Surface hydrology of an arctic ecosystem: Multiscale analysis of a flooding and draining experiment using spectral reflectance

In the Arctic, surface hydrology plays an important role in controlling plant community composition and ecosystem processes such as land-atmosphere carbon and energy balance. Investigating how climate change in this region will affect surface hydrology and subsequent biotic, atmospheric, and climatic feedbacks could be key to understanding the future state of the Arctic and Earth systems. Improved methods for monitoring surface hydrology at large spatial scales are needed in the Arctic. Near Barrow, Alaska, a large-scale experiment with flooded, drained, and control treatment areas, each exceeding 9 ha, was initiated during summer 2008 following 3 years of monitoring under nonmanipulative conditions. Throughout the 2008 growing season, hyperspectral reflectance data were collected in the visible to near-infrared (IR) range using a 300 m long robotic tram system. Water table depth, surface water depth, and percent surface water cover were also measured. A spectral index (Normalized Difference Surface Water Index (NDSWI)) was developed using reflectance in the IR region (R-1000 strong absorbance) and blue region (R-460 poor absorbance). NDSWI was strongly correlated with both surface water depth and surface water cover, and was used to monitor spatial and temporal patterns of surface hydrology in the experimental treatment. Using 2002 and 2008 Quickbird satellite imagery, the index was also used to examine differences in NDSWI between experimental treatments. Using this approach, we demonstrate that the flooded treatment was significantly different from the other two treatments (drained and control) and that the new index can be used to monitor surface hydrology in arctic wetlands.