Tracking Effects of Pollution Sources on In-Stream Water Quality Using a Modeling Approach

This paper presents a modeling approach that establishes cause-effect relationship between individual pollution sources and in-stream water quality. It introduces a conceptual model of constituent network that mimics in-stream water quality dynamics. The network consists of water quality constituents (e.g., nutrients, DO, algae) and links among the constituents, which are the fundamental processes that convert chemical/biological mass from one constituent to another (e.g., algal growth). The network structure allows implementation of a tracking algorithm that quantifies the mass flux transferred among constituents via the processes. Impact of a pollution source is viewed as mass flux propagating through the constituent network and is quantified by the tracking algorithm. This approach makes differentiating impacts of individual sources on water quality feasible. In addition, the approach can be used to examine interactions of multiple pollution sources and their effects on reaction kinetics. Monitoring propagation of the mass flux in each river segment also can help investigate how small-scale process dynamics affects large-scale watershed response such as pollutant export from the river system. The proposed methodology is useful for assisting regulatory programs such as the Total Maximum Daily Load (TMDL) for setting load/wasteload allocations and nutrient trading. It also is a useful tool for formulating effective best management practices and developing watershed management plans.