Citation:

Impact/Purpose:

Documentation of outcomes of Everglades Regional Environmental Monitoring and Assessment Program (R-EMAP) study, conducted during May - December, 2005.

Description:

Distinct seasonal wetting and drying cycling results in fluctuations in hydrometeorological, physical, chemical, and biological characteristics and may subsequently lead to seasonality in mercury (Hg) cycling and bioaccumulation in the Everglades. We investigated seasonal variations in Hg cycling and bioaccumulation in mosquitofish by analyzing data obtained for water, soil, flocculent material (floc), periphyton and mosquitofish collected at approximately 250 stations in the entire Everglades freshwater marsh in 2005 dry and wet seasons. Atmospheric Hg deposition likely plays a primary role in THg cycling, which results in higher THg in soil, floc, and periphyton owing to substantially greater Hg deposition in the wet season than in the dry season. Seasonal difference was absent for water THg, due to parallel increases in water level and Hg deposition in the wet season. In addition to Hg deposition, methylmercury (MeHg) production and transport are important factors in MeHg cycling and bioaccumulation. The seasonal differences in these factors, plus in mass of ecosystem compartments, lead to mixed seasonal patterns for MeHg, with higher water and soil MeHg and lower periphyton MeHg in the dry season while no seasonality for floc MeHg. Compared with the dry season, the wet season is more favorable for Hg bioaccumulation, indicated by higher mosquitofish THg, bioaccumulation factor (BAF), and biomagnification factor (BMF) from periphyton to mosquitofish. Substantially elevated MeHg production in floc and periphyton and changes in food web structure in the wet season could play an important role in seasonality in Hg bioaccumulation. Some physicochemical characteristics, such as water level, temperature, dissolved organic matter (DOM), and sulfate/sulfide, affect Hg cycling and bioaccumulation.

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