Abstract

In situ optical examinations of small-scale variability in suspended particle size distribution (PSD) and concentration (N) within the Connecticut River plume and adjacent Long Island Sound indicate areas within the water column where particle population dynamics may be characterized by the local forcing mechanisms.

1) Within the benthic boundary layer, where particles are resuspended due to wave and current shear, there appears to be a balance between particle size and concentration and defined by the size-dependent particle settling rate.

2) Within the interior of the river plume, shifts in particle size are consistent with local mixing between the plume water and the adjacent Long Island Sound water.

3) Within a few tens of meters of the lateral plume boundary, a region referred to as the frontal zone and characterized by elevated turbulent kinetic energy associated with current shear and convective overturn, observed changes in PSD appear to be controlled by both mixing and the vertical transport of particles sorted by differential sinking.

While there may be conditions when particle aggregation processes affect or even control PSD, most of the observed variability, at least on the small spatial scales that were examined, may be explained in terms of water mass mixing and size-dependent particle settling. 

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