A method to measure marine particle aggregate disruption in situ

Particle aggregation within aquatic environments is a primary factor controlling the vertical flux of suspended matter. The aggregation process is controlled by the rate of particle interaction, enhanced by turbulent motions and differential settling, and the probability that particles making contact will stick together. The larger the particle aggregate, the faster it will sink. We describe a new and novel method to measure the state of particle aggregation in situ as a function of turbulent energy using an inexpensive attachment, the in situ dis-aggregation system (iDAS), to a commercially available particle size instrument, a Sequoia Scientific LISST-100X. A small chamber is attached to the instrument tand sample is drawn into the chamber using an inexpensive, variable speed thruster designed for remotely operated underwater vehicles. Ambient water drawn into the sample chamber passes through a flexible tube of defined diameter and length. The flow velocity through the tube and tube dimensions are used to estimate the turbulent energy that particles experience. As turbulence increases, particle aggregations disrupt, shifting the size distribution towards smaller particles. The method was tested under controlled laboratory conditions using standard test clay material and within several coastal environments along the East Coast of the United States. In all instances, particle aggregations are shown to disrupt as turbulence increases, causing the particle size distribution to shift toward smaller fractured aggregates and component particles. The iDAS can be used to directly measure the aggregation state of suspended material and potentially to estimate the bonding strength between aggregated particles of different type.