1.0 Introduction
Sediments in urban estuaries have received much attention in the literature over the past few decades; they are well understood to be a critical component of estuarine ecosystems supporting biota and benthic organisms and microbial communities. Sediments also serve as a key environmental matrix in the form of a sink or source for chemicals and pollutants emanating from land areas surrounding the estuary. It is well established that sediments in estuarine systems are continuously changing over time due to the complex hydrodynamic interactions within the estuarine environment and human interventions that have altered natural flow patterns causing changes in freshwater inflows and sediment loads into estuaries.
While changes in sediment nature, character, and quality occur under daily flow regimes; they are amplified as a result of severe storms and hurricanes. In the case of hurricanes, especially when accompanied by storm surge, the elevated water velocities may mobilize the bed sediment moving it upstream and transporting and depositing it in other parts of the estuary. Alternations in salinity and pH during a hurricane (Kiaghadi & Rifai, 2019), although for a limited amount of time, may also alter sediment quality and associated ecosystems (Ravisangaret al. , 2001; Carlin et al. , 2015). In the case of heavy rainfall accompanying hurricanes, such as was experienced during Harvey in the Houston-Galveston region, storm water runoff can cause significant shifts in the nature and character of sediment in estuarine environments (Du et al. , 2019), the pollutants within them, and their microbial communities.
Research studies in the literature have reported on various aspects of sedimentation and erosion following natural hazards, however, none as of yet, have elucidated the observed longitudinal patterns in estuarine sediments in response to daily flow conditions and their response and recovery from a natural disaster such as Hurricane Harvey. Hurricane Harvey, a Category 4 storm that landed on August 25, 2017 on the coast of Texas has had a significant impact on the Galveston Bay Estuarine System (GBES)(NOAA National Centers for Environmental Information and (NCEI), 2018; Du et al. , 2019). The storm with its historic 50+ inches of rainfall, delivered more than 7,500 km3 of freshwater just from the Greater Houston watersheds, the Trinity River, and rainfall over the surface of the Houston Ship Channel-Galveston Bay (HSC-GB) water body; approximately 2.5 times the GBES volume. As a result, the GBES experienced its lowest salinities ever for an extended period of time after Harvey with associated adverse effects on its biota.
In addition to historic rainfall, an important consequence of Hurricane Harvey was the delivery of astounding amounts of sediment (~ 9.86 × 107 metric tons) to the GBES (Du et al. , 2019). Houston’s waterways, referred to as Rivers of Brown, were the main transport pathways for silts and sand into Galveston Bay and the Gulf of Mexico (Figure S1A and B in the Supplementary Information, SI). Sediment mobilization, polluted runoff, and spills and leaks during Harvey are thought to have caused acute and chronic changes in the physical, chemical and microbiological characteristics of water and sediment in Galveston Bay as reported in other estuaries after similar natural disasters (Sansalone et al. , 1998; SedNet, 2004; Stachel et al. , 2004; Pardue et al. , 2005; Hagy et al. , 2006; Mallin and Corbett, 2006; Adamset al. , 2007; Gong et al. , 2007; Amaral-Zettler et al. , 2008; Huang et al. , 2013; Horowitz et al. , 2014; Personna et al. , 2015; Reilly et al. , 2016; Romanoket al. , 2016; Mandigo et al. , 2016; Artigas et al. , 2017). It is noted, however, that while the type and grain size distribution of sediment and the changes in sediment pollutant concentrations have been well studied after natural disasters, few studies have focused on changes in microbial communities. Analyzing the microbial community within the sediment and water column may provide valuable information on ecosystem health (Cao et al. , 2006), especially since microbial communities exposed to environments enriched with complex toxics require several years to recover and return to their original composition (Bell et al. , 1990; Ahmann et al. , 1997; Ford et al. , 1998; Zhou et al. , 2002; Torsvik and Øvreås, 2002; Gillan, 2004; Branco et al. , 2005; Gillan et al. , 2005; Yannarell et al. , 2007; Allison and Martiny, 2008; Haller et al. , 2011; Zhao et al. , 2014; Yu et al. , 2018; Beattie et al. , 2018).
This paper takes a holistic look at sediment in the Galveston Bay Estuarine System (GBES), and presents historical Total Suspended Sediment (TSS), sediment grain size, trace metals, and flow data within the system; the data are used to characterize the longitudinal nature and character of sediment in the GBES under normal flow regimes. Uniquely, the paper presents sediment-sampling data collected after Hurricane Harvey including metals concentrations and diversity of microbial communities within the estuary and places the post-Harvey data in context relative to the historical dataset and relative to the recovery of the GBES from this natural disaster. The paper is novel because it answers the question of whether specific impacts of natural hazards can be effectively observed in sediment from natural water systems and whether sediment microbial communities can be used as indicators of system health in terms of exposure to increased pollutant loads from the estuarine watersheds due to increased sediment and associated pollutant loads. Importantly, the research presents a unique dataset of sediment analyses that were collected from deposited soil along the banks of two urban bayous, Brays Bayou and Buffalo Bayou, in Houston. The dataset is unique and illustrates the specific nature and character and pollutant entrainment within eroded sediment from watersheds that drain into the GBES.