Wetlands of Cook Inlet Basin, Alaska: Classification and Contributions to Stream Flow

Abstract

Wetlands face threats from global change, even as protections have been institutionalized to conserve the amenities they provide. These institutional protections frequently rely on a wetland classification system to guide conservation. In the Cook Inlet Basin of Alaska, USA (CIB), for example, best wetland assessment practices require the use of a classification system to ensure the conservation of the most valuable amenities. However, the systems used widely in the USA outside of Alaska, where peatlands are not common, inadequately describe the diversity of peatlands on the glaciated landscape of the CIB. Here I present a new Cook Inlet Classification system (CIC) organized around the hydrogeologic settings of wetlands in the CIB. The variables most strongly correlated with ecological differences within major geomorphic classes were used to construct a system supported by ample field data. The CIC produced greater within-class similarity than other widely-used systems, likely due to the overriding importance of the seasonal variability of water levels in CIB peatlands. The CIC has been mapped over an area of 7600 km2 and has guided wetland functional assessments in the CIB, and may be adaptable to any region supporting peatlands on glacial landforms. The harmful effects of a warming climate on aquatic resources may be partially ameliorated by discharge of shallow groundwater from peatlands to streams. This potential benefit of peatlands was investigated in the CIB using end-member mixing analysis (EMMA) and a sensitivity analysis of a water budget to quantify the contribution from extensive peatlands formed over glacial lake deposits to stream flow during the dry-season. Although peatlands in this hydrogeologic setting are common globally, the discharge from them is challenging to quantify. A spatially distributed sampling protocol at a single point-in-time produced a reliable EMMA showing that over half of stream flow on a day during the summer dry period originated near the surface of peatlands. This finding is being used to establish the value of peatlands for buffering increases in stream temperature, which have exceeded tolerances of commercially important fishes in the CIB. The analysis also suggests that differences in hydrogeologic setting influence shallow groundwater hydrology in peatlands.