Drivers of Stream Drying and Network Connectivity Across Spatial Scales

Abstract

Nonperennial streams are widespread and abundant around the globe. Although these streams are societally and ecologically important, they are understudied relative to those that flow continuously. Because of this, we lack fundamental knowledge of nonperennial streams, such as when and where they dry and the consequences of those drying patterns. Drying patterns largely determine stream network connectivity in nonperennial systems. Stream drying and network connectivity patterns are driven by processes that act at global, regional, and local spatial scales. The goal of this dissertation is to explore the patterns and drivers of stream drying and connectivity. Chapter One explores the impact of global climate change on network connectivity in the Blue River, Oklahoma. The findings from this research suggest that stream drying is likely to increase in the future. This research also identified a threshold around which a small change in stream drying leads to a large change in connectivity. Chapter Two investigates how the influence of stream drying on network connectivity varies in relation to network-scale properties. This work found that the rate of connectivity loss is faster for larger stream networks and when drying occurs in mainstem reaches. As stream drying is expected to become more extensive due to changes in climate, this research underscores the need for managers to be vigilant about fragmentation when managing at large spatial scales and when managing systems where drying occurs in mainstem reaches. Chapter Three investigates how streamflow and connectivity are influenced by cross-scale interactions between global-scale climate change and regional-scale aridity. This analysis suggests that changes in connectivity due to climate change vary predictably in relation to aridity. Stream networks in arid regions will have more high connectivity days in the future while stream networks in wetter regions will experience increases in the number of low connectivity days in the future. The ability to predict future changes in network connectivity allows for better anticipation of and improved ability to manage for the consequences of climate change. Overall, this dissertation demonstrates how complex patterns of stream drying and connectivity vary predictably in relation to network scale, regional scale, and global scale processes.