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Resilience, measured by the distribution of passage times between alternate states, indicates persistence of a state in stochastic dynamic systems such as blooms of cyanobacteria in lakes. We used high‐frequency datasets to compare the resilience of low and high states of phycocyanin, a pigment indicator of cyanobacteria, in Lake Mendota, Wisconsin, USA, for three growing seasons that ranged sevenfold in external phosphorus (P) load. Each year we observed 139–265 passage times across the unstable threshold that separated the low‐ from high‐phycocyanin states. Each sample of passage times is highly skewed with low median, larger mean, much larger SD, and wide tails extending to long lifetimes of a state. About 25% of events, whether low or high phycocyanin, lasted a day or more. Among these 3 years of contrasting external P load, there were no discernible differences in the resilience of either ecosystem state. We attribute this lack of contrast to the sustained recycling of P from sediments and the high stochasticity of phycocyanin in this lake. [ABSTRACT FROM AUTHOR]

Phytoplankton blooms often follow nutrient enrichment. Differences among lakes in light‐absorbing dissolved organic carbon (DOC) may shift bloom thresholds to higher nutrient loads and thereby increase resilience of lakes to enrichment. To explore this idea, we measured resilience to experimental enrichment of two lakes with contrasting DOC concentrations. We compared bloom thresholds in both lakes using a model of phytoplankton response to DOC and nutrients, a dynamic time series indicator of resilience, and two empirical measures of stochastic resilience, mean exit time and median survival time. For the dynamic indicator and ecosystem model the lake with higher DOC was more resilient to enrichment. However, the distributions overlapped for stochastic indicators of resilience of the two lakes. These analyses show that DOC interacts with mixing depth and zooplankton biomass to affect resilience. Strong contrasts in DOC and many observations are needed to discern effects of DOC on resilience to enrichment. [ABSTRACT FROM AUTHOR]

Lake ecosystems are shifting due to many drivers including climate change and landscape‐scale habitat disturbance, diminishing their potential to support some fisheries. Walleye Sander vitreus (Mitchill) populations, which support recreational and tribal fisheries across North America, have declined in some lakes. Climate change, harvest, invasive species and concurrent increases in warm‐water fishes (e.g. Centrarchidae) may have contributed to declines. To test the utility of an intensive management action to resist walleye loss, an experimental removal of ~285,000 centrarchids from a 33‐ha lake over 4 years was conducted while monitoring the fish community response. Centrarchid abundance declined and yellow perch Perca flavescens (Mitchill) increased, yet no evidence of walleye recruitment was observed. These findings explore the feasibility of intensive resistance as a management strategy in supporting walleye facing environmental change and provide a platform for management discussions to move beyond resist strategies in the Resist‐Accept‐Direct (RAD) framework to navigate ecosystem change. [ABSTRACT FROM AUTHOR]

Jonathan J. Cole, a prominent figure in the field of limnology and oceanography, passed away in July 2023. He was known for his contributions to the American Society of Limnology and Oceanography (ASLO) and his role as a scientific leader, colleague, mentor, and friend. Cole's research focused on the aquatic carbon cycle, particularly the production and respiration of organic matter by phytoplankton. He also investigated the impacts of the zebra mussel invasion on the Hudson River Estuary and played a key role in quantifying the role of inland waters in the global carbon cycle. Cole received numerous awards and honors for his work and was recognized for his sense of humor and wide range of interests. His influence will continue to be felt in the scientific community. [Extracted from the article]

Resilience was compared for alternate states of phytoplankton pigment concentration in two multiyear whole‐lake experiments designed to shift the manipulated ecosystem between alternate states. Mean exit time, the average time between threshold crossings, was calculated from automated measurements every 5 min during summer stratification. Alternate states were clearly identified, and equilibria showed narrow variation in bootstrap analysis of uncertainty. Mean exit times ranged from 13 to 290 h. In the reference ecosystem, Paul Lake, mean exit time of the low‐pigment state was about 100 h longer than mean exit time of the high‐pigment state. In the manipulated ecosystem, Peter Lake, mean exit time of the high‐pigment state exceeded that of the low‐pigment state by 30 h in the cascade experiment. In the enrichment experiment mean exit time of the low‐pigment state was longer than that of the high‐pigment state by about 100 h. Mean exit time is a useful measure of resilience for stochastic ecosystems where high‐frequency measurements are made by consistent methods over the full range of ecosystem states. [ABSTRACT FROM AUTHOR]

Historically, estimates of pelagic primary production in lake ecosystems were made by measuring the uptake of carbon‐14 (14C)‐labeled inorganic carbon in samples incubated under laboratory or in situ conditions. However, incubation approaches are increasingly being replaced by methods that analyze diel changes in high‐frequency in situ data such as free‐water dissolved oxygen (O2). While there is a rich literature on the comparison of approaches for estimating primary production using incubations (e.g., 14C and O2 bottle experiments), as well for approaches using high‐frequency data (e.g., diel O2 and CO2 metabolism models), there are few direct comparisons of 14C incubations and free‐water O2 approaches for estimating primary production. We used 20 lake‐years of concurrent measurements of primary production quantified from high‐frequency free‐water O2 data and 14C incubations in four different lakes (4–7 years per lake) to compare these different approaches. Across all lakes, 61% of the 14C production estimates were within the 95% credible intervals of the free‐water O2 production estimates. Error‐in‐variable regressions support the assumption that 14C methods estimate a production value between gross primary production and net primary production and the bottle effect is constant across the entire range of production values considered here. There was little evidence that daily pelagic, epilimnetic estimates of primary production differed substantially based on the selection of free‐water O2 or 14C approaches in these lakes during summer stratified conditions. [ABSTRACT FROM AUTHOR]

