Hannah Richardson

Evolving Stream Drivers in a Rapidly Warming Alaska: Examining the Source of Stream Water as Glaciers Disappear

Abstract

Glaciers are disappearing at an alarming rate worldwide, and glaciers in coastal Alaska are melting at one of the highest rates on Earth. This makes this region a compelling place to study the way streamflow is changing in response to glacier melt. Landscapes recently covered by ice are quickly replaced by vegetation and high mountain streams. These changing landscapes will alter the timing and amount of water flowing in streams. This has direct consequences for downstream organisms such as salmon that rely on certain water qualities to survive. This research measures the proportion of snowmelt, rain, and groundwater in streamflow across seasons and across large elevation gradients. I calculate these proportions by measuring stream chemistry and using a three end-member mixing model. Across seasonal scales, my results show that snowmelt dominates streamflow across all elevations in the spring and tapers off through the fall. Rain contributions to streamflow slowly increase through late summer and peaks in the fall. Spatially, my results
show that high elevation streams have more snowmelt contributing to streamflow as compared to low elevation streams. Conversely, low elevation streams have higher proportions of groundwater. These findings support weather patterns observed in the region and existing literature regarding groundwater contribution to streams. By better understanding when and where different stream sources contribute most to streamflow, we can predict the way stream qualities like temperature, sediment and nutrient load will change. This will have direct implications for managing downstream ecosystems and resources that rely on mountain streamflow.