Browsing by Subject "Salinity"
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Item The ecology of blue crab (Callinectes sapidus) megalopae in the Mission-Aransas Estuary, Texas : salinity, settlement, and transport(2013-12) Bittler, Kimberly Marie; Buskey, Edward Joseph, 1952-Blue crabs are a widely distributed estuarine species with broad economic and ecological importance. Several studies have linked blue crabs to freshwater inflows, but the precise nature of this link is still uncertain, as blue crabs have a complex life cycle that utilizes both marine and estuarine environments. One potential link between blue crabs and freshwater inflows is during recruitment, when megalopae developing offshore return to estuaries before molting into juvenile crabs. Megalopae swim during the flood tide to ensure delivery into and farther up estuaries. The behaviors regulating selective tidal stream transport (STST) on the flood tide were originally studied in North Carolina in an estuary with regular freshwater inflows and a strong salinity gradient. The model of STST was re-examined in the Mission-Aransas, an estuary with episodic freshwater inflows and salinity gradients ranging from normal estuarine conditions to hypersaline during droughts. The behavioral responses of megalopae to a range of rates of salinity increase were tested, and then modeled onto rates of salinity change observed in the field to determine the theoretical ecological consequences of STST for blue crab populations in the Mission-Aransas Estuary. To validate the ecological trends predicted by the behavioral model of STST, a simple, long-term data set reflecting changes in megalopae abundance is needed. Hog’s hair collectors are a simple and widely used method of quantifying abundance of brachyuran megalopae, including blue crabs. However, the efficiency of hog’s hair collectors in sampling for megalopae is unknown. Several studies have reported poor correlations between settlement on hog’s hair collectors, transport, and abundance of megalopae in the plankton due to disparate temporal scales and potentially turbulence-driven decoupling. Each of these issues were addressed in field and flume experiments, which were used to develop a model for interpreting settlement on hog’s hair collectors in terms of transport and planktonic abundance.Item Experimental and mathematical investigation of dynamic availability of metals in sediment(2009-12) Hong, Yongseok; Reible, Danny D.; Kinney, Kerry A.Contaminated sediments are periodically subjected to resuspension processes during either storm events or due to dredging. In sediments, metals are often contained in insoluble low bioavailability forms. Upon resuspension, however, biogeochemical processes associated with the exposure to more oxic conditions may lead to transformation and release of the metals, giving rise to exposure and risk in the water column. Batch experiments suggested that oxidation of reduced species and corresponding pH decrease were the most importance processes controlling metals release upon sediment resuspension. A mathematical model was implemented to better understand the complex underlying biogeochemical reactions that affect metals release. The model described the metals dynamics and other inter-related important biogeochemical factors well and was successful at predicting the metals release from different sediment reported in the literature. Tidal and other cyclic variations in oxygen, pH and other relevant parameters in the overlying water may also lead to cyclic transformations and release of metals from surficial sediments. In simulated estuarine microcosm experiments, cyclic variations in pH and salinity due to freshwater/saltwater exchange were shown to lead to cyclic variations in metal release. Both pH and salinity were important factors controlling interstitial dissolved metals concentrations, however, in terms of freely dissolved metals concentrations, which have been considered to be more related with toxicity and bioavailability, pH was the single most important parameter. The mathematical model was extended to the conditions of the cyclic behavior in an estuary and successfully described metals release under such conditions. It is believed that the model can be used to predict the metals behavior in other sediments and conditions by model calibration with a similar experimental approach to that used in this study.Item Genetic basis for ichthyotoxicity and osmoregulation in the euryhaline haptophyte, Prymnesium parvum N. Carter(2014-05) Talarski, Aimee Elizabeth; La Claire, John W., 1951-There is limited information currently available regarding the underlying physiological responses and molecular mechanisms of osmoregulation, acetate metabolism [in relation to the synthesis of glycerolipids, polyunsaturated fatty acids (PUFA), and