Lake respiration is supported by a mixture of autochthonous and allochthonous resources, but the relative significance and interaction of these sources are uncertain across gradients of primary production and organic matter inputs. We manipulated autochthonous resources by adding inorganic nitrogen and phosphorus to two lakes during three summers and monitored a third reference lake. Allochthonous resources were measured as fluorescent dissolved organic matter (FDOM). In the reference and two experimental lakes, daily estimates of respiration were made from continuously deployed oxygen sensors. Daily mean values of temperature and FDOM were determined from high‐frequency measurements along with daily measures of chlorophyll a, an index of phytoplankton biomass. We analyzed time series of respiration and tested models that used combinations of the independent variables chlorophyll, FDOM, and temperature. The best models included all three of the independent variables. Respiration increased twofold over the temperature range of 14.5–28.6°C. Respiration increased in association with phytoplankton blooms caused by the nutrient additions, but did not track blooms closely, because of large day‐to‐day variability. Respiration varied positively with FDOM that was primarily allochthonous and differed among lakes and years. We did not detect an interaction between chlorophyll and FDOM despite the large number of observations and range of chlorophyll and FDOM. Hydrologic, climatic, and land use changes are altering temperature and inputs of nutrients and organic matter to lakes. Our results indicate that these changes may lead to linear responses in ecosystem processes like respiration for the wide range of inputs represented in this study. [ABSTRACT FROM AUTHOR]

Ecosystems are changing in complex and unpredictable ways, and analysis of these changes is facilitated by coordinated, long‐term research. Meeting diverse societal needs requires an understanding of what populations and communities will be dominant in 20, 50, and 100 yr. This paper is a product of a synthesis effort of the U.S. National Science Foundation funded Long‐Term Ecological Research (LTER) network addressing the LTER core research area of populations and communities. This analysis revealed that each LTER site had at least one compelling story about what their site would look like in 50 or 100 yr. As the stories were prepared, themes emerged, and the stories were grouped into papers along five themes for this special issue: state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the resilience theme and includes stories from the Baltimore (urban), Hubbard Brook (northern hardwood forest), Andrews (temperate rain forest), Moorea (coral reef), Cedar Creek (grassland), and North Temperate Lakes (lakes) sites. The concept of resilience (the capacity of a system to maintain structure and processes in the face of disturbance) is an old topic that has seen a resurgence of interest as the nature and extent of global environmental change have intensified. The stories we present here show the power of long‐term manipulation experiments (Cedar Creek), the value of long‐term monitoring of forests in both natural (Andrews, Hubbard Brook) and urban settings (Baltimore), and insights that can be gained from modeling and/or experimental approaches paired with long‐term observations (North Temperate Lakes, Moorea). Three main conclusions emerge from the analysis: (1) Resilience research has matured over the past 40 yr of the LTER program; (2) there are many examples of high resilience among the ecosystems in the LTER network; (3) there are also many warning signs of declining resilience of the ecosystems we study. These stories highlight the need for long‐term studies to address this complex topic and show how the diversity of sites within the LTER network facilitates the emergence of overarching concepts about this important driver of ecosystem structure, function, services, and futures. [ABSTRACT FROM AUTHOR]

Although climate change has shifted the phenological timing of plankton in lakes, few studies have explicitly addressed the relative contributions of climate change and other factors, including planktivory and nutrient availability. The spring clear‐water phase is a period of marked reduction in algal biomass and increased water transparency observed in many lakes. Here, we quantified the phenological patterns in the start date, maximum date, duration, and magnitude of the clear‐water phase over 38 yr in Lakes Mendota and Monona, and examined the effects of water temperature, total phosphorus, and food web structure (proportion of large‐bodied Daphnia pulicaria and density of invasive Bythotrephes) and interactions between temperature and other predictors on these clear‐water phase metrics. We found that climate and food web structure affected the clear‐water phase, but the effects differed among the metrics. Higher water temperature led to earlier clear‐water phase start dates and maximum dates in both lakes. The proportion of D. pulicaria affected all clear‐water phase metrics in both lakes. When D. pulicaria proportion was higher, the clear‐water phase occurred earlier, lasted longer, and the water was clearer. Moreover, high Bythotrephes density delayed clear‐water phase start dates (both lakes), and decreased clear‐water phase duration (Lake Mendota) in the following year. These results suggest that variation in food web structure changes the full phenological dynamics of the clear‐water phase, while variation in climate condition affects clear‐water phase timing only. Our findings highlight the importance of large‐bodied grazers for managing water quality under climate change. [ABSTRACT FROM AUTHOR]

Concentrations of phycocyanin, a pigment of Cyanobacteria, were measured at 1‐min intervals during the ice‐free seasons of 2008–2018 by automated sensors suspended from a buoy at a central station in Lake Mendota, Wisconsin, U.S.A. In each year, stochastic‐dynamic models fitted to time series of log‐transformed phycocyanin concentration revealed two alternative stable states and random factors that were much larger than the difference between the alternate stable states. Transitions between low and high states were abrupt and apparently driven by stochasticity. Variation in annual magnitudes of the alternate states and the stochastic factors were not correlated with annual phosphorus input to the lake. At daily time scales, however, phycocyanin concentration was correlated with phosphorus input, precipitation, and wind velocity for time lags of 1–15 d. Multiple years of high‐frequency data were needed to discern these patterns in the noise‐dominated dynamics of Cyanobacteria. [ABSTRACT FROM AUTHOR]

