Regime Shifts Research Articles

Dynamics of the generalized Rosenzweig–MacArthur model in a changing and patchy environment

In this paper, we propose a generalized Rosenzweig–MacArthur predator–prey model with two patches and Allee effects in predators. In a constant environment, for the single-patch model we show the existence of degenerate Bogdanov–Takens bifurcation with codimension up to 4 and degenerate Hopf bifurcation with codimension up to 3, which indicate that the nilpotent cusp of codimension 4 is the organizing center of the bifurcation set. Our results show that Allee effects in predators can not only induce much more complex bifurcations and dynamics (such as three limit cycles, multitype tristability), but also serve as a destabilizing factor to make predators extinction (deterministically) when the environment is sufficiently enriched, which provides strong support for the so-called “paradox of enrichment”. For the two-patch model, we numerically reveal the existence of eight positive steady states including two new coexisting attractors, which means that population dispersal can help species coexist or increase the population abundance. In a changing environment, for the single-patch model we find that the population can track unstable states, fast positive or slow negative environmental change can be beneficial to predators by delaying or even avoiding extinction; while for the two-patch model we observe some interesting phenomena: fast negative (or slow positive) environmental change can make predators in different patches trend to extinction synchronously, and rate-induced different regime shifts.

Globorotalia truncatulinoides as indicator of Subtropical Convergence and thermocline change during the late Quaternary in the Southeast Atlantic

Planktic foraminifera in biogenic sediments are widely applied as palaeoceanographic tools and the abundances of Globorotalia truncatulinoides have been used over the past few decades as indicators of upper water column changes over geologic time. The two morphological coiling directions of this species (sinistral and dextral) can provide valuable insight into how the upper water masses of the South Atlantic vary in response to climate change. This study aims to document and analyse the abundances of the planktic foraminiferal species G. truncatulinoides and its two morphological coiling directions in two cores from the continental slope of western South Africa at >3500 m water depth to assess the response of upper water masses to Quaternary climate change. The relative abundances of total G. truncatulinoides in the >125 μm size fraction, abundances of the dextral and sinistral forms in the >212 μm fraction and the division into further size fractions (212 μm, 250 μm, 300 μm, 355 μm, >400 μm) were analysed and considered to determine whether these abundances can be related to oceanographic regime shifts in the eastern South Atlantic during the late Pleistocene from MIS 6 to MIS 1. It was found that the Subtropical Convergence was located at a more southern location during MIS 5 and MIS 1, which allows for warmer subtropical species to increase in abundance with increasing Agulhas leakage around the southwestern margin. The thermocline is interpreted to have deepened during glacial terminations and interglacial periods when productivity was relatively lower and temperatures increased. The size fraction of the sinistral form in the >355 μm is dominant in MIS 5, MIS 3 and MIS1, indicating implications for the use of this species at certain size ranges. This study therefore indicates that G. truncatulinoides is a useful tracer of past Quaternary oceanographic changes along the western margin of South Africa, particularly when the coiling directions at the larger size fraction is taken into account.

Mafic microgranular enclaves and magmatic fabrics in the Ediacaran granitoids of Saghro, Eastern Anti-Atlas: Insights into magma emplacement and tectonic evolution

