Quantifying the Effects of Hurricanes Irma and Maria on Coastal Water Quality in Puerto Rico using Moderate Resolution Satellite Sensors

Abstract

Coastal, benthic communities, such as coral reefs, are at particular risk due to poor water quality caused by hurricanes. In addition to the physical impacts from wave action and storm surge, hurricanes bring significant rainfall resulting in increased runoff from land. Hurricanes Irma and Maria caused record or near-record floods at many locations across Puerto Rico and resulted in major impacts on coastal and benthic ecosystems from heavy rainfall and river discharge. In this study, we use imagery from the moderate resolution Visible Infrared Imaging Radiometer Suite (VIIRS) satellite to quantify the impacts of hurricanes Irma and Maria, which struck Puerto Rico during September 2017, on the water quality of the coastal waters of Puerto Rico using the chlorophyll-a (Chl-a) and the diffuse attenuation coefficient at 490 nm (Kd490) products. The objectives include: (1) quantify the water quality and light attenuation after the hurricanes; (2) compare this event to the climatology of these parameters, and 3) evaluate long-term exposure and exceedances of various coastal areas to low levels of turbidity. The Chl-a inner shelf values increased in 2017 during the months of June (8% above baseline), July (17%), August (5%), September (8%), October (19%), and November (28%) when compared to 2012–2016 baseline data. The values for Chl-a concentration reached and exceeded 0.45 µg/L by August 2017 and persisted above that value until December 2017. The Kd490 inner shelf values for 2017 increased (in percent) for the months of June (4% above baseline), July (9%), August (10%), September (5%), October (12%), and November (7%) when compared to 2012–2016 baseline data. The values of Kd490 in August, September, and December 2017 were the highest seen during 2012–2017. Even with the limitations of spatial resolution and loss of data to cloud cover, the 6-year imagery time-series analysis can provide a useful evaluation of the effects of these two hurricanes on the coastal water quality in Puerto Rico, and quantify the exposure of benthic habitats to higher nutrient and turbidity levels.

Water Quality Anomalies following the 2017 Hurricanes in Southwestern Puerto Rico: Absorption of Colored Detrital and Dissolved Material

“…These authors reported anomalous attenuation coefficient values for July 2017 (0.06 m −1 ) being persistently high until December. Chlorophyll-a is a parameter highly correlated with K d 490 on ocean color data [18,20]. It is important to highlight the oligotrophic water conditions on this study area, being influenced by Guánica Bay dynamics.…”

“…García-Sais and collaborators (2017) studied K d 490 and Chl-a trends over individual coral reefs in Puerto Rico using L2 and L3 imagery from SeaWiFS and MODIS Aqua satellite data [10]. A recent publication based on VIIRS data described the tendencies of K d 490 and Chl-a parameters on water quality around PR using a value of 0.1 m −1 for K d 490 and 0.45 µg/L for Chl-a as a threshold value for coastal waters [20]. Despite the detrimental effects documented by several authors [26,[53][54][55], an intermittent high turbidity over coral reefs can be photo-protective [10].…”

“…Gilbes and collaborators (2001) documented changes in Chl-a due to hurricane Georges up to two and a half weeks after the event [18]. Recently, Hernández and collaborators (2020) documented high K d 490 and Chl-a values from July to December 2017 all around Puerto Rico using VIIRS data; reporting Chl-a values above 0.45 µg/L in August and November 2017 [20]. These authors reported anomalous attenuation coefficient values for July 2017 (0.06 m −1 ) being persistently high until December.…”

“…Several studies have been conducted on coastal water quality following hurricane events using remote sensing techniques [4,5,12]. These have focused primarily on the continental estuarine and coastal habitats as well lacustrine [5,[13][14][15][16][17], with a few studies available for the Caribbean Sea [18][19][20], where our study area, La Parguera Natural Reserve (LPNR), is located.…”

“…K d 490 is another important parameter for water quality since it provides a measure of turbidity related to the total organic and inorganic matter held in solution and suspension in the water column. It can be used to quantify light availability and sediment loading for benthic organisms (i.e., coral reefs and seagrasses) [20,38].…”