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Improved endmember mixing analysis (EMMA): application to a snowmelt-dominated stream in northern Utah
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DOI：10.3389/frwa.2026.1876382.png)
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Abstract
En 中文
An endmember mixing analysis (EMMA) is a sophisticated hydrograph separation technique used to determine the primary endmembers (water sources) in a watershed and estimate their inputs to a stream over time; but no software exists to implement this type of model in a standardized manner. We created EMMALAB; a software application that simplifies and accelerates the established approach to EMMA through a rapid iterative process of selecting tracers and endmembers. The iterative analysis for selecting endmembers and tracers is easily implemented through EMMALAB; allowing for a uniform and simplified approach to apply the complex mathematics behind EMMA for more accurate hydrograph separation calculations. In addition to the established EMMA approach; we implemented a simple methodological improvement to EMMA; calculating endmember contributions using the original water chemistry data (tracer-space) rather than the subspace defined by a principal component analysis (U-space); to allow for more complex and representative models. For example; the number of endmembers possible in an EMMA model is restricted by the number of retained principal components or tracers; and the number of tracers is always greater than the number of retained principal components. We applied EMMALAB and our methodological improvement to EMMA to the upper Provo River watershed (262 km2); a snowmelt-dominated catchment in northern Utah. Our approach included more endmembers than are typically considered (five); allowing for a more descriptive model. Groundwater and snow were the dominant endmembers during spring runoff; contributing 46 and 39% of flow on average; respectively; while groundwater contributed 67% during baseflow. When EMMA models include a larger number of tracers; deviations of the data from model predictions can be used to infer complexities in the natural system that have not been captured by the model architecture.
Keywords:
water resources
hydrograph separation
snowmelt
emma
conservative tracers
EMMALAB
endmember mixing analysis
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