ichthyotoxins], and transport in Prymnesium parvum N. Carter, a microalga that causes devastating harmful algal blooms (HAB) worldwide. This dissertation examines gene expression under environmental conditions that are associated with HAB formation, including phosphate limitation and low salinity, using microarrays and RNA sequencing (RNA-Seq). A comparative fatty acid methyl ester (FAME) analysis at 30 vs. 5 practical salinity units (psu) was performed to gain additional insight into acetate metabolism. The RNA-Seq analysis included a de novo assembly of the P. parvum transcriptome, generating 47,289 transcripts, of which 35.4% were identifiable. This permitted the evaluation of the expression of many more genes compared with the microarray analysis, which examined ~3,500 genes. Relevant candidate genes identified included those whose products are involved in osmolyte production, salinity stress, and ion transport. With respect to the putative synthesis of polyketide ichthyotoxins, 32 different polyketide synthase (PKS) transcripts were identified in the transcriptome assembly, none of which were differentially expressed. Hemolysin and monogalactosyldiacylglycerol synthase were downregulated at 30 vs. 5 psu, suggesting the increased presence of additional ichthyotoxins at the lower salinity. Evidence for several PUFA synthesis pathways was also revealed. Fatty acid compositions were largely similar at the two salinities, containing relatively prominent quantities of the PUFA stearidonic acid, but compositions varied among strains. The transcription of genes whose products are associated with vesicular transport was elevated, and higher levels of extracellular prymnesins were observed in HAB-forming conditions. Thus, with regard to acetate metabolism, I have revealed evidence for the post-transcriptional regulation of the production of prymnesins and the contributory effects of hemolysin, monogalactosyldiacylglycerol, and PUFA towards ichthyotoxicity. Further, I propose that toxin transport is triggered in HAB-forming conditions, in which the toxins are actively being excreted. Collectively, these data shed light on the transcriptional responses that occur following alterations in phosphate availability and salinity, including those associated with the synthesis and delivery of a number of potential ichthyotoxins from P. parvum.Item Influence of the Mississippi River plume on diazotroph distributions in the northern Gulf of Mexico during summer 2011(2012-08) Knapke, Ellen Marie; Villareal, Tracy A.; Buskey, Edward J.; Erdner, DeanaIn the subtropical oligotrophic ocean, nitrogen fixation is an important source of new nitrogen (N) for supporting biological production. Previous studies have found that nitrogen-fixing Diatom-Diazotroph Associations (DDAs) are in high abundance in the intermediate salinity zone of large river plumes such as the Amazon and Mekong rivers, while Trichodesmium spp. becomes more abundant at higher salinities. This recurring pattern in the Amazon River plume suggests that strong salinity and nutrient gradients within the river plumes may lead to a cascade in diazotroph communities. I hypothesized that the Mississippi River, a major source of freshwater, nutrients and sediments to the northern Gulf of Mexico, creates a similar distribution of diazotroph communities. The relationship between large diazotrophs and salinity was examined in samples collected in July 2011 during a flood outflow from the Mississippi River. The dominant DDA, Hemiaulus spp. – Richelia spp., was at greatest abundance (≈31,000 cells L-1) west of the birdfoot delta on the periphery of the plume (≈29 salinity) where bottom water hypoxia was also observed. Trichodesmium spp., a cyanobacterium genus that occurs in both colonial and free trichome morphologies, was abundant at both high (≈35) salinities east of the delta reaching 20+ colonies L-1, as well as in the fresher (≈28) waters of the plume where it reached 3,500 trichomes L-1. Diazotroph distributions were separated east and west of the Mississippi River outflow, with DDAs being most abundant over bottom water hypoxic regions to the west and Trichodesmium spp. in high abundance to the east. The diazotroph – salinity gradient relationships present within the Amazon River plume were not present within the Gulf of Mexico. This study suggests that environmental factors other than salinity, such as nutrients or hypoxia, are influencing the distribution of diazotrophs around the Mississippi River plume. The seasonal hypoxia seen in the Gulf of Mexico with the co-occurring DDA increase could appear in other river systems.Item Physiological Effects of Saline Water on Two Economically Important Horticultural Crops in South Texas(2013-12-02) Simpson, Catherine RossCitrus and watermelons are valuable economic crops worldwide, contributing approximately $120 