Water Sources and Hydrodynamics of Closed-Basin Depressions, Cook Inlet Region, Alaska

摘要

Among the most prevalent wetland and deep-water habitats in Alaska are ponds, many of which are subarctic ponds occurring as moraine, ice-scour, or dead-ice depressions. Many are closed-basin depressions, where surface-water inflows and outflows are negligible. The objective of this study was to quantify the water sources and hydrodynamics of these subarctic ponds, particularly with respect to the role they play in groundwater recharge. There are two types of ponds on the study site. Perched-precipitation ponds have inflows by melt water and direct precipitation, outflows by evapotranspiration and ground-water recharge, and are seasonally inundated because surface water is perched above the water table and infiltration through the low-permeability surficial deposits to the water table is slow. Flow-through ponds have inflows by melt water, direct precipitation, and groundwater discharge, outflows by evapotranspiration and groundwater recharge, and are perennially inundated because of ground-water throughflow. Both are groundwater recharge focal points. This is particularly true for perched-precipitation ponds, where net groundwater recharge rates were 215% larger than in flow-through ponds, and 332% larger than in the broader landscape. Most of the additional groundwater recharge occurs immediately following breakup, as aeolian-transported snow trapped in the depressions melts which results in enhanced groundwater recharge rates.