Colloid particle sizes in the Mississippi River and some of its tributaries, from Minneapolis to below New Orleans

An on‐board technique was developed that combined discharge‐weighted pumping to a high‐speed continuous‐flow centrifuge for isolation of the particulate‐sized material with ultrafiltration for isolation of colloid‐sized material. In order to address whether these processes changed the particle sizes during isolation, samples of particles in suspension were collected at various steps in the isolation process to evaluate changes in particle size. Particle sizes were determined using laser light‐scattering photon correlation spectroscopy and indicated no change in size during the colloid isolation process. Mississippi River colloid particle sizes from twelve sites from Minneapolis to below New Orleans were compared with sizes from four tributaries and three seasons, and from predominantly autochthonous sources upstream to more allochthonous sources downstream. © 1998 John Wiley & Sons, Ltd.