Global Environmental Assessments (GEAs) are intended to gather expert knowledge on a topic of global importance and present it in a useful format to those who could use the knowledge in decision-making. GEAs have disseminated new knowledge, influenced environmental policy, changed the evolution of science, and furthered many careers. The GEA community has always adapted to changing circumstances, often by increasing the complexity of the assessment process. The current level of complexity of most GEAs, alongside today’s increasingly polarized societies, changes in international trade, biophysical changes to the planet, greater interest in cross-sectoral problems and solutions, enhanced technological capacity, and increasingly contested nature of some aspects of environmental science may indicate that we’ve reached a point where further adaptation cannot be achieved merely by adding more complexity. It may be time for more fundamental changes to the GEA scope, process, and delivery. We use the MA as a touchstone in exploring how GEAs have evolved, considering both challenges and possible paths forward to retain legitimacy, credibility, and salience in a changing world. One strong possibility is for GEAs to reorient to serve as support structures for a broader diversity of levels and types of decision-making and a broader array of decision-making actors. In a rapidly changing world, a diverse ecosystem of assessment approaches is likely to be more robust, have more impact, and evolve more quickly. Continuing to experiment with different models for delivering multi-scale environmental information will help GEAs fit the needs of the 21st century.

Climate change is transforming the ecology of lakes at a rapid pace, shifting some lakes toward warmwater‐dominant habitats. As a result, warmwater fishes are increasingly becoming more prevalent in lakes where they already existed, altering the patterning and strength of species interactions. Understanding shifting species interactions (e.g., competition, predation), and the role of lake management in shaping these interactions, will be critical for lake stewardship in response to climate change. Here, we present results from an intensive 5‐year experimental removal of ~285,000 warmwater fishes from a north‐temperate lake. The goal of the experiment was to test whether warmwater fish reduction is effective for rewiring lake food webs to reverse undesirable conditions for coolwater species, leading to increased recruitment and abundance of coolwater fishes. Throughout the experiment, warmwater fishes were resilient to reductions, with biomass declines of 23% averaged across five species. Among coolwater fishes, the top predator walleye showed no biomass response, while yellow perch biomass increased by ~914%. Fish species biomass changes translated to food web shifts, including a yellow perch trophic position decline of 0.4, decreased zooplankton abundances, and increased zoobenthos abundances. Our results highlight differential species responses to a management action aimed at adapting to climate change. Despite similar thermal tolerances, two coolwater species responded differently to removal of warmwater fishes, highlighting the characteristics (e.g., life history strategies, adaptive capacity) that contribute to species resilience. Given the importance of biotic interactions, climate adaptation may need to go beyond a “one‐size‐fits‐all” approach even when species have similar thermal tolerances.

Underpinned by systemic thinking, social-ecological systems (SES) research has emerged as a critical field for addressing the challenges of the Anthropocene, marked by a cross-scale focus, inter-and transdisciplinary approaches, and a strong emphasis on place-based work. Thanks to the efforts of many networks and institutes, the field has advanced new theoretical and methodological approaches, fostered dedicated journals, and spurred educational programs. It has also significantly influenced sustainability initiatives and policy from local to global scales, and has richly informed place-based efforts. Despite this progress, SES research faces persistent challenges, including conceptual and methodological fragmentation, difficulty in scaling localized insights to global frameworks (and vice versa), and capturing cross-scale connections and processes while retaining contextual relevance. Inclusivity also remains a critical issue, with regional, Indigenous, and local contributions often underrepresented, as there is still a reliance on short-term, inequitably distributed grant funding for much of the research in the field. This paper introduces the Society for Social-Ecological Systems (SocSES), a global platform designed to build on and connect to the rich legacy of SES networks. SocSES aims to advance and support SES-based research, practice, and action toward a just and sustainable future. We outline how SocSES will provide a home for SES institutes, networks, researchers, and practitioners working at the science-practice-policy interface to connect and amplify existing efforts through thematic streams, regional hubs, an institutional hub, an early-career professionals hub, and synthesis groups. The society will provide a stable infrastructure to foster interdisciplinary and transdisciplinary collaboration, enhance the generalizability and policy relevance of SES research, bolster education, research, and knowledge co-production, and support the next generation of SES professionals. By addressing the persistent challenges facing the field and fostering transformative spaces and communities for innovation and action, SocSES aspires to support and leverage SES knowledge as a cornerstone of global sustainability science. In line with the society's commitment to linguistic diversity and equitable access, this abstract has been translated into 12 languages by authors of this paper and additional contributors. These translations are available in Appendix 2 and at https://socses.org/about/paper.