million combined each year in Texas alone. Both citrus and watermelons are sensitive to saline conditions, which can be problematic in the Lower Rio Grande Valley where they are commonly produced. As Texas increases the percentage of irrigated agriculture each year, and in turn the amount of land potentially exposed to salinization through this practice, grafting salt sensitive plants to tolerant rootstocks becomes a more feasible way to overcome this challenge. Grafting typically improves disease resistance, cold tolerance, yield, fruit quality and has been shown to improve salt tolerance as well. While citrus is commonly grafted to rootstocks that induce desirable qualities in the scion, watermelon grafting is only common in Asia and several European countries due to cost constraints. The main goal of this research was to assess selected rootstocks for salinity tolerance by evaluating plant growth and physiological parameters when subjected to several salinity levels. In the first experiment, potential sour orange replacement rootstocks C22 and C146 were evaluated for salinity as ungrafted trees and grafted to the Olinda Valencia scion. These trees were then compared to the performance of grafted and ungrafted sour orange trees. The results suggest that C22 and C146 rootstocks are more tolerant to saline conditions than sour orange rootstocks at moderate salinity levels. However, grafting significantly decreased all measured growth and physiological parameters for all rootstocks implying that this scion-rootstock combination may not be ideal. In the second experiment, TAMU mini watermelons were grafted to four rootstocks to determine if any of these would improve their performance when subjected to poor quality irrigation water. Of the four rootstocks and ungrafted TAMU mini watermelon, Strong Tosa showed the most growth when subjected to moderate salinity. Salinity treatments were found to increase fruit quality by increasing the percentage of sugar (brix) and fruit flesh firmness.Item Salinity routing in reservoir system modeling(Texas A&M University, 2007-04-25) Ha, Mi AeThis research evaluates and improves capabilities incorporated in the Water Rights Analysis Package (WRAP) modeling system for tracking salt loads, particularly for applications dealing with natural salt pollution problems that are prevalent in several major river basins in Texas and neighboring states. WRAP is the river/reservoir system simulation model incorporated in the Water Availability Modeling (WAM) System applied by agencies and consulting firms in Texas in planning and water right regulatory activities. A salinity simulation component of WRAP called WRAP-SALT was developed recently at Texas A&M University. WRAP-SALT was based on the premise of complete mixing within the monthly computational time step. However, salt concentrations actually have time variation throughout a reservoir. This thesis research investigates more realistic salinity routing methods. Historical gauged data provide a basis for calibration of routing parameters. The timing of the inflow load to determine outflow concentration is calculated by lag parameters with the monthly time steps. Complete mixing occurs during the lag months. Two options are incorporated into WRAP-SALT for setting the lag parameter. With the first option, the model-user sets a constant that is applied during every month of the simulation. This option requires calibration studies to determine the lag. With the alternative option, a variable lag is computed within the model in each month based on the concept of retention time, which is a representation of the time required for a monthly volume of water and its salt load to flow through a reservoir. When the lag is activated, the accuracy between observed and computed mean monthly salinity concentrations through the reservoir is generally improved. The basin-wide simulation was performed for the Brazos River Basin for conditions with and without salt control dams proposed by the Corps of Engineers. The proposed salt control impoundments improve water quality throughout the basin.Item Screening of alfalfa (Medicago sativa) cultivars for salt tolerance in West Texas(2008-12) Scasta, John D.; Foster, Mike; Trostle, Calvin S.; Green, Cary J.; Zhang, Hong; Auld, Dick L.Alfalfa (Medicago sativa) is a very important crop commodity in the Trans-Pecos region of Texas and New Mexico where salinity problems occur in the soil and irrigation water resources. There has been significant research in the area of salt tolerance of alfalfa but there is need for screening current and experimental alfalfa cultivars to assist growers with variety selection. Due to the complexity of salinity tolerance in plants, it is also necessary to compare laboratory and greenhouse screening methodologies and results to field conditions. These experiments