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Fluxes of organic matter across habitat boundaries are common in food webs. These fluxes may strongly influence community dynamics, depending on the extent to which they are used by consumers. Yet understanding of basal resource use by consumers is limited, because describing trophic pathways in complex food webs is difficult. We quantified resource use for zooplankton, zoobenthos, and fishes in four low-productivity lakes, using a Bayesian mixing model and measurements of hydrogen, carbon, and nitrogen stable isotope ratios. Multiple sources of uncertainty were explicitly incorporated into the model. As a result, posterior estimates of resource use were often broad distributions; nevertheless, clear patterns were evident. Zooplankton relied on terrestrial and pelagic primary production, while zoobenthos and fishes relied on terrestrial and benthic primary production. Across all consumer groups terrestrial reliance tended to be higher, and benthic reliance lower, in lakes where light penetration was low due to inputs of terrestrial dissolved organic carbon. These results support and refine an emerging consensus that terrestrial and benthic support of lake food webs can be substantial, and they imply that changes in the relative availability of basal resources drive the strength of cross-habitat trophic connections.

Allochthonous organic carbon can subsidize consumers in aquatic systems, but this subsidy may only be significant in relatively small systems with high organic matter loading. We tested the importance of allochthonous carbon to consumers in a relatively large ($258,000 m^2$) clear-water lake by adding $H^{13}CO_3$ daily for 56 d. Dissolved inorganic carbon (DIC) was substantially enriched in 13C by the addition, but it was also variable over diel cycles because of exchange with the atmosphere and photosynthesis. By measuring the δ13C value of a physically separated phytoplankton concentrate as well as the δ13C of phospholipid fatty acids, we were able to follow $^{13}C-labeling$ dynamics of specific groups of phytoplankton and bacteria. The δ13C values of particulate organic carbon (POC), dissolved organic carbon (DOC), phytoplankton, bacteria, zooplankton, and the invertebrate predator, Chaoborus spp. all increased to a maximum during the addition and declined once the addition ceased. Autochthony (% C derived from internal primary production) of carbon pools (POC, DOC) and consumers was assessed by fitting dynamic models to time series of δ13C. Autochthonous carbon was the dominant source (88-100%) for POC, gram-positive bacteria, a copepod, zooplankton biomass, and Chaoborus spp. Autochthonous carbon provided a lower fraction (<70%) of carbon to DOC, gram-negative bacteria, and cladoceran zooplankton. In comparison to smaller and more humic lakes, terrestrially derived allochthonous C was less significant to the pelagic food web in this larger, clear-water lake. Among lakes, the relative importance of autochthonous versus allochthonous carbon to planktonic consumers is positively correlated to the ratio of color (absorbance of light at 440 nm, an indicator of terrestrially derived organic carbon) to chlorophyll.

High-frequency measurements are increasingly available and used to model ecosystem processes. This growing capability provides the opportunity to resolve key drivers of ecosystem processes at a variety of scales. We use a unique series of highfrequency measures of potential predictors to analyze daily variation in rates of gross primary production (GPP), respiration (R), and net ecosystem production (NEP = GPP – R) for two north temperate lakes. Wind speed, temperature, light, precipitation, mixed layer depth, water column stability, chlorophyll a, chromophoric dissolved organic matter (CDOM), and Zooplankton biomass were measured at daily or higher-frequency intervals over two summer seasons. We hypothesized that light, chlorophyll a, and Zooplankton biomass would be strongly related to variability in GPP. We also hypothesized that chlorophyll a, CDOM, and temperature would be most strongly related to variability in R, whereas NEP would be related to variation in chlorophyll a and CDOM. Consistent with our hypotheses, chlorophyll a was among the most important drivers of GPP, R, and NEP in these systems. However, multiple regression models did not necessarily include the other variables we hypothesized as most important. Despite the large number of potential predictor variables, substantial variance remained unexplained and models were inconsistent between years and between lakes. Drivers of GPP, R, and NEP were difficult to resolve at daily time scales where strong seasonal dynamics were absent. More complex models with greater integration of physical processes are needed to better identify the underlying drivers of short-term variability of ecosystem processes in lakes and other systems.

