Studies of humic and fulvic acid dynamics in coastal marine waters of South Florida

Humic and fulvic acid concentrations (HA + FA) were monitored over a two-year period in different areas of Florida and Biscayne Bay. These studies were undertaken in an effort to determine fluctuations in the quantity and chemical nature of humic substances in productive coastal environments in South Florida and, retrospectively, to discern the extent of potential terrestrial influences. Additional studies have been undertaken with material from a South Florida mangrove environment and material isolated from offshore Gulf Stream waters. Dramatic fluctuations in humic substances were observed in all coastal areas. In East-Central Florida Bay, for example, humic materials (HA + FA, collectively) were found to fluctuate as much as elevenfold. In both Biscayne Bay and Florida Bay, these fluctuations appeared to follow the artificially-controlled input to water from the South Florida mainland. The ratios of FA to HA varied dramatically between terrestrially-influenced and oligotrophic marine environments (i.e. a progressive increase of the FA/HA ratio with this transition). In all marine locations studied, coarse particulate humic substances were low in comparison to the dissolved component of this chemical class.