Many Bluegill Lepomis macrochirus populations are dominated by fish ≤125 mm total length (TL) that may be underrepresented when using standard sampling gears. To identify efficient sampling methods for these populations, we compared catch per unit effort (CPUE) and TL frequency distributions of Bluegill captured in cloverleaf traps, boat electrofishing, mini‐fyke nets, and beach seine hauls from two northern Wisconsin lakes supporting populations dominated by fish ≤125 mm TL. Mean Bluegill CPUE ranged from 41 (SE = 11) fish per cloverleaf trap lift to 16 (SE = 8) fish per beach seine haul. Cloverleaf traps generally captured smaller Bluegill relative to other gears and were the only gear to consistently capture Bluegill ≤80 mm TL. Conversely, boat electrofishing captured the widest TL range of Bluegill, and fish ≥80 mm TL composed a greater proportion of catch (37%) relative to other gears. With few exceptions, the effort required to detect 10% or 25% changes in Bluegill CPUE was >100 units of effort regardless of lake, sampling gear, or month. Furthermore, there was no consistency between lakes or months in terms of which sampling gear required the fewest number of samples to detect a 50% change in CPUE. Estimated units of effort needed to detect 10% or 25% changes in mean Bluegill TL were ≤16 for all sampling gears on the lake with consistently higher CPUE (i.e., more fish to measure per unit). In the lake with lower CPUE, cloverleaf traps consistently required less effort to detect changes in mean TL. We note that comparing sample size requirements among gears is not straightforward because gears are sampling differing segments of the Bluegill population. Our study emphasizes the importance of evaluating gear biases and sampling efficiency so that fisheries managers can develop suitable sampling protocols. [ABSTRACT FROM AUTHOR]

We conducted a 33‐yr series of whole‐lake experiments to measure ecosystem responses to food web structure and nutrient load, compare aquatic and terrestrial carbon flows to consumers, and evaluate indicators of ecosystem resilience. These manipulations showed that chlorophyll responded to nutrient loading and to grazing controlled by a trophic cascade. In this article, we synthesized experimental results using a new analysis of heretofore unrecognized variation in water color, measured as light absorbance at 440 nm. Long‐term data revealed fluctuations in precipitation that drive water color variation. We compared effects of nutrient loading, zooplankton biomass, zooplankton body size, and water color on chlorophyll. Water color was an important factor in the chlorophyll response. This driver of the chlorophyll response to manipulation was not resolved until decades of data were available. A long‐term context enriched insights from ecosystem experiments and exemplified the complementarity of experimental and long‐term approaches in limnology. [ABSTRACT FROM AUTHOR]

Abstract: Ecosystem regime shifts are abrupt changes from one dynamical state to another, such as the shift from a clear‐water state to an algal bloom state in lakes. These transitions are hard to forecast but theory suggests that early warning indicators can predict impending regime shifts that may allow for management intervention to prevent or mitigate an unwanted change. The efficacy of early warning indicators has been demonstrated in modeling and laboratory experiments, but rarely in the field, where environmental drivers are numerous and interacting. It is unclear if early warning indicators are observable or timely enough to allow for intervention under these conditions. We performed six whole‐lake experimental nutrient additions to test the utility of early warning indicators for predicting the regime shift from a clear‐water state to a cyanobacteria‐dominated state. The lakes were monitored for increases in resilience indicators including rises in standard deviation and autocorrelation of algal pigments and dissolved oxygen saturation. A statistical method, quickest detection, determined when resilience indicators in manipulated lakes deviated substantially from those in a reference ecosystem. Blooms occurred in five of the six lake‐years. Although there was substantial variability in bloom size and timing, at least one indicator foreshadowed the peak chlorophyll a concentration in all instances. Early warnings occurred 1–57 d prior to a bloom, which in some instances, may allow managers to notify the public or intervene to prevent blooms. The resilience indicators generally identified changes in resilience over time within a lake and also ranked large differences in resilience among lakes. Our findings suggest that resilience indicators can be useful for classifying ecosystems on a landscape and across time with respect to proximity to a critical threshold. [ABSTRACT FROM AUTHOR]

Abstract: Phosphorus runoff from agricultural land is a major cause of eutrophication in lakes and reservoirs. Frequency and intensity of extreme precipitation events are increasing in agricultural regions of the Upper Midwestern U.S., and these increases are projected to continue as climate warms. We quantified the linkage between extreme daily precipitation and extreme daily discharge, phosphorus (P) load, and P concentration for Pheasant Branch and the Yahara River, two tributaries of Lake Mendota, Wisconsin, U.S.A. using the generalized Pareto distribution. Although precipitation extremes have increased since 1940, over the shorter period of stream monitoring (1994–2015 for Pheasant Branch and 1991–2015 for Yahara) there is no significant trend in extreme precipitation. Nonetheless a disproportionate number of extreme precipitation events (for example seven of the 11 largest 24‐h events since 1901) occurred during the period of stream monitoring. Daily precipitation extremes were associated with extremes in daily discharge and P load. P load return levels increased steeply and almost linearly with precipitation on log‐log axes. The trend toward more frequent and intense precipitation extremes will increase P loading and intensify the eutrophication of the lake, unless the excessive P enrichment of the watershed is reversed. [ABSTRACT FROM AUTHOR]

