Submarine groundwater discharge and hypoxia: lessons learned from an estuary in the semi-arid of South Texas




McBee, William A.


Journal Title

Journal ISSN

Volume Title




Formations of hypoxia in Corpus Christi Bay (CCB) and algal blooms in the Upper Laguna Madre have become a concern as they have cyclically surfaced during the late spring through the fall months. The semi-arid climate of South Texas experiences limited precipitation and surface freshwater inflows, which in turn would point to non-riverine sources such as groundwater as a contributor to the overall nutrient budget. Groundwater has a tendency to accumulate high concentrations of nutrients and organic matter. Despite the potential impact that submarine groundwater discharge (SGD, including groundwater discharge and sediment fluxes) has on estuary systems worldwide, this input has not been well understood. The objective of this study is to use a combination of geophysical and geochemical techniques to enhance the understanding of spatial and temporal occurrence of SGD and related nutrient fluxes and the effects of these inputs on the hypoxia formation in a semiarid estuarine system. Results from multiple continuous electrical resistivity (ER) profiles, spanning from near shore to 2 km offshore, were used to characterize subsurface hydrogeologic heterogeneity and select sampling sites for nutrient and SGD analyses during three seasonal events (winter, summer, and fall). SGD measurements were conducted at three locations using both continuous ER and radon measurements. During summer and late fall, SGD rates show large spatial variances, with the highest average discharge rates measured at the Oso Bay (a secondary bay) inlet (13.1 m3/mˑd), followed by Shamrock Island (2.6 m3/mˑd) and Laguna Madre inlet (1.1 m3/mˑd). On average, SGD rates were higher during late fall (6.5 m3/mˑd) than summer (4.7 m3/mˑd). As a result of higher SGD rates and more enriched nutrient levels in porewater, nutrient fluxes during fall are one order of magnitude higher than summer. Based on the good spatial correlation between dissolved oxygen levels and high 222Rn-derived nutrient fluxes, this study indicates that SGD is not only a significant contributor to the nutrient budget but there is also a possible correlation between these inputs, algal blooms, and hypoxia.



Environmental Science, Geology, Geophysics, Hydrogeology



This material is made available for use in research, teaching, and private study, pursuant to U.S. Copyright law. The user assumes full responsibility for any use of the materials, including but not limited to, infringement of copyright and publication rights of reproduced materials. Any materials used should be fully credited with its source. All rights are reserved and retained regardless of current or future development or laws that may apply to fair use standards. Permission for publication of this material, in part or in full, must be secured with the author and/or publisher.