For most dissolved major ions in the main stem of the Hudson, atmospheric influxes and chemical weathering of soils and rocks dominates observed concentrations. For Cl-, however, the situation appears to be more complex. The Mohawk River median [Cl-] of 18 mg l-1 is more than 40 times that of West Point precipitation [Cl-] of 0.42 mg l-1. Taking into account inputs of dry deposition of
Cl- and effects of evapotranspiration water losses of about 50 percent, approximately 90 percent of Mohawk [Cl-] appears to be derived from non-atmospheric sources. Plausible additional sources include: (1) natural evaporite mineral weathering,
(2) wastewater treatment plant effluents, and
(3) road salting. If the contribution of natural halite weathering could be better documented, the magnitude of the latter two types of anthropogenic influxes could be estimated. Chloride fluxes, as a conservative ion in surface waters, could then be used as an important constraint on integrated influxes of other, non conservative contaminants from wastewaters and transportation corridors.
Further studies of DOC and chlorinationbyprod-uct formation within the Hudson basin could provide important background information relevant to future water supply options in the region. Given the previous history of Hudson withdrawals by NYC during extended droughts, and proposals for large diversions from the tidal freshwater Hudson during high spring discharges, it is plausible that chlorina-tion byproducts and other associated water quality issues may become important public policy considerations in future water supply decisions in the Hudson basin.
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