We explore the role of lakes in carbon cycling and global climate, examine the mechanisms influencing carbon pools and transformations in lakes, and discuss how the metabolism of carbon in the inland waters is likely to change in response to climate. Furthermore, we project changes as global climate change in the abundance and spatial distribution of lakes in the biosphere, and we revise the estimate for the global extent of carbon transformation in inland waters. This synthesis demonstrates that the global annual emissions of carbon dioxide from inland waters to the atmosphere are similar in magnitude to the carbon dioxide uptake by the oceans and that the global burial of organic carbon in inland water sediments exceeds organic carbon sequestration on the ocean floor. The role of inland waters in global carbon cycling and climate forcing may be changed by human activities, including construction of impoundments, which accumulate large amounts of carbon in sediments and emit large amounts of methane to the atmosphere. Methane emissions are also expected from lakes on melting permafrost. The synthesis presented here indicates that (1) inland waters constitute a significant component of the global carbon cycle, (2) their contribution to this cycle has significantly changed as a result of human activities, and (3) they will continue to change in response to future climate change causing decreased as well as increased abundance of lakes as well as increases in the number of aquatic impoundments.

This study tests the effects of elevated CO 2 and ultraviolet radiation (UVR) on phytoplankton photosynthesis through in situ incubations in Lake Giles, Pennsylvania. In a first experiment, CO 2 was supplied from a tank to simulate atmospheric CO 2 concentrations predicted in scenarios of future global change. In a second experiment, elevated CO 2 conditions were obtained by the mineralization of added colored dissolved organic matter (CDOM) of terrestrial origin (400 mmol L 21 final concentration). The results demonstrated that for natural assemblages from Lake Giles, atmospheric CO 2 concentrations similar to those predicted for the end of the century can increase primary productivity up to 23% in the absence of photoinhibition. However, elevated CO 2 concentrations also increased sensitivity of phytoplankton to UVR, making cells more susceptible and increasing photoinhibition. Increased sensitivity was observed in samples incubated with the artificial CO 2 supply as well as with the CDOM addition, the latter resulting in CO 2 partial pressures close to three times present atmospheric levels. Photosynthetic rate modeled for elevated CO 2 and midday solar exposure just below the lake surface was 17% of potential production compared with 21% under usual CO 2 levels in the lake, resulting in similar rates between phytoplankton assemblages grown under high and low CO 2 levels. Understanding the effect on primary productivity of the interaction between factors that may be affected by global change is essential to predict future changes in ecosystems and climate.

The Association of College and Research Libraries recommends incorporating information literacy (IL) skills across university and college curricula, for the goal of developing information literate graduates. Congruent with this goal, the Departments of Biological Sciences and Information Science developed an integrated IL and scientific literacy (SL) exercise for use in a first-year biology course. Students were provided the opportunity to access, retrieve, analyze, and evaluate primary scientific literature. By the completion of this project, student responses improved concerning knowledge and relevance of IL and SL skills. This project exposes students to IL and SL early in their undergraduate experience, preparing them for future academic advancement.

Predicting the effects of dissolved organic matter (DOM) on pelagic food webs can be difficult because DOM modifies water column optics and can have contrasting effects on species across trophic levels. We combined large mesocosm, smaller-scale experiments and autoregressive modeling driven bu DOC concentration or DOM optical quality (colored DOM, or CDOM, measured as DOC-specific absorbance at 320 nm, SUVA 320 ) to assess how heterotrophic and phototrophic microbial populations were altered in a temperate oligotrophic lake. DOM additions yielded DOC concentrations of 1.6 mg L 21 (control) 2.5 mg L 21, 3.0 mg L 21, and 4.3 mg L 21. Primary (PP) and bacterial (BP) production as well as heterotrophic and autotrophic protist abundances were stimulated in the higher DOM additions. BP responded rapidly to DOM additions, but unlike PP, returned to the level of controls within 2-7 d. A bioassay showed that the DOM was a nitrogen source for phytoplankton. The two models revealed that BP and edible phytoplankton were stimulated by CDOM (SUVA 320 ), but only BP was stimulated by DOC concentration. Ultraviolet radiation (UV) inhibited protists in both models, but stimulated edible phytoplankton only in the SUVA 320 model runs. These results suggest that in transparent oligotrophic lakes large influxes of terrestrial (high SUVA 320 ) DOM will stimulate the microbial food web by providing a nutrient subsidy to bacteria and reducing exposure of protists to damaging UV. Nutrients associated with moderate DOM input may also stimulate PP relative to BP, as was observed in these and other experiments, rather than causing an overall system shift toward heterotrophy.

Summary The effects of changes in chromophoric dissolved organic matter (CDOM) on zooplankton grazers in pelagic food webs can be difficult to predict due to the potential for conflicting direct and indirect effects of CDOM on water column optics and food‐web dynamics. We compared the responses of two dominant zooplankton groups, Daphnia spp. and calanoid copepods, to elevated CDOM in two mesocosm experiments conducted in a transparent, oligotrophic lake. In the first experiment, low, medium and high additions of CDOM [dissolved organic carbon (DOC) = 2.7, 3.0 and 4.3 mg L−1, respectively] and non‐manipulated controls (DOC = 1.6 mg L−1) were used to test the hypothesis that food‐web stimulation will increase with CDOM concentration. In the second experiment, we manipulated both CDOM (control and addition) and ultraviolet radiation (UV; ambient and shielded) to determine the importance of CDOM as a UV screen, as well as to examine the role of UV in food‐web stimulation by CDOM. We also conducted short‐term bioassays alongside this second experiment to assess the food resources for Daphnia and calanoids in treatments with UV‐exposed and non‐UV‐exposed CDOM. Daphnia abundance increased in the low and medium CDOM additions in the first experiment, and when food resources were simultaneously stimulated by CDOM and protected from the direct negative effects of UV in the second experiment. In contrast, calanoid copepod abundance declined or remained unchanged when CDOM was added, and this response was not mediated by food resources. Overall, our findings suggest that increased CDOM in clear lakes could alter the relative abundance of zooplankton groups through a combination of direct and indirect effects.