Limnology and Oceanography BulletinVolume 33, Issue 1 p. 28-29 Member News Jonathan J. Cole (1953-2023) Michael L. Pace, Michael L. Pace [email protected] [email protected] orcid.org/0000-0001-5945-6131 Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USASearch for more papers by this authorStephen R. Carpenter, Stephen R. Carpenter orcid.org/0000-0001-8097-8700 Center for Limnology, University of Wisconsin, Madison, Wisconsin, USASearch for more papers by this authorGene E. Likens, Gene E. Likens Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut, USA Cary Institute of Ecosystem Studies, Millbrook, New York, USASearch for more papers by this author Michael L. Pace, Michael L. Pace [email protected] [email protected] orcid.org/0000-0001-5945-6131 Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USASearch for more papers by this authorStephen R. Carpenter, Stephen R. Carpenter orcid.org/0000-0001-8097-8700 Center for Limnology, University of Wisconsin, Madison, Wisconsin, USASearch for more papers by this authorGene E. Likens, Gene E. Likens Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut, USA Cary Institute of Ecosystem Studies, Millbrook, New York, USASearch for more papers by this author First published: 20 December 2023 https://doi.org/10.1002/lob.10611Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References Caraco, N. F., J. J. Cole, and D. L. Strayer. 2005. Top-down control from the bottom: regulation of eutrophication in a large river by benthic grazing. Limnol. Oceanogr. 51: 664–670. 10.4319/lo.2006.51.1_part_2.0664 Web of Science®Google Scholar Caraco, N. F., J. E. Bauer, J. J. Cole, S. Petsch, and P. A. Raymond. 2010. Millennia aged organic carbon subsidies to a modern river food web. Ecology 91: 2385–2393. 10.1890/09-0330.1 CASPubMedWeb of Science®Google Scholar Cole, J. J. 2013. Freshwater ecosystems and the carbon cycle. International Ecology Institute. Google Scholar Cole, J. J., and G. E. Likens. 1979. Measurements of mineralization of phytoplankton detritus in an oligotrophic lake. Limnol. Oceanogr. 24: 541–547. 10.4319/lo.1979.24.3.0541 CASWeb of Science®Google Scholar Cole, J. J., N. F. Caraco, G. W. Kling, and T. W. Kratz. 1994. Carbon dioxide supersaturation in the surface waters of lakes. Science 265: 1568–1570. 10.1126/science.265.5178.1568 CASPubMedWeb of Science®Google Scholar Cole, J. J., S. R. Carpenter, M. L. Pace, M. C. Van de Bogert, J. L. Kitchell, and J. R. Hodgson. 2006. Differential support of lake food webs by three types of terrestrial organic carbon. Ecol. Lett. 9: 558–568. 10.1111/j.1461-0248.2006.00898.x PubMedWeb of Science®Google Scholar Cole, J. J., and others. 2007. Plumbing the global carbon cycle: integrating inland waters into the terrestrial carbon budget. Ecosystems 10: 171–184. 10.1007/s10021-006-9013-8 CASWeb of Science®Google Scholar Volume33, Issue1February 2024Pages 28-29 ReferencesRelatedInformation

AbstractResilience, 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.

