Conclusions

Visual differentiation of aggregated sediment particles both moving in the stream and stored in the gravel bed indicates the presence of variable subpopulations of particle types. The settling behavior of the particles is modified by their size, density, and shape which appear to be modified by the hydrological, physical, and biological conditions within the stream. Both the energy of turbulent streamflow and the energy imparted by fish reworking the gravel bed are associated with a predominance of small, denser compact particles. In periods when internal stream energy is lower and when there is abundant organic matter delivery to the stream the composite structures are largest and are comprised predominantly of loosely bound flocs.

While structural and behavioral differences are associated with the different events occurring in the system, a more complete investigation of the open water season, incorporating storm events and summer base flows would be valuable. As well an evaluation of the types of organic matter comprising the composite structures throughout the season could potentially elucidate the processes which regulate the structure and morphology of these particles.

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