Glacier thinning rates along the Gulf of Alaska (GOA) are commonly as high as 6-8 m yr-1. This rapid glacial recession has important implications for coastal watershed hydrology and biogeochemistry because the loss of glacier ice decreases hydrologic storage and dramatically alters catchment landcover by exposing new land to the process of primary succession. The ecological development of terrestrial and aquatic ecosystems following deglaciation has been explored extensively, however there has been very little research on how landcover change will alter material delivery into and through the river network to coastal estuaries. This project will fill this critical knowledge gap by evaluating how glacial recession is altering hydrologic and biogeochemical processes in coastal watersheds in southeastern Alaska. In particular, our research will develop a comprehensive understanding of how the speciation, fate and transport of riverine nutrients and dissolved organic matter (DOM) will be altered by ongoing glacial retreat. Weekly and storm sampling combined with continuous discharge measurements will provide the first detailed and complete comparison of nutrient and DOM yields between paired glacial and non-glacial watersheds. Continuous measurements of discharge, oxygen, temperature and turbidity will be used to quantify the effects of glacial meltwater on hydrologic and physical parameters. Experimental approaches (laboratory and field-scale) combined with longitudinal surveys and stream tracers will be used to elucidate the fate of nutrients and DOM during downstream transport. Finally, longitudinal synoptics and source sampling will also be used to access the primary landscape sources of nutrients and carbon to the stream. Ultimately, project findings will provide new insights into how land-to-ocean fluxes of organic and inorganic nutrients are being altered by glacial recession along the GOA and in other glaciated coastal regions. The project will provide laboratory and field research opportunities for undergraduates at the University of Alaska Southeast (UAS), a small, undergraduate university with a high (16%) enrollment of native Alaskan students. Additionally, the project will provide training for one graduate student and one post-doctoral researcher. The integration of undergraduate students in this research project will provide a framework for students and researchers to cooperatively investigate important linkages among climate, landcover change, and hydrological and biogeochemical processes in coastal watersheds. In addition, the project will strengthen an existing partnership between scientists at UAS and naturalists at the Mendenhall Glacier Visitor Center who will work collaboratively to incorporate project results into an interpretive display at the center. The Mendenhall Glacier is the most visited glacier in the United States and hosts over 300,000 visitors each year and thus provides a unique and effective opportunity for public outreach and education related to the findings of this project. Finally, a science educator from Montgomery County, VA will partake in field work during one of the summers. The science educator will bring their experience into the local classrooms and share their experience with their peers.
Glaciers currently cover about 20% of the land area along the Gulf of Alaska and the majority of these glaciers are thinning and retreating. The goal of our project was to study how the hydrology and chemistry of rivers and streams in Alaska will be impacted by the loss of glaciers. The major scientific findings of our project were as follows: 1) Glaciers make a significant contribution to the amount of freshwater that flows from rivers and streams into the Gulf of Alaska (GOA). We showed that almost half of the water the flows into the GOA consists of runoff from glaciers. Glaciers in Alaska are changing rapidly, which will result in changes in the amount of freshwater flowing into the GOA. This is important because freshwater flow into the GOA controls the strength of the Alaska Coastal Current which, in turn, influences oceanographic conditions in the productive near-shore waters of the GOA. 2) The chemistry and nutrient content of glacier meltwater is fundamentally different from water in forested streams. As a result, the chemistry of streams and the nutrient loads delivered to the coastal ocean will change as glaciers disappear from watersheds in Alaska. One example is that our work demonstrated glacier meltwater can be an important source of phosphorus and iron to downstream ecosystems that receive streamflow from glaciers. This is important because phosphorus and iron are both important contributors to primary productivity (the growth of phytoplankton) in aquatic ecosystems. 3) Glaciers are much more biologically active than previously thought and microbial communities on glaciers can impact the chemistry and nutrient content of glacial meltwater. In addition, we showed for the first time that glacier melt can be an important source of organic carbon to streams and estuaries. We found that the organic carbon coming from glaciers is very bio-available meaning that it can be readily consumed by microbial organisms in the water. This is important because organic carbon supports productivity at the bottom of the aquatic food chain. 4) Glaciers have a pronounced impact on both the amount and temperature of water flowing in streams that receive glacier melt. In particular, glaciers can contribute meltwater and keep water temperatures cool during warm, dry periods in the summer months. Thus, changes in glacier extent and volume will alter the temperature regime of streams and rivers downstream from the glaciers. This is important because water temperature is a master variable that controls many ecological processes in freshwater ecosystems. One example is that salmon require cool, well oxygenated water in their spawning streams. In addition to our scientific work, our project conducted a wide variety of education and outreach activities. The project provided research and training opportunities for nine undergraduate students, one PhD graduate student, one high school student, and one postdoctoral scholar. All of the participants in the research participated in lab and field research and received training in hydrologic and biogeochemical techniques. We also brought an elementary teacher from Virginia to Alaska to participate in the project and she took her experiences back to her school and incorporated them into lesson plans being used in her school district. We conducted several public outreach lectures to audiences in Alaska and presented our findings to the interpreters at the Mendenhall Glacier Visitor Center during their annual training. These interpreters interact with about 350,000 visitors each year. Overall, our project provided a host of novel information about how runoff from glaciers influences the hydrology and chemistry of downstream rivers and estuaries. The information from our project will contribute to understanding how ongoing changes in glaciers will impact a variety of economically important activities including: coastal fisheries in areas that receive runoff from glaciers, habitat in salmon spawning streams, and hydropower resources in watersheds that have glaciers.
