Beneficial and detrimental interactive effects of dissolved organic matter and ultraviolet radiation on Zooplankton in a transparent lake

Abstract

While changes in dissolved organic matter (DOM) concentrations are expected to affect zooplankton species through attenuation of potentially damaging ultraviolet (UV) radiation, generation of potentially beneficial or harmful photoproducts, pH alteration, and microbial food web stimulation, the combined effects of such changes on zooplankton community structure have not been studied previously. Our purpose was to determine how an increase in allochthonous DOM and associated changes in pH in an initially transparent lake may affect zooplankton community structure, and how exposure to solar UV may alter these DOM and pH effects. We ran microcosm experiments manipulating UV, DOM, and pH near the surface of Lake Giles in northeastern Pennsylvania. We found that when DOM was added in the presence of ambient UV, Daphnia and copepod UV-mortality was reduced by approximately three and two times compared to UV exposure without extra DOM. When DOM was added in the absence of UV, adult Daphnia and copepods were reduced compared to no DOM addition in the absence of UV. Daphnia and cyclopoid egg production and rotifer abundance were generally higher in the presence of DOM, regardless of UV treatment. The lower abundance yet high egg production in the presence of DOM and absence of UV may be explained by higher abundance of egg-bearing adults compared to non-egg-bearers. We conclude that allochthonous DOM benefits some zooplankton in a high-UV environment, but may be detrimental under low-UV conditions. Overall, Daphnia abundance and egg production were higher than that of calanoid copepods in the DOM additions, indicating that in some lakes an increase in allochthonous DOM may lead to a zooplankton community shift favoring Daphnia over calanoid copepods.

Cladocera assemblages from the surface sediments of south-central Ontario (Canada) lakes and their relationships to measured environmental variables

“…Elevated DOC concentrations may benefit zooplankton by attenuating deleterious UV radiation (Williamson et al, 1999;Cooke et al, 2006), and reducing the ability of visual predators to see some Cladocera. Planktivorous fish, for example, have been shown to select larger, more visible prey when sufficient light is available (Brooks & Dodson, 1965;Taylor, 1980).…”

Impact des coupes forestières sur l'écologie des jeunes stades de vie chez la perchaude (Perca flavescens) :

“…Moreover, Daphnia species are recognized to be more sensitive to P-input than other crustacean zooplankton since these cladocerans have a higher P-demand compared to copepods that have a higher nitrogen demand (Hessen 1997). DOC may also create bottom-up effects on Daphnia abundance through its influence on bacterioplankton and protists (Wetzel 1995, Arvola et al 1996, De Lange et al 2003 on which Daphnia efficiently graze (Sanders et al 1996), or an indirect effect by reducing the detrimental ultra-violet radiation (Cooke et al 2006). As a result, the TP-and DOC-input following forest harvesting could together have caused a multitrophic bottom-up effect on Daphnia abundance or a reduction in harmful radiation.…”

UV–vis spectral modifications of water samples under irradiation: Lake vs. subterranean water

“…CDOM is usually the main radiation absorber in water in the 300-500 nm wavelength interval, and its ability to absorb UVA and UVB radiation has important consequences for aquatic organisms. Indeed, CDOM protects the aquatic biota from exposure to UV radiation [2], which can be very significant during summertime in CDOM-poor environments such as mountain lakes located above the tree-line [3]. Another important issue is that radiation absorption by CDOM yields reactive species, such as • OH, 1 O 2 and the triplet states 3 CDOM*, which can be involved into transformation of dissolved compounds, including xenobiotics, as well as into the photoprocessing of CDOM itself [4][5][6][7].…”