Galveston Bay Research Articles

Global change—Local values: Assessing tradeoffs for coastal ecosystem services in the face of sea level rise

Anthropogenic climate change poses a significant threat to Texas’ coastal habitats and in the Galveston Bay region, there is just under 1200 square miles of freshwater marsh and undeveloped dry upland. These habitats provide residents with a variety of key ecosystem services but are threatened by global climate change. Effective management of these resources requires multidisciplinary knowledge, combining an understanding of the potential biophysical habitat alterations associated with sea level rise with the measurement of residents’ value for coastal resources. In this study, we utilize a discrete choice experiment to investigate individuals’ preferences for future conditions of Texas habitats within the Galveston Bay region. Utilizing modeled output for coverage of freshwater marsh and undeveloped dry upland in the year 2050, respondents are asked to make trade-offs between coastal conditions with no further management actions and outcomes associated with specific management interventions. From this framework, we estimate Galveston Bay regional residents’ value for freshwater marshes and undeveloped uplands. Our results indicate that individuals are willing to conserve habitat under threat from sea level rise, but that they are likely unaware of the dynamic nature of that change. As a result, residents may place less emphasis on the role of the habitat migration in response to sea level rise.

Water quality trends in Texas estuaries

Coastal watersheds in Texas have experienced significant human population growth over the past several decades, yet there have been no comprehensive assessments of water quality trends in Texas estuaries. Here, analysis of historical estuarine water quality data indicates regional “hot spots” of change. Galveston Bay and Oso Bay, which have highly urbanized watersheds, currently exhibit symptoms of eutrophication. Symptoms of eutrophication were also found in the Baffin Bay-Upper Laguna Madre complex, which has a sparsely populated but agriculturally-intensive watershed. Increasing salinity was observed in estuaries of the central Texas coast and are attributed to long-term decreases in freshwater inflow. Another artifact of decreasing freshwater inflow is a reduction in the delivery of carbonate minerals to estuaries, which manifests as decreases in pH. With findings from this study, targeted studies can now be directed at the estuaries that are experiencing water quality degradation in order to guide future management efforts.

Oxidative Potential of Chemical Mixtures Extracted from Contaminated Galveston Bay, TX Seafood Using a Human Cell Co-culture Model.

Increasing levels of pollution in Galveston Bay, TX, are of significant concern for populations that directly depend on fishing activities. Efforts to evaluate contaminant levels in commercial fish have been largely limited to the quantification of chemical mixtures in fish tissue, but little information exists about the toxicological potential of these chemicals on consumption of contaminated seafood. The present study makes use of a human cell co-culture model, mimicking the digestive system, to address the oxidative potential of chemical mixtures in seafood. Chemical extractions were performed on fillets from three fish species and oysters collected from different areas in Galveston Bay. The resulting extracts were used to expose intestinal and liver cells before the measurement of cytotoxicity and activity of antioxidant enzymes. The pesticide 4,4'-DDE was found in nearly all samples from all sites in concentrations ranging from 0.23-9.4µg/kg. Similarly, total PCBs found in fish and oyster tissue ranged from 0.68-65.65µg/kg, with PCB-118 being the most common congener measured. In terms of cytotoxicity, oyster extracts led to significant cell mortality, contrary to observations for fish extracts. Antioxidant enzymes, while not directly related to the presence of chemical mixtures in tissue, presented evidence of potential increases in activity from spotted trout extracts. Observations from this study suggest the need to evaluate toxicological aspects of contaminated seafood and support the use of in vitro models for the screening of accumulated chemicals.

Massive pollutants released to Galveston Bay during Hurricane Harvey: Understanding their retention and pathway using Lagrangian numerical simulations

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.

Baseline data for distribution of contaminants by natural disasters: results from a residential Houston neighborhood during Hurricane Harvey flooding

Hurricane Harvey made landfall in Texas August 25, 2017, bringing massive rains and flooding that impacted soils in a residential neighborhood in East Houston. Trace elements, organochlorine pesticides, polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ether fire retardants (PBDEs) and polychlorinated biphenyls (PCBs) were determined in 24 soil samples. The highest concentrations found in soils were total PAHs, which ranged from 1,310 μg/kg to 85,700 μg/kg with a mean of 12,600 μg/kg. Analysis of specific PAH ratios indicate the source of the PAHs were dominated by pyrogenic rather than petrogenic sources. Chlordanes were detectable in the area where the likely local source is for ant control. The trace metal concentrations were below any environmental health concern concentrations but As, Cd, Hg, Pb, Se, Ag, Zn were enriched over the crustal abundance. While Hurricane Harvey was responsible for the redistribution of many contaminants, the large volume of rain and floodwater likely transported contaminants from the land areas and into the Houston Ship Channel and Galveston Bay. The findings from this study will serve as baseline data for determining the mobilization of contaminants caused by natural disasters.

