Assessment of the water quality and habitat functions of natural, restored, and created wetlands of the Hawaiian Islands

Natural wetlands (NWs) exhibit water quality benefits at the watershed scale, such as trapping sediment, sorbing phosphorus, and promoting denitrification.  As various species depend upon wetlands for all or part of their life cycles, they also provide critical habitat for waterfowl and fish, many of which are endemic.  Urban development, highway construction, conversion to agriculture and aquaculture, and introduced species have all contributed to the degradation and loss of wetlands across the Hawaiian Islands.  Currently numerous wetland restoration and creation projects are being undertaken across the state of Hawai’i by an array of governmental, non-governmental organizations, and private land owners.  It remains to be seen, however, if restored (RWs) and created wetlands (CWs) actually provide similar water quality and habitat functions as the NWs they were designed to replace.  We addressed this issue with an assessment of the water quality and habitat functions of RWs, CWs, and NWs of the Hawaiian Islands.  We assessed these functions with an innovate, interdisciplinary approach that involved sampling surface water quality (conductivity, pH, salinity, total nitrogen, nitrate-nitrogen, ammonium-nitrogen, and total phosphorus), soil properties (moisture, pH, texture, total carbon and nitrogen, extractable phosphorus), vegetation (percent cover), and fish community composition of a representative selection of 40 sites on Hawai’i, Kauai, Maui, Moloka’i, and Oahu in the spring of 2007.  Results indicated that the majority of coastal lowland wetland sites, including those within the most remote, undeveloped watersheds were dominated by invasive vegetation and fish species.  There were significant differences in water quality and soil properties within sites (i.e. across hydrologic gradients) and among different types of sites (i.e. freshwater versus brackish, and CW versus RW versus NWs).  This is the first comprehensive ecological inventory of coastal lowland wetlands in Hawai’i.  These results will lay a foundation for the development of biocriteria for wetlands in Hawai’i.