Do algae facilitate wetland development in high latitude regions

Wetlands are the dominant land cover type in Alaska and are critical migratory waterfowl breeding and nesting grounds.  Climate warming is particularly evident in high latitude regions and has been correlated with a decrease in surface area of lakes in interior Alaska wetlands since 1950.  However, despite a net decrease in total surface water area of lakes, some lakes have remained stable since 1950.  Understanding the mechanisms behind this heterogeneity is essential in order to identify the implications of lake drying to wetland habitats and to predict future changes.  Using estimates of lake drying based on remotely sensed imagery from 1950 to present, we selected 12 lake pairs consisting of drying and nondrying lakes to study the mechanisms behind lake drying in the Yukon Flats National Wildlife Refuge, Alaska.  Our field observations indicate that lake drying involves the encroachment of a floating mat of vegetation which is a stage in the process of wetland formation due to terrestrialization.  Drying lakes with extensive floating mat vegetation supported greater algal primary productivity with large masses of N-fixing cyanobacteria, and higher concentrations of N than lakes that have not dried. We hypothesize that N-fixing cyanobacteria may facilitate lake terrestrialization by increasing sediment quality and stimulating growth of floating mat vegetation.  This scenario presents a potential negative feedback on global warming, whereby increased N-fixation by algae promotes long-term C sequestration by mosses and vascular plants in interior Alaska wetlands.