REFLECTIVE SPECTROSCOPY TO SUPPORT ENVIRONMENTAL MONITORING IN A UNIQUE COASTAL ENVIRONMENT AT GUANAJIBO RIVER, MAYAGÜEZ, PUERTO RICO

Environmental studies of coastal settings are important to help predict and understand changes and redistribution of pollutants as sea levels rise. This would allow tracking of overall improvements or increases in pollution, and better support recovery efforts in the event of disasters. Hyperspectral remote sensing or image spectroscopy (HRS/IS) is a technique that could be used to monitor or assess pollution in coastal settings. This technique is best applied if there are samples that are characterized from the region. The Guanajibo River and associated coastal setting is an example of a complex environment in Puerto Rico, and was chosen for study owing to its unique sand mineralogy, the occurrence of a single river delta environment, and observed pollution issues. Olivine, pyroxenes, and oxides dominate the sands of the site and have a dark green to brown to black appearance. Extensive plastic as well as vehicle tires were observed and are attributed to waste being derived from the river and local dumping at the shore. The coastal environment at Guanajibo, Puerto Rico presents a challenging environment to detect plastics using HRS/IS owing to the overall dark or low reflectance expected. A collection of plastic debris was obtained from field sampling efforts at the site in January 2024. The area was photographed and significant amounts of tire waste were observed. Reflective spectra of sand samples are nearly uniform and nearly featureless with total reflectance at approximately 4-7%. Multiple reflective spectra of a new tire were acquired and used as an analog for tires observed in the field. The spectra of the tire were nearly featureless with a low total reflectance of approximately 3-5% and did not show any NIR or SWIR features. Reflective spectra from various plastic debris were distinct, with several observable features enabling discrimination from the sand substrate. These initial results integrate with ongoing studies of pollutants in coastal settings of Puerto Rico to provide new constraints for the potential of HRS/IS for pollution studies in the region.