The Saghro inlier in the Anti-Atlas belt of Morocco comprises several granitoids dating from 600 to 550 million years ago (Ma), which are overlain by a volcano-sedimentary series. In particular, the granodioritic plutons exhibit widespread enclaves, which is a tool for emplacements mode and magma interaction processus during the Ediacaran evolution of the Anti-Atlas belt. This paper presents a detailed field mapping, petrographic analysis, and deformation quantification of the mafic microgranular enclaves (MMEs) and their host granitoids to characterize the emplacement mode of the plutons and the origin of MMEs.Macroscopically, the MMEs are rounded to ellipsoidal shapes and characterized by sharp, crenulated contacts, fine-grained textures, and some of them include fragments of host rock and feldspar xenocrysts. Petrographically, the MMEs exhibit a range of compositions from gabbroic to quartz diorite, and they are characterized by the presence of acicular apatite, quartz-feldspar ocelli, poikilitic and zoned plagioclases, which are the result of mixing/mingling of mafic and felsic magmas during the genesis of MMEs. The magmatic structures and enclave's organization in Saghro granitoids indicate two styles of emplacement. The c. 600 Ma Iknioun granodiorite exhibits an S-sigmoidal structure, representative of a syntectonic emplacement model within a transpressive dextral movement along E-W shear zones. While, in the 580-560 Ma Oussilkane, Tagmout, Igoudrane, and Bou Teglimt plutons, the organization of magmatic flow and orientations of enclaves suggest that the magma was emplaced as a post-tectonic dome. The variation in emplacement mode and the decrease in deformation intensity from the c. a. 600 Ma in the Iknioun pluton to the 580-560 Ma for the others plutons indicate a progressive shift in deformation regime from transpressive during the middle Ediacaran to a transtensive regime in the late Ediacaran, highlighting the progressive transition from Pan-African/Cadomian orogeny to Cambrian rifting.

Evolution of an arid social-ecosystem with different water utilization spanning 12,000 years

Understanding the regime shifts of social-ecological systems (SES) and their local and spillover effects over time is crucial for ensuring future sustainability. However, limited research has focused on regime changes in SES under different modes of water resource utilization. In this study, we employ a concise theoretical framework to analyze regime shifts in the arid Tarim River Basin, considering changes in SES components. Additionally, we explore the drivers and local and regional effects of these shifts. The regime shifts in SES are categorized into four evolutionary phases: “Low productivity,” “Slow population expansion,” “Rapid environmental destruction,” and “Ecological restoration and improvement” over the past 12,000 years. The reciprocal coupling of SES components plays a vital role in determining the regime of SES, which is heavily influenced by the utilization of water resources and the degradation of the environment. While increasing water consumption is a core factor leading to environmental destruction, it also drives socioeconomic growth. During the process of SES shift, the rational allocation and use of water resources can shape an ideal regime that promotes regional ecosystem restoration. The empirical connections between the different phases of SES in the regime shift, their drivers, and their adverse or beneficial impacts provide valuable insights for sustainable SES management. Lessons from basin management that solely pursues single goals and focuses on local aspects, without considering these connections, have significant implications for long-term planning and policy formulation in arid basins worldwide.

Power-law productivity of highly biodiverse agroecosystems supports land recovery and climate resilience

Transformative change in primary food production is urgently needed in the face of climate change and biodiversity loss. Although there are a growing number of studies aimed at global policymaking, actual implementations require on-site analyses of social feasibility anchored by ecological rationale. This article reports the in-depth characterizations of low-input mixed polyculture of highly diverse crops managed on the self-organization of ecosystems, which performed better compared to conventional monoculture methods in Japan and Burkina Faso. Analyses on crop productivity and diversity showed that the primary production of ecosystems followed a power law, and through the underlying mechanisms excelled in (1) promoting diversity and total quantity of products along with the rapid increase of in-field biodiversity, especially useful for the recovery of local regime shift in a semi-arid environment; (2) a fundamental reduction of inputs and environmental load; and (3) ecosystem-based autonomous adaptation of the crop portfolio to climatic variability. The overall benefits imply substantial possibilities of a new typology of sustainable farming for smallholders sensitive to climate change, which could overcome the historical trade-off between productivity and biodiversity based on the human-guided augmentation of ecosystems.

Online learning of order flow and market impact with Bayesian change-point detection methods

Financial order flow exhibits a remarkable level of persistence, wherein buy (sell) trades are often followed by subsequent buy (sell) trades over extended periods. This persistence can be attributed to the division and gradual execution of large orders. Consequently, distinct order flow regimes might emerge, which can be identified through suitable time series models applied to market data. In this paper, we propose the use of Bayesian online change-point detection (BOCPD) methods to identify regime shifts in real-time and enable online predictions of order flow and market impact. To enhance the effectiveness of our approach, we have developed a novel BOCPD method using a score-driven approach. This method accommodates temporal correlations and time-varying parameters within each regime. Through empirical application to NASDAQ data, we have found that: (i) Our newly proposed model demonstrates superior out-of-sample predictive performance compared to existing models that assume i.i.d. behavior within each regime; (ii) When examining the residuals, our model demonstrates good specification in terms of both distributional assumptions and temporal correlations; (iii) Within a given regime, the price dynamics exhibit a concave relationship with respect to time and volume, mirroring the characteristics of actual large orders; (iv) By incorporating regime information, our model produces more accurate online predictions of order flow and market impact compared to models that do not consider regimes.

