Lavaca Bay Research Articles

Linking watershed nutrient loading to estuary water quality with generalized additive models.

Evaluating estuary water quality responses to reductions (or increases) in nutrient loading attributed to on the ground management actions can be challenging due to the strong influence of environmental drivers on nutrient loads and non-linear relationships. This study applied generalized additive models to calculate watershed nutrient loads and assess responses in estuary water quality to seasonally-adjusted freshwater inflow and flow-adjusted nutrient loads in Lavaca Bay, Texas. Lavaca Bay is a secondary embayment on the Texas coast displaying early potential for eutrophication and water quality degradation. Use of flow-adjusted nutrient loads allowed the study to evaluate the response in water quality to changes in nutrient loads driven by anthropogenic sources. Cross-validation indicated that, despite data constraints, semiparametric models performed well at nutrient load prediction. Based on these models, delivered annual nutrient loads varied substantially from year to year. In contrast, minimal changes in flow-normalized loads indicate that nutrient loadings were driven by natural variation in precipitation and runoff as opposed to changes in management of nonpoint sources. Models indicated no evidence of long-term changes in dissolved oxygen or chlorophyll-a within Lavaca Bay. However, site specific long-term increases in both organic and inorganic nitrogen are concerning for their potential to fuel eutrophication. Further analysis found freshwater inflow had strong influences on nutrient and chlorophyll-a concentrations but there was no evidence that changes in watershed nutrient loading explained additional variation in dissolved oxygen and limited evidence that watershed nutrient loadings explained chlorophyll-a concentrations. In addition to providing a baseline assessment of watershed nutrient loading and water quality responses in the Lavaca Bay watershed, this study provides methodological support for the use of semiparametric models in load regression models and estuary assessments.

Influence of an industrial discharge on long-term dynamics of abiotic and biotic resources in Lavaca Bay, Texas, USA

The current study seeks to identify possible anthropogenic and/or natural environmental stressors that may account for the long-term decline of ecosystem health in Lavaca Bay, Texas, USA. The Formosa Plastics Corporation instituted monitoring of an industrial discharge into the bay with 16 fixed point stations and quarterly sampling from 1993 to 2020. Comprehensive measurements included organic and inorganic solutes in surface water, porewater and sediment, sediment content, plankton, nekton, and infaunal benthos. All parameter trends changed over time due to climate, freshwater inflow events, and/or seasonal changes. Biological community structure and sediment changed with distance from the discharge site. Dominance characterized community structure because three to four taxa comprised > 70% of individuals for nekton (trawl and gill net), phytoplankton, zooplankton, and ichthyoplankton samples. Sediment became sandier over time (48 to 75%) and away from the discharge. Surface water and porewater at reference (R) stations and stations near the discharge site had similar hydrographical and biological trends over time, indicating no long-term impact due to the discharge. However, 99.9% of 424,671 measurements of organic contaminants were non-detectable because the methods were insensitive to ambient concentrations. Thus, it is still not known if contaminants play a role in the long-term decline of ecosystem health in Lavaca Bay. Furthermore, only four R stations were sampled and were all 3810 m from the discharge site, so it is possible that trends in R stations do not represent the natural background. Future studies should include more R stations and lower detection limits for contaminants.

Marine Archaeological Survey for the Webster to Seadrift Pipeline Project in Calhoun and Jackson Counties, Texas

Marine Archaeological Survey for the Webster to Seadrift Pipeline Project in Calhoun and Jackson Counties, Texas

Enrichment of nitrous oxide reducing bacteria from coastal marsh sediments

We attempted to recover organisms capable of respiratory nitrous oxide reduction with acetate as an electron donor from a variety of coastal marine sediments from Lavaca Bay area, Texas by use of liquid enrichment cultures. Putative positive cultures were analyzed by amplifying eubacterial and archaeal 16S rRNA gene fragments and analyzing their diversity by separating them by a denaturing gradient gel electrophoresis (DGGE). No Archaea was detected in our enrichments; however, positive enrichments from coastal salt marsh indicated the presence of putative nitrous oxide reducing bacteria. DGGE patterns of the amplified DNA were similar between enrichments, with ca. 7 obvious bands. The dominant bands were tentatively identified as members of the Gammaproteobacteria class, closely related to various denitrifying pseudomonads. Our results indicate that coastal marine environments may sustain a nitrous oxide reducing community, although nitrous oxide reduction is probably an opportunistic form of metabolism in that environment.