Fluctuation and diversity of Hydromedusae (Hydrozoa, Cnidaria) in a highly productive region of the Gulf of Mexico inferred from high frequency plankton sampling.

Hydrozoa medusae undergo blooms and seasonal fluctuations; however the drivers of such fluctuations are unknown. To understand how medusa populations fluctuate in response to seasonal factors such as temperature, salinity, dissolved oxygen, and chlorophyll a, and to enhance our taxonomic knowledge of Hydrozoa in Galveston Bay (TX), we performed frequent plankton sampling from September 2015 to September 2016. We collected 1,321 medusae in 190 sampling days. Using molecular barcoding and morphological analyses we identified 25 species, of which 21 are a first record for Galveston Bay and eight for the Gulf of Mexico. Daily medusa abundance is non-linearly related to temperature, with peak abundance estimated with multivariate regression analysis at approximately 21C. The role that temperature plays in driving medusa abundance has implications for future climate change scenarios, given that temperature in the Gulf of Mexico is expected to rise 4 °C by the end of the century. We also show that the biodiversity of the Galveston Bay and the Gulf of Mexico is underestimated and that molecular barcoding is an important and efficient tool to identify large number of medusae. We conclude that dense plankton sampling is necessary to capture both diversity and abundance of planktonic medusae.

A closer look at the effects of restoration design on biologic function in restored estuarine wetlands: A case study in Galveston Bay, Texas

A significant amount of coastal marsh restoration work has been implemented in estuarine coastal areas in an effort to reclaim previously degraded aquatic habitats. Design approaches vary according...

Deepwater Horizon Oil could have naturally reached Texas beaches.

Following the Deepwater Horizon (DWH) spill, oil residues were found in all five Gulf states of the United States (Texas, Louisiana, Mississippi, Alabama and Florida). However, only a small amount was found in Texas, leading to speculation that it may have arrived there via ship through bilge water instead of naturally via currents. We report on a numerical modeling effort to simulate surface drifters during and after the DWH spill to demonstrate that surface water parcels - and therefore oil carried by those parcels - could reasonably have reached Texas waters at the appropriate time and location from known oiled locations without human interference. We additionally give context for the conditions in 2010 through a study of summer connectivity with the Galveston Bay coastline, which shows that in some years oil from the DWH pipe likely would not have reached Texas.

Updated abundance estimates for common bottlenose dolphins (Tursiops truncatus) inhabiting West Bay, Texas

Abstract West Bay is located along the south‐west portion of Galveston Bay, Texas, and has been delimited as a bay, sound, and estuary (BSE) common bottlenose dolphin (Tursiops truncatus) stock area under the Marine Mammal Protection Act of 1972. The most recent abundance estimate available for the West Bay BSE stock is from 2001 and is considered outdated for management purposes. This study provides an updated abundance estimate using photo‐identification capture‐mark‐recapture (CMR) data collected from West Bay during the winter of 2014 and summer of 2015. The CMR data were analysed using both Pollock's robust design models and Poisson‐log normal mark‐resight models. Differences between the model types are discussed, and the abundance estimates derived from the mark‐resight models are recommended for management use (50.63 [unconditional SE 2.23] in the winter and 44.36 [unconditional SE 1.18] in the summer). Whereas the updated abundance estimates are higher than the previously reported estimates, which varied between 28 and 38, they still indicate that West Bay supports a small population of bottlenose dolphins. As a result, the West Bay BSE stock should be closely monitored for impacts, particularly those related to human caused stressors.

