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.