REFLECTANCE VARIATIONS OF PUERTO RICAN MANGROVES ASSOCIATED TO HEAVY METAL CONTAMINATION

Remote sensing techniques have been frequently used to monitor vegetation in coastal environments. Also, several authors have shown that high concentrations of heavy metals change the spectral reflectance of mangrove leaves. However, spectral studies in mangroves of Puerto Rico are limited. Therefore, this study aimed to retrieve information concerning variation in leaf reflectance of these ecosystems related to the presence of heavy metals. Such correlation was evaluated in three mangrove sites along the coast of Puerto Rico (Guánica, Arecibo, and Cabo Rojo). Chemical analyses for sediments and mangrove leaves were done for Cd, Cu, Ni, Cr, Pb, Zn and Co using digestion with nitric acid (HNO₃) and an air-acetylene flame detection Atomic Absorption Spectrophotometer (AAS). Leaves reflectance was measured in situ using the GER-1500 spectroradiometer. The Normalized Difference Vegetation Index (NDVI) was calculated using field reflectance data and IKONOS images. Several environmental parameters, such as temperature, salinity, pH, and tidal events were also measured. The study obtained valuable data that can be applied in further research about the transport of certain metals in red mangroves. It also helped to better understand the potential application of remote sensing to monitor mangroves areas highly contaminated with metals. It was proven that field reflectance measurements, hence NDVI, can be used for detecting metal contamination in mangrove trees. However, the application of these techniques to digital images, like IKONOS and AVIRIS, requires more investigation and improvement of the processing methods.