Colloidal sediments/soils are possible in wetland soils. Additional data can help you determine if your results are really results and not artifacts. The biggest one could be the "feel" of the sediment/soil, ultimately doing a pedological determination of the soil. You could also take another soil core from the same area to confirm. Additional analysis such as mineral analysis on each fraction could also help confirm as well.

The particle size analysis done by laser scattering may underestimate the fine fraction of the sediment. If your result shows the presence  of colloids then you probably have the colloidal fraction in your sample. In addition, it is very difficult to obtain the "true" result of the particle size analysis for any kind of sample  since it depends graeatly on the handling of sample, eg. wether the sample was used wet or was it dried; the addition of dispersant; the use of  ultrasonic treatment and so on...

I do agree with Ned Vdovic. The particle sizer usually developped an artefact for the smaller particle sizes.

We are currently developping a system to measure particle size by settling. Can have a look to the publications of our group among which the work done by T.Grangeon.

N.

colloids are natural constituents of every sediment. They have inorganic (like clays) and organic (microorganisms, debris from plants etc.) nature.

Various organic and inorganic colloids are common and abundant in nature, and they are major constituents of fine-grained sediments and suspended matter.  They include humic substances, non-humic organic matter, clay minerals, iron and manganese oxyhydroxides, and bacterial cells.  I cannot comment on the HORIBA technique, but on general principles I imagine that your wetland soils are made up largely of colloidal organic matter, especially humic matter.  By the way, your reference to "collide" in the sediment was obviously a malapropism:  I presume that you had intended to write "colloid"!