Water Resources Research Act Program

Details for Project ID 2017GU316B

Impact of Stormwater from a Constructed Wetland in American Memorial Park, Saipan, CNMI, on Receiving Waters and Fisheries Resources

Institute: Guam
Year Established: 2017 Start Date: 2017-03-01 End Date: 2019-02-28
Total Federal Funds: $69,009 Total Non-Federal Funds: Not available

Principal Investigators: Gary Denton

Project Summary: The American Memorial Park (AMME) is a 54 ha parcel of land that borders the central region of Saipan Lagoon. The park was established 1978 under the Administrative oversight of the National Park Service (NPS). In the 1990s, an artificial wetland was created in the park to redirect floodwaters from the Garapan commercial center into the ocean. Overflow from this wetland discharges into a shallow coastal embayment adjacent to Micro Point. The bay is partially enclosed by land and land-based structures and as a consequence water movement within it is highly restricted. Two emperor fish (Lethrinus harak) recently analyzed from these waters yielded mercury levels that were remarkably high. WERI has acquired an extensive mercury database for this species over the years (Denton et al. 2010) and the two recent additions are substantially higher in this element than similar sized individuals analyzed to date. Based on these preliminary findings, it is postulated that sediments within the embayment act as a permanent sink for recalcitrant contaminants flushed into the system from the AMME constructed wetland. Mercury is rarely detected in urban runoff (USEPA 1983), although in Saipan it is frequently encountered in stormwater discharges (Environet 1977). This is believed to reflect the widespread use of fulminated mercury in WWII munitions during the US invasion (Denton et al. 2014). Soils throughout the park also carry a mercury footprint (own unpublished data) associated with the detonation and disposal of residual munitions on the property immediately after WWII (AMPRO 2005). Much of the Garapan area was also contaminated with mercury residues linked to a nearby medical waste incinerator that operated for over 20 years before it was shut down in 2006 for violations of the Clean Air Act (Denton et al. 2011a). The mild mercury enrichment previously determined by WERI in stream deposits from the constructed wetland (own unpublished data) is, therefore, not surprising. This project will evaluate the mercury sequestering capacity of the embayment sediments and extend the fish monitoring program for emperor fish in this area. To this end surface sediments will be collected for analysis at 25-m intervals around the perimeter of the embayment and along 5 linear transects extending out from Micro Point in a northwesterly direction towards the marina causeway. The primary objectives of the study are to: a) identify and delineate hitherto unknown mercury distribution patterns in surface sediments from within the study area; b) determine the collective impact these environmental levels have on the edible quality of popular table fish harvested from the area; c) evaluate potential health risks (if any) associated with unrestricted consumption of these fish and, if necessary make recommendations to extend the survey at some later date to include other fisheries resources taken from these waters; d) provide additional data that will assist with the identification and delineation of areas of contaminant enrichment within Saipan Lagoon, and e) enhance ongoing marine water quality monitoring and sustainable management activities, and the formulation and development of pollution mitigation strategies for Saipan’s coastal waters.