Using Numerical Modeling and Direct Observation to Investigate Hypoxia in a Shallow Wind-Driven Bay

Abstract

Corpus Christi (CC) Bay, Texas, USA is a shallow (average depth around 3 m) wind-driven bay that is subjected to diurnal wind variation. However, our observations suggests that this bay becomes stratified during the summer time and hypoxic (< 2 mg/l dissolved oxygen [DO]) condition develops in the southeast part of it, near the Laguna Madre and at the mouth of Oso Bay. As this system is very energetic, it is not possible to capture or fully understand the dynamic patterns of DO concentrations through spatially- or temporally-limited sampling schemes typical of discrete sampling or continuous monitoring at limited locations. Therefore, in this study, a system is being developed to measure various water quality parameters at higher spatial and temporal resolution. To get the vertical variation of different water quality parameters, a vertical profiling robot has been installed at one of our fixed monitoring platforms in the bay. Four more platforms/profilers are targeted for installation in the near future. This profiler's instrumentation suite measures DO, temperature, salinity, chlorophyll concentration and particle size. The same spectrum of environmental parameters is measured 'synchronically' over a highly-resolved spatial regime through our mobile platform equipped with an IDACC (Integrated Data Acquisition, Communication and Control) system. Short time analysis of observed data indicates the potential of these observation systems in identifying the factors that may affect hypoxia. In addition, a 2-dimensional hydrodynamic model which produces water surface elevation and depth-averaged velocity variation with time has been developed for CC Bay using the ADCIRC (ADvanced CIRCulation) model. This model will be extended into a 3-dimensional model which is then coupled to a water quality model for DO. Integrating model output with observed data will contribute into the understanding of processes that lead to the development of hypoxia and other environmental phenomena