A hydrodynamic model for Galveston Bay and the shelf in the northern Gulf of Mexico

Abstract. A 3-D unstructured-grid hydrodynamic model for the northern Gulf of Mexico was developed, with a hybrid s–z vertical grid and high-resolution horizontal grid for the main estuarine systems along the Texas–Louisiana coast. This model, based on the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), is driven by the observed river discharge, reanalysis atmospheric forcing, and open boundary conditions from global HYCOM output. The model reproduces the temporal and spatial variation of observed water level, salinity, temperature, and current velocity in Galveston Bay and on the shelf. The validated model was applied to examine the remote influence of neighboring large rivers, specifically the Mississippi–Atchafalaya River (MAR) system, on salinity, stratification, vertical mixing, and longshore transport along the Texas coast. Numerical experiments reveal that the MAR discharge could significantly decrease the salinity and change the stratification and vertical mixing on the inner Texas shelf. It would take about 25 and 50 d for the MAR discharge to reach the mouth of Galveston Bay and Port Aransas, respectively. The influence of the MAR discharge is sensitive to the wind field. Winter wind constrains the MAR freshwater to form a narrow lower-salinity band against the shore from the Mississippi Delta all the way to the southwestern Texas coast, while summer wind reduces the downcoast longshore transport significantly, weakening the influence of the MAR discharge on surface salinity along Texas coast. However, summer wind causes a much stronger stratification on the Texas shelf, leading to a weaker vertical mixing. The decrease in salinity of up to 10 psu at the mouth of Galveston Bay due to the MAR discharge results in a decrease in horizontal density gradient, a decrease in the salt flux, and a weakened estuarine circulation and estuarine–ocean exchange. We highlight the flexibility of the model and its capability to simulate not only estuarine dynamics and shelf-wide transport, but also the interactions between them.

Examining reciprocal influence between posttraumatic stress and depressive symptoms among natural disaster survivors

BackgroundThe current study examined reciprocal effects of symptoms of posttraumatic stress disorder (PTSD) and major depressive disorder (MDD) among individuals affected by Hurricane Ike, which made landfall on September 13, 2008 MethodsParticipants were 658 survivors, who participated in the Galveston Bay Recovery Study (GBRS; National Center for Disaster Mental Health Research, Galea, and Norris, 2016). Assessment was conducted at 3, 6, and 15 months after the disaster. Bivariate latent change score modeling was conducted to examine the nature of the time-sequential associations between symptoms of PTSD and MDD ResultsResults revealed a unidirectional coupling effect from depression to change in PTSD, but unidirectional coupling effect from PTSD to change in depression was not supported. LimitationsOnly linear relations of within-individual change and time-sequential associations between PTSD and depression were examined, and therefore, it precludes potential nonlinear relations between these constructs. Also, the results of the current study are limited to the studied timespan (i.e., 3 to 15 months). Lastly, other factors that could be confounding the change in PTSD symptoms were not examined, leaving a possibility of other constructs that may influence the change in future PTSD symptoms ConclusionsThe current study suggests that disaster survivors with higher symptoms of depression may be at higher risk of experiencing increased PTSD symptoms even after one year, raising an importance of tailoring a treatment to alleviate depressive symptoms and to mitigate the risk of future symptoms of PTSD

Bay Breeze and Sea Breeze Circulation Impacts on the Planetary Boundary Layer and Air Quality From an Observed and Modeled DISCOVER‐AQ Texas Case Study

AbstractThe role of the sea/bay breeze in the planetary boundary layer evolution and air quality during a high ozone event day in the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER‐AQ) Texas 2013 campaign was examined. Data from surface air quality monitoring network stations, airborne lidar data, and additional ground‐based lidar instrumentation deployed during the campaign allowed for a unique three‐dimensional spatial and temporal study of the progression of both meteorological and air quality conditions in the Houston‐Galveston regions on 25 September 2013. The Weather Research and Forecasting model coupled with Chemistry model was used to examine the relationship of the land and bay/sea breeze circulations and its influence on air quality during the case study. Comparisons between observations and simulations revealed the largest discrepancies near the Galveston Bay shore areas where the highly localized ozone concentrations were observed and were linked to the strength and timing of the bay/sea breeze progression. Additionally, results indicate vertical downmixing from the remnants of the nighttime residual layer during morning hours into the convective boundary layer and from the lofted offshore return flow into the subjacent bay breeze flow.