Mercury exposure through diet in pregnant women and women of childbearing age

The study examined the stage of clean-up of the Port Lavaca bay sites in Texas, which were polluted during the early 1990's by effluent containing mercury (Hg) from a chloralkali plant. In addition to Hg intoxication through environmental contaminations, human exposure through dietary fish and other seafoods occurred. Bacteria converts inorganic Hg to alkyl organic compounds and subsequently the metal crosses the blood brain barrier thus exerting adverse effects on the fetal developing nervous system. In order to conduct a survey of dietary Hg exposure, blood was collected from pregnant women and those of childbearing age at routine clinic visits at each of three centers in South Texas cities (Galveston, Texas City, Port Lavaca/Victoria, TX). A questionnaire sought dietary and lifestyle information including consumption, sources of fish and other seafoods. A significant number of subjects (119 out of 175, 68%) ate fish caught locally. The blood Hg concentrations (µg L−1) range varied with the location of the study centers: City of Galveston 2.6–62; Texas City 2.8–111.8; and the Port Lavaca areas 3.02–126.7. The concentrations of blood Hg was directly proportional to the number of fish meals consumed for each species considered. Mean blood Hg concentrations for no fish meals per week were: Port Lavaca 4.5 (N = 3), Galveston 4.3 (N = 3), Texas City 3.5 (N = 10). For >3 fish meals per week, the mean blood Hg concentrations were: Port Lavaca, 48.0 (N = 53), Galveston 29.1 (N = 35), Texas City, 36.1 (N = 31). Data show that residues of Hg were still present in 1994 despite the clean-up efforts.

The role of freshwater inflow in lagoons, rivers, and bays

The aim of this study was to compare the impact of different freshwater inflow volumes on benthic communities and water column dynamics in different estuary classes. Benthic and water column spatial dynamics were contrasted in lagoons (with no direct inflow sources), tidal rivers that empty directly into the Gulf of Mexico, and bar-built bay systems (with direct inflow sources) along the Texas (USA) coast to determine the role of inflow in regulating ecosystem structure and function. Chlorophyll-a and nutrient concentrations were inversely correlated with salinity and were thus highest in the river systems, but lowest in lagoons. All Texas estuary types studied have conservative mixing for silicate and ammonium but are sinks for nitrite plus nitrate and phosphate. Macrobenthic production (abundance and biomass) was lowest in rivers and highest in lagoons. Diversity was low in estuaries with salinities between 1 and 17, but increased with salinities of up to 30, before decreasing in hypersaline conditions. Macrofaunal community structure divided the estuaries into two groups. The first group represented polyhaline communities and contained lagoons (East Matagorda, Matagorda, Christmas, and South Bays). The second group represented oligo-mesohaline community characteristics and contained the secondary bays (Lavaca Bay and Cedar Lakes) and rivers (San Bernard River, Brazos River, and the Rio Grande). The implications of these results for managing freshwater flows is that altered hydrology can change the character of estuarine systems regardless of their classification as bays, lagoons, or tidal rivers.

Relative Value of Deep Subtidal Oyster Reefs to Other Estuarine Habitat Types using a Novel Sampling Method

Subtidal eastern oyster Crassostrea virginica (Gmelin) cover large expanses of many Gulf of Mexico estuaries; however, few researchers have attempted to quantify the value of deep, open-water, subtidal reefs as habitat for fishes and crustaceans as a result of gear limitations. We developed quantitative sampling gear for live oyster reefs by slightly modifying an epibenthic sled. Gear comparison trials showed similar effectiveness among marsh edge, submerged aquatic vegetation, and nonvegetated bottom for both epibenthic sled types. We then quantified the density and community assemblage of nekton and benthic crustaceans on deep subtidal oyster reefs in Lavaca Bay, TX, and compared it with densities found in nearby marsh edge, submerged aquatic vegetation, and nonvegetated bottom habitats. We found significantly fewer nektonic and benthic crustaceans on nonvegetated bottom and oyster reefs than in marsh edge and submerged aquatic vegetation over all seasons and regions, and community analysis revealed similar differences among habitat assemblages. Using gill nets, the greatest catch of transient fishes and crustaceans were collected on oyster reefs and nonvegetated bottom. Although relatively low densities of small juvenile fishes were observed over deep oyster reefs, our community analyses and the high catch-per-unit-effort of large, transient species provide evidence that subtidal reefs are a critical habitat for numerous estuarine fishes and crustaceans.

