Modeling In situ sediment oxygen demand in the Arroyo Colorado

Abstract

The Arroyo Colorado River is the principal source of fresh water inflow to the Southern Laguna Madre, an economically and ecologically important resource for the Lower Rio Grande Valley region of Texas. The Arroyo Colorado serves as a principal drainage system for municipal waste treatment effluent (from the cities of Harlingen and McAllen, Texas), agricultural production runoff, and storm water runoff from the Lower Rio Grande Valley. The lower reaches of the Arroyo Colorado have historically failed to meet their use under subsection 303 (b) of the US-Clean Water Act (CWA) due to fecal coliform bacteria and low dissolved oxygen. Sections of the Arroyo Colorado are listed in the 1998 CWA 303(d) report of non-compliant water bodies and are targeted for rehabilitation under the Total Maximum Daily Load (TMDL) program. In some rivers, sediment oxygen demand (SOD) accounts for as much as 50% of the total oxygen depletion, making SOD a critical element in water quality modeling studies. SOD is the rate of oxygen consumption, biologically or chemically, on or in the sediment at the bottom of a water body. SOD is an integral part of assessing the quality of water in a system. This study attempts to address SOD in the Arroyo Colorado to aid in the understanding of oxygen dynamics in this system.