UC Berkeley

Rivers act as dynamic forces that shape Earth’s changing surface, and whose scars we can still see punctuating our landscapes. Characteristically everchanging, they have inspired many poets, thinkers, and wanderers with their mutable nature. The quote “no man steps in the same river twice, for it is not the same river and he is not the same man” – attributed to the Ancient Greek philosopher Heraclitus – is known to be true for anyone who has seen a river swell beyond its banks, only to watch it shrink back to a narrow passage. But what about the streams that dry? The temporary, the seasonal, the irregular, the ephemeral, the discontinuous? These waterways, termed in this dissertation as ‘intermittent’, periodically, and naturally, cease to flow. They are similarly unpredictable, where the patterns and extent of drying are highly variable, with some reaches going dry year after year, regardless of previous conditions, while others respond more proportionally to the amount of antecedent rainfall. While riverine theory and study has been traditionally based on perennial model systems, recognition of the importance of intermittent streams has grown in recent years. However, critical gaps remain around the causes and consequences of intermittent stream drying across space and time. These systems are especially sensitive to climate fluctuations, and there is considerable potential for such ecosystems, and the species and services they support, to shift in response to climate change. Yet, relatively little attention has been given to identifying and evaluating the factors that influence variability in intermittent stream drying. Without documenting how intermittent streams vary within and across years, an essential component of their character is lost. With increasing precipitation volatility and rising temperatures, there is an urgent need to characterize where and when intermittent streams will be buffered from, or vulnerable to, altered climate conditions. In this dissertation, I explore the causes and consequences of intermittent stream variability, with a focus on the interannual variation in the hydrological and ecological patterns within these systems. These themes are explored at multiple scales, from the watershed to the stream reach, in three core chapters. I first evaluate the challenges and opportunities of monitoring intermittent streams in Chapter 1, before moving to understanding the controls on wetted channel extent and variability in Chapter 2, to finally characterizing the shifting habitat mosaic in Chapter 3. These three chapters together illustrate the importance of intermittent streams in shaping the environments they flow (and cease to flow) through, and underscore the need to capture the patterns of drying across space and time.