Implications of Colorado river (Texas, USA) freshwater inflow to benthic ecosystem dynamics: A modeling study

Estuaries are defined by mixing of freshwater from rivers and saltwater from seas. Water resource development can reduce river flows to the coast, but it is difficult to predict effects on estuaries. The Lavaca-Colorado Estuary is a major estuarine system along the Texas coast that provides major economic benefit to the region by supporting a variety of agricultural, residential, industrial, and recreational functions. New water projects could divert freshwater from Matagorda Bay. So, what environmental effects could result from further changes to inflow patterns in the Matagorda Bay system? To answer this question, a bioenergetic model, calibrated using a long-term dataset of benthic biomass, was run to investigate dynamics of macrobenthic biomass related to salinity regimes in the estuary. The model simulation results were interpreted to assess the role of freshwater inflow in controlling benthic productivity. Simulations, based on calibrated parameters (1988–1999), were run for a long-term period from 1988 to 2005. The model performance was found to be promising with the best percent root mean square (RMS) difference being 63% and worst being 92%. Sensitivity tests for the benthic responses to changes in salinity show that, in general, when salinity increased with decreasing nutrient concentrations, deposit feeder biomass increased while suspension feeder biomass decreased. Estuary-wide comparison predicts that reducing freshwater inflow may cause the upper and lower bay communities to respond in different ways. Reduced inflow to Lavaca Bay would result in decreasing benthic biomass; whereas, in Matagorda Bay, biomass would increase. Also, functional diversity would decrease in both bays with decreasing inflow. These effects are probably due to the benthic community acclimating to different salinity regimes, or more (or less) salt tolerant species populating the area. It is concluded that freshwater inflow plays an important role in maintaining the observed character of estuarine productivity through the combined effects of the frequency, duration, timing, and magnitude of inflow, particularly during droughts or low-flow periods.

An evaluation of the health status of the Lavaca Bay, Texas ecosystem using Crassostrea virginica as the sentinel species

Locational risks for compromised ecosystem health for the eastern oysters ( Crassostrea virginica) harvested from Lavaca Bay, Texas were estimated. Flow cytometric evaluation of variations in DNA content and the lysosomal destabilization assay were used for evaluation of genotoxicity and stress, respectively. Bayesian geo-statistical methods were utilized to estimate and evaluate spatial effects. For models with spatial risks, continuous surface maps of predicted parameter values were created to evaluate risk location. Lysosomal destabilization assay results were spatially oriented whereas flow cytometry results were fit best with the random effects model. While not spatially oriented, the highest levels of variations in DNA content were also present near industrial facilities. Locational risks of increased biomarkers of genotoxicity and stress in the eastern oyster ( Crassostrea virginica) were increased with proximity to industrial facilities

Geostatistical analysis of DNA damage in oysters, Crassostrea virginica, in Lavaca Bay, Texas

This study evaluated the health of the marine ecosystem in Lavaca Bay, Texas using the Eastern oyster (Crassostrea virginica) as the sentinel species. Lavaca Bay has a history of having gradients of concentrations of pollutants present with some areas containing concentrations high enough to pose a threat to marine ecosystem health. The Comet assay was used to evaluate for the presence of genotoxic response in oyster hematocytes. Bayesian geostatistical analysis was then used to determine if the DNA damage in oyster hematocytes was spatially oriented and to develop continuous surface maps of the risk of DNA damage in this sentinel species. Results indicated that proximity to industrial facilities increased the locational risk of genotoxicity in this species.

