Declines of Suspended Particle Abundances in the Oxygen-Deficient Zone of the Chesapeake Bay

Particles, including aggregates, fecal pellets, and inorganic matter, modulate the transport of carbon and nutrients through estuarine environments. Particles’ size, mass, and density influence their trajectories and ability to transport carbon and other elements. In the Chesapeake Bay, particles fuel the emergence of a seasonal oxygen-deficient zone, with their origin and trajectories being shaped by their characteristics. However, the variability of particle characteristics has not previously been characterized across the length of the Chesapeake Bay, particularly in and around the oxygen-deficient zone. In this study, we measured of the size, abundance, and mass of suspended particles along the Chesapeake Bay during a major deoxygenation event. We demonstrate that particles in the anoxic region have a sandwich structure, with higher particle abundance and mass in the oxic overlying waters and in the deep nepheloid layer, than in the pelagic anoxic zone. These particles in the anoxic zone appear to have similar size properties as particles elsewhere. Stratified water above the oxygen minimum zone may keep particles from the productive top layer from mixing into this region, and our results suggest that this lack of mixing isolates the anoxic zone and limits the amount of reductant entering this environment. Particles in the less saline northern end of the Bay were less massive relative to size than particles farther south, suggesting differences in origin and physical makeup of these particles.