Previous studies have used sondes to measure diel changes in dissolved oxygen and thereby estimate gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP). Most of these studies estimate rates for the surface layer and require knowing the depth of the mixed layer (Z mix ), which is usually determined from discrete daily or weekly temperature profiles. However, Z mix is dynamic, as the thermal structure of lakes may change at scales of minutes rather than days or weeks. We studied two thermally stratified lakes that exhibited intermittent microstratification in the mixed layer. We combined sonde-based estimates of metabolism with high-frequency measurements of stratification using thermistor chains to determine how the short-term dynamics of stratification affect metabolic rates. We calculated estimates of metabolism using time series of Z mix measured at seasonal, weekly, daily, and 5-min intervals. Areal rates of GPP and R were up to 24 and 29% less, respectively, using the 5-min measurements of Z mix rather than weekly Z mix , while NEP was not significantly different. These reduced areal rates are mostly the consequence of the reduction in the depth of the mixed layer. Microstratification occurred frequently in both lakes and affected volumetric rates in one lake where R was significantly lower, NEP was significantly higher, and GPP was marginally lower compared to days without microstratification. Hence, microstratification not only affects the depth of the mixed layer, but also alters the processes that influence photosynthesis and respiration. Future studies should consider microstratification and possibly employ multiple sondes with thermistor chains that enable integrating metabolic rates to a specific depth, rather than assuming a stable upper mixed layer as the basis for calculations.

Fluxes of organic matter across habitat boundaries are common in food webs. These fluxes may strongly influence community dynamics, depending on the extent to which they are used by consumers. Yet understanding of basal resource use by consumers is limited, because describing trophic pathways in complex food webs is difficult. We quantified resource use for zooplankton, zoobenthos, and fishes in four low-productivity lakes, using a Bayesian mixing model and measurements of hydrogen, carbon, and nitrogen stable isotope ratios. Multiple sources of uncertainty were explicitly incorporated into the model. As a result, posterior estimates of resource use were often broad distributions; nevertheless, clear patterns were evident. Zooplankton relied on terrestrial and pelagic primary production, while zoobenthos and fishes relied on terrestrial and benthic primary production. Across all consumer groups terrestrial reliance tended to be higher, and benthic reliance lower, in lakes where light penetration was low due to inputs of terrestrial dissolved organic carbon. These results support and refine an emerging consensus that terrestrial and benthic support of lake food webs can be substantial, and they imply that changes in the relative availability of basal resources drive the strength of cross-habitat trophic connections.

Fluxes of organic matter across habitat boundaries are common in food webs. These fluxes may strongly influence community dynamics, depending on the extent to which they are used by consumers. Yet understanding of basal resource use by consumers is limited, because describing trophic pathways in complex food webs is difficult. We quantified resource use for zooplankton, zoobenthos, and fishes in four low‐productivity lakes, using a Bayesian mixing model and measurements of hydrogen, carbon, and nitrogen stable isotope ratios. Multiple sources of uncertainty were explicitly incorporated into the model. As a result, posterior estimates of resource use were often broad distributions; nevertheless, clear patterns were evident. Zooplankton relied on terrestrial and pelagic primary production, while zoobenthos and fishes relied on terrestrial and benthic primary production. Across all consumer groups terrestrial reliance tended to be higher, and benthic reliance lower, in lakes where light penetration was low due to inputs of terrestrial dissolved organic carbon. These results support and refine an emerging consensus that terrestrial and benthic support of lake food webs can be substantial, and they imply that changes in the relative availability of basal resources drive the strength of cross‐habitat trophic connections.

The exchange of information between researchers, resource managers, decision makers, and the general public has long been recognized as a critical need in environmental science. We examine the challenges in using ecological knowledge to inform society and to change societal actions, and identify a set of options and strategies to enhance this exchange. Our objectives are to provide background information on societal knowledge and interest in science and environmental issues, to describe how different components of society obtain information and develop their interests and values, and to present a framework for evaluating and improving communication between science and society. Our analysis strongly suggests that the interface between science and society can only be improved with renewed dedication to public outreach and a wholesale reconsideration of the way that scientists communicate with society. Ecologists need to adopt new models of engagement with their audiences, frame their results in ways that are more meaningful to these audiences, and use new communication tools, capable of reaching large and diverse target groups.