking acid rain and eutrophication - and the study region, the Rutland Water catchment. This is achieved through the definition of a catastrophe indicator which indicates both the proximity and magnitude of catastrophe arising from the non-linear and discontinuous acid-phosphorus relationship within the soil domain which lies at the heart of this Chemical Time Bomb phenomenon. This facilitates assessment of the vulnerability of the Rutland Water catchment to potential propagation of this CTB given continued acidification and phosphate accumulation. The main contributions of this research may thus be found in the following areas: Development of a dynamic complex systems model - transferable to alternative catchments due to the minimal data requirements and its generic representation - which may be used to describe non-point sources of phosphates as part of assessments of potential eutrophication, overcoming such limitations found in existing models. * Definition of a catastrophe indicator( Re)- which highlights both the proximity and magnitude of catastrophe describing a specific Chemical Time Bomb phenomenon whereby the soil suddenly changes from being a sink to a source of phosphates; long-term accumulations of phosphate in the soil being released as a consequence of soil acidification in the short-term. Presentation of a complex systems approach - hinged upon this concept of a catastrophe indicator - to the representation of non-linearities and discontinuities between heretofore apparently disparate phenomena which are 'competing for a common resource.