Real Time Monitoring of Water Quality Parameters in Corpus Christi Bay to Understand Hypoxia

Abstract

Corpus Christi Bay (Texas, USA) is home to the nation's seventh largest port with numerous petrochemical facilities. This shallow wind-driven bay (average depth 3 m) is very dynamic, and is typically a well-mixed system. However, the water column becomes stratified during the summer months in the south-east portion of the bay, and so dissolved oxygen (DO) in the upper-layer water column is not able to mix with the lower-layer water column. Therefore, an hypoxic condition can develop at the lower portion of the water column in the bay, and as this bay is very stochastic in nature, this condition lasts on the order of hours. It is difficult to 'capture' this kind of episodic events through discrete sampling at limited locations in the bay. Our research group has developed an integrated data acquisition system which can measure horizontal and vertical variation of various water quality parameters 'synchronically' over a highly-resolved spatial regime. Also, software has been developed in our laboratory which can display the horizontal and vertical variation of these parameters in real time and thereby, guides in determining the spatial extent of the water quality parameters of interest. As part of our routine monitoring of Corpus Christi (CC) Bay, we conducted an east-west transect of the bay's ship channel on November 29, 2006 and March 22, 2007. The data collected by our system suggests that the inverse estuary situation exists in the ship channel, i.e., the water becomes more saline and dense as we moved away from the mouth of the Gulf of Mexico towards the bay interior. The prevailing south-east wind on those days 'pushed' the high saline water from the mouth of the Laguna Madre and Oso Bay toward the ship channel. The preliminary results of the hydrodynamic model developed by our research collaborators showed the similar circulation pattern. Integrating the model with the observed data will help us in characterizing the stratification pattern of the bay and therefore, greater understanding of the hypoxic phenomena. Also, particle concentrations measured by a particle sizer (one of the instruments in our suite of instruments) are well correlated with the acoustic backscatter intensity measured by our acoustic Doppler current profiler. This kind of relationship is very important because it provides a greater capability to characterize the particle dynamics of the bay. Particles can transport 'particulate BOD' (biochemical oxygen demand), thus affecting hypoxia. Quantification of the particle influx/outflux to the Gulf of Mexico through the ship channel may help us to understand the contribution of the ship channel effects on hypoxia in the bay.