Water Resources Research Act Program

Details for Project ID 2016GU299B

Identification and Delineation of Land-Based Mercury Sources Impacting Fisheries in the Southern Central Coastal Region of Saipan Lagoon

Institute: Guam
Year Established: 2016 Start Date: 2016-03-01 End Date: 2017-02-28
Total Federal Funds: $37,823 Total Non-Federal Funds: Not available

Principal Investigators: Gary Denton, Michael Trianni, Michael Tenorio, Hyun-Jong Hahm

Abstract: The southern half of Saipan Lagoon is heavily impacted by urban runoff that primarily flows from roads (paved and unpaved) and properties (residential and commercial) within 0.5 km of the coast. Frequent mercury detections have previously been reported in discharges from several stormdrains in this part of the lagoon (Environet Inc. 2007). Such findings are unusual because mercury is rarely detected in runoff outside of industrialized areas (USEPA 1983). The highest level recorded was 150 ng/L, which again is remarkable given that detectable levels in runoff seldom exceed 0.01 ng/L (Morace 2012). Denton et al. (2014) noted unusual mercury distribution patterns in sediments from the lagoon's southern waters and concluded that inputs washed into the ocean from land-based sources were superimposed upon a scattering of mercury contamination emanating from within the lagoon itself. They attributed their findings to the extensive use of mercury in artillery shells and other explosive devices manufactured during WWII, and to the heavy shelling of Japanese defenses positioned along the shoreline of the lagoon prior to the US invasion in 1944. Continuing mercury releases from corroding munitions left behind after the war most likely account for the Environet findings noted above. The aftermath of these cataclysmic wartime events on fisheries in the lagoon is currently unknown although an earlier study revealed elevated mercury concentrations in a popular table fish (Lethrinus atkinsoni) from a 3-km stretch of coastline just north of the invasion beaches (Denton et al. 2010). Levels encountered here were higher than in the same species and a close relative (L. harak) from waters further north in the lagoon. They were also sufficient to issue an advisory warning against the unrestricted consumption of fish from the offending region (Bearden et al. 2010). Concerns over the possibility of even higher mercury levels in fish from the invasion beach area seemed justified under the circumstances and prompted further testing by WERI. However, nothing out of the ordinary has so far been found (Denton et al.2015). The study proposed here seeks funding to revisit the 3-km coastal strip from whence the earlier contaminated fish were captured and identify the primary source or sources of mercury impacting them. The study will initially focus on a smaller targeted area determined by reference to the earlier Environet and WERI studies (Environet Inc. 2007; Denton et al. 2014). Thus we will examine mercury levels in surface deposits from coastal drainage pathways and discharge points between Gualo Rai Road and Quartermaster Road. This is a distance of approximately 1.5 km. We will then track backwards from any identified points of enrichment and proceed along any discovered concentration gradients in order to pinpoint the source(s) of contamination. We will also reexamine mercury levels in marine sediments from suspect discharge points and continue to collect fish for analysis from immediately adjacent nearshore waters. The assistance of local personnel and other government agencies in procuring samples from this region will be obtained where necessary. The primary objectives of the study are to: a) determine mercury concentrations in surface deposits from stormwater drainage pathways servicing the Gualo Rai area; b) back-track along obviously enriched pathways to pinpoint sources of contamination within the watershed; c) delineate the extent of contamination in the lagoon target area (via sediment analysis) and evaluate the impact on popular table fish with bioindicator potential; and d) weigh the fish data against established USEPA benchmarks to determine potential health risks and advisable maximum monthly consumption rates.