Investigating Rangia cuneata Clams as Ecological Response Bioindicators to Three Decades of Variable Freshwater Inflows

Windham, R.; Nunnally, A.P., and Quigg, A., 2019. Investigating Rangia cuneata clams as ecological response bioindicators to three decades of variable freshwater inflows. Journal of Coastal Research, 35(6), 1260–1270. Coconut Creek (Florida), ISSN 0749-0208.Freshwater inflow management (quality and quantity) is critical for both environmental and human demands. Inflows needed to maintain ecosystem functionality can be assessed by observing how organisms sensitive to environmental change (bioindicators) respond to varying flow conditions. In Galveston Bay (Texas, U.S.A.), Rangia cuneata clams were proposed as bioindicators of ecological response to freshwater inflows. Rangia cuneata abundance has decreased and their distribution has retracted proximal to freshwater sources from 1983 to 2010. From 2010 to 2014, the highest mean shell lengths (Trinity River delta, 48.0 ± 0.4 mm) and meat indexes (Clear Lake, 13.3% ± 0.3%) of R. cuneata were observed in areas most influenced by freshwater inputs. In the Trinity River delta, clam biomass and density averaged 3.4 (± 0.3) kg m–3 and 25.6 (± 3.5) clams m–2, respectively. A general decreasing trend was observed in biomass and density between like seasons after the drought of 2011, which persisted throughout most of 2014. Sex ratios (62.8% ± 2.4% male) and juvenile abundance (highest in winters and summers after spawning) were consistent with life-history observations. Life-cycle observations were not available before 2010 and are important to consider in future studies. Without them, long-term decadal declines in R. cuneata clams are difficult to explain when limited to terms of natural and anthropogenic stressors. Rangia cuneata's utility as bioindicators of the ecological functionality of an estuary affected by changing freshwater inflows requires further investigation for resource management.

Impact of Hurricane Harvey on Galveston Bay Saltmarsh Nekton Communities

Coastal saltmarshes are a unique habitat at the interface of tidal coastal waters and freshwater inflow providing foraging and nursery habitat for a dynamic nekton community. Saltmarshes are particularly exposed to natural disturbances such as tropical storms, which can cause shifts in water chemistry and nekton community composition. Hurricane Harvey resulted in widespread flooding and record freshwater inflow into Galveston Bay in late August 2017. This study examined the influence of the hurricane on nekton community composition of two saltmarshes in Galveston Bay, TX. Nekton were monitored from February to December 2017 using minnow seines and Breder traps. Reduced abundance and increased diversity, despite the overall reduced number of taxa of the nekton community, were documented following the hurricane. Exacerbating these differences were reduced catches of the numerically dominant daggerblade grass shrimp, Palaemonetes pugio, following the event. For some key dominant species, a significant reduction in length was measured between pre- and post-disturbance; therefore, it is likely that new recruits, rather than the return of displaced adults, drove the community recovery. A complete recovery to a pre-disturbance state will likely require at least a full year due to seasonal recruitment patterns of many of the saltmarsh nekton species. Short-term but large-scale natural disturbances can significantly impact saltmarsh nekton communities, but because of their dynamic nature, they are generally resilient.

Quantitative PCR enumeration of vcgC and 16S rRNA type A and B genes as virulence indicators for environmental and clinical strains of Vibrio vulnificus in Galveston Bay oysters.

Oysters from a reef in Galveston Bay, Texas, USA, were screened for more virulent clinical strains versus less virulent environmental strains of Vibrio vulnificus using a combination of quantitative PCR assays for the virulence correlating gene (clinical variant, vcgC) and 16S rRNA types A and B (type A = environmental, type B = clinical). The combination of vcgC and 16S rRNA type B loci to determine clinical type strains was suitable, as indicated by the strong correlation (R2 = 0.98; p < 0.001) between these gene counts over time and their relative proportion (up to 93.8% and 94.3%, respectively) to vvhA genes used to quantify all strains of V. vulnificus. A strong seasonal shift of V. vulnificus strain types was observed. Environmental strains (16S rRNA type A) predominated from April to mid-June as salinities increased from 22 to 27 PSU (practical salinity unit) and temperatures rose 20 to 28 °C, with peak gene quantities of 16 812 ± 56 CFU/g. As temperatures increased to ≥30 °C from mid-June to September and salinities rose above 27 PSU, clinical strains (16S rRNA type B; vcgC) predominated with peak quantities 31 868 ± 287 and 32 360 ± 178 CFU/g, respectively.