Bayesian spatial modeling of Lavaca Bay pollutants

Locational risk of increased mercury and PAH concentrations in Lavaca Bay, Texas sediments and eastern oysters ( Crassostrea virginica) harvested from Lavaca Bay, Texas were analysed. Chemical analysis results were evaluated utilizing Bayesian geo-statistical methods for comparison of the model fit of a random effects model versus a convoluted model which included both random and spatial effects. For those results fit best with the convoluted model, continuous surface maps of predicted parameter values were created. Sediment and oyster concentrations of mercury and the majority of measured PAHs were fit best with the convoluted model. The locational risks of encountering elevated concentrations of these pollutants in Lavaca Bay sediments and oysters were highest in close proximity to industrial facilities.

The effect of freshwater inflow on net ecosystem metabolism in Lavaca Bay, Texas

Estuaries and other coastal ecosystems depend on freshwater inflow to maintain the gradients in environmental characteristics that define these transitional water bodies. Freshwater inflow (FWI) rates in many estuaries are changing due to changing land use patterns, water diversions for human consumption, and climate effects, but there are no standard criteria to determine minimum inflow rates. An ecological indicator is required so models can be produced to predict how changing hydrology might affect estuarine metabolic rates, productivity, or impairment. One indicator of estuarine metabolic rates is net ecosystem metabolism (NEM). It is hypothesized that metabolic rates (as indicated by NEM) will depend on recently delivered FWI. To test this hypothesis, daily NEM was calculated from high frequency changes in dissolved oxygen measurements in a shallow water estuary, Lavaca Bay, Texas, USA and related to FWI and other environmental conditions. There was a significant relationship between NEM and cumulative ten-day FWI in upper Lavaca Bay, with more heterotrophic conditions occurring after high FWI events. No significant relationship existed between NEM and FWI in lower Lavaca Bay, where other environmental conditions, such as tidal forcing, may be more influential. An empirical model simulating NEM's response to FWI in upper Lavaca Bay was more accurate during moderate to high flows than during low base-flow conditions. Thus, quantity of FWI and distance from the inflow point source constrained the dependence of NEM on FWI. NEM can be quite variable over time and within a bay dominated by a river at one end and ocean exchange at the other end. The range of environmental gradients over time and within an estuary will determine how representative NEM at a single location is for an entire estuary. However, during high flow period pulses NEM can accurately predict shifts from balanced to heterotrophic conditions. Therefore, use of the NEM model as an indicator of FWI effects is constrained to regions in estuaries that are most effected by FWI because of proximity to the source or the size of FWI pulse events. The unique geologic, geographic, and climate signature's of individual estuaries will dictate the fit of this model in space and time. Inclusion of other environmental factors, such as temperature or irradiance, is necessary to improve the NEM model during low base-flow conditions. It is concluded that the NEM model does provide a useful indicator of FWI effects on ecosystem metabolic rates as it works well in the upper regions of Lavaca Bay and during freshwater inflow pulses where and when freshwater inflow has more influence than other environmental factors.

A comparison of the speciation and fate of mercury in two contaminated coastal marine ecosystems: The Venice Lagoon (Italy) and Lavaca Bay (Texas)

We compared the speciation of Hg in two estuaries, Lavaca Bay (Texas) and the Venice Lagoon (Italy). Both are large, shallow embayments that are contaminated by direct discharges from mercury‐cell chlor‐alkali plants and dominated by rapid tidal flushing. Although contaminated by discharges into Lavaca Bay from 1966 to 1979 and into the Venice Lagoon from 1951 to 1989, Hg concentrations have dwindled to similar moderate levels in sediments (200‐2,000 ng g‐1) and water (1‐3 ng L‐1 dissolved) since the advent of pollution abatement. The Venice Lagoon contains lower levels of CH3Hg than Lavaca Bay, which is surprising, given the much larger degree of wetlands coverage in the lagoon. A narrow temporal peak in methylation was seen in early spring at both sites, although it was much stronger in Lavaca Bay. Data indicated that sediment CH3Hg is more strongly correlated with variables such as habitat and seasonality than with total Hg. In Lavaca Bay, because of high sedimentation rates and low remixing, the highest levels of Hg are buried 10‐30 cm below the surface. Combined with previous observations of strong Hg methylation after dredging activities, this argues for leaving Hg‐contaminated sediment in place, to be buried by the deposition of cleaner sediments. In Venice Lagoon, decisions may be complicated by continuous remixing of the upper sediment layers, moving the highest levels of Hg toward the surface and distributing it over a far larger area than has been seen in Lavaca Bay.

