Sediment aggregation in a salt-marsh complex, Great Sound, New Jersey

Abstract

Suspended sediments in a major tidal channel in southern New Jersey consist dominantly of three inorganic particle types: single grains, organic-mineral aggregates and fecal pellets. Single mineral grains range from clays (<2 μm) to fine sands (200 μm), but are dominant only in size fractions above 88 μm. Organic-mineral aggregates are characterized by low settling velocities (<4.7 × 10 −2 cm/s) and densities (<1.4 mg/m 3), and comprise approximately 70% of the suspensate under fair-weather conditions. Fecal pellets are somewhat more dense (1.7–1.8 mg/m 3) and settle more rapidly (4.7 × 10 −2–5×10 −1 cm/s) than organic-mineral aggregates. Because of the contrasting settling velocities, organic-mineral aggregates constitute an ever present background suspensate population, whereas single grains and fecal pellets are dominant only on maximum tidal flow or under storm conditions. Organic-mineral aggregates are composed almost exclusively of grains smaller than 6 μm, so that they are the dominant vehicle by which fine-grained particles are transported and deposited. Fecal pellets are most commonly comprised of a wide range of particle sizes, although occasionally their constituent grains exhibit a well-defined mode of particles ≈6-<16 μm in size. Given their relatively rapid settling velocities, fecal pellets are probably an important mechanism by which silt- and clay-size particles are introduced to the coarse-grained deposits (sands) which characterize the major tidal channels.