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a See Tables 7.1 and 7.2 for years Included In each data set; Green Island (GI), Poughkeepsie (Po), Esopus Creek (Es), Waterford

(Wf), Cohoes (Co). b Discharge-weighted average Including pollution (Meybeck, 1979). c Discharge-weighted average corrected for pollution (Bernerand Berner, 1996).

SO42- and Cl-, based on our research at Black Rock Forest (unpublished), that regional dry deposition inputs are similar in magnitude to wet deposition. If this is accurate, the minimum expected surface water [SO42-] or [Cl-], assuming no contribution from chemical weathering or pollution and no loss of SO42- in soils, would be about four times that of precipitation.

The Esopus Creek gauging station in the Catskills (Table 7.6) has the lowest TDS value (median = 35 ppm) of the stream stations discussed here. The median value for SO42- (7.6 mg l-1) is slightly less than a factor of four greater than the amount-weighted average for West Point precipitation (2.1 mg l-1; Table 7.1). These data are consistent with atmospheric sources (wet plus dry deposition) providing much of the inputs of SO42- in Catskill streams. Chloride median concentration at Esopus Creek is about a factor of eight greater than West Point wet deposition (Table 7.1), indicating that about half of stream [Cl-] probably came from either chemical weathering or pollution influxes, such as road salting. The ratio of [Na+] in Esopus Creek to [Na+] inWest Point precipitation is similar to thatfor [Cl-], also consistent with a halite source for both ions beyond that provided by atmospheric deposition.

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