Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Samples were collected every two weeks (March-October) or monthly (November-February) using Mission-Aransas National Estuarine Research Reserve Small Boat.  Water samples from both the surface (~0.5 meters) and the bottom of the water column (within 0.5 m from the sediment-water interface) were obtained using a Van Dorn water sampler. 

Following the standard ocean acidification operating protocol, unfiltered water samples were collected in 250 mL borosilicate glass bottles for carbonate system characterization. 100 µL saturated mercuric chloride (HgCl2) was added into the sample bottles and bottle stoppers were replaced after the application of Apiezon® L grease and secured with a rubber band and hose clamp. These preserved samples were used for salinity, total alkalinity (TA), total dissolved inorganic carbon (DIC), and pH analyses within two months of sample collection.

In-situ temperatures at both the surface (~0.5 m) and the bottom of the water column (within 0.5 m from the sediment-water interface) were obtained using a calibrated YSI 6920 multisonde. Salinity was measured using a benchtop salinometer (Orion Star™ A12, Thermo Scientific) which was calibrated using MilliQ and known salinity certified reference material (CRM). Total Alkalinity (TA) was analyzed at 22±0.1°C using Gran titration on an automated titration system (AS-Alk2, Apollo Scitech Inc.). DIC was analyzed using infrared detection on an AS-C3 DIC analyzer (Apollo Scitech Inc.). Certified reference material was used to ensure the quality of the analysis and optimal performance of the instruments. Total scale pH for salinity ≥20 samples was measured on a spectrophotometer at 25°C using purified m-cresol purple. The equation in Liu et al. (2011) was used in the calculation of pH values. For low salinity waters (<20) prior to September 28th, 2017, a potentiometric method was used to measure pH. An Orion® Ross™ high precision glass electrode was used and three pH standards (4.01, 7.00, and 10.01) were used to calibrate the electrode. Beginning September 28th, 2017, the low salinity samples were also run on the spectrophotometer, and the Douglas and Byrne (2017) equation was used to calculate pH on total scale.  Calcium concentration ([Ca2+]) was measured (from non-preserved water samples) using an automatic titration with an ethylene glycol tetraacetic acid (EGTA) titrant on a Metrohm Titrando. The end-point was detected using a Metrohm calcium ion-selective electrode.

NSF Award Abstract:

This project is a CAREER award to Xinping Hu at Texas A&M University-Corpus Christi. Hu proposes to integrate research and education in an investigation of carbon cycling and ocean acidification in the Mission-Aransas Estuary in South Texas. This coastal system is strongly affected by changes in river flow between seasons and from year to year. The relationship of changing river flows to carbon cycling in estuaries is not well understood. This lack of understanding in turn contributes to uncertainty in estimating global estuarine carbon budgets. In addition, climate change and other human activities heavily influence riverine input into estuaries and the coastal ocean, which then affect biogeochemistry and metabolism in these environments. Despite the need for this information, long-term records that can help to address the change in the strength and directions of CO2 fluxes in these ecosystems are very rare. Using high-intensity field sampling and analysis of historical data, this project aims to improve understanding of carbon cycling in this estuary and in the coastal ocean in general. The results obtained from this study will also provide key information about the biogeochemical response of estuaries to changing hydrologic conditions, as the southwestern U.S. grows drier with overall declining precipitation.

The research objectives of this project include 1) investigating the relationship between hydrologic state and estuarine CO2 partial pressure (pCO2) in a case study of the Mission-Aransas Estuary, a subtropical semiarid estuary, 2) understanding the extent of CO2 flux and its hydrologic control in one of the world's largest lagoonal estuarine systems along the northwestern Gulf of Mexico, and 3) elucidating the mechanisms that lead to estuarine acidification and its feedback to CO2 fluxes. Intensive field campaigns for high-temporal resolution pCO2 and water carbonate chemistry sampling as well as sediment incubation will be carried out; analysis of multidecadal carbonate chemistry parameters that have been collected by Texas Commission on Environmental Quality will be used to obtain temporal trends of estuarine water pCO2 against the backdrop of increasing freshwater scarcity in this region. The education component of this CAREER award includes 1) creating an ocean and estuarine acidification research course and redesigning two existing courses for both undergraduate and graduate students, 2) collaborating with Foy Moody High School on their Aquatic Science education to engage high school students predominantly from underrepresented and economically challenged backgrounds in field and lab experiences. The ultimate educational goal is to encourage high school students to follow a STEM path for their college education, and undergraduate STEM students to pursue graduate degrees. This will be a part of the concerted effort to enhance diversity in the future workforce by increasing the number of underrepresented graduates with bachelor's or higher degrees in the STEM fields. This project will train one Ph.D. student. High school students and undergraduate interns from underrepresented and economically challenged backgrounds will also be supported to participate in summer research. Broader dissemination of the project findings will include undergraduate student presentations at symposiums organized by both TAMU-CC and the Texas A&M University System, public seminars by both the graduate students and the principal investigator at various meetings organized by regional estuarine programs, presentations at national and international meetings, and publications in peer-reviewed journals.