REEVALUATION OF COLORIMETRIC CL- DATA FROM NATURAL-WATERS WITH DOC

Colorimetric Cl- data from natural solutions that contain dissolved or ganic carbon (DOG) may be biased high. We evaluated aquatic Cl- concen trations in ecosystem compartments at the Bear Brook Watershed, Maine, and from lakes in Maine, using ion chromatography and colorimetry. DO C imparts a positive interference on colorimetric Cl- results proporti onal to DOC concentrations at approximately 0.8 mu eq Cl-/L per mg DOC /L. The interference is not a function of Cl- concentration. The resul ting bias in concentrations of Cl- may be 50% or more of typical envir onmental values for Cl- in areas remote from atmospheric deposition of marine aerosols. Such biased data in the literature appear to have le d to spurious conclusions about recycling of Cl- by forests, the usefu lness of Cl- as a conservative tracer in watershed studies, and calcul ations of elemental budgets, ion balance, charge density of DOG, and d ry deposition factors.