Hurricane Maria in Puerto Rico: Effects on Reservoir Water Quality and Fish Community Structure and Resilience

Hurricane Maria, a Category 4 storm with sustained winds of 249 km h?1, made landfall on Puerto Rico on 20 September 2017. The extreme precipitation resulting from this hurricane, combined with already saturated soil and the steep, mountainous terrain of the island, led to historic flooding across most of Puerto Rico. Reservoirs in many of the river systems on the island were preemptively drawn down in an attempt to absorb the volume of floodwaters but were quickly overwhelmed. Since many of these reservoirs had been the focus of previous studies, a rare opportunity arose to evaluate how extreme flooding affects lentic systems. We sampled seven of Puerto Rico?s 13 large reservoirs in April and May 2018 using previously-used, published methodologies to compare pre- and post-hurricane characteristics of water quality and fish communities. Average discharge from reservoirs during the 24-h period of the day of the hurricane ranged 64?1807 m3 sec?1 with a peak discharge of 5097 m3 sec?1, or 827 times annual mean flow. Ammonia and specific conductance increased post-hurricane, mean temperature and nitrate decreased, and other water quality parameters remained unchanged. Sport fish communities showed minimal differences between pre- and post-hurricane samples in all island reservoirs except for Loiza Reservoir, which largely collapsed post-hurricane with the primary sport fish species, butterfly peacock bass (Cichla ocellaris), disappearing from the reservoir. Other sport fish species decreased in abundance and maximum size, while invasive species were less affected. The hydraulic residence time of Loiza Reservoir during the hurricane averaged about 1 h, indicating the reservoir changed its entire volume of water nearly 24 times in a 24-h period. Our research concluded that extreme flood events resulting from hurricanes may influence reservoir fisheries and water quality under certain circumstances, although many systems may handle these perturbations with resilience.

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