DIET OF DOUBLE-CRESTED CORMORANTS (PHALACROCORAX AURITUS) WINTERING ON THE CENTRAL TEXAS COAST

Abstract Diets of double-crested cormorants (Phalacrocorax auritus) wintering on the central Texas coast were determined from the contents of 51 stomachs from Lavaca Bay and 28 stomachs from upper Laguna Madre. Diets consisted primarily of striped mullet (Mugil cephalus) and Gulf menhaden (Brevoortia patronus) in Lavaca Bay and striped mullet and Gulf toadfish (Opsanus beta) in upper Laguna Madre. Birds seemed to prefer striped mullet in both bays, and these fish were significantly larger than the other fish consumed. There were no differences between bays in the numbers of fish in bird stomachs; however, fish consumed by birds in upper Laguna Madre were larger than those taken by birds in Lavaca Bay. Based on the results of this study, there is no evidence that double-crested cormorants pose a significant threat to commercial or sport fisheries on the Texas Gulf Coast.

Long-term variation in mercury concentrations in estuarine organisms with changes in releases into Lavaca Bay, Texas

Mercury releases into Lavaca Bay resulted in public health notices and a fishing closure for crabs and finfish. Mercury containing wastewater discharges were halted in 1970, but sediments were contaminated with mercury. The sediments are a source of mercury to the benthic food web via methylation. Mercury in water column feeding organisms has decreased markedly. Concentrations in benthic food web organisms remain elevated. Human consumption concerns for oysters have ended, but a closure for fishing for crabs and finfish continues. Monitoring of mercury in organisms since 1977 shows a gradual downward trend in mercury in crabs and finfish, but this was not sufficient to remove the closure. Continued releases of mercury, man's activities, and resuspension of sediments keep mercury in the sediment's biologically active zone. This enables the uptake of mercury via the benthic food web. If releases are ended, it will take years for the mercury to decrease to concentrations not of concern for human consumption. If more remediation to reduce the mercury concentrations in the sediments takes place, decrease of mercury in the organisms might occur more quickly.

Sediment quality assessment survey and toxicity identification evaluation studies in Lavaca Bay, Texas, a marine superfund site

A sediment quality assessment survey was conducted in Lavaca Bay, Texas, in proximity to a marine Superfund National Priority List (NPL) site. Previous studies at this site had focused primarily on the degree and extent of mercury contamination. The purpose of this survey was to determine the potential ecotoxicological impacts of contaminants, using sensitive sediment toxicity tests in conjunction with a comprehensive chemical analysis of the sediments. In addition, phase I toxicity identification evaluation (TIE) studies were conducted at several of the more toxic sites. Sea urchin (Arbacia punctulata) fertilization and embryological development tests with sediment pore water were employed to assess the toxicity of the sediments. Elevated levels of mercury were found in a number of samples as much as 10–20 times that of background. Six stations had total polycyclic aromatic hydrocarbon (PAH) concentration above the probable effect level (PEL) guideline value, and some stations had concentrations as much as 1000 times above background levels. Eighteen of the 24 stations exhibited toxicity in one of the toxicity tests, while 14 stations were toxic in both tests. A number of stations within the fish closure area exceeded 8–16 of the PEL guidelines. Both aeration and the C18 column treatments were effective in reducing toxicity from the pore water of the two stations included in the TIE. This information, in conjunction with the fact that two of the four stations with the highest mercury concentrations were not toxic, suggests that the toxicity observed in this study is primarily due to organics, probably PAHs, and not mercury. We recommend that these other contaminants of concern be considered in any remedial actions that are planned for this NPL site and that impacts on the ecosystem, as well as human health issues, also be considered. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 20–30, 2001

Sediment quality assessment survey and toxicity identification evaluation studies in Lavaca Bay, Texas, a marine superfund site