Sustaining food production, water quality, soil retention, flood, and climate regulation in agricultural landscapes is a pressing global challenge given accelerating environmental changes. Scenarios are stories about plausible futures, and scenarios can be integrated with biophysical simulation models to explore quantitatively how the future might unfold. However, few studies have incorporated a wide range of drivers (e.g., climate, land-use, management, population, human diet) in spatially explicit, process-based models to investigate spatial-temporal dynamics and relationships of a portfolio of ecosystem services. Here, we simulated nine ecosystem services (three provisioning and six regulating services) at 220 × 220 m from 2010 to 2070 under four contrasting scenarios in the 1,345-km2 Yahara Watershed (Wisconsin, USA) using Agro-IBIS, a dynamic model of terrestrial ecosystem processes, biogeochemistry, water, and energy balance. We asked (1) How does ecosystem service supply vary among alternative future scenarios? (2) Where on the landscape is the provision of ecosystem services most susceptible to future social-ecological changes? (3) Among alternative future scenarios, are relationships (i.e., trade-offs, synergies) among food production, water, and biogeochemical services consistent over time? Our results showed that food production varied substantially with future land-use choices and management, and its trade-offs with water quality and soil retention persisted under most scenarios. However, pathways to mitigate or even reverse such trade-offs through technological advances and sustainable agricultural practices were apparent. Consistent relationships among regulating services were identified across scenarios (e.g., trade-offs of freshwater supply vs. flood and climate regulation, and synergies among water quality, soil retention, and climate regulation), suggesting opportunities and challenges to sustaining these services. In particular, proactive land-use changes and management may buffer water quality against undesirable future climate changes, but changing climate may overwhelm management efforts to sustain freshwater supply and flood regulation. Spatially, changes in ecosystem services were heterogeneous across the landscape, underscoring the power of local actions and fine-scale management. Our research highlights the value of embracing spatial and temporal perspectives in managing ecosystem services and their complex interactions, and provides a system-level understanding for achieving sustainability of the food-water-climate nexus in agricultural landscapes. [ABSTRACT FROM AUTHOR]

The Safe Operating Space ( SOS) of a recreational fishery is the multidimensional region defined by levels of harvest, angler effort, habitat, predation and other factors in which the fishery is sustainable into the future. SOS boundaries exhibit trade-offs such that decreases in harvest can compensate to some degree for losses of habitat, increases in predation and increasing value of fishing time to anglers. Conversely, high levels of harvest can be sustained if habitat is intact, predation is low, and value of fishing effort is moderate. The SOS approach recognizes limits in several dimensions: at overly high levels of harvest, habitat loss, predation, or value of fishing effort, the stock falls to a low equilibrium biomass. Recreational fisheries managers can influence harvest and perhaps predation, but they must cope with trends that are beyond their control such as changes in climate, loss of aquatic habitat or social factors that affect the value of fishing effort for anglers. The SOS illustrates opportunities to manage harvest or predation to maintain quality fisheries in the presence of trends in climate, social preferences or other factors that are not manageable. [ABSTRACT FROM AUTHOR]

Rapid changes in state have been documented for many of Earth's ecosystems. Despite a growing toolbox of methods for detecting declining resilience or early warning indicators (EWIs) of ecosystem transitions, these methods have rarely been evaluated in whole-ecosystem trials using reference ecosystems. In this study, we experimentally tested EWIs of cyanobacteria blooms based on changes in the spatial structure of a lake. We induced a cyanobacteria bloom by adding nutrients to an experimental lake and mapped fine-resolution spatial patterning of cyanobacteria using a mobile sensor platform. Prior to the bloom, we detected theoretically predicted spatial EWIs based on variance and spatial autocorrelation, as well as a new index based on the extreme values. Changes in EWIs were not discernible in an unenriched reference lake. Despite the fluid environment of a lake where spatial heterogeneity driven by biological processes may be overwhelmed by physical mixing, spatial EWIs detected an approaching bloom suggesting the utility of spatial metrics for signaling ecological thresholds. [ABSTRACT FROM AUTHOR]

Predicting species responses to perturbations is a fundamental challenge in ecology. Decision makers must often identify management perturbations that are the most likely to deliver a desirable management outcome despite incomplete information on the pattern and strength of food web links. Motivated by a current fishery decline in inland lakes of the Midwestern United States, we evaluate consistency of the responses of a target species (walleye [ Sander vitreus]) to press perturbations. We represented food web uncertainty with 193 plausible topological models and applied four perturbations to each one. Frequently the direction of the focal predator response to the same perturbation is not consistent across food web topologies. Simultaneous application of management perturbations led to less consistent outcomes compared to the best single perturbation. However, direct manipulation of the adult focal predator produced a desirable outcome in 77% of 193 plausible topologies. Identifying perturbations that produce consistent outcomes in the face of food web uncertainty can have important implications for natural resource conservation and management efforts. [ABSTRACT FROM AUTHOR]

The scale, rate, and intensity of humans' environmental impact has engendered broad discussion about how to find plausible pathways of development that hold the most promise for fostering a better future in the Anthropocene. However, the dominance of dystopian visions of irreversible environmental degradation and societal collapse, along with overly optimistic utopias and business-as-usual scenarios that lack insight and innovation, frustrate progress. Here, we present a novel approach to thinking about the future that builds on experiences drawn from a diversity of practices, worldviews, values, and regions that could accelerate the adoption of pathways to transformative change (change that goes beyond incremental improvements). Using an analysis of 100 initiatives, or 'seeds of a good Anthropocene', we find that emphasizing hopeful elements of existing practice offers the opportunity to: (1) understand the values and features that constitute a good Anthropocene, (2) determine the processes that lead to the emergence and growth of initiatives that fundamentally change human-environmental relationships, and (3) generate creative, bottom-up scenarios that feature well-articulated pathways toward a more positive future. [ABSTRACT FROM AUTHOR]

Terrestrial organic matter can be assimilated by aquatic consumers but implications for biomass and production are unresolved. An ecosystem model was fit to estimate effects of phosphorus (P) load, planktivory, and supply rate of terrestrial particulate organic carbon ( TPOC) on phytoplankton and zooplankton in five whole-lake experiments. Phytoplankton biomass increased with P load and planktivory and decreased with TPOC supply rate. Zooplankton biomass increased with P load and responded weakly to planktivory and TPOC supply rate. Zooplankton allochthony (proportion of carbon from terrestrial sources) decreased with P load and planktivory and increased with TPOC supply rate. Lakes with low allochthony (< 0.3) had wide ranges of phytoplankton and zooplankton biomass and production, depending on P load and planktivory. Lakes with high allochthony (> 0.3) had low biomass and production of both phytoplankton and zooplankton. In summary, terrestrial OC inhibits primary production and is a relatively low-quality food source for zooplankton. [ABSTRACT FROM AUTHOR]