Floodwater impact on Galveston Bay phytoplankton taxonomy, pigment composition and photo-physiological state following Hurricane Harvey from field and ocean color (Sentinel-3A OLCI) observations

Abstract. Phytoplankton taxonomy, pigment composition and photo-physiological state were studied in Galveston Bay (GB), Texas (USA), following the extreme flooding associated with Hurricane Harvey (25–29 August 2017) using field and satellite ocean color observations. The percentage of chlorophyll a (Chl a) in different phytoplankton groups was determined from a semi-analytical IOP (inherent optical property) inversion algorithm. The IOP inversion algorithm revealed the dominance of freshwater species (diatom, cyanobacteria and green algae) in the bay following the hurricane passage (29 September 2017) under low salinity conditions associated with the discharge of floodwaters into GB. Two months after the hurricane (29–30 October 2017), under more seasonal salinity conditions, the phytoplankton community transitioned to an increase in small-sized groups such as haptophytes and prochlorophytes. Sentinel-3A Ocean and Land Colour Instrument (OLCI)-derived Chl a obtained using a red ∕ NIR (near-infrared) band ratio algorithm for the turbid estuarine waters was highly correlated (R2&gt;0.90) to the (high-performance liquid chromatography) HPLC-derived Chl a. Long-term observations of OLCI-derived Chl a (August 2016–December 2017) in GB revealed that hurricane-induced Chl a declined to background mean state in late October 2017. A non-negative least squares (NNLS) inversion model was then applied to OLCI-derived Chl a maps of GB to investigate spatiotemporal variations of phytoplankton diagnostic pigments pre- and post-hurricane; results appeared consistent with extracted phytoplankton taxonomic composition derived from the IOP inversion algorithm and microplankton pictures obtained from an Imaging FlowCytobot (IFCB). OLCI-derived diagnostic pigment distributions also exhibited good agreement with HPLC measurements during both surveys, with R2 ranging from 0.40 for diatoxanthin to 0.96 for Chl a. Environmental factors (e.g., floodwaters) combined with phytoplankton taxonomy also strongly modulated phytoplankton physiology in the bay as indicated by measurements of photosynthetic parameters with a fluorescence induction and relaxation (FIRe) system. Phytoplankton in well-mixed waters (mid-bay area) exhibited maximum PSII photochemical efficiency (Fv∕Fm) and a low effective absorption cross section (σPSII), while the areas adjacent to the shelf (likely nutrient-limited) showed low Fv∕Fm and elevated σPSII values. Overall, the approach using field and ocean color data combined with inversion models allowed, for the first time, an assessment of phytoplankton response to a large hurricane-related floodwater perturbation in a turbid estuarine environment based on its taxonomy, pigment composition and physiological state.

Natural attenuation of indicator bacteria in coastal streams and estuarine environments

One of the most significant causes of poor water quality is the presence of pathogens. To reduce the cost of human exposure to microbial contamination, monitoring of Fecal Indicator Bacteria (FIB), as a surrogate for the presence of pathogens in natural waters, has become the norm. A total maximum daily load (TMDL) framework is used to establish limits for microbial concentrations in impaired waterbodies. In order to meet microbial loads determined by the TMDLs, reductions in microbial sources varying from 50% to almost complete elimination are required. Such targets are fairly difficult, if not impossible, to achieve. A natural attenuation (NA) framework is proposed that takes into account the connectivity between freshwater streams and their receiving coastal estuaries. The framework accounts for destructive and non-destructive mechanisms and defines three regimes: NA 1 - reaction-dilution mixing at the freshwater-tidal interface, NA 2 - advection-reactions within the tidally influenced coastal stream, and NA 3 - dilution-discharge at the interface with the estuary. The framework was illustrated using the Houston Metropolitan area freshwater streams, their discharge into the Houston Ship Channel (HSC) and into Galveston Bay. FIB concentrations in Galveston Bay were much lower when compared to FIB concentrations in Houston streams. Lower enterococci concentrations in tributary tidal waters were found compared to their counterparts in fresh waters (NA1 regime). Additionally, 70% reduction in FIB loads within the HSC was demonstrated as well as a decreasing trend in enterococci geometric means, from upstream to downstream, on the order of 0.092 day−1 (NA2 regime). Lower enterococci concentrations in Galveston Bay at the confluence with the HSC were also demonstrated (NA3 regime). Statistical testing showed that dilution, tide-associated processes, and salinity are the most important NA mechanisms and indicated the significant effect of ambient temperature and rainfall patterns on FIB concentrations and the NA mechanisms.

Physical, Chemical, and Microbial Quality of Floodwaters in Houston Following Hurricane Harvey.

