Abstract

Particulate matter modulates the transport of carbon and nutrients through estuarine environments. In the Chesapeake Bay, sinking of particles and their consumption by microbes likely modulates the emergence of a seasonal oxygen deficient zone. The relationship between particle size and abundance affects the transport dynamics of the particles and the biology of associated organisms. The variability of particle characteristics has not previously been characterized across the length of the Chesapeake Bay, nor has it been compared to the oxygen deficient zone. Therefore, we measured the size to mass and size to abundance relationship of suspended particles along the Chesapeake Bay during a major deoxygenation event. A laser scattering instrument measured particle size and abundance at six stations. Five particle size classes were sampled at surface and bottom depths. Particles in the less saline northern end of the Bay were less massive relative to size than particles farther south. Estimates of total particle mass, calculated by combining particle size to mass and particle size to abundance data, suggested that the anoxic region has lower particulate mass than overlying oxic water, perhaps because stratified water above the oxygen minimum zone keeps particles from the productive top layer from mixing into this region. Total particle mass was higher just above the sediment, suggesting resuspension of benthic particles. Our data provide the first systematic survey of size resolved particle abundances across the Chesapeake Bay oxygen minimum zone and provide context to future work in evaluating the biogeochemical role of particles in this environment.