The abundance and source of mercury-binding organic ligands in Long Island Sound

The abundance and strength of mercury (Hg)-complexing organic matter was measured in samples collected from Long Island Sound (LIS) and related locations. A range in ligand-equivalent concentrations was found in LIS (0.3–6 nN). Rivers, lakes, sewage effluent, and marine porewaters were also sampled. When the ligand concentrations were normalized to dissolved organic carbon (DOC) concentrations, the samples fell into broad groups. Offshore and sewage effluent samples were relatively ligand-poor, while river, lake, and porewater samples were ligand-rich. Normalized ligand abundance in LIS water was intermediate. A first-order mass balance for ligand and DOC suggests that terrestrial organic matter and phytoplankton exudates are the dominant sources of ligand to LIS, while tidal exchange and an unknown term are the dominant sinks. Concentration distributions through the Connecticut River (CTR) estuary suggest pseudo-conservative mixing of the ligand derived from the Connecticut River watershed. The identity of the material is unknown, but ligand-to-DOC ratios are well below the ratio of bulk reduced sulfur to DOC.