Browsing by Subject "ecosystem metabolism"
Results Per Page
Sort Options
Item Open Access Effects of urbanization on stream ecosystem functions(2011) Sudduth, ElizabethAs the human population continues to increase, the effects of land use change on streams and their watersheds will be one of the central problems facing humanity, as we strive to find ways to preserve important ecosystem services, such as drinking water, irrigation, and wastewater processing. This dissertation explores the effects of land use change on watershed nitrate concentrations, and on several biogeochemical ecosystem functions in streams, including nitrate uptake, ecosystem metabolism, and heterotrophic carbon processing.
In a literature synthesis, I was able to conclude that nitrate concentrations in streams in forested watersheds tend to be correlated with soil solution and shallow groundwater nitrate concentrations in those watersheds. Watershed disturbances, such as ice storms or clear-cutting, did not alter this relationship. However both urban and agricultural land use change increased the nitrate concentrations in streams, soil solution, and groundwater, and altered the correlation between them, increasing the slope and intercept of the regression line. I conclude that although the correlation between these concentrations allows for predictions to be made, further research is needed to better understand the importance of dilution, removal, and transformation along the flowpaths from uplands to streams.
From a multi-site comparison of forested, urban, and urban restored streams, I demonstrated that ecosystem functions like nitrate uptake and ecosystem metabolism do not change in a linear unidirectional way with increasing urbanization. I also showed that Natural Channel Design stream restoration as practiced at my study sites had no net effect on ecosystem function, except those effects that came from clearing the riparian vegetation for restoration construction. This study suggested further consideration is needed of the ecosystem effects of stream restoration as it was practiced at these sites. It also suggested that more study was needed of the effects of urbanization on ecosystem metabolism and heterotrophic processes in streams.
In a 16-month study of ecosystem metabolism at four sites along an urbanization gradient, I demonstrated that ecosystem metabolism in urban streams may be controlled by multiple separate effects of urbanization, including eutrophication, light, temperature, hydrology, and geomorphology. One site, with high nutrients, high light, and stable substrate for periphyton growth but flashy hydrology, demonstrated a boom-bust cycle of gross primary production. At another site, high benthic organic matter standing stocks combined with low velocities and high depths to create hypoxic conditions when temperature increased. I propose a new conceptual framework representing different trajectories of these effects based on the balance of increases in scour, thermal energy and light, eutrophication, and carbon loading.
Finally, in a study of 50 watersheds across a landscape urbanization gradient, I show that urbanization is correlated with a decrease in particulate carbon stocks. I suggest that an increase in dissolved organic matter quality may serve to compensate for the loss of particulate carbon as fuel for heterotrophic microbial activity. Although I saw no differences among watershed landuses in microbial activity per gram of sediment, there was a strong increase in the efficiency of microbial activity per unit organic sediment with increasing watershed urbanization. Ultimately, I hope that this research contributes to our understanding of stream ecosystem functions and the way land use change can alter these functions, with the possibility of better environmental management of urban streams in the future.
Item Open Access Habitat loss, alteration, and fragmentation in river networks: Implications for Freshwater Mussels and Their Landscape Genomics(2017) Fuller, Matthew RobertThis dissertation focuses on the implications of habitat change in freshwater ecosystems. Habitat change has three primary components that are inextricably connected; habitat loss, alteration, and fragmentation. Habitat loss is the physical removal and/or replacement of “core” habitat such that a new “matrix” habitat exists in its place. Habitat alteration is the modification of core habitat that causes a quality change (either positive or negative depending on the target species). Habitat fragmentation affects the connectivity between core habitat patches in the landscape. Rivers are highly fragmented both naturally and anthropogenically, so they represent a system readily available to study the impacts of habitat change on ecosystems.
Four approaches were used to evaluate the impacts of habitat change on freshwater ecosystems. First (Chapter 1 as published in the Annals of the New York Academy of Sciences with co-authors Dr. Martin Doyle and Dr. David Strayer; see Fuller et al. (2015)), a review of the major causes and consequences of habitat change in river networks was conducted with the goal of also bridging a theoretical gap between terrestrial and freshwater systems related to habitat change ecology. Second (Chapter 2), an empirical evaluation of a fragmented (dammed) river reach was used to evaluate the local impacts of habitat loss and alteration on physical (sediment), biogeochemical (dissolved oxygen), and biological (freshwater mussels) response variables. Third (Chapter 3), gene flow model simulations were used to identify the genetic impacts of habitat fragmentation at the river-network scale. This simulation effort contrasted the impact of habitat fragmentation with species longevity to see how organisms using different life history strategies related to lifespan respond genetically to habitat fragmentation. Fourth (Chapter 4), an empirical landscape genomics evaluation of a species of freshwater mussel (Elliptio complanata) was conducted to identify its genetic response to a river network with a long history of habitat change.
Conclusions from this research make several contributions to the ecological theory of habitat change. First, by applying the habitat change lexicon in terrestrial systems to freshwater systems, sharing results and theory across the terrestrial-aquatic literature becomes simple and may advance the theory behind habitat change ecology more rapidly with more empirical results to draw upon. Second, temporally dynamic matrix habitat and species capitalizing on altered edge habitat were identified surrounding a local habitat fragmentation agent (a dam), suggesting some species may strongly benefit from the presence of edge habitat in river networks. Third, from the gene flow model simulations, the life history of a species played an important role in how organisms respond genetically to habitat fragmentation where long-lived species appear buffered from the genetic diversity loss caused by habitat fragmentation. Finally, the empirical evaluation of a freshwater mussel species that has experienced a long history of anthropogenic-driven habitat change via water quality alterations, inundation losses, and dam fragmentation appears to have maintained a population genetic structure unrelated to the expected habitat change in the system.