Empirical Evidence on the Stock–Bond Correlation

The correlation between stock and bond returns is a cornerstone of asset allocation decisions. History reveals abrupt regime shifts in correlation after long periods of relative stability. We investigate the drivers of the correlation between stocks and bonds and find that inflation, real rates, and government creditworthiness are important explanatory variables. We examine the implications of a shift in the stock–bond correlation and find that increases are associated with higher multi-asset portfolio risk and higher bond risk premia.

The “Turning Point” for the Fall Goose Hunt in Eeyou Istchee: A Social-Ecological Regime Shift from an Indigenous Knowledge Perspective

We present a perspective on how the Eeyou (James Bay Cree) from Eeyou Istchee (Eastern James Bay, Québec) understand the transformation of their traditional fall goose hunt system as a consequence of social and environmental changes across marine and terrestrial ecosystems with drivers operating at the local, regional and continental scales. Eeyou land users from the Chisasibi and Wemindji First Nations report that their traditional fall goose hunt underwent a “turning point” during the early 2000s. Not only did the abundance of Canadian geese reach a historical low, but their feeding and migratory behavior became unpredictable. Eeyou land users associate such abrupt changes with the massive eelgrass die-off of the late 1990s, the onset of the effects of climate change on coastal habitats experienced since the 1970s, and agricultural development along geese flyways. This manuscript is an outcome of the Eeyou Knowledge component of the Coastal Habitat Comprehensive Research Project (2016–2022) and followed a community-based case study approach that included 28 semi-structured interviews and 14 mapping interviews with Eeyou research contributors. The findings presented here underscore the capacity of Indigenous knowledge to make sense of the multifaceted impacts of environmental change across various dimensions and layers of their social-ecological system, including management strategies and values.

A Holocene history of climate, fire, landscape evolution, and human activity in northeastern Iceland

Abstract. Paleoclimate reconstructions across Iceland provide a template for past changes in climate across the northern North Atlantic, a crucial region due to its position relative to the global northward heat transport system and its vulnerability to climate change. The roles of orbitally driven summer cooling, volcanism, and human impact as triggers of local environmental changes in the Holocene of Iceland remain debated. While there are indications that human impact may have reduced environmental resilience during late Holocene summer cooling, it is still difficult to resolve to what extent human and natural factors affected Iceland's late Holocene landscape instability. Here, we present a continuous Holocene fire record of northeastern Iceland from proxies archived in Stóra Viðarvatn sediment. We use pyrogenic polycyclic aromatic hydrocarbons (pyroPAHs) to trace shifts in fire regimes, paired with continuous biomarker and bulk geochemical records of soil erosion, lake productivity, and human presence. The molecular composition of pyroPAHs and a wind pattern reconstruction indicate a naturally driven fire signal that is mostly regional. Generally low fire frequency during most of the Holocene significantly increased at 3 ka and again after 1.5 ka BP before known human settlement in Iceland. We propose that shifts in vegetation type caused by cooling summers over the past 3 kyr, in addition to changes in atmospheric circulation, such as shifts in North Atlantic Oscillation (NAO) regime, led to increased aridity and biomass flammability. Our results show no evidence of faecal biomarkers associated with human activity during or after human colonisation in the 9th century CE. Instead, faecal biomarkers follow the pattern described by erosional proxies, pointing toward a negligible human presence and/or a diluted signal in the lake's catchment. However, low post-colonisation levels of pyroPAHs, in contrast to an increasing flux of erosional bulk proxies, suggest that farming and animal husbandry may have suppressed fire frequency by reducing the spread and flammability of fire-prone vegetation (e.g. heathlands). Overall, our results describe a fire frequency heavily influenced by long-term changes in climate through the Holocene. They also suggest that human colonisation had contrasting effects on the local environment by lowering its resilience to soil erosion while increasing its resilience to fire.