Many ecosystems are likely to experience abrupt changes and extreme conditions due to forces such as climate change. These events and their consequences--including the loss of ecosystem services--may be predictable or may occur without warning. Given these considerations, greater efforts are needed in two areas of research: improvements in early warning capability and advances in the management of ecosystems to enhance resilience. Current research has provided enhanced forecasting ability, scenario analysis, and detection of statistical anomalies that indicate abrupt change, but two key concerns remain: the detection of early warning signs near thresholds of change and the use of such warnings for ecosystem management. Furthermore, there may be no advance warning for some types of abrupt change, reinforcing the need to enhance resilience by managing ecosystems to reduce the possibility of crossing thresholds of change. Designing and implementing large-scale management programs is one way to confront these problems. [ABSTRACT FROM AUTHOR]

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Invasive Rainbow SmeltOsmerus mordaxhave been associated with reductions in WalleyeSander vitreusrecruitment, and predation by adult smelt on age-0 Walleyes has been identified as one of the potential mechanisms contributing to recruitment failure. Predation effects could be mitigated by stocking Walleye fingerlings based on smelt and Walleye morphometric relationships. By combining 0.95 quantile regression of smelt gape size on TL and 0.05 quantile regression of Walleye body depth on TL, we constructed a stocking tool to determine the appropriate size to stock Walleye fingerlings in lakes invaded by smelt such that few Walleyes are vulnerable to predation by smelt. In lakes where the largest smelt TL is known, Walleye fingerlings can be stocked according to the model: TLWYE= 0.819(TLRWS) − 23.838. In cases where the smelt population size structure is unknown, Walleyes should be stocked at sizes larger than 142 mm, which would be a sufficient size for Walleye fingerlings to avoid predation by Rainbow Smelt in all lakes in this study. Received January 16, 2014; accepted June 30, 2014 [ABSTRACT FROM AUTHOR]

Massive changes to ecosystems sometimes cross thresholds from which recovery can be difficult, expensive and slow. These thresholds are usually discovered in post hoc analyses long after the event occurred. Anticipating these changes prior to their occurrence could give managers a chance to intervene. Here we present a novel approach for anticipating ecosystem thresholds that combines resilience indicators with Quickest detection of change points. Unlike existing methods, the Quickest detection method is updated every time a data point arrives, and minimizes the time to detect an approaching threshold given the users' tolerance for false alarms. The procedure accurately detected an impending regime shift in an experimentally manipulated ecosystem. An ecosystem model was used to determine if the method can detect an approaching threshold soon enough to prevent a regime shift. When the monitored variable was directly involved in the interaction that caused the regime shift, detection was quick enough to avert collapse. When the monitored variable was only indirectly linked to the critical transition, detection came too late. The procedure is useful for assessing changes in resilience as ecosystems approach thresholds. However some thresholds cannot be detected in time to prevent regime shifts, and surprises will be inevitable in ecosystem management. [ABSTRACT FROM AUTHOR]

Lake food webs can be supported by primary production from within the lake, organic matter imported from the catchment or some mixture of these two sources. Generalisations about food-web subsidies to lake ecosystems are often based on data from only a few ecosystems and therefore do not consider the potential variability of subsidies among diverse ecosystems in a landscape., We measured the variation among lake ecosystems in terrestrial (allochthonous) utilisation by pelagic consumers and developed models to describe the variability. Stable isotope ratios of hydrogen and carbon were measured for Chaoborus spp. and crustacean zooplankton taxa in 40 lakes to quantify consumer allochthonous resource use (allochthony)., The median fraction of consumer allochthony estimated using a two-source Bayesian mixing model varied between 4 and 82% (mean among all lakes = 36%) for Chaoborus sp. among lakes and between 1 and 76% in a more limited sample of crustacean zooplankton consumers. The degree of allochthonous resource use increased linearly with the availability of allochthonous resources., Terrestrial support of Chaoborus was correlated (using best fitting relationships) with covariates for lake organic matter sources including dissolved inorganic carbon, total phosphorus, chlorophyll α, colour and catchment area. However, the most parsimonious model was an inverse relationship between lake surface area and consumer allochthony, indicating that allochthonous subsidies are more important in smaller than larger systems. Given the preponderance of small waterbodies, allochthonous subsidies are important in a large number of lake ecosystems. [ABSTRACT FROM AUTHOR]

Rapid transitions in ecosystem structure, or regime shifts, are a hallmark of alternative stable states (ASS). However, regime shifts can occur even when feedbacks are not strong enough to cause ASS. We investigated the potential for ASS to explain transitions between dominance of an invasive species, rusty crayfish (Orconectes rusticus), and native sunfishes (Lepomis spp.) in northern Wisconsin (USA) lakes. A rapid transition from Lepomis to rusty crayfish dominance occurred as rusty crayfish invaded Trout Lake, and the reverse transition resulted from an eight-year experimental removal of rusty crayfish from Sparkling Lake. We fit a stage-structured population model of species interactions to 31 years of time-series data from each lake. The model identified water level as an important driver, with drought conditions reducing rusty crayfish recruitment and allowing Lepomis dominance. The maximum-likelihood parameter estimates of the negative interaction between rusty crayfish and Lepomis led to ASS in the model, where each species was capable of excluding the other within a narrow range of environmental conditions. However, uncertainty in parameter estimates made it impossible to exclude the potential that rapid transitions were caused by a simpler threshold response lacking alternative equilibria. Simulated forward and backward transitions between species dominance occurred at different environmental conditions (i.e., hysteresis), even when the parameters used for simulation did not predict ASS as a result of slow species responses to environmental drivers. Thus, ASS are possible, but by no means certain, explanations for rapid transitions in this system, and our results highlight the difficulties associated with distinguishing ASS from other types of threshold responses. However, whether regime shifts are caused by ASS may be relatively unimportant in this system, as the range of conditions over which transitions occur is narrow, and under most conditions, the system is predicted to exist in only a single state. [ABSTRACT FROM AUTHOR]