were designed to evaluate commercial and experimental alfalfa cultivars at different growth stages and varying salinity concentrations and assess correlations between laboratory, greenhouse and field experiments. In addition to salinity tolerance, there is a need to evaluate alfalfa cultivars for potential quality differences between varying fall dormancy (FD) ratings to assist growers in cultivar selection. The first experiment evaluated plant germination under increasing levels of salt concentrations conducted in the laboratory. Statistical differences were observed for percentage germination among cultivars which could influence stand establishment of alfalfa in saline conditions. These differences in turn are exhibited in the IC(50) values which reflect osmotic potential required to inhibit 50% of seed from germination. The second experiment evaluated forage production under two levels of salt concentration conducted in the greenhouse. There were no significant differences in raw or transformed SCR values among the 32 cultivars at Cut 2, Cut 3 or Cut 4 when subject to analysis of variance. SCR values were then evaluated for statistical differences using the three harvests as replications over time. Significant differences in raw and transformed SCR values were found between cultivars with Cut 2, Cut 3 and Cut 4 serving as replications over time. The third experiment evaluated forage production under saline field conditions that exist at the Texas AgriLife Research Station west of Pecos, TX. Throughout the two-year project significant differences among cultivar yields were observed only 4 out of the 13 (31%) harvests at alpha = 0.05 (6 out 13 exhibited significant differences when using alpha = 0.1). There were no significant differences when two-year totals or when two-year averages were subjected to ANOVA. It should be noted that all 12 of the cultivars in this experiment were selected for the potential to tolerate saline conditions (based upon breeding or adaptation of the cultivar) and therefore all were expected to perform well under saline conditions. However, the differences seemed to become more apparent later in the growing season, perhaps indicating salt stress has a more severe impact over the long term (i.e., salt loading during the year, salt loading during the life of the stand, etc). When comparing data from the three experiments several principles become evident. First, as percentage germination increases regrowth potential decreases indicating a negative correlation. However, as percent germination increases potential yield under saline conditions increases. Second, as percent germination increases the potential field production and yield also increases. Third, as Salt/Control Ratio (SCR) values increase production potential in the field decreases indicating a negative correlation. However, as average saline yields in the greenhouse increase potential yield under saline conditions in the field also increased. The fourth experiment compared fall dormancy (FD) ratings and forage quality data and no significant differences between FD8 and FD10 alfalfa cultivars evaluated were found to exist over the course of a growing season. The data does, however, show that differences can exist at individual cuttings during the growing season although it seems to be more the exception than the rule. Therefore, forage quality differences between FD8 and FD10 alfalfa cultivars may occur, but in general should not be a factor for producers when selecting cultivars.Item The role of naturally occurring waterholes in determining the distribution of Florida Key Deer(2009-05-15) Kim, Ji YeonThe purpose of my research was to test the hypothesis that the availability of fresh, naturally occurring water may limit the distribution of Florida Key Deer (Odocoileus virginianus clavium). More specifically, I was trying to determine if there was enough fresh, drinkable water for the deer on each of the islands. To test the hypothesis, I developed a model that simulated likely seasonal fluctuations in fresh water availability in naturally occurring waterholes within the Key Deer range. I estimated 60 scenarios representing different weather (precipitation and evaporation) conditions, different literature estimates of the daily water requirement of Key Deer and also different upper salinity thresholds for drinkable water. Results showed that 1) even under the most favorable conditions in terms of fresh water availability, there was not enough fresh, drinkable water for the deer on any of the islands. Results also showed that 2) high salinity was important in determining the fresh water availability to the deer, in addition to the lack of water volume. Although these results suggest a prolonged seasonal shortage of fresh, naturally occurring water on each of the islands, deer were present on all