Graduate Thesis Defense
|Title:||Shrinking boreal lakes as agents of change: Untangling structure and function in hydrologically-coupled lakes and wetlands|
|Date:||Friday, 27 October 2017|
|Location:||Murie Bldg, rm 107|
|Major Professor:||Brad Griffith and Eugenie Euskirchen|
Widespread lake shrinkage has occurred over the last 30 years throughout interior Alaska and other boreal regions. This trend has been broadly linked to climate change, via multiple proximate drivers including permafrost thaw, shifting water balance, and terrestrialization caused by peat growth. The ecological effects of shrinking boreal lakes are still poorly understood. I used space-for-time substitution based on field surveys from a spatially balanced random sample of lakes (n=130) to examine the implications of shrinking lakes in the lowland floodplain of the Yukon River within the Yukon Flats National Wildlife Refuge in northern Alaska. Historical lake shrinkage over the last 30 years increased plant functional diversity, woodiness and aboveground biomass in lake-margin wetlands, despite a significant loss of wetland and lake area, and shrinking lakes were associated with decreased hydrological connectivity and organic matter inputs from wetlands into lakes. However, lake shrinkage trends alone could not explain the majority of observed spatial variation in wetland size and wetland characteristics, suggesting that the effects of lake change may be overwhelmed by fire history, wetland community functional traits, and other aspects of a lake’s landscape context. Net change in carbon stocks could not be projected with certainty due to limited available data on lake sediment carbon. However, a synthesis of recent literature and results from this project suggested that current rates of lake shrinkage in some regions of boreal Alaska could lead to an order-of-magnitude decrease in soil organic carbon stocks if sustained over the next 100 years. Lake shrinkage will most likely affect plant and animal biodiversity, habitat quality, and carbon storage in contrasting ways, and management of drying landscapes may require difficult trade-offs to be made as a result. These decisions would be aided by process-based modeling that accounts for the role of plant functional traits and explicitly represents hydrological interaction between terrestrial and freshwater ecosystems.