Changes in Atlantic climatic regulation mechanisms that underlie mesozooplankton biomass loss in the northern Baltic Sea

The effects of climate-induced, long-term changes on mesozooplankton biomasses were studied based on monitoring data collected since 1966 in the northern Baltic Sea. We found that the biomasses of marine and brackish mesozooplankton had decreased significantly from 1966 to 2019, and a remarkable biomass and functional biodiversity loss took place in the mesozooplankton community. Our results put emphasis on the impact of two climate-driven regime shifts for the region's mesozooplankton community. The regime shifts took place in 1975 and 1976 and in 1989 and 1990, and they were the most important factor behind the abrupt biomass changes for marine mesozooplankton and total and marine Copepoda. Only the latter regime shift influenced the biomasses of brackish Copepoda, marine Cladocera, and total Rotifera. The decreasing length of the ice-cover period drove the decrease of the biomass of limnic Limnocalanus macrurus (Copepoda), while the winter North Atlantic Oscillation was behind biomass changes in the total and the brackish Cladocera. These findings may have important implications for planktivorous fish, such as Baltic herring, particularly in terms of their impact on commercial fishing.

Cryptocurrency Adoption in Traditional Banking: Challenges and Opportunities

The advent of cryptocurrencies has introduced a paradigm shift in the financial ecosystem, offering a novel approach to traditional banking and financial transactions. This Master's thesis titled "Cryptocurrency Adoption in Traditional Banking: Challenges and Opportunities" provides a comprehensive analysis of the integration process of cryptocurrencies into the traditional banking sector. It scrutinizes the multifaceted challenges banks face in adopting cryptocurrencies while highlighting the unprecedented opportunities this new form of currency presents. The study commences with a detailed overview of the cryptocurrency market, emphasizing its growth, volatility, and the technological underpinnings that distinguish it from conventional banking systems. It delves into the historical perspective of cryptocurrencies, with a specific focus on Bitcoin, Ethereum, and other significant players, to understand their evolution, current market dynamics, and potential future trajectories.

Resilience assessment in complex natural systems.

Ecological resilience is the capability of an ecosystem to maintain the same structure and function and avoid crossing catastrophic tipping points (i.e. undergoing irreversible regime shifts). While fundamental for management, concrete ways to estimate and interpret resilience in real ecosystems are still lacking. Here, we develop an empirical approach to estimate resilience based on the stochastic cusp model derived from catastrophe theory. The cusp model models tipping points derived from a cusp bifurcation. We extend cusp in order to identify the presence of stable and unstable states in complex natural systems. Our Cusp Resilience Assessment (CUSPRA) has three characteristics: (i) it provides estimates on how likely a system is to cross a tipping point (in the form of a cusp bifurcation) characterized by hysteresis, (ii) it assesses resilience in relation to multiple external drivers and (iii) it produces straightforward results for ecosystem-based management. We validate our approach using simulated data and demonstrate its application using empirical time series of an Atlantic cod population and marine ecosystems in the North Sea and the Mediterranean Sea. We show that Cusp Resilience Assessment is a powerful method to empirically estimate resilience in support of a sustainable management of our constantly adapting ecosystems under global climate change.

Taxa-dependent temporal trends in the abundance and size of sea urchins in subtropical eastern Australia.

