Ecosystems - Texas

Collaborators – Stephen Davis, James Pinckney, Fran Gelwick, James Heilman, Kevin McInnes, David Zuberer

Graduate Students – Hsiu-Ping Li (Erin), George Gable, Carrie Miller
Former Graduate Students – Yesim Buyukates, Justin Murdock, Elizabeth Fejes

Freshwater inflows and health of the San Antonio Bay System

Given the state’s plans for water diversion in the San Antonio River watershed, an understanding of the importance of freshwater inflow events on the health of the San Antonio Bay System is needed. In this research we are sampling parameters in the bay that are linked to system health, which include primary productivity and community respiration, phytoplankton and zooplankton community structure, internal and external nutrient loading, and various system-wide water-quality parameters. Volume-flux of freshwater from the Guadalupe River into the San Antonio Bay System is also being measured using in-field flow meters, data loggers, and refrigerated autosamplers. The system-wide water-quality parameters are being measured using a newer technology, i.e., Dataflow, which will enable us to measure temporal changes in a variety of parameters, which include salinity, chlorophyll a, and FDOM (click here for data information). In addition to the field sampling, laboratory microcosm experiments are being conducted to ascertain the effect of inflow periodicity and magnitude on natural plankton assemblages from the bay. The synthesis of information collected from this study and other ongoing studies in this system will provide a better understanding of the relationships between the nature of pulsed inflow events (periodicity and magnitude of inflow) and estuarine ecosystem health, thus allowing water managers to optimize their diversion of freshwater while minimizing impact to estuarine integrity

Freshwater inflows and health of the Galveston Bay System

The Galveston metropolitan area is predicted to grow significantly in the coming decades. This will undoubtably stress the Galveston Bay System in terms of freshwater inflows (periodicity and magnitide), nutrient loading, and pollution. As with the San Antonio Bay System, we are undertaking studies that will increase our understanding of the importance of freshwater inflow events on the health of the Galveston Bay System. In this research we are sampling parameters in the bay that are linked to system health, which include primary productivity and community respiration, phytoplankton and zooplankton community structure, internal and external nutrient loading, and various system-wide water-quality parameters (click here for data information). We are again measuring the volume-flux of freshwater into this system, this time from the Trinity and San Jacinto Rivers. The system-wide water-quality parameters will be measured using a newer technology, i.e., Dataflow, which will enable us to measure temporal changes in a variety of parameters, which include salinity, chlorophyll a, and FDOM. As with the San Antonio Bay research, we anticipate that the synthesis of information collected from this study will provide a better understanding of the relationships between the nature of pulsed inflow events (periodicity and magnitude of inflow) and estuarine ecosystem health.

Microalgal productivity, community composition, and pelagic food web dynamics in a semi-tropical, turbid salt marsh isolated from freshwater inflow

Carbon entering the foodweb originating from microalgal productivity may be as important to salt-marsh consumers as carbon originating from vascular plant production. The objective of this study was to further our understanding of the role played by microalgae in salt marshes. We focused on microalgal productivity, community dynamics, and pelagic food web linkages. We sampled the upper Nueces Delta in southeast Texas, USA, a shallow, turbid system of ponds and elevated vegetated areas stressed by low freshwater inflow and salinities ranging from brackish (11) to hypersaline (300). Despite high turbidity and low external nutrient loadings, microalgal productivity was on the order of that reported for vascular plants. Primary productivity in surface waters ranged from ~0 to 2.02 g-C m-2 day-1 and was usually higher than primary productivity associated with the benthos, which ranged from ~0 to 1.14 g-C m-2 day-1. This was likely due to high amounts of wind-driven resuspended sediment limiting production at greater depths. Most of the water column microalgal biovolume seemed to originate from the benthos and was comprised mostly of pennate diatoms. But true phytoplankton taxa were also observed, which included cryptomonads, chlorophyhtes, dinoflagellates, and cyanobacteria. Interestingly, succession from r-selected to K-selected taxa with the progression of spring, a common phenomena in aquatic systems, was not observed. Rather, co-dominance by both potentially edible and less-edible taxa was found. This was likely due to decreased grazing pressure on r-selected taxa as salinity conditions became unfavorable for grazers. In addition to a decoupled foodweb, reduced primary and net productivity, community respiration, and microalgal and zooplankton population densities were all observed at extreme salinities. Our findings suggest that a more accurate paradigm of salt marsh functioning within the landscape must account for microalgal productivity as well as production by vascular plants. Because the value of microalgal productivity to higher trophic levels is taxa-specific, the factors that govern microalgal community structure and dynamics must also be accounted for. In the case for the Nueces Delta, these factors included wind-mixing and increasing salinities.

Interactions between flow, periphyton, and nutrients in a heavily impacted urban stream: Implications for stream restoration effectiveness

Urban stream restoration is a very complex task due largely to the interactions between the physical, chemical, and biological stream components. Because of these interactions, restoring only a single component to a more natural state could have a negative affect on stream health. We studied pre-restoration interactions between hydrology, nutrients, and periphyton in a stream where wastewater effluent and a highly developed urban watershed dominated stream flow. Floods capable of scouring all visible periphyton from the stream were produced from rainfall events as small as 1.3 cm and created 47 periphyton biomass reset events during our 22-month study period. Despite these disturbances, periphyton biomass rapidly accumulated throughout the stream and reached nuisance levels after five days of growth during every season. Floods did however severely limit the occurrence of steady state assemblages, which attained biomass levels 30 times the nuisance level. Although the high frequency of floods did not prevent nuisance levels of periphyton, it did allow more edible early-stage periphyton assemblages to become far more common than late-stage, less edible assemblages. In the case of the stream studied, a successful restoration strategy must consider coupled processes relating to hydrology, chemistry, and biota.