of the islands during all seasons. One possible reason for the lack of correlation between Key Deer distribution and naturally occurring waterholes is the availability of man-made water sources (e.g. birdbaths, swimming pools).Item Understanding salinity tolerance of three high plains bedding plant species in a hydroponics setting(2013-08) Grubbs, Rebecca; McKenney, Cynthia B.; Montague, David T.; Oswalt, SteveIncreased salinity levels in irrigation water are often attributed to natural weathering, as well as runoff from industrial and agricultural production. As fresh water sources rapidly deplete on a global scale, availability of quality irrigation water has become an issue in many regions of the United States. Salinity tolerance mechanisms in plants are generally sorted into one or more of three established salt responses (exclusion, excretion, and accumulation). Although poorly understood, tolerance mechanisms may be enhanced through any number of environmental variables including presence of soluble calcium in soil or water. Three species of bedding plants, Artemisia schmidtiana ‘Silver Mound’ (Silver Mound Artemisia), Eustoma exaltatum ssp. russellianum (Texas Bluebells) and Anisacanthus quadrifidus (Hummingbird Bush) were evaluated for their respective salinity tolerance to increased levels of sodium (Na) and calcium (Ca). Species were suspended in a hydroponic system using a randomized complete block design with a control (~1.5 dS/m) and three salinity treatments (3 mS/cm, 6 mS/cm and 12 mS/cm) mixed using a 2:1 ratio of Na to Ca. Nutrients were provided via a half-strength Hoagland’s solution. After 90 days, dry weight and length measurements were taken on root and shoot tissue. Tissue was then dried and ground for tissue analysis to determine % Na, % Ca and Cl ppm and identify salt mobility into the leaves. Tissue analysis could only be performed on A. schmidtiana ‘Silver Mound’ and A. quadrifidus, as E. exaltatum ssp. russellianum had insufficient tissue. Generally, no differences were found between treatments with either A. schmidtiana ‘Silver Mound’ or E. exaltatum Texas Tech University, Rebecca Grubbs, June 2013 iv ssp. russellianum. Linear regression analyses indicate there was a decrease in root and shoot lengths in A. quadrifidus with increasing salinity levels. Additional regression analysis also indicates shoot dry weights decreased with increasing salinity. However, there was no relationship between root dry weight and salinity level. As expected, an increase in salinity yielded a positive slope with % Na and Cl ppm. There was no relationship determined between higher salinity and % Ca suggesting the possibility that limited calcium mobility may have been overwhelmed by sodium influx resulting in the overall decline in plant health.Item Wettability alteration in high temperature and high salinity carbonate reservoirs(2011-08) Sharma, Gaurav, M.S. in Engineering; Mohanty, Kishore Kumar; Pope, Gary A.The goal of this work is to change the wettability of a carbonate rock from oil wet-mixed-wet towards water-wet at high temperature and high salinity. Only simple surfactant systems (single surfactant, dual surfactants) in dilute concentration were tried for this purpose. It was thought that the change in wettability would help to recover more oil during secondary surfactant flood as compared to regular waterflood. Three types of surfactants, anionic, non-ionic and cationic surfactants in dilute concentrations (<0.2 wt%) were used. Initial surfactant screening was done on the basis of aqueous stability at these harsh conditions. Contact angle experiments on aged calcite plates were done to narrow down the list of surfactants and spontaneous imbibition experiments were conducted on field cores for promising surfactants. Secondary waterflooding was conducted in cores with and without the wettability altering surfactants. It was observed that barring a few surfactants, most were aqueous unstable by themselves at these harsh conditions. Dual surfactant systems, a mixture of a non-ionic and a cationic surfactant increased the aqueous stability of the non-ionic surfactants. One of the dual surfactant system, a mixture of Tergitol NP-10 and Dodecyl trimethyl ammonium bromide, proved very effective for wettability alteration and could recover 70-80% of OOIP during spontaneous imbibition. Secondary waterflooding with the wettability altering surfactant (without alkali or polymer) increased the oil recovery over the waterflooding without the surfactants (from 29% to 40% OOIP). Surfactant adsorption calculated during the coreflood showed an adsorption of 0.24 mg NP-10/gm of rock and 0.20 mg DTAB/gm of rock. A waterflood done after the surfactant flood revealed change in the relative permeability before and after the surfactant flood suggesting change in wettability towards water-wet.