“Water quality, nutrient and phytoplankton dynamics in Baffin Bay (Texas)” currently funded by Celanese Corporation, Texas General Land Office/NOAA Coastal Management Program; previously funded by Kleberg County, Coastal Conservation Association, Saltwater Fisheries Enhancement Association, Coastal Bend Bays & Estuaries Program

Baffin Bay is undergoing significant eutrophication, as exemplified by a long-term increase in nitrogen, phosphorus and chlorophyll a concentrations.  Additional symptoms include blooms of the brown tide organism, Aureoumbra lagunensis, and other potential HAB species (Pyrodinium bahamense), episodic hypoxia and fish kills.  In response to concerns over water quality changes in Baffin Bay, we recently initiated an integrated water quality monitoring program using discrete sample collections and field deploy-able sensor networks to:  1) quantify the spatial-temporal extent of indicators of water quality degradation, and 2)  characterize the ecosystem response to loading events, including from episodic storm events.





“Identification of organic matter sources contributing to hypoxia formation in two eutrophic South Texas estuaries: relationships to watershed land use practices” funded by Texas Sea Grant

South Texas coastal embayments are undergoing dramatic environmental changes due to climate change (i.e., prolonged drought, increasing air and water temperatures), land use change (i.e., increasing prevalence of agricultural activities or urbanization) and increasing human freshwater needs. Two systems of particular concern, Baffin Bay and Oso Bay, currently exhibit a number of symptoms of water quality degradation. Each system receives elevated allochthonous inorganic nutrient and organic matter loads and experiences persistent phytoplankton blooms as well as episodic hypoxia.  Despite this, the source(s) of organic matter fueling hypoxia in each are largely unknown.  The main project goal is to identify the dominant source(s) of organic matter fueling hypoxia in Baffin Bay and Oso Bay. Study objectives are to: 1) quantify the lability of organic matter from phytoplankton and tributaries varying in land use coverage in each system, and 2) quantify oxygen consumption rates in the water column and sediments of each system.



Vibrio as a model microbe for opportunistic heterotrophic response to Saharan dust deposition events in marine waters” funded by NSF Biological Oceanography

Dust and mineral aerosols are a significant source of micro and macronutrients to oligotrophic ocean surface waters. Evidence is growing that heterotrophic microbes may play key roles in processing deposited minerals and nutrients. Yet it is not known which components of dust stimulate the heterotrophic bacteria, which cellular mechanisms are responsible for the utilization of those components and how the activity of these bacteria affects the availability and utilization of dust-derived minerals and nutrients by marine autotrophs. Knowledge of these factors is key to understanding how dust deposition impacts carbon cycles and for predicting the response of tropical oceans to future changes in the frequency and intensity of dust deposition events. The objective of this study is to examine the specific effects of aeolian dust on heterotrophic microbes in a tropical marine system under controlled conditions. The central hypothesis is that in oligotrophic tropical systems numerically minor opportunistic bacteria are the first responders to influx of dust constituents and respond primarily by rapidly accessing soluble trace metals and limiting nutrients that are deposited with Saharan dust. The study focuses on two specific aims: 1) 1uantify changes in community structure, composition and transcriptional activity among marine microbial populations upon exposure to dust, and 2) identify key components in Saharan dust aerosols that stimulate or repress growth and/or activity in Vibrio spp., a model opportunistic marine heterotrophic bacteria.


Dust_schematic mesocosms



“The hydrological switch: a novel mechanism explains eutrophication and acidification of estuaries” funded by NOAA CSCOR

Humans have had a significant influence on estuaries through land use change and increased use of fertilizers, causing proliferation of algal blooms, hypoxia, and presence of harmful microbes. Now, acidification due to myriad processes has been identified as a potential threat to many estuaries. In Texas estuaries for example, short-term acidification as a result of episodic hypoxia is a well-documented phenomenon. Unfortunately, a longer-term trend toward chronic acidification (decreasing alkalinity, pH) has now been observed. The alkalinity decrease is likely caused by a reduction in riverine alkalinity export due to precipitation declines under drought conditions and freshwater diversions for human consumption. Significant human population growth and land use change has also occurred in Texas coastal watersheds, resulting in growing symptoms of eutrophication. Thus it is conceivable that multiple stressors could be coupled spatially or temporally in these systems, including dense algal blooms, hypoxia and acidification, with potential for direct (mortality) and indirect (reduced growth/reproductive output, increased disease prevalence) effects on estuarine organisms. With projected future ocean acidification scenarios, continuing freshwater shortages due to climate change, increased water diversions, and rapidly growing human populations in coastal watersheds, these estuaries will likely face more serious acidification risks and deteriorating ecosystem health. Based on our existing long-term data, we hypothesize that hydrology acts as a switch, where increased river flows cause hypoxia and short-term acidification due to increased loads of organic matter, whereas prolonged low flows cause long-term acidification due to reduced loads of riverine alkalinity and calcification. In urbanized, wastewater-influenced systems, we hypothesize that reduced flows out of the watershed may lead to long-term acidification and chronic hypoxia due to reduced loads of riverine alkalinity and presence of low pH, high nutrient/organic matter wastewater. To test our hypotheses, field and modeling studies will be conducted to examine the relationships between estuarine acidification and other stressors (i.e., reduced freshwater inflow, hypoxia, and nutrient loading).

Fish_kil Oso_export