Suspended particulate matter along the land–ocean continuum

Abstract

Suspended particulate matter (SPM) — composed of interacting minerals and organic matter — influences the transport and fate of carbon, nutrients and contaminants in all natural aquatic environments. In this Review, we synthesize physical, sedimentological and biogeochemical evidence to explore how and why SPM concentration, composition and size vary along the land–ocean continuum. Despite the large variability in SPM characteristics, its concentration is robustly correlated with its composition, size, density and settling velocity. In general, organic matter content and floc size increase with decreasing SPM concentration. In addition, flocs are small and consist mostly of minerals in turbidity maximum zones, with particle size and organic matter content increasing as waters become clearer. SPM concentrations also influence carbon partitioning, with the ratio of particulate to dissolved organic carbon increasing with SPM concentration. Therefore, SPM concentrations can reflect a combination of physical and biogeochemical processes and ecosystem properties. Climate change and human activities, such as dam construction and land use change, are perturbing SPM dynamics, with implications for wetland stability, contaminant mobility and carbon export and sequestration. Future research should prioritize in situ and remote sensing observations to constrain anthropogenic perturbations of SPM dynamics in natural systems and improve understanding of the implications for sediment accretion or erosion, pollutant mobility and the carbon cycle. Suspended particulate matter (SPM) influences the transport and fate of carbon and environmental contaminants in natural aquatic systems. This Review explores SPM dynamics along the land–ocean continuum and discusses how human activities and climate change might affect its role in the carbon cycle and sediment transport.