Characterization of suspended particles in Everglades wetlands

We report the concentration, phosphorus (P) and nitrogen (N) content, and size and chemical fractionation of fine suspended particles (0.2-100 mu m) and colloids (3 kilodalton [kDa]-0.1 mu m) in the surface water of Everglades wetlands along regional and P-enrichment gradients. Total suspended sediment concentrations ranged from 0.7 to 2.7 mg L-1. Total particulate P concentrations increased from 0.05 mu mol L-1 to 0.31 mu mol L-1 along the Penrichment gradient. Particles contained from 20% to 43% of total P but < 12% of total N in surface water. Dissolved (< 0.2 mu m) organic N contained about 90% of total N, with the 3-100-kDa colloidal size class containing the most N of any size class. The 0.45-2.7-mu m size fraction held the most particulate P at all sites, whereas particulate N was most abundant in the 2.7-10-mu m size class at most sites. Standard chemical fractionation of particles identified acid-hydrolyzable P as the most abundant species of particulate P, with little reactive or refractory organic P. Sequential chemical extraction revealed that about 65% of total particulate P was microbial, while about 25% was associated with humic and fulvic organic matter. The size and chemical fractionation information suggested that P-rich particles mostly consisted of suspended bacteria. Suspended particles in Everglades wetlands were small in size and had low concentrations, yet they stored a large proportion of surface-water P in intermediately reactive forms, but they held little N.