Regime shifts are massive changes among alternate ecosystem states. Predicting regime shifts is difficult, but statistical indicators such as increasing variance or autocorrelation may provide early warnings of their impending onset. We conducted a 4 yr lake manipulation to test for early warnings prior to a food-web transition by adding largemouth bass (Micropterus salmoides) to a lake dominated by small fishes, and thereby drive a trophic cascade that altered zooplankton biomass, community composition, and body size. Declining catches of small fishes were associated with shifts to larger bodied species of Daphnia. We measured zooplankton biomass daily in a reference and manipulated lake and calculated variance and autocorrelation of the zooplankton time series using 28 d rolling windows. We asked whether the variance in the manipulated lake (relative to the reference lake) increased and whether autocorrelation approached unity (a value suggested by theory) prior to the food-web regime shift. The variance and autocorrelation of zooplankton biomass were similar between the two lakes in the first 2 yr of the manipulation. During the third year, variance was much higher and autocorrelation approached unity for sustained periods in the manipulated but not in the reference lake. Variance and autocorrelation were similar between the two lakes during the fourth year as the food-web transition moved to completion. The joint response of variance and autocorrelation in year 3 provided an early warning of the food-web transition consistent with theoretical expectation. [ABSTRACT FROM AUTHOR]

Recreational freshwater fisheries are key components of local economies in many regions. The quality of these fisheries can be affected not only by harvest but also by catch-and-release practices. Documenting catch and release among sport fish taxa is, therefore, important to fisheries researchers studying sport fishes and managers regulating these fisheries. We used an angler diary survey to assess taxon-specific effort, catch, harvest, release, and reason for release during the 2011 open-water season. Our study included information on 5,007 fishing trips taken by 652 anglers. These anglers visited 279 lakes spanning 11,761.5 km2 of northern Wisconsin. Muskellunge Esox masquinongy, black bass (i.e., Smallmouth Bass Micropterus dolomieu and Largemouth Bass M. salmoides), Northern Pike E. lucius, Walleye Sander vitreus, and panfish were released at rates of 99, 97, 86, 67, and 67%, respectively, when targeted by anglers. This study is the first to document black bass catch-and-release rates in the region and corroborates previous findings of Muskellunge and Walleye catch-and-release rates based on creel surveys. Voluntary catch and release was the most common reason for release. Our findings suggest that regulations may be much more generous than the harvest rates practiced by anglers and that catch-and-release angling practices may be an important factor affecting these sport fish populations. [ABSTRACT FROM AUTHOR]

To characterize the spatial variability of metabolism estimates (gross primary production [GPP], respiration [R], and net ecosystem production [NEP]) in two Northern Wisconsin lakes, we collected data from 27 and 35 dissolved oxygen sensors placed in a two-dimensional array throughout the upper mixed layers over a period of 10 d per lake in midsummer. Averaged over the deployment, aerial metabolism estimates among sensor locations varied 1-2 orders of magnitude and were largely unrelated to physical habitat within the lake. For all sites and days, 76-90% of the explainable variance in GPP and R was attributable to location in the lake rather than day of the deployment. NEP, on the other hand, was less affected by location, with 79-93% of the explained variance attributable to the day of the deployment. Single-location estimates can yield errors of more than an order of magnitude in estimates of daily GPP and R and can mischaracterize the trophic status of the lake. Using a rarefaction approach, we found that using four randomly placed sensors increased the precision of the resulting daily metabolism estimates fourfold over single-location measures in both lakes. [ABSTRACT FROM AUTHOR]

A Bayesian mixing model and stable isotopes of carbon, nitrogen, and hydrogen were used to evaluate the extent to which six consumers (three fishes, two zooplankton, and a snail) in a naturally productive lake used terrestrial resources, epilimnetic and metalimnetic phytoplankton, benthic algae, and macrophytes. Resource use varied with consumer habitat use and feeding ability, but allochthony was consistently low (averaging 15% among consumers). The pelagic invertebrates Skistodiaptomus oregonensis and Chaoborus spp. relied on phytoplankton from the epilimnion (59% and 49%, respectively) and to a lesser extent from the metalimnion (28% and 26%, respectively); terrestrial resources comprised 9% and 18% of the diet of these consumers, respectively. The snail Helisoma trivolvis relied mainly on littoral resources (floating-leafed macrophytes; 68% of diet), but terrestrial resources also constituted a substantial portion of its diet (21%). The fishes integrated among habitats more evenly than the other consumers, but pelagic resources formed the largest portion of their diets (Pimephales promelas = 64%, Lepomis gibbosus = 47%, and Perca flavescens = 47%). L. gibbosus was the fish with the most allochthonous diet (23%). The consumers of this productive lake were not highly dependent on allochthonous materials and tended to rely most heavily on local resources, including macrophytes. [ABSTRACT FROM AUTHOR]