Rivers, wetlands, lakes, and other freshwater ecosystems collectively cover only 1% of the Earth's surface. Yet, these ecosystems support a disproportionately large and vast array of biodiversity. Currently, these ecosystems face many threats, including pollution, habitat alteration, fragmentation, invasive species, overexploitation, overabstraction, climate change, and other emerging stressors. According to the World Wide Fund for Nature's Living Planet Index, freshwater ecosystems and biodiversity are considered among the most threatened on the planet, with average declines of approximately 83% in the populations of freshwater organisms since 1970. Such losses are impactful not only from a fundamental biodiversity perspective but also from a human health and wellbeing perspective. Freshwater systems are so crucial to people that more than 50% of human populations live within 3 km of surface fresh waters and only 10% live more than 10 km away.1Kummu M de Moel H Ward PJ Varis O How close do we live to water? A global analysis of population distance to freshwater bodies.PLoS One. 2011; 6e20578 Crossref PubMed Scopus (204) Google Scholar Loss and degradation of freshwater ecosystems directly affect the health and wellbeing of people and communities.2Lynch AJ Cooke SJ Arthington AH et al.People need freshwater biodiversity.WIREs Water. 2023; 10e1633 Crossref Scopus (8) Google Scholar For example, freshwater biodiversity in the form of fisheries provides a key source of micronutrients and fatty acids for some of the most food insecure people on the planet, as well as recreational benefits and many cultural connections, as exemplified by Indigenous ceremony and spirituality. Freshwater biodiversity also supports livelihoods and upholds many regional and even national economies. Inland wetlands disperse floodwaters, recharge groundwater supplies, and remove many harmful pollutants—important functions that are even more crucial as the climate changes and both floods and droughts become more common. People clearly need and benefit from healthy freshwater ecosystems;2Lynch AJ Cooke SJ Arthington AH et al.People need freshwater biodiversity.WIREs Water. 2023; 10e1633 Crossref Scopus (8) Google Scholar Given the precarious state of these important systems and services, current efforts to address the freshwater biodiversity crisis remain insufficient.3Tickner D Opperman JJ Abell R et al.Bending the curve of global freshwater biodiversity loss: an emergency recovery plan.Bioscience. 2020; 70: 330-342Crossref PubMed Scopus (458) Google Scholar Planetary health is an emerging framework that aims to secure the state of natural systems within environmental limits that ensure humanity can flourish.4Whitmee S Haines A Beyrer C et al.Safeguarding human health in the Anthropocene epoch: report of The Rockefeller Foundation–Lancet Commission on planetary health.Lancet. 2015; 386: 1973-2028Summary Full Text Full Text PDF PubMed Scopus (1430) Google Scholar The planetary health concept is tied to the planetary boundaries framework in which various ecological thresholds are identified with the goal of constraining human activity to within those boundaries (so-called safe operating spaces). Freshwater systems are influenced by some planetary-scale processes like the climate systems and phosphorus and nitrogen cycles. Nonetheless, safe boundaries to guide the conservation and management of freshwater ecosystems need to consider their uneven distribution around the globe, and their ecological and hydrologic limits, which are often site and context dependent.5Montoya JM Donohue I Pimm SL Planetary boundaries for biodiversity: implausible science, pernicious policies.Trends Ecol Evol. 2018; 33: 71-73Summary Full Text Full Text PDF PubMed Scopus (73) Google Scholar, 6Vollmer D Harrison IJ H2O ≠ CO2: framing and responding to the global water crisis.Environ Res Lett. 2021; 16011005 Crossref Scopus (15) Google Scholar Efforts to down-scale planetary boundaries concepts to the management of freshwater recreational fisheries at the lake scale,7Carpenter SR Brock WA Hansen GJ et al.Defining a safe operating space for inland recreational fisheries.Fish Fish. 2017; 18: 1150-1160Crossref Scopus (83) Google Scholar suggest that there are opportunities for rethinking planetary health as a nested cross-scale approach from the planet to the watershed. Planetary health is now at the forefront of global policy discussions, and it could provide a means for elevating freshwater ecosystem health on that level. In practice, freshwater ecosystem health is usually excluded or overlooked in planetary health discussions, being only considered in terms of water quantity and quality (ie, eutrophication). For example, relatively few (<1%—close to negligible) of the papers published to date in The Lancet Planetary Health focus on freshwater ecosystems or biodiversity. This lack of representation is also well aligned with national and international discourse and policy instruments, which have long ignored, forgotten, and undervalued freshwater systems. For example, freshwater ecosystems and biodiversity are rather hidden in the UN Sustainable Development Goals; goal 14 (ie, life below water) is focused on marine systems and goal 6 (ie, water and sanitation for all) makes only cursory mention of freshwater life. Fortunately, freshwater systems were explicitly recognised as distinct from terrestrial and marine systems and in need of bespoke conservation efforts at the December, 2022, Kunming–Montreal Global Biodiversity Convention meeting and the Freshwater Challenge was launched at the March 2023 UN Water Conference to "substantiate, integrate, and accelerate targeted interventions" for freshwater systems at global and national scales.8Freshwater ChallengeWhat is the freshwater challenge?.www.freshwaterchallenge.orgDate accessed: December 18, 2023Google Scholar Hence, the challenge is to ensure that freshwater ecosystems and their biodiversity are neither omitted from global dialogues on planetary health, nor included in such a way that any targets or recommendations are meaningless for practical conservation and management of the ecosystems and the services they provide. Clearly there are substantial problems with attempting to apply a generic global framework onto freshwater ecosystem integrity and health, which are local issues and are multidimensionally diverse and complex from one place to another. Freshwater ecosystem protection and restoration depend on local and regional efforts, driven by local practitioners9Twardek WM Nyboer EA Tickner D et al.Mobilizing practitioners to support the Emergency Recovery Plan for freshwater biodiversity.Conserv Sci Pract. 2021; 3: e467Crossref Scopus (14) Google Scholar and stewardship efforts by community groups.10Zhang W El Didi H Masuda YJ et al.Community-based conservation of freshwater resources: learning from a critical review of the literature and case studies.Soc Nat Resour. 2023; 36: 733-754Crossref Scopus (1) Google Scholar The planetary health concept can recognise the essential role of local and regional efforts that engage practitioners, communities, rights holders, and other stewards in efforts to protect and restore systems. For example, halting and reversing freshwater biodiversity loss at the watershed scale will yield positive effects throughout surrounding food webs and nutrient cycles (eg, riparian and upland areas, estuaries, and coastal marine systems). In conclusion, working across spatial and institutional scales provides opportunity for bottom-up and top-down efforts to advance cross-scale coherence in policy and action.11Cid N Erős T Heino J et al.From meta-system theory to the sustainable management of rivers in the Anthropocene.Front Ecol Environ. 2022; 20: 49-57Crossref PubMed Scopus (24) Google Scholar These integrative actions have a strong chance of truly reversing the freshwater biodiversity crisis for people and the planet. But a crucial part of any large-scale approach to planetary health of freshwater ecosystems includes ensuring that nations and regions have the capacity to conduct their own monitoring at the watershed scale and understand the ecological limits of their basins, so they can define their local safe operating space.6Vollmer D Harrison IJ H2O ≠ CO2: framing and responding to the global water crisis.Environ Res Lett. 2021; 16011005 Crossref Scopus (15) Google Scholar Such monitoring has been lacking for freshwater biodiversity despite their relevance to the Intergovernmental Science–Policy Platform on Biodiversity and Ecosystem Services (IPBES) processes. These assessments would also serve as a baseline for monitoring and understanding the limits needed to identify interventions that will bend the curve for freshwater biodiversity.3Tickner D Opperman JJ Abell R et al.Bending the curve of global freshwater biodiversity loss: an emergency recovery plan.Bioscience. 2020; 70: 330-342Crossref PubMed Scopus (458) Google Scholar More work is sorely needed on how to implement those concepts and ideas in practice—something that we hope will be the outcome of this Comment. Moreover, we also hope that this Comment will stimulate additional discourse around the roles of planetary boundaries and health as concepts that can be applied to the freshwater biodiversity crisis. We declare no competing interests. This paper was supported by the Natural Sciences and Engineering Research Council of Canada and Carleton University. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. SJC is supported by the Natural Sciences and Engineering Research Council of Canada (319774) and Carleton University.