Subtropical reefs host a dynamic mix of tropical, subtropical, and temperate species that is changing due to shifts in the abundance and distribution of species in response to ocean warming. In these transitional communities, biogeographic affinity is expected to predict changes in species composition, with projected increases of tropical species and declines in cool-affinity temperate species. Understanding population dynamics of species along biogeographic transition zones is critical, especially for habitat engineers such as sea urchins that can facilitate ecosystem shifts through grazing. We investigated the population dynamics of sea urchins on coral-associated subtropical reefs at 7 sites in eastern Australia (28.196° S to 30.95° S) over 9 years (2010-2019), a period impacted by warming and heatwaves. Specifically, we investigated the density and population size structure of taxa with temperate (Centrostephanus rodgersii, Phyllacanthus parvispinus), subtropical (Tripneustes australiae) and tropical (Diadema spp.) affinities. Counter to expectation, biogeographic affinity did not explain shifts in species abundances in this region. Although we expected the abundance of tropical species to increase at their cold range boundaries, tropical Diadema species declined across all sites. The subtropical T. australiae also showed declines, while populations of the temperate C. rodgersii were remarkably stable throughout our study period. Our results show that temporal patterns of sea urchin populations in this region cannot be predicted by bio-geographic affinity alone and contribute critical information about the population dynamics of these important herbivores along this biogeographic transition zone.

An abrupt regime shift of bacterioplankton community from weak to strong thermal pollution in a subtropical bay.

Thermal pollution from the cooling system of the nuclear power plants greatly changes the environmental and the ecological conditions of the receiving marine water body, but we know little about their impact on the steady-state transition of marine bacterioplankton communities. In this study, we used high-throughput sequencing based on the 16S rRNA gene to investigate the impact of the thermal pollution on the bacterioplankton communities in a subtropical bay (the Daya Bay). We observed that thermal pollution from the cooling system of the nuclear power plant caused a pronounced thermal gradient ranging from 19.6°C to 24.12°C over the whole Daya Bay. A temperature difference of 4.5°C between the northern and southern parts of the bay led to a regime shift in the bacterioplankton community structure. In the three typical scenarios of regime shifts, the steady-state transition of bacterioplankton community structure in response to temperature increasing was more likely consistent with an abrupt regime shift rather than a smooth regime or a discontinuous regime model. Water temperature was a decisive factor on the regime shift of bacterioplankton community structure. High temperature significantly decreased bacterioplankton diversity and shifted its community compositions. Cyanobium and Synechococcus of Cyanobacteria, NS5 marine group of Bacteroidota, and Vibrio of Gammaproteobacteria were found that favored high temperature environments. Furthermore, the increased water temperature significantly altered the community assembly of bacterioplankton in Daya Bay, with a substantial decrease in the proportion of drift and others, and a marked increase in the proportion of homogeneous selection. In summary, we proposed that seawater temperature increasing induced by the thermal pollution resulted in an abrupt regime shift of bacterioplankton community in winter subtropical bay. Our research might broad our understanding of marine microbial ecology under future conditions of global warming.

Development of a temperate rainforest zonation on the Pacific slopes of the North Patagonian Andes since ∼18 ka

Few studies along the western slopes of the Andes in Northwestern Patagonia (NWP: 40°-44°S) allow examining vegetation development through environmental gradients in latitude and elevation along a time continuum since the Last Glacial Termination (T1, ∼18-11 ka). This complete biostratigraphic context is necessary for assessing the sequence, timing, rates, and direction of compositional/structural changes of the former vegetation, and for deciphering their environmental drivers. Here we report palynological results from two NWP sites spaced ∼22 km apart on the western Andean slopes, Caleta Puelche roadside section located near sea level and Lago Reflejos at mid elevations (∼800 m a.s.l.) and assess their continuous records since local ice-free conditions against other NWP sites. We find that cold-tolerant early successional trees dominated the initial stages of vegetation development in the Seno Reloncaví lowlands (∼18-17 ka), followed by thermophilous shade-tolerant North Patagonian rainforest (NPRF) trees, which achieved their maxima between ∼17 and 15 ka at low-elevations. A spread of cold- and shade-tolerant hygrophilous NPRF conifers ensued (∼14.8-13 ka) reaching similar magnitude at low- and mid-elevations, interrupted by increases in trees favored by canopy fragmentation linked to fire and explosive volcanism (∼13-11 ka). Thermophilous, shade-intolerant, summer-drought tolerant Valdivian rainforest (VRF) trees increased and achieved maxima between ∼10 and 8 ka, most notably in the lowlands, coeval with peak abundance of the NPRF conifers Fitzroya/Pilgerodendron and Podocarpus nubigena in mid-elevation Lago Reflejos, contemporaneous with their virtual disappearance near sea level. Widespread increases in cold-tolerant hygrophilous NPRF trees occurred after ∼8 ka, followed by mixing of NPRF and VRF elements in the lowlands after ∼6.3 ka with centennial-scale alternations. Inter-site and regional coherences of our findings suggest that variations in Southern Westerly Wind influence, along with disturbance regimes of natural and human origin, have driven the composition, structure, dynamics, and zonation of temperate rainforests in NWP since T1. We observe that Lago Reflejos features the highest abundance of Fitzroya cupressoides at regional scale since ∼12 ka, attesting to the importance of mid-elevation Andean environments for the persistence of these highly valued trees in the context of postglacial climate evolution, shifts in fire regimes, volcanic, and human disturbance in NWP.