It is virtually impossible to quantify the limnological characteristics of every aquatic ecosystem all the time. The goal of this study was to assess the capacity of lake-monitoring data to predict annually resolved characteristics in systems where measurements are not always made. To address this, we provide an analysis of interpolation (i.e., predicting a current lake characteristic based on current characteristics of other lakes) and forecasting (i.e., predicting a current lake characteristic based on historical trends and characteristics of a set of study lakes) in seven lakes over a 28-yr time frame. The most effective interpolations are generated using 12-15 yr of training data. Interpolation models are 29% more effective, on average, when historical trends (forecasting) are also incorporated into the models. Forecasting models that predict lake characteristics using long-term trends in the focal lake were improved by including historical observations from other lakes. Direct comparisons of different prediction models further demonstrated that it is sometimes more effective to generate predictions based on a set of previously measured conditions (forecasts) rather than a set of known regional conditions that have been recently quantified (interpolations). Basic monitoring data have the potential to be upscaled to generate predictions of lake characteristics, but the effectiveness of predictions depend on the training data characteristics and prediction approaches employed. [ABSTRACT FROM AUTHOR]

The article discusses on effect of invasive species in aquatic ecosystems. It mentions that after invasions, eradication should be considered whenever the potential loss of ecosystem services outweighs the cost of eradication methods. Water temperature simulations were used and found that destratification can eliminate optimal rainbow smelt thermal habitat resulting in mortality. It states that bioenergetics simulations predicted a weight loss of adult rainbow smelt.

The global reach of human activities affects all natural ecosystems, so that the environment is best viewed as a social-ecological system. Consequently, a more integrative approach to environmental science, one that bridges the biophysical and social domains, is sorely needed. Although models and frameworks for social-ecological systems exist, few are explicitly designed to guide a long-term interdisciplinary research program. Here, we present an iterative framework, "Press-Pulse Dynamics" (PPD), that integrates the bio-physical and social sciences through an understanding of how human behaviors affect "press" and "pulse" dynamics and ecosystem processes. Such dynamics and processes, in turn, influence ecosystem services - thereby altering human behaviors and initiating feedbacks that impact the original dynamics and processes. We believe that research guided by the PPD framework will lead to a more thorough understanding of social-ecological systems and generate the knowledge needed to address pervasive environmental problems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The development of complete regional carbon (C) budgets for different biomes is an integral step in the effort to predict global response and potential feedbacks to a changing climate regime. Wetland and lake contributions to regional C cycling remain relatively uncertain despite recent research highlighting their importance. Using a combination of field surveys and tower-based carbon dioxide (CO) flux measurements, modeling, and published literature, we constructed a complete C budget for the Northern Highlands Lake District in northern Wisconsin/Michigan, a ∼6400 km region rich in lakes and wetlands. This is one of the first regional C budgets to incorporate aquatic and terrestrial C cycling under the same framework. We divided the landscape into three major compartments (forests, wetlands, and surface waters) and quantified all major C fluxes into and out of those compartments, with a particular focus on atmospheric exchange but also including sedimentation in lakes and hydrologic fluxes. Landscape C storage was dominated by peat-containing wetlands and lake sediments, which make up only 20% and 13% of the landscape area, respectively, but contain >80% of the total fixed C pool (ca. 400 Tg). We estimated a current regional C accumulation of 1.1±0.1 Tg yr, and the largest regional flux was forest net ecosystem exchange (NEE) into aggrading forests for a total of 1.0±0.1 Tg yr. Mean wetland NEE (0.12±0.06 Tg yr into wetlands), lake CO emissions and riverine efflux (each ca. 0.03±0.01 Tg yr) were smaller but of consequence to the overall budget. Hydrologic transport from uplands/wetlands to surface waters within the region was an important vector of terrestrial C. Regional C fluxes and pools would be misrepresented without inclusion of surface waters and wetlands, and C budgets in heterogeneous landscapes open opportunities to examine the sensitivities of important fluxes to changes in climate and land use/land cover. [ABSTRACT FROM AUTHOR]

Are environmental science students developing the mindsets and obtaining the tools needed to help address the considerable challenges posed by the 21st century? Today's major environmental issues are characterized by high-stakes decisions and high levels of uncertainty. Although traditional scientific approaches are valuable, contemporary environmental issues also require new tools and new ways of thinking. We provide an example of how such new, or "post-normal", approaches have been taught at the graduate level, through practical application of scenario planning. Surveyed students reported that they found the scenario planfling course highly stimulating, thought-provoking, and inspiring. Key learning points included recognizing the need for multiple points of view when considering complex environmental issues, and better appreciating the pervasiveness of uncertainty. Collaborating with non-academic stakeholders was also particularly helpful. Most students left the course feeling more positive about the potential contribution they can make in addressing the environmental challenges that society faces. [ABSTRACT FROM AUTHOR]

Understanding the drivers and consequences of disease epidemics is an important frontier in ecology. However. long-term data on hosts, their parasites, and the corresponding environmental conditions necessary to explore these interactions are often unavailable. We examined the dynamics of Daphnia pulicaria, a keystone zooplankter in lake ecosystems, to explore the long-term causes and consequences of infection by a chytridiomycete parasitoid (Polycaryum laeve). After quantifying host pathogen dynamics from vouchered samples collected over 15 years, we used autoregressive models to evaluate (I) hypothesized drivers of infection, including host density, water temperature, dissolved oxygen, host-food availability, and lake mixing: and (2) the effects of epidemics on host populations. Infection was present in most years but varied widely in prevalence, from <1% to 34%, with seasonal peaks in early spring and late fall. Within years, lake stratification strongly inhibited P. laeve transmission, such that epidemics occurred primarily during periods of water mixing, Development of the thermocline likely reduced transmission by spatially separating susceptible hosts from infectious zoospores. Among years, ice duration and cumulative snowfall correlated negatively with infection prevalence, likely because of reductions in spring phytoplankton and D. pulicaria density in years with extended winters. Epidemics also influenced dynamics of the host population. Infected D. pulicaria rarely (< 1%) contained eggs, and P. laeve prevalence was positively correlated with sexual reproduction in D. pulicaria, Analyses of D. pulicaria density-dependent population dynamics predicted that, in the absence of P. laeve infection, host abundance would be 11-50% higher than what was observed. By underscoring the importance of complex physical processes in controlling host parasite interactions and of epidemic disease in influencing host populations, our results highlight the value of long-term data for understanding wildlife disease dynamics. [ABSTRACT FROM AUTHOR]