Planetary boundaries represent thresholds in major Earth system processes that are sensitive to human activity and control global-scale habitability and stability. These processes are interconnected such that movement of one planetary boundary process can alter the likelihood of crossing other boundaries. Here we argue that the observed deoxygenation of the Earth's freshwater and marine ecosystems represents an additional planetary boundary process that is critical to the integrity of Earth's ecological and social systems, and both regulates and responds to ongoing changes in other planetary boundary processes. Research on the rapid and ongoing deoxygenation of Earth's aquatic habitats indicates that relevant, critical oxygen thresholds are being approached at rates comparable to other planetary boundary processes. Concerted global monitoring, research and policy efforts are needed to address the challenges brought on by rapid deoxygenation, and the expansion of the planetary boundaries framework to include deoxygenation as a boundary helps to focus those efforts.

Financial advisers recommend a diverse portfolio to respond to market fluctuations across sectors. Similarly, nature has evolved a diverse portfolio of species to maintain ecosystem function amid environmental fluctuations. In urban planning, public health, transport and communications, food production, and other domains, however, this feature often seems ignored. As we enter an era of unprecedented turbulence at the planetary level, we argue that ample responses to this new reality — that is, response diversity — can no longer be taken for granted and must be actively designed and managed. We describe here what response diversity is, how it is expressed and how it can be enhanced and lost. A varied repertoire of responses helps manage fluctuations, as in markets. This Perspective argues that society needs to strengthen the diversity of options for responding to disruptions, exploring how this response diversity is expressed, how it can be built and lost, and what we can do to promote it.

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 similar to 285,000 centrarchids from a 33-ha lake over 4 years was conducted while monitoring the fish community response. Centrarchid abundance declined arid yellow perch Perca fiavescens (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.

