The attenuation of ultraviolet radiation in high dissolved organic carbon waters of wetlands and lakes on the northern Great Plains

Abstract

We used a scanning spectroradiometer to conduct underwater optical surveys of 44 waterbodies during the ice‐free seasons of three consecutive years in wetlands and lakes in central Saskatchewan, Canada. The waterbodies ranged widely in dissolved organic carbon (DOC) concentration (4.1–156.2 mg L −1 ) and conductivity (270–74,300 mohms cm −1 ). Although penetration of UV radiation (UV‐R; 280–400 nm) in these systems was largely a function of DOC concentration, as has been reported previously, UV‐R penetrated more deeply in saline waterbodies than in freshwater systems with similar DOC concentrations. Power models representing our K dUV‐B or K dUV‐A versus DOC relationships were described by K dUV−B = 0.604DOC 1.287 ( r 2 = 0.76, N = 23) and K dUV‐A = 0.428DOC 1.136 ( r 2 = 0.55, N = 24) for freshwater systems and K dUV‐B = 2.207DOC 0.732 ( r 2 = 0.40, N = 20) and K dUV‐A = 1.436DOC 0.600 (r 2 = 0.18, N = 20) for saline systems. Our data, when combined with data from other researchers, resulted in the more general freshwater models K dUV−B = 0.705DOC 1.248 ( r 2 = 0.84, N = 43) and K dUV‐A = 0.470DOC 1.112 ( r 2 = 0.70, N = 44). UV‐B radiation (280–320 nm) is not expected to penetrate deeply (typically <50 cm) in prairie lakes and wetlands because of high intrinsic DOC concentrations. However, the central plains are characteristically windy and this, coupled with the shallowness of many of these systems, suggests that biota may still be at risk from present‐day and future‐enhanced levels of UV‐B (which may result from ozone depletion). Moreover, this risk may be exacer‐bated in saline systems. This could be significant, especially because saline waterbodies are often highly productive and represent important North American staging areas for shorebirds and waterfowl.