1. Secondary production of benthic invertebrates in lakes is supported by current autochthonous primary production, and by detritus derived from a combination of terrestrial inputs and old autochthonous production from prior seasons. We quantified the importance of these two resources for the dominant benthic insects in Crampton Lake, a 26 ha, clear-water system. 2. Daily additions of NaH13CO3 to the lake caused an increase in the stable carbon isotope ratios ( δ13C) of the current primary production of phytoplankton and periphyton. We measured the response of four insect groups (taxon-depth combinations) to this manipulation, quantifying their current autochthony (% reliance on current autochthonous primary production) by fitting dynamic mixing models to time series of insect δ13C. 3. The δ13C of all four groups increased in response to the manipulation, although the magnitude of response differed by taxon and by depth, indicating differences in current autochthony. Odonate larvae (Libellulidae and Corduliidae) collected at 1.5 m depth derived 75% of their C from current autochthonous primary production. Chironomid larvae collected at 1.5, 3.5 and 10 m depths derived, respectively, 43%, 39% and 17% of their C from current autochthonous primary production. 4. Both taxon-specific diet preferences and depth-specific differences in resource availability may contribute to differences in current autochthony. Our results demonstrate significant but incomplete support of insect production by current autochthony, and indicate that allochthonous inputs and old autochthonous detritus support a substantial fraction (25–83%) of insect production. [ABSTRACT FROM AUTHOR]

1. Lakes are a prominent feature of the Northern Highland Lake District (NHLD) of Wisconsin, covering 13% of the landscape. Summarising the physical, chemical, or biological nature of NHLD lakes at a regional scale requires a representative sample of the full size distributions of lakes. In this study, we selected at random 168 lakes from the full size distribution of lakes in the NHLD and sampled each lake for a broad suite of limnological variables. 2. Most lakes were small. The median lake area was 1.1 ha, however, half of the surface area of water was in a relatively small number of lakes larger than 162 ha. Smaller lakes tended to be low in dissolved inorganic carbon (DIC) and high in dissolved organic carbon (DOC). Inclusion of small lakes (<4 ha) in the survey resulted in an acid neutralising capacity (ANC) median (76.5 μEq L−1) much lower than previous estimates, and a DOC median (10.1 mg L−1) about 50% higher than it would have been without the smaller lakes. Unlike DOC, total P tended to be evenly distributed across lake sizes. 3. The implications of these findings are that regional summaries of lake characteristics for the NHLD are influenced by the inclusion of small lakes in the sample, even though most of the water surface area is in lakes larger than 162 ha. Excluding small lakes introduces bias in the estimates of organic carbon and inorganic carbon values, for example. Similar biases may be introduced for lake characteristics at the global scale if small lakes are not sampled, because the size distribution of lakes globally is dominated in number by small lakes. [ABSTRACT FROM AUTHOR]

It has been suggested that differences in body size between consumer and resource species may leave important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator-prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator-prey body-size ratios are on average significantly higher (1) in freshwater habitats, than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer-resource interaction strengths may vary systematically across different habitat categories and consumer types. [ABSTRACT FROM AUTHOR]

Dissolved inorganic carbon (DIC) and dissolved oxygen (DO) are commonly measured to compute metabolism of aquatic ecosystems. However, concentrations of DIC and DO depend on many factors in addition to ecosystem metabolism, such as water temperature, gas exchange with the atmosphere, abiotic chemical reactions, and inputs in precipitation, groundwater, and surface water. We used 20-year time series from seven lakes to understand how DIC and DO concentrations are controlled as a function of time scale. Diel cycles of both solutes are controlled primarily by metabolism, exchange with the atmosphere, and temperature. At seasonal and annual scales, metabolism is important, but physical processes associated with Spring and autumn mixing, as well as solute loading from the watershed, have comparably large effects. At decadal scales, effects of metabolism are negligible. Controls of the two solutes diverge, with variance in DIC explained largely by solute inputs and variance in DO explained largely by water temperature. Like other indicators in many ecosystems, variability of DIC and DO is strongly scale dependent and associated with different drivers depending on the time scale of the analysis. [ABSTRACT FROM AUTHOR]

Despite growing interest in ecological interactions between predators and pathogens, few studies have experimentally examined the consequences of infection for host predation risk or how environmental conditions affect this relationship. Here we combined mesocosm experiments, in situ foraging data, and broad-scale lake surveys to evaluate (1) the effects of chytrid infection (Polycaryum laeve) on susceptibility of Daphnia to fish predators and (2) how environmental characteristics moderate the strength of this interaction. In mesocosms, bluegill preferred infected Daphnia 2–5 times over uninfected individuals. Among infected Daphnia, infection intensity was a positive predictor of predation risk, whereas carapace size and fecundity increased predation on uninfected individuals. Wild-caught yellow perch and bluegill from in situ foraging trials exhibited strong selectivity for infected Daphnia (3–10 times over uninfected individuals). In mesocosms containing water high in dissolved organic carbon (DOC), however, selective predation on infected Daphnia was eliminated. Correspondingly, lakes that supported chytrid infections had higher DOC levels and lower light penetration. Our results emphasize the strength of interactions between parasitism and predation while highlighting the moderating influence of water color. P. laeve increases the conspicuousness and predation risk of Daphnia; as a result, infected Daphnia occur predominantly in environments with characteristics that conceal their elevated visibility. [ABSTRACT FROM AUTHOR]