Transformation toward a sustainable future requires an earth stewardship approach to shift society from its current goal of increasing material wealth to a vision of sustaining built, natural, human, and social capital-equitably distributed across society, within and among nations. Widespread concern about earth's current trajectory and support for actions that would foster more sustainable pathways suggests potential social tipping points in public demand for an earth stewardship vision. Here, we draw on empirical studies and theory to show that movement toward a stewardship vision can be facilitated by changes in either policy incentives or social norms. Our novel contribution is to point out that both norms and incentives must change and can do so interactively. This can be facilitated through leverage points and complementarities across policy areas, based on values, system design, and agency. Potential catalysts include novel democratic institutions and engagement of non-governmental actors, such as businesses, civic leaders, and social movements as agents for redistribution of power. Because no single intervention will transform the world, a key challenge is to align actions to be synergistic, persistent, and scalable.

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.

Regime shifts have large consequences for ecosystems and the services they provide. However, understanding the potential for, causes of, proximity to, and thresholds for regime shifts in nearly all settings is difficult. Generic statistical indicators of resilience have been proposed and studied in a wide range of ecosystems as a method to detect when regime shifts are becoming more likely without direct knowledge of underlying system dynamics or thresholds. These early warning statistics (EWS) have been studied separately but there have been few examples that directly compare temporal and spatial EWS in ecosystem-scale empirical data. To test these methods, we collected high-frequency time series and high-resolution spatial data during a whole-lake fertilization experiment while also monitoring an adjacent reference lake. We calculated two common EWS, standard deviation and autocorrelation, in both time series and spatial data to evaluate their performance prior to the resulting algal bloom. We also applied the quickest detection method to generate binary alarms of resilience change from temporal EWS. One temporal EWS, rolling window standard deviation, provided advanced warning in most variables prior to the bloom, showing trends and between-lake patterns consistent with theory. In contrast, temporal autocorrelation and both measures of spatial EWS (spatial SD, Moran's  I) provided little or no warning. By compiling time series data from this and past experiments with and without nutrient additions, we were able to evaluate temporal EWS performance for both constant and changing resilience conditions. True positive alarm rates were 2.5-8.3 times higher for rolling window standard deviation when a lake was being pushed towards a bloom than the rate of false positives when it was not. For rolling window autocorrelation, alarm rates were much lower and no variable had a higher true positive than false positive alarm rate. Our findings suggest temporal EWS provide advanced warning of algal blooms and that this approach could help managers prepare for and/or minimize negative bloom impacts.

Historically, estimates of pelagic primary production in lake ecosystems were made by measuring the uptake of carbon-14 (C-14)-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 (O-2). While there is a rich literature on the comparison of approaches for estimating primary production using incubations (e.g., C-14 and O-2 bottle experiments), as well for approaches using high-frequency data (e.g., diel O-2 and CO2 metabolism models), there are few direct comparisons of C-14 incubations and free-water O-2 approaches for estimating primary production. We used 20 lake-years of concurrent measurements of primary production quantified from high-frequency free-water O-2 data and C-14 incubations in four different lakes (4-7 years per lake) to compare these different approaches. Across all lakes, 61% of the C-14 production estimates were within the 95% credible intervals of the free-water O-2 production estimates. Error-in-variable regressions support the assumption that C-14 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 O-2 or C-14 approaches in these lakes during summer stratified conditions.

The Programme on Ecosystem Change and Society (PECS) was established in 2011, and is now one of the major international social-ecological systems (SES) research networks. During this time, SES research has undergone a phase of rapid growth and has grown into an influential branch of sustainability science. In this Perspective, we argue that SES research has also deepened over the past decade, and helped to shed light on key dimensions of SES dynamics (e.g. system feedbacks, aspects of system design, goals and paradigms) that can lead to tangible action for solving the major sustainability challenges of our time. We suggest four ways in which the growth of place-based SES research, fostered by networks such as PECS, has contributed to these developments, namely by: 1) shedding light on transformational change, 2) revealing the social dynamics shaping SES, 3) bringing together diverse types of knowledge, and 4) encouraging reflexive researchers.

Extreme daily values of precipitation (1939-2021), discharge (1991-2021), phosphorus (P) load (1994-2021), and phycocyanin, a pigment of Cyanobacteria (June 1-September 15 of 2008-2021) are clustered as multi-day events for Lake Mendota, Wisconsin. Long-range dependence, or memory, is the shortest for precipitation and the longest for phycocyanin. Extremes are clustered for all variates and those of P load and phycocyanin are most strongly clustered. Extremes of P load are predictable from extremes of precipitation, and precipitation and P load are correlated with later concentrations of phycocyanin. However, time delays from 1 to 60 d were found between P load extremes and the next extreme phycocyanin event within the same year of observation. Although most of the lake's P enters in extreme events, blooms of Cyanobacteria may be sustained by recycling and food web processes.

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.

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 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.