The effects of natural and anthropogenic disturbance in lotic ecosystems

The prevalence of large-scale anthropogenic and natural disturbance has increased in recent decades around the world. For example, over 50% of the world’s large rivers are currently dammed and the frequency of large wildfires has nearly quadrupled in western North America since the mid-1980s. Disturbances such as these are principal drivers of change in lotic ecosystems and we seek to improve our understanding of how they affect recipient ecosystems in the context of fisheries management and conservation. My thesis research combines empirical studies and modeling to improve our ability to predict and measure the effects of several major types of natural and anthropogenic disturbance in lotic ecosystems. In Chapter 1 I improved the accuracy of hydrodynamic habitat models for juvenile salmon by up to 10% by applying Akaike information criterion and model averaging. In Chapters 2 and 3 I applied multiple regression and bioenergetic models to illustrate how wildfire, by burning riparian vegetation, can elevate stream temperatures by up to 0.6°C adding ~5 kJ of metabolic costs to salmonids. As well, I found concentrations of food web resources such as nitrate and fine particulate organic matter increased in burned compared to unburned regions by 244% and 44%, respectively, and I found significantly greater seasonal changes in terrestrial and aquatic invertebrate abundance than changes attributable to wildfire. Despite similar regional invertebrate prey abundance, Bayesian stable isotope mixing models revealed seasonal and regional differences in salmonid diets, with higher trophic level prey contributing more to diets in the burned compared to a reference region. Lastly, in Chapter 4 I found that forest harvest and rising air temperatures are warming waters in the Fraser River basin at 0.07°C per decade on average by applying Spatial Stream Network models. In total, my thesis research builds on previous work and illuminates how disturbance can affect abiotic and biotic responses in lotic ecosystems at spatial scales ranging from less than 10 m2 to over 200,000 km2. Thus, results from my thesis research will aid fisheries management and conservation by improving our understanding of how natural and anthropogenic disturbance may alter streams and rivers in our future.