LAKE AREA CHANGE IN ALASKAN NATIONAL WILDLIFE REFUGES: MAGNITUDE, MECHANISMS, AND HETEROGENEITY A DISSERTATION Presented to the Faculty of the University of Alaska Fairbanks In Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Jennifer Roach, B.S. Fairbanks, Alaska December 2011 iii Abstract The objective of this dissertation was to estimate the magnitude and mechanisms of lake area change in Alaskan National Wildlife Refuges. An efficient and objective approach to classifying lake area from Landsat imagery was developed, tested, and used to estimate lake area trends at multiple spatial and temporal scales for ~23,000 lakes in ten study areas. Seven study areas had long-term declines in lake area and five study areas had recent declines. The mean rate of change across study areas was -1.07% per year for the long-term records and -0.80% per year for the recent records. The presence of net declines in lake area suggests that, while there was substantial among-lake heterogeneity in trends at scales of 3-22 km a dynamic equilibrium in lake area may not be present. Net declines in lake area are consistent with increases in length of the unfrozen season, evapotranspiration, and vegetation expansion. A field comparison of paired decreasing and non-decreasing lakes identified terrestrialization (i.e., expansion of floating mats into open water with a potential trajectory towards peatland development) as the mechanism for lake area reduction in shallow lakes and thermokarst as the mechanism for non-decreasing lake area in deeper lakes. Consistent with this, study areas with non-decreasing trends tended to be associated with fine-grained soils that tend to be more susceptible to thermokarst due to their higher ice content and a larger percentage of lakes in zones with thermokarst features compared to study areas with decreasing trends. Study areas with decreasing trends tended to have a larger percentage of lakes in herbaceous wetlands and a smaller mean lake size which may be indicative of shallower lakes and enhanced susceptibility to iv terrestrialization. Terrestrialization and thermokarst may have been enhanced by recent warming which has both accelerated permafrost thawing and lengthened the unfrozen season. Future research should characterize the relative habitat qualities of decreasing, increasing, and stable lakes for fish and wildlife populations and the ability of the fine- scale heterogeneity in individual lake trends to provide broad-scale system resiliency. Future work should also clarify the effects of terrestrialization on the global carbon balance and radiative forcing. v Table of Contents Page Signature Page ..................................................................................................................... i Title Page ............................................................................................................................ ii Abstract .............................................................................................................................. iii Table of Contents ................................................................................................................ v List of Figures .................................................................................................................... xi List of Tables ................................................................................................................... xiv List of Appendices .......................................................................................................... xvii Acknowledgements ........................................................................................................ xviii Chapter 1: General Introduction .................................................................................... 1 References ..................................................................................................................... 4 Chapter 2: Mechanisms influencing changes in lake area in Alaskan boreal forest .. 7 Abstract ......................................................................................................................... 7 Introduction ................................................................................................................... 8 Heterogeneous Changes in Lake Area .................................................................... 9 Potential Sources of Heterogeneity ........................................................................ 9 Study Design ......................................................................................................... 11 Materials and Methods ................................................................................................ 13 vi Page Study Design ......................................................................................................... 13 Study Areas ........................................................................................................... 14 Lake Area Change Analysis and Lake Pair Selection .......................................... 14 Scenario Expectations ........................................................................................... 16 Variable 1: 18O Enrichment ............................................................................ 17 Variable 2: Electrical Conductivity ................................................................ 19 Variable 3: Surface:Volume Index ................................................................. 20 Variable 4: Bank Slope ................................................................................... 21 Variable 5: Floating Mat Width ...................................................................... 22 Variable 6: Peat Depth .................................................................................... 22 Variable 7: Thaw Depth at Shoreline .............................................................. 22 Variable 8: Thaw Depth at Forest Boundary .................................................. 24 Supplemental Variable 9: Tree Age ................................................................ 24 Transect Sampling ................................................................................................ 25 Statistical Analysis of Differences in Lake Characteristics .................................. 28 Results ......................................................................................................................... 30 Discussion ................................................................................................................... 34 Acknowledgements ..................................................................................................... 41 References ................................................................................................................... 41 vii Page Chapter 3: Comparison of three methods for estimating number and area of boreal lakes from TM/ETM+ Landsat imagery ...................................................................... 73 Abstract ....................................................................................................................... 73 Introduction ................................................................................................................. 74 Objectives .............................................................................................................. 76 Methods....................................................................................................................... 77 Study Area ............................................................................................................. 77 Imagery ................................................................................................................. 77 Classification Methods.......................................................................................... 78 Training Data........................................................................................................ 79 Quantitative Method/Band Combination Comparisons........................................ 81 Evaluation of Method Performance ................................................................ 81 Statistical Analyses ......................................................................................... 83 Minimum Size Criteria ................................................................................... 84 Comparison of Methods After Applying Optimal Minimum Size Criteria .... 86 Qualitative Comparisons ...................................................................................... 87 Results ......................................................................................................................... 87 Quantitative Method/Band Combination Comparisons........................................ 87 Comparison of Band Combinations ................................................................ 87 Comparison of Three Methods ....................................................................... 89 Minimum Size Criteria ................................................................................... 90 viii Page Comparison of Methods After Applying Optimal Minimum Size Criteria .... 90 Qualitative Comparisons ...................................................................................... 91 Discussion ..................................................................................................................