Late Glacial and Holocene vegetation and lake changes in SW Yakutia, Siberia, inferred from sedaDNA, pollen, and XRF data

Only a few palaeo-records extend beyond the Holocene in Yakutia, eastern Siberia, since most of the lakes in the region are of Holocene thermokarst origin. Thus, we have a poor understanding of the long-term interactions between terrestrial and aquatic ecosystems and their response to climate change. The Lake Khamra region in southwestern Yakutia is of particular interest because it is in the transition zones from discontinuous to sporadic permafrost and from summergreen to evergreen boreal forests. Our multiproxy study of Lake Khamra sediments reaching back to the Last Glacial Maximum 21 cal ka BP, includes analyses of organic carbon, nitrogen, XRF-derived elements, sedimentary ancient DNA amplicon sequencing of aquatic and terrestrial plants and diatoms, as well as classical counting of pollen and non-pollen palynomorphs (NPP). The palaeogenetic approach revealed 45 diatom, 191 terrestrial plant, and 65 aquatic macrophyte taxa. Pollen analyses identified 34 pollen taxa and 28 NPP taxa. The inferred terrestrial ecosystem of the Last Glacial comprises tundra vegetation dominated by forbs and grasses, likely inhabited by megaherbivores. By 18.4 cal ka BP a lake had developed with a high abundance of macrophytes and dominant fragilarioid diatoms, while shrubs expanded around the lake. In the Bølling-Allerød at 14.7 cal ka BP both the terrestrial and aquatic systems reflect climate amelioration, alongside lake water-level rise and woodland establishment, which was curbed by the Younger Dryas cooling. In the Early Holocene warmer and wetter climate led to taiga development and lake water-level rise, reflected by diatom composition turnover from only epiphytic to planktonic diatoms. In the Mid-Holocene the lake water level decreased at ca. 8.2 cal ka BP and increased again at ca. 6.5 cal ka BP. At the same time mixed evergreen-summergreen forest expanded. In the Late Holocene, at ca. 4 cal ka BP, vegetation cover similar to modern conditions established. This study reveals the long-term shifts in aquatic and terrestrial ecosystems and a comprehensive understanding of lake development and catchment history of the Lake Khamra region.

Late Holocene decoupling of lake and vegetation ecosystem in response to centennial-millennial climatic changes in arid Central Asia: A case study from Aibi Lake of western Junggar Basin

