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The Regional Water Quality Control Board (RWQCB) is in the process of issuing a Total Maximum Daily Load (TMDL) under Section 303(d) of the Clean Water Act for the lower San Joaquin River for Dissolved Oxygen (DO). The Central Valley Regional Water Quality Control Board (CVRWQCB) and the California Bay-Delta Authority (CBDA) have sponsored the creation of two Web-based conceptual models as tools to understand the physical and chemical conditions in the river that lead to episodes of low DO concentrations and the effects of these low DO episodes on the biological and ecological resources in the river. A conceptual model describes the current state of scientific understanding of a subject. The purpose of a conceptual model is to provide enough information on each model component to allow the subject to be understood at a conceptual level.
The subject of these conceptual models is DO concentrations in the Stockton Deep Water Ship Channel (DWSC) on the San Joaquin River of California. To address this complex subject, two conceptual models have been developed:
These two conceptual models have been created in a web-based format to allow easy access to the information in the model and other related information. Additionally, the models describe how important each driver is in influencing either DO concentrations or the effects of low DO concentrations on the ecosystem and how well understood the mechanisms behind each driver are.
- The Physical and Chemical Processes Conceptual Model describes the physical and chemical factors and conditions that lead to episodes of low DO in the DWSC.
- The Biological and Ecological Effects Conceptual Model describes the drivers and conditions that determine whether the low DO episodes have effects on fish and other aquatic organisms, and what the effects of exposure are on eight fish species.
These models are meant to be living documents. Much work is being done in studying the causes and effects of low DO concentrations, and it is the intent that the models will be modified as new data or studies become available.