Ortiz Rosa, Suhey

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    Bio-optical and biogeochemical characterization of “Dark Water” events in southwestern Puerto Rico
    (2023-12-08) Ortiz Rosa, Suhey; Armstrong, Roy A.; College of Arts and Sciences - Sciences; Hernández López, William J.; Weil, Ernesto F.; Williams, Stacey M.; Department of Marine Sciences; Román Pérez, Rosa I.
    This dissertation characterized and traced black water events (BWE) in southwestern Puerto Rico (PR) coastal and offshore waters. This study provides a dataset to validate ocean color data and to derive empirical algorithms for the Caribbean region. In addition, it contributed to the understanding of light attenuation in surface waters. Furthermore, two of the chapters demonstrated the feasibility of remote sensing data for water quality assessments using two different satellite sensors in Puerto Rican coastal waters. Black water events (BWE) are common in coastal areas associated with wetlands or river outfalls, rich in organic humic matter. In Puerto Rico, BWE can be found along the insular shelf and in oligotrophic waters. In chapter two we integrated in-situ and satellite data for BWE characterization through reflectance band ratios to develop a dark water index. BWE were identified in 8 Sentinel-3A (S3A) images in 2018. A dark water index combining bands (B1+B2)/B6 was used to distinguish these events from the surrounding clear, oligotrophic waters. Our results suggest that an index of less than 7 defines BWE. The S3A absorption of colored dissolved organic matter at 443 nm (ADG443_NN) product values inside the BWE are 15.1 % higher than the values of adjacent clear waters. We suggest that the highest contribution to the BWE optical signal is Colored Dissolved Organic Matter (CDOM), but it is also highly influenced by chlorophyll. The occurrence of BWE around the island appears to be frequent. Follow-up studies are needed to monitor prolonged BWE and examine their impact on coral reefs and associated ecosystems. Chapters three and four assessed the impact of Hurricanes Irma and María (2017) using ocean color data. These studies combined field and satellite data to determine hurricane impacts in water quality using absorption of CDOM (aCDOM) /ADG, Chlorophyll-a, total suspended matter (TSM) and attenuation coefficient (Kd490) parameters as indicators. We determined anomalies in water quality parameters using existing ocean color products from Sentinel 3A at La Parguera Nature Reserve (LPNR) and evaluated the Chlorophyll-a and Kd490 products with the Visible Infrared Imaging Radiometer Suite (VIIRS) data around Puerto Rico.