How tropical cyclone flooding caused erosion and dispersal of mercury-contaminated sediment in an urban estuary: The impact of Hurricane Harvey on Buffalo Bayou and the San Jacinto Estuary, Galveston Bay, USA

Abstract

Hurricane Harvey (Harvey), a slow-moving storm, struck the Texas coast as a category 4 hurricane. Over the course of 53 days, the floodwaters of Harvey delivered 14 × 10 9 m 3 of freshwater to Galveston Bay. This resulted in record flooding of Houston bayous and waterways, all of which drained into the San Jacinto Estuary (SJE,) with its main tributaries being Buffalo Bayou and the San Jacinto River. The lower SJE and lower Buffalo Bayou has experienced up to 3m of land subsidence in the past 100 years and, as a result, prior to Hurricane Harvey, up to 2m of sediment within the upper seabed contained an archive of high concentrations of Total Hg (HgT) and other particle-bound and porewater contaminants. Within the SJE, Harvey eroded at least 48 cm of the sediment column, resulting in the transport of an estimated 16.4 × 10 6 tons of sediment and at least 2 tons of Hg into Galveston Bay. This eroded sediment was replaced by a Harvey storm deposit of 7.73 × 10 6 tons of sediment and 0.96 tons within the SJE, mostly sourced from Buffalo Bayou. Considering that the frequency of slow-moving tropical cyclones capable of delivering devastating rainfall may be increasing, then one can expect that delivery of Hg and other contaminants from the archived sediment within urbanized estuaries will increase and that what happened during Harvey is a harbinger of what is to come.

Assessing the Risk of Contaminant Dispersion From Fibrous Sediments of Industrial Origin

“…To conclude, this means that the estimated risk for our case study is an underestimation rather than an overestimation, even considering the lower levels of the 90% confidence intervals. It also confirms the importance of taking into account advective dispersion pathways in risk assessments (e.g., Erickson et al, 2005;Davis et al, 2007;Reible, 2014;Howell and Rifai, 2015;Dellapenna et al, 2020).…”

“…This outcome is probably also true for many other fiberbank deposits, and for contaminated sediments located in shallow waters (e.g., Butcher and Garvey, 2004;Davis et al, 2007;Howell and Rifai, 2015). Even archived contaminants may become exposed to dispersion because of sediment scouring during extreme weather-events like hurricanes (Dellapenna et al, 2020). Our study also includes the potential for contaminant dispersion from submarine landslides, and the results indicate that a submarine landslide will disperse most contaminants per unit area (i.e., flux), followed by advection through ship induced resuspension, river flow resuspension, wind-wave current resuspension, and least by chemical diffusion.…”

“…It is known that major flood events may re-mobilize contaminants from contaminated sediments (e.g., Haag et al, 2001;Westrich and Förstner, 2005;Roberts, 2012) and that propeller wash may re-suspend contaminated sediments (e.g., Michelsen et al, 1998;Superville et al, 2014;Prygiel et al, 2015). It has also been shown that extreme weather-events like hurricanes may increase dispersion of contaminants from contaminated sediments (Howell and Rifai, 2015;Dellapenna et al, 2020). Only a few studies have considered submarine landslides and other underwater mass movements as a pathway for contaminant dispersion, but they have been highlighted in a review paper by Kane and Clare (2019).…”

7Be/210Pbxs Ratio-Derived Age and Residence Time of Suspended Sediments in Galveston Bay

“…For example, surface sediment was measured in Galveston Bay, and it was found that various particle reactive metals (e.g., lead, barium, mercury, copper, manganese, zinc, etc.) and polycyclic aromatic hydrocarbons (PAHs) sorbet onto the sediment, meaning that they have a great chance of resuspending during resuspension events (Santschi et al, 2001;Dellapenna et al, 2020;Camargo et al, 2021). Therefore, our estimated residence time of suspended sediments (51-105 days, Table 2) suggest these pollutants that adsorb to suspended sediment may spend months before they leave the Galveston Bay.…”

“…Wind-induced currents and wave resuspension are important sources of energy for sediment transport within an ecosystem and can be dominant in shallow, microtidal estuaries, affecting a large portion, if not all of the water column (Booth et al, 2000). Sediment resuspension associated with strong weather events can reintroduce trace elements and pollutants back into the water column, which can have significant environmental impacts in an estuary (e.g., Dellapenna et al, 2006Dellapenna et al, , 2020. These constituents can be stored in the sediment during periods of sediment deposition and are resuspended during wind-induced wave resuspension, in addition to any other resuspension events (Dellapenna et al, 2006).…”