A sediment quality assessment survey was conducted in Lavaca Bay, Texas, in proximity to a marine Superfund National Priority List (NPL) site. Previous studies at this site had focused primarily on the degree and extent of mercury contamination. The purpose of this survey was to determine the potential ecotoxicological impacts of contaminants, using sensitive sediment toxicity tests in conjunction with a comprehensive chemical analysis of the sediments. In addition, phase I toxicity identification evaluation (TIE) studies were conducted at several of the more toxic sites. Sea urchin (Arbacia punctulata) fertilization and embryological development tests with sediment pore water were employed to assess the toxicity of the sediments. Elevated levels of mercury were found in a number of samples as much as 10-20 times that of background. Six stations had total polycyclic aromatic hydrocarbon (PAH) concentration above the probable effect level (PEL) guideline value, and some stations had concentrations as much as 1000 times above background levels. Eighteen of the 24 stations exhibited toxicity in one of the toxicity tests, while 14 stations were toxic in both tests. A number of stations within the fish closure area exceeded 8-16 of the PEl guidelines. Both aeration and the C18 column treatments were effective in reducing toxicity from the pore water of the two stations included in the TIE. This information, in conjunction with the fact that two of the four stations with the highest mercury concentrations were not toxic, suggests that the toxicity observed in this study is primarily due to organics, probably PAHs, and not mercury. We recommend that these other contaminants of concern be considered in any remedial actions that are planned for this NPL site and that impacts on the ecosystem, as well as human health issues, also be considered.

Determination of a site-specific reference dose for methylmercury for fish-eating populations.

Determination of a site-specific reference dose for methylmercury for fish-eating populations.

Trophic accumulation and depuration of mercury by blue crabs ( Callinectes sapidus) and pink shrimp ( Penaeus duorarum)

Mercury concentrations in blue crabs ( Callinectes sapidus) collected from an area of mercury-contaminated sediments in Lavaca Bay, TX, USA, are more than an order of magnitude greater than concentrations in penaeid shrimp from the same area. Laboratory feeding experiments using mercury-contaminated fish as food showed that both blue crabs and pink shrimp ( Penaeus duorarum) could accumulate mercury concentrations comparable to those in their food in 28 days. Calculated mercury assimilation efficiencies averaged 76% for blue crabs and 72% for pink shrimp. Significant depuration of mercury by blue crabs was not observed during a subsequent 28-day period, but pink shrimp lost mercury at a rate of about 0.012 day −1. Model calculations predict biomagnification factors of mercury of about two to three at steady state for both species. The large difference in observed concentrations of mercury in field-collected blue crabs and penaeid shrimp does not result from differences in efficiency of mercury assimilation from their food or from differences in excretion rates. It is more likely the result of differences in residence times in the contaminated area and of differences in feeding habits.

Changes in mercury speciation and the release of methyl mercury as a result of marine sediment dredging activities

During the dredging of a moderately contaminated marine waterway (Lavaca Bay, Texas, USA), high concentrations of total mercury (THg, 75–1533 ng/l) and methyl mercury (MHg, 5–70 ng/l) were observed in the decant water from an upland dredge spoils settling basin. By comparison, the water column of the bay contains 7–200 ng/l THg and 0.05–0.8 ng/l MHg. The Hg concentrations observed in the decant water were higher than could be accounted for by the release of sediment pore water, which contained elevated MHg (2–200 ng/l) in the surface 3 cm of the sediments, but diminished exponentially with depth. Laboratory mixing experiments showed that approximately 5% of the sediment bound MHg, and less than 1% of the total mercury was released upon shaking with seawater. Although significant MHg releases could occur from the upper 0–5 cm of the sediments, when integrated over the entire dredged volume, this source is insufficient to account for the levels found in the settling basin decant water. The settling basin became very biologically active, containing algal blooms and releasing hydrogen sulfide to the air, suggesting that increased methylation in the disturbed sediment was responsible for the releases. A laboratory mesocosm study was performed to simulate the findings in the settling pond, but no obvious increase in biological activity occurred, and MHg concentrations increased only to 0.6 ng/l. The implications of these observations may be significant for the local region approximately a dredging site, although crude mass balance considerations show that the MHg flux from this source is trivial compared to bay-wide processes.