Central Asian lakes are crucial for sustaining fragile oasis ecosystems in arid regions. Understanding the response of ecosystems in these lake basins to climate change is essential for predicting future variations in these ecosystems. Aibi Lake is a notable terminal lake in arid Central Asia. In this study, a 95 cm lacustrine sediment core was drilled from Aibi Lake to investigate the response of lacustrine and terrestrial ecosystems in the lake basin to climate change over the past 3200 years. Accelerator mass spectrometry (AMS) 14C dating and multi-proxy analyses of diatoms, pollen, grain size, total organic content (TOC), total nitrogen (TN), and total hydrogen (TH) are applied to the sediment core. The grain size and geochemical results show that the lake experienced elevated levels and improved productivity and nutrition during the periods of 708–181 BCE, 0–740 CE, and 1428–1900 CE. The periods align with the Roman Warm Period, Dark Age Cold Period, and Little Ice Age, respectively. For the past 3200 years, benthic diatoms have consistently been the dominant species in the lake. During the climatic transition periods of the Dark Age Cold Period, Medieval Warm Period, and Little Ice Age, there were significant changes in the abundance and survival of certain species of diatoms. Specifically, the halophilic species (Nitzschia dissipata and Nitzschia hungarica), basophilic species (Synedra acus), and the nutrition level-relevant species (Navicula menisculus) experienced notable shifts. These changes ultimately resulted in a noticeable alteration in the structure and function of the diatom community. Over the past 3200 years, the lake ecosystem has undergone three noticeable regime shifts. In contrast, the vegetation in the lake catchment has remained relatively stable, primarily consisting of desert steppe. These results suggest that aquatic ecosystems in arid central Asia are more susceptible and exhibit more rapid responses to climate change compared to terrestrial vegetation.

Quickest Detection of Ecological Regimes for Natural Resource Management

We study the stochastic dynamics of natural resources under the threat of ecological regime shifts. We establish a Pareto optimal framework of regime shift detection under uncertainty that minimizes the delay with which economic agents become aware of the shift. We integrate ecosystem surveillance in the formation of optimal resource extraction policies. We fully solve the case of a profit-maximizing monopolist, study its response to regime shift detection and show the generality of our framework by extending our results to other decision makers and functional forms. We apply our framework to the case of the Cantareira water reservoir in São Paulo, Brazil, and study the events that led to its depletion and the consequent water supply crisis.

Advancement in ice-jam flood risk management: Integrating dynamic adaptive behavior by an agent-based modeling in Fort McMurray, Canada

Ice-jam flooding is a prevalent extreme event that impacts flood hazard and vulnerability. We introduce a conceptual model framework for Dynamic Ice-jam Flood Risk Assessment (DIFRA). DIFRA integrates ice-jam flood hazard, ice-jam flood risk, and human adaptation. Using agent-based modeling, we captured top-down (artificial breakup) and bottom-up (flood-proofing) adaptive behavior. Our study in Fort McMurray, Canada, shows the complex interaction between micro-level behaviors and macro-level phenomena over time. Our variance-based global sensitivity analysis shows the role of dynamic adaptive behavior in ice-jam flood risk, where the artificial breakage by the government can lead to a regime shift and a decrease in the ice-jam flood risk. However, it can also decrease the number of newly adapted residents to flood-proofing and the role of residents in ice-jam flood risk. DIFRA offers a comprehensive approach to understanding and managing ice-jam flood risk, with potential applications to similar riverine communities in cold regions.

Increasing water nutrient reduces the availability of high-quality food resources for aquatic consumers and consequently simplifies river food webs

While eutrophication has led to serious habitat degradation and biotic shifts in freshwater ecosystems, most current studies have focused on changes in community assemblages, with few considering the effect of eutrophication on food webs. We conducted a field study in subtropical headwater streams with a gradient of water nutrient levels to examine the effect of increasing water nutrients on food webs by using the long-chain polyunsaturated fatty acid eicosapentaenoic acid (EPA) as a measure of the nutritional quality of food. Basal food resources (macrophytes, submerged leaf litter, and periphyton), and aquatic consumers (macroinvertebrates and fish) were collected, and their fatty acid (FA) profiles were analyzed. Our results showed that periphyton was the dominant source of EPA for macroinvertebrates and fish, and a high-quality resource for consumers. As water nutrient concentrations increased, nutritional quality of periphyton significantly decreased and, in turn, the correlation between FA profiles of periphyton and macroinvertebrates declined. However, periphyton FA profiles did not account for the variability of fish FA, which may be induced by the increasing proportions of omnivorous fish in eutrophic streams that derived EPA from other sources. Further, the reduced periphyton EPA was associated with decreased trophic links and simplified stream food webs. Our study highlights the importance of high-quality food resources for aquatic food webs as water nutrients increased in stream ecosystems and provides a nutritional perspective to understand the mechanisms how eutrophication affects aquatic ecosystems.