| dc.description.abstract | Rivers and streams are among the world’s most threatened ecosystems despite the importance of freshwater to human society. Rivers have been dammed, dried, and moved for human needs and consumption. They have experienced a dramatic loss of biodiversity, particularly in response to human population growth and climate change. Understanding the drivers of ecological community change is vital to mitigate threats to water scarcity and biodiversity. In my dissertation, I explore how elements of climate change, river drying, and dam management alter river biodiversity. By quantifying how aquatic assemblages change in response to multiple stressors, my work highlights ways to better manage river ecosystems in a future that will be increasingly defined by changes in climate and water use. Further, the development of effective management strategies depends on effective communication of research findings. Therefore, I also analyze language use describing dry river systems, and provide universal definitions. Combined, my research addresses multiple threats to freshwater diversity across space and over time in complementary ways to allow for better river management and protection.
Rivers and streams that sometimes cease to flow (non-perennial streams) are the most common form of flowing waterways on the planet. In the past 20 years, research on these systems has increased exponentially across multiple disciplines. Despite the need to connect research across scientific fields to better understand these dynamic systems, a consensus on terminology has not been reached, making meta-analyses, syntheses, management, and policy difficult. Published in 2020, my first chapter quantitatively explored 12 frequently used names for non-perennial streams over time and suggest universal terms and definitions. I found no consensus for a single name in any scientific field, but found substantial research overlap when exploring research topics across terms. I also found significant thematic overlap in definitions across papers from various fields of study, indicating redundancy across many terms. Finally, I suggest universal definitions for three specific terms to better facilitate effective communication across research fields, the public, and policy makers.
As climate change alters physical environments, understanding changes in community structure is essential for effective management and species conservation. While species diversity has historically been the focus of community studies, research demonstrates the value of using functional and phylogenetic diversity. Functional traits describe differences in ecological roles among species and phylogenetic diversity captures the evolutionary relatedness among species. For my second chapter, published in 2023, I explored changes in fish community composition in streams across Oklahoma over a 42 year time frame to see how shifts in the physical environment alter functional and phylogenetic diversity. I found that historical diversity influenced how communities changed over time. That is, historically less diverse communities changed in a different way than historically more diverse communities did. Changes in functional richness demonstrated the importance of environmental conditions while phylogenetic diversity trends showed no clear trend of community structure. Both types of diversity, however, were significantly correlated to annual changes in maximum temperature. Overall, I found that community assembly has changed over time, although specific changes were related to the historical diversity of the community.
Though aquatic ecologists have long recognized the importance of flow variation in flowing rivers, these variations do not represent the full conditions biological communities may experience in streams that seasonally dry, known as non-perennial streams. For non-perennial stream communities, equally important to flow variation are the drying and wetting regimes, or the characteristics of drying and wetting events. Drying and wetting can act as disturbances on these systems, and the timing, duration, frequency, magnitude, and rate of drying and wetting could have varying effects on riverine communities. My third chapter connected drying and wetting characteristics with patterns of macroinvertebrate, soft-bodied algal, and diatom assemblages. I found the amount of flow duration prior to sampling was correlated with macroinvertebrate and soft-bodied algal assemblage structures, though I found no drying or wetting characteristics predicted richness of these two assemblages. Diatom richness and structure, however, were heavily influenced by the date of drying. Thus, I found no single characteristic that explained structure or richness across every assemblage, highlighting the need for multiple ecological and hydrological benchmarks to meet management goals. Given the increasing prevalence of non-perennial freshwater ecosystems, understanding how various drying events influence stream communities is important to understanding these dynamic systems.
Humans have a long history of controlling water flow, particularly through the construction of dams. Dams vary in size, purpose, and management strategy, which combined can significantly change the temperature, flow, and physical structure of downstream waters. Southeastern Oklahoma provides a unique opportunity to compare management strategies across rivers of similar ecological and evolutionary histories. Three out of four major rivers in southeastern Oklahoma are dammed; each dam is managed for a different purpose and the presence of a fourth, unimpounded river provides a unique opportunity to understand how management alters ecological communities. In my last chapter, I used field surveys to sample sites above and below dams, as well as sites along a fourth unimpounded river. I found significant biological differences among the four rivers, but smaller differences among site types across the rivers, regardless of dam presence or management type. While biologic metrics did not show differences among site types, ordinations with full assemblage data did indicate some effect of dams on assemblage composition. We found biological metric and assemblage differences in this study were correlated to both local and watershed environmental variables. The higher elevation regions between these four watersheds may lead to biogeographic barriers, isolating the assemblages within each river. In addition, the strong aerial dispersal ability of many of the common taxa we found may allow for dispersal longitudinally along the rivers, damping the influence of dams on differences between communities upstream and downstream of the impoundment. The nuances within the results of our data highlight the importance of site-specific studies to fully understand how anthropogenic activities alter riverine ecosystems. As demands for freshwater continue to grow, clearly understanding how dam management strategies alter river communities will allow for clearer policies to protect these ecosystems.
Taken together, my dissertation broadly examines the impacts humans have on freshwater systems. Understanding the effects of multiple stressors on these diverse ecosystems and sharing common language is crucial to understanding how to properly manage them. My research highlights how rivers have responded to environmental alterations, which, via climate change, are only expected to continue and increase in magnitude and will provide novel ways to manage these diverse, dynamic, and threatened systems. | en_US |