Hurricane Harvey brought more than 50 in. of rainfall to some areas of the Greater Houston Metro area (GHMA) starting on August 25, 2017; the Hurricane was also associated with damage to environmental infrastructure such as wastewater facilities, superfund sites, and leaks and spills from industrial and municipal facilities. This study collected post-Harvey water quality data in multiple streams for several weeks after the Hurricane. In addition to measuring impact, the study compared the observed concentrations of several physical, chemical, and microbial constituents and water properties to their historical counterparts in an effort to understand the water quality impacts of Harvey on the natural water systems within the GHMA. Unusual water quality findings such as low pH were observed that likely had acute and chronic effects on ecosystems including the loss of oyster populations in Galveston Bay. In-stream microbial concentrations, using E. coli as the indicator, were within historical norms typically reported for the GHMA. The observed levels of measured dissolved metals post Harvey, while relatively low, when multiplied by the significant volume of water discharged from bayous to Galveston Bay, meant the delivery of a substantial load of trace metals to the estuary. Specifically, the load in the particulate phase would be expected to accumulate and gradually repartition to the dissolved phase for a long period of time. Total metal concentrations, when elevated relative to their historical counterparts, could be associated with the presence of industrial activities. Overall, anthropogenic activities including the presence of hydraulic flood control structures, local runoff from industrialized areas, and active superfund sites were recognized as key factors affecting short-term acute water quality impacts. Watersheds with very little human alterations experienced minimal water quality changes and had relatively rapid recoveries post-Harvey.

Estuarine salinity recovery from an extreme precipitation event: Hurricane Harvey in Galveston Bay

With a warming climate and a more humid atmosphere, extreme precipitation events are projected to occur more frequently in future. Understanding how coastal systems respond to and recover from such acute events is of fundamental significance for environmental assessment and management. A hydrodynamic model was used to examine the estuarine responses in Galveston Bay to Hurricane Harvey, an extreme precipitation event with a return period of larger than 1000 years. The enormous freshwater input during Harvey caused long-lasting elevated water level, extraordinarily strong along-channel velocity, sharp decreases in salinity, and huge river plumes, all of which were well reproduced by the model. The salinity recovery time (TR) was estimated as a measure of the system resiliency to stormwater input. Over the entire bay, the TR had a mean of two months, but with great variability ranging from less than 10 days near the bay entrance to over three months in the inner part of Trinity Bay and the middle of East Bay. The spatially varying TR was explained by different contributions of exchange flow and tidal pumping to salt flux. At the bay entrance, tidal pumping facilitated by the shelf current was the dominant mechanism for salt influx, while exchange flow and tidal pumping had a comparable contribution to salt influx to Trinity Bay. The spatial pattern of the TR appears consistent with the changes in the phytoplankton community in the bay. A series of numerical experiments with different amounts of stormwater reveals a non-linear relationship between the bay-wide mean TR and the amount of stormwater, with the rate of increase in TR decreasing when stormwater input increases. The present approach using a hydrodynamic model will be able to provide a quick assessment of the environmental pressure from extreme events.

Spatiotemporal Variability in Autotrophic and Heterotrophic Microbial Plankton Abundances in a Subtropical Estuary (Galveston Bay, Texas)

Williams, A.K. and Quigg, A., 2019. Spatiotemporal variability in autotrophic and heterotrophic microbial plankton abundances in a subtropical estuary (Galveston Bay, Texas). Journal of Coastal Research, 35(2), 434–444. Coconut Creek (Florida), ISSN 0749-0208.The subtropical estuary Galveston Bay (Texas) is influenced by frequent riverine pulses from two important rivers in its northern sector and by ocean tides from the Gulf of Mexico in its southern sector. This study examined combinations of abiotic and biotic factors that synergistically influence spatiotemporal variability of autotrophic and heterotrophic microbial plankton abundances (0.2–20 µm). Potential nutrient limitation observed in situ was supported by in vitro enrichment bioassays. Shifts in the relative in situ abundance of autotrophs and heterotrophs, stained with SYBR Green I and enumerated on a flow cytometer, were significantly related to temperature, total nitrogen, dissolved inorganic nitrogen-to-phosphorus ratios, and total organic carbon concentrations along estuarine gradients. Observations reveal a pattern of serial colimitation of the microbial plankton community. Among the variables tested, nitrogen became the principal limiting factor for growth if phosphorous was available and temperatures were warm. In vitro nutrient enrichment bioassays performed with inorganic nitrogen (as nitrate) and Pi revealed variations in the responses between autotrophic and heterotrophic microbes under nutrient-limiting conditions, particularly during co-occurring phytoplankton blooms. The measured dynamics in planktonic relationships will have important impacts on understanding estuarine nutrient processing.