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

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 mu ohms cm(-1)). Although penetration of UV ra diation (UV-R; 280-400 nm) in these systems was largely a function of DOC c oncentration, as has been reported previously, UV-R penetrated more deeply in saline waterbodies than in freshwater systems with similar DOC concentra tions. Power models representing our KdUV-B or KdUV-A versus DOC relationsh ips were described by KdUV-B = 0.604DOC(1.287) (r(2) = 0.76, N = 23) and Kd UV-A = 0.428DOC(1.136) (r(2) = 0.55, N = 24) for freshwater systems and KdU V-B = 2.207DOC(0.732) (r(2) = 0.40, N = 20) and KdUV-A = 1.436DOC(0.600)(r( 2) = 0.18, N = 20) for saline systems. Our data, when combined with data fr om other researchers, resulted in the more general freshwater models KdUV-B = 0.705DOC(1.248) (r(2) = 0.84, N = 43) and KdUV-A = 0.470DOC(1.112) (r2 = 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 concent rations. 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 exacerba ted in saline systems. This could be significant, especially because saline waterbodies are often highly productive and represent important North Amer ican staging areas for shorebirds and waterfowl.