Ultraviolet absorbance in lakes near the metal smelters in Sudbury, Canada.

Ultraviolet (UV)-dissolved organic carbon (DOC) models were developed using surface samples collected from 58 lakes located 8-128 km from the metal smelters in Sudbury, Canada. Highly significant (R2 = 0.93-0.95) relationships were found between absorbance coefficients (K(a)lambda) and DOC within the UV-A and UV-B range (310, 30, 365 nm). Changes in UV absorbance with water depth were assessed in a subset of four lakes. Two study lakes with intermediate levels of DOC (DOC = 10-2.5 mg L(-1)) showed very marked depth related absorbance profiles, with evidence of photodegradation and much reduced absorbance in surface waters, particularly evident in late summer. These changes may affect complexation of metals and UV habitat characteristics for sensitive biota. These findings suggest that UV absorbance is an important variable for inclusion in long-term monitoring programs.