Abstract
Increasing frequency of extreme precipitation events under the future warming climate makes the storm-related pollutant release more and more threatening to coastal ecosystems. Hurricane Harvey, a 1000-year extreme precipitation event, caused massive pollutant release from the Houston metropolitan area to the adjacent Galveston Bay. 0.57 × 106 tons of raw sewage and 22,000 barrels of oil, refined fuels and chemicals were reportly released during Harvey, which would likely deteriorate the water quality and damage the coastal ecosystem. Using a Lagrangian particle-tracking method coupled with a validated 3D hydrodynamic model, we examined the retention, pathway, and fate of the released pollutants. A new timescale, local exposure time (LET), is introduced to quantitatively evaluate the spatially varying susceptibility inside the bay and over the shelf, with a larger LET indicating the region is more susceptible to the released pollutants. We found LET inside the bay is at least one order of magnitude larger for post-storm release than storm release due to a quick recovery in the system's flushing. More than 90% of pollutants released during the storm exited the bay within two days, while those released after the storm could stay inside the bay for up to three months. This implies that post-storm release is potentially more damaging to water quality and ecosystem health. Our results suggest that not only the amount of total pollutant load but also the release timing should be considered when assessing a storm's environmental and ecological influence, because there could be large amounts of pollutants steadily and slowly discharged after storm through groundwater, sewage systems, and reservoirs.
Highlights
Pollutant release frequently happens during storm events, especially those accompanied by strong precipitation
Taking the massive pollutants released from the Houston metropolitan area in Texas to the adjacent Galveston Bay during Hurricane Harvey as an example, we show here that the release timing is critically important and the susceptibility of coastal waters to pollutant can be more serious than expected when pollutants are released after the storm discharge
We demonstrate here that pollutants released after the storm will be more influential on the water quality and ecosystem health, as they will stay much longer inside the bay, than those released during storm (Fig. 5) the amount of pollutants released after the storm is usually much smaller than that during storm
Summary
Pollutant release frequently happens during storm events, especially those accompanied by strong precipitation. Nutrient, bacteria, heavy metal, or petrochemical products can be washed away by surface runoff or spilled due to flooding and discharged into receiving waters Their influence on coastal environments can be catastrophic, for coastal embayment where water exchange with the coastal ocean is slow and pollutants can stay for a long time. Damages to the water quality, marine environment, marine mammals, and fishery due to released pollutants have been extensively observed (Weyhenmeyer et al, 2004; Cardoso et al, 2008; Wetz and Yoskowitz, 2013) Recovery time from such extreme events for the receiving waters in terms of hydrodynamics or ecosystem health can take months or even years, depending on the amount of freshwater load, pollutant concentration, flushing capacity, and resiliency of the ecosystem (Paerl et al, 2001)
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