Explaining Wetland Inundation Dynamics by Catchment Hydrology

Inundation and saturation dynamics of wetlands (i.e., hydroperiod) is the key abiotic factor that controls the extent and ecosystem functioning of wetlands. This dynamics can inform changes in hydrological responses due to climate and land use changes from the landscape unit and may reveal the hydrological connectivity with downstream and catchment hydrology. Wetland inundation is highly dynamic and varying at multiple temporal scales. Little information is available to characterize this dynamics at the landscape scale and to study hydrological linkage to catchment and downstream. Here we have produced new wetland inundation maps using time-series Landsat observations over last two decades. These maps showed inter-annual inundation dynamics of forested wetlands at a very high spatial resolution (30-m). They were the headwater wetlands, located in Choptank Watershed in the coastal plain of the Chesapeake Bay Region. They were mostly depressional wetlands and believed to be isolated from each other and other water bodies. The derived inundation maps were validated against field observation and highly accurate inundation percentage maps derived from LiDAR intensity data. The relationship between the temporal trend of wetland inundation, the local climate, and catchment hydrology was examined. As inundation dynamics from multiple wetlands vary across the landscape, their change patterns were characterized according to the Hydrologic Modifiers of the National Wetland Inventory (NWI) using Geographic Information Systems. The results showed the wetland inundation trend reflected the climatic condition and were highly highly correlated with catchment streamflows. Wetter wetlands (with longer duration of wetness) exhibited stronger relationship with catchment streamflow, particularly due to base flows. This study showed the promise of predicting inundation dynamics of wetlands at a landscape scale using satellite observation. It demonstrates the hydrological linkage between headwater wetlands and catchment streamflow, particularly due to baseflows, emphasizing the importance of protection of wetlands regardless of obvious surface water connection to the streams.