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

Abstract

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.

Exposure of dissolved organic matter to UV-radiation increases bacterial growth efficiency in a clear-water Alpine stream and its adjacent groundwater

“…Relatively few studies have examined the optical properties of CDOM in streams, and its resistance to photooxidation and biodegradation (Belmont et al 2009;Brisco and Ziegler 2004;Jaffe et al 2008). Our study suggests that even in ''clear water'' streams with low organic carbon concentration and colour, DOC is susceptible to UV-irradiation with implications for microbial heterotrophs.…”

Assessing changes in microbial respiration, bacterial growth efficiency, and bacterial production with nutrient addition to batch cultures

“…All of the sampling sites were preselected using water quality data collected from 2002 to 2005 (Belmont et al 2009). We wanted to study nutrient limited systems in both forested and agricultural areas.…”

“…These sites (AG1, AG2, and AG4) were located near the town of Bath, Pennsylvania. The hydrology and land use characteristics of each site were previously classified by Belmont et al (2009) and can be found in Table 1. Detailed information about site locations and sampling dates can be found in the Supplementary Information (SI; Table 1).…”

“…In lotic ecosystems, organic carbon is usually most abundant in the form of dissolved organic carbon (DOC). The composition of DOC varies in streams depending on source material, landscape, and climate (Meyer 1990;Belmont et al 2009). The quality of organic carbon is related to its composition and can span a spectrum of biolability, with some material being readily available (biolabile) for microbial degradation, and other material being more recalcitrant (not readily available).…”

Influence of Irrigated Paddy Fields on the Fluorescence Properties of Fluvial Dissolved Organic Matter

“…The quantity and the quality of DOM can be strongly influenced by the anthropogenic activities such as agriculture (Wiegner and Seitzinger, 2004; Raymond et al, 2008; Belmont et al, 2009) and the release of domestic sewage (Amano et al, 2004; Mattsson et al, 2009). In this study, we did not observe any relationship between the quality of DOM and the percentage of the watershed used for residential development.…”