USGS Researchers Collaborate with National Park Service Scientists to Understand the Impact of Watershed Erosion on Coral Reefs in War-in-the-Pacific National Historical Park, Guam


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USGS Researchers Collaborate with National Park Service Scientists to Understand the Impact of Watershed Erosion on Coral Reefs in War-in-the-Pacific National Historical Park, Guam

By Curt Storlazzi
October 2007

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Above: View of the Asan Unit of War-in-the-Pacific National Historical Park, which extends from this viewpoint approximately 2 km offshore. Sediment exposed by the landslides visible in the photograph is transported down to the fringing coral reef by the Asan River, which runs through Asan village in the center of the photograph. Photograph by Curt Storlazzi. [larger version]

Above: Guam, showing the six units of War-in-the-Pacific National Historical Park (red). An interactive map of the park is posted on the War-in-the-Pacigic Web site. [larger version]

Above: Josh Logan deploying a wave/tide gauge and temperature/salinity sensor. Because of the complex bathymetry and delicate nature of coral-reef environments, the scientists must deploy instruments using scuba gear and lift bags (yellow) to avoid damaging the corals or the instruments. Water depth is approximately 10 m (33 ft). Photograph by Curt Storlazzi. [larger version]

Above: One of two dozen U.S. Marine Amtrac (assault amphibious tractor) landing craft that sank off Agat beach during the invasion on July 21, 1944. Most of these landing craft were destroyed by a Japanese gun emplaced in a hardened concrete bunker that still stands at Ga'an Point in War-in-the-Pacific National Historical Park's Agat Unit. Water depth is approximately 13 m (42 ft). Photograph by Curt Storlazzi. [larger version]

Above: Two World War II artillery shells, outlined in yellow, in a previously unmapped field of unexploded ordnance near one of the USGS instrument sites in War-in-the-Pacific National Historical Park. Water depth is approximately 20 m (66 ft). Photograph by Curt Storlazzi. [larger version]

Guam, the largest of the Mariana Islands and an American territory since the end of the Spanish-American War in 1898, had quickly and easily fallen into Japanese hands in the early morning of December 10, 1941, putting approximately 20,000 Chamorros (natives of Guam) and U.S. citizens under the flag of the Rising Sun. Two and a half years later, on the morning of July 21, 1944, first elements of the U.S. 3rd Marine Division landed at Asan, Guam, and lead assault troops of the U.S. 1st Provisional Marine Brigade landed at Agat, about 10 km to the south, on the other side of Apra Harbor. These 30,000 Marines faced 18,500 Japanese defenders entrenched in caves, pillboxes, and bunkers on the island. The battle for Guam lasted a month and cost more than 12,000 American and Japanese lives. In commemoration of the United States and Guam's involvement in World War II, the National Park Service (NPS) established War-in-the-Pacific National Historical Park in 1978. The park, which honors the bravery and sacrifice of those participating in the campaigns of the Pacific Theater of World War II, seeks to conserve and interpret outstanding natural, scenic, and historic values and objects on the Island of Guam (see URL http://www.nps.gov/wapa/). The two beaches where the U.S. Marines landed at Asan and Agat were incorporated as the two largest (of six total) units in the park; the other four units are old Japanese defensive positions in the hills overlooking west-central Guam.

War-in-the-Pacific National Historical Park comprises 926 acres of land and 1,002 acres of marine waters. The marine waters are home to more than 3,500 marine species and 200 species of coral, giving the park one of the highest levels of species diversification within the National Park system. Corals generally need clear, oligotrophic waters (low in nutrients and suspended sediment). Human activity has significantly increased the rate of sedimentation along many areas of Guam's coastline, including within the park. These human activities are related primarily to land-management practices, including urban development, unregulated use of off-road vehicles, and illegal wildfires. The wildfires, which are intentionally set by hunters to clear lines-of-sight and draw in new game, remove the grasses and small trees that stabilize the soil. Typhoons strike Guam frequently, commonly dropping more than 30 cm of rain in 24 hours and flushing the unstabilized soil down to the coast and into the park's waters. Studies by the park's Natural Resource Division staff have shown that

soil loss from burned areas is nearly sixfold higher than from vegetated areas,
sediment-collection rates in tube traps on the park's fringing reef are very high,
the trapped material is composed dominantly of fine terrestrial sediment, and
trap-collection rates vary widely.

