Penetration of ultraviolet radiation in streams of eastern Pennsylvania: Topographic controls and the role of suspended particulates

• Published in: Aquatic sciences 2009-06, Vol.71 (2), p.189-201
• Main Authors: Belmont, Patrick, Morris, Donald P., Pazzaglia, Frank J., Peters, Stephen C.
• Format: Article
• Language: English
• Subjects: Agricultural land; Agriculture; Aquatic ecosystems; Aquatic sciences; Base flow; Biomedical and Life Sciences; Careers; Dissolved organic carbon; Earth sciences; Earth, ocean, space; Ecology; Exact sciences and technology; Fluorescence; Freshwater; Freshwater & Marine Ecology; Freshwater ecology; Geochemistry; Hydrology; Hydrology. Hydrogeology; Land use; Life Sciences; Marine & Freshwater Sciences; Mineralogy; Oceanography; Optical properties; Organic contaminants; Photochemistry; Research Article; Silicates; Suspended particulate matter; Suspended sediments; Topography; Ultraviolet radiation; Water geochemistry; Watersheds; Wetlands
• ISSN: 1015-1621; 1420-9055
• DOI: 10.1007/s00027-009-9120-7

. Penetration of ultraviolet radiation (UVR) in stream ecosystems is determined by the concentration and optical properties of suspended sediment and dissolved organic carbon (DOC). This study documents the base-flow optical environment of 37 first- and second-order tributaries distributed throughout the Lehigh River watershed, eastern Pennsylvania, over a four year period. We measured a large range of attenuation coefficients (K d380 : 0.68 – 151.1 m −1 , K d320 : 0.95 – 316.2 m −1 ) and 1 % transmission depths (2 cm – 147 cm). In addition, we quantified the significance of particulate material in UVR attenuation in streams, which generally accounted for 10–30 % of attenuation for the UV-B waveband. Our results indicated that basin morphology, particularly mean watershed slope (MWS), was highly correlated with UVR penetration (MWS:K d320 , r 2 = 0.68, P < 0.0001),DOC concentration (MWS:DOC, r 2 =0.65, P < 0.0001), and DOC optical quality (MWS:Fluorescence Index, r 2 = 0.71, P < 0.0001). The fact that these relationships are robust across a variety of watersheds that differ in land use, forest coverage, and wetland coverage, indicates that the geomorphic coevolution of hillslope form and process exert a strong control on stream optical environments via the establishment of hydrologic and edaphic conditions. Agricultural land use exerts secondary, but discernable effects on DOC concentration (% Agriculture:DOC, r 2 = 0.39, P = 0.012) and optical quality (% Agriculture:Fluorescence Index, r 2 = 0.32, P = 0.036) in watersheds devoid of wetlands.