| Summary: | The goal of this project is to assess how geomorphology and seasonal changes in the thawed region of soil and sediment around the open channel (i.e. the thaw bulb) control hydraulic and biogeochemical dynamics in the hyporheic zone of Arctic streams. Our premise is that a) stream geomorphology sets a physical template that controls the seasonal development of the sub-stream active layer around Arctic streams, b) the thaw bulb extent controls the potential for development of the hyporheic zone, and c) the hyporheic zone substantially contributes to C, N, and P processing in streams. We expect that climate change in the Arctic has the potential to significantly alter the thaw bulb and hyporheic dynamics through its influences directly on precipitation, runoff, average annual temperature, and thaw season duration, as well as indirectly on stream geomorphology. To address this central hypothesis we propose four objectives: 1. Select and characterize stream reaches that represent the range of geomorphic conditions in rivers of the North Slope. 2. Monitor the sub-stream thaw bulb size through the thaw season using ground penetrating radar and subsurface temperature measurement in several stream cross-sections within each reach. 3. Conduct repeated hyporheic exchange studies (stream solute addition experiments) through the thaw season in each reach to determine hyporheic hydraulic characteristics. 4. Conduct repeated measurements of nutrient (N and P) concentrations and turnover time in the hyporheic zone through the thaw season in each reach to determine biogeochemical characteristics. These objectives will be addressed through a combination of field monitoring (thermistor arrays and hyporheic sampling), field experiments (solute additions), and modeling (groundwater transport and transient storage) efforts. This proposed activity is important because there is virtually no reported literature on the structure and functions of the hyporheic zone in Arctic systems. Furthermore, considerable research in temperate regions suggests that hyporheic zones are critical components of stream ecosystems. Thus, research on this subject will provide direct input to our understanding of the hydrological and ecological functions of Arctic streams.
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