Their work further shows that the input of terrestrial sediment to the park's nearshore waters is greater during the wet season (July-December), which coincides with peak coral spawning and larval settlement.

In 2006, War-in-the-Pacific National Historical Park asked the U.S. Geological Survey (USGS) to develop studies that would provide quantitative information about the deposition, residence time, and movement of fine terrestrial sediment through the park's fringing coral-reef system, so that the NPS can better manage the park's marine resources. The USGS Coral Reef Project established a plan with NPS, and in July 2007, Curt Storlazzi, Josh Logan, and Kathy Presto (USGS, Santa Cruz, California), along with Greg Piniak (National Oceanic and Atmospheric Administration [NOAA], formerly a USGS Mendenhall Postdoctoral Research Fellow in Santa Cruz), traveled to Guam to conduct a cooperative study with NPS for increasing our understanding of geologic and oceanographic processes on Guam's coral reefs. Storlazzi, Logan, Presto, and Piniak worked with the park's Natural Resource Division scientists Allison Palmer and Holley Voegtle to scout out sites for USGS and NPS oceanographic and terrestrial instrument packages. Over the next 2 weeks, the USGS team installed seven benthic instrument packages, three moorings, a terrestrial digital-camera system, a weather station, and a stream gauge in the park. These instruments will provide quantitative time-series measurements (measurements collected at regular time intervals) of oceanographic processes (currents, surface waves, internal waves), meteorologic forcing (winds, rainfall, barometric pressure), and water-column properties (temperature, salinity, turbidity, photosynthetically available radiation). This study will last 7 months, and the results will be used to identify flow and transport patterns under various forcing conditions.

USGS staff will return to Guam in late October to recover the instruments, download data, and refurbish and redeploy the instruments until the end of the typhoon season in January. This work will be another chapter in ongoing USGS research to investigate the impact of land-based pollution on coral reefs in the United States and U.S. Trust Territories (see URL http://coralreefs.wr.usgs.gov/sediment.html), and will build on continuing USGS-NPS multidisciplinary cooperative coral-reef research efforts (see NPS Web page on coral at URL http://www.nature.nps.gov/water/coral.cfm). This experiment will also provide NPS with quantitative baseline data to compare with possible future measurements during the planned large-scale expansion of U.S. military installations at Apra Harbor, less than 2 km from the park. Furthermore, this work will address shared objectives with the U.S. Coral Reef Task Force (USCRTF)'s Guam Local Action Strategy (LAS; scroll down to factsheet link at URL http://www.coralreef.gov/las/), which designated the Asan watershed as one of its five priority watersheds for study. USGS researchers, along with the NPS staff, hope to continue this cooperative-science program on behalf of the coral reefs and reef ecosystems in one of our Nation's historic battlegrounds.

During the USGS scientists' time on Guam, they experienced several interesting events. Just before the group arrived, Super Typhoon Man-Yi passed Guam with 140- to 160-mph winds and 35-ft waves that caused several ships (including a 530-ft container ship) to sink in the Philippine Sea to the west of Guam; during their first days on the island, the USGS researchers frequently saw U.S. Coast Guard aircraft performing search-and-rescue operations. During instrument deployment inside the park on July 18, the USGS group discovered an unmapped field of unexploded ordnance, consisting of artillery shells left over from World War II. On July 20, a magnitude 5.0 earthquake struck the Mariana Trench just 20 mi east of where the USGS scientists were staying. The following day, July 21, was the 62nd anniversary of the landing of U.S. Marines, celebrated in west-central Guam with an annual Liberation Day parade. This year's parade included numerous floats, two local mayors riding a carabao (a Guamanian water buffalo), and a flyover at low altitude by U.S. bombers, fighters, and helicopters out of Andersen Air Force Base and Naval Base Guam.

Sediment on Coral Reefs
USGS (U.S. Geological Survey)

War in the Pacific National Historical Park
National Park Service

Coral Reefs in the National Parks
Nation Park Service