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  • 1. Cael, B. B.
    et al.
    Heathcote, A. J.
    Seekell, David
    Umeå universitet, Arktiskt centrum vid Umeå universitet (Arcum). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Climate Impacts Research Centre, Umeå University, Abisko, Sweden.
    The volume and mean depth of Earth's lakes2017Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 1, s. 209-218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Global lake volume estimates are scarce, highly variable, and poorly documented. We developed a rigorous method for estimating global lake depth and volume based on the Hurst coefficient of Earth's surface, which provides a mechanistic connection between lake area and volume. Volume-area scaling based on the Hurst coefficient is accurate and consistent when applied to lake data sets spanning diverse regions. We applied these relationships to a global lake area census to estimate global lake volume and depth. The volume of Earth's lakes is 199,000km(3) (95% confidence interval 196,000-202,000km(3)). This volume is in the range of historical estimates (166,000-280,000km(3)), but the overall mean depth of 41.8m (95% CI 41.2-42.4m) is significantly lower than previous estimates (62-151m). These results highlight and constrain the relative scarcity of lake waters in the hydrosphere and have implications for the role of lakes in global biogeochemical cycles.

  • 2. Cael, B. B.
    et al.
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    The size-distribution of Earth's lakes2016Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, artikel-id 29633Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Globally, there are millions of small lakes, but a small number of large lakes. Most key ecosystem patterns and processes scale with lake size, thus this asymmetry between area and abundance is a fundamental constraint on broad-scale patterns in lake ecology. Nonetheless, descriptions of lake size-distributions are scarce and empirical distributions are rarely evaluated relative to theoretical predictions. Here we develop expectations for Earth's lake area-distribution based on percolation theory and evaluate these expectations with data from a global lake census. Lake surface areas >= 8.5 km(2) are power-law distributed with a tail exponent (T = 1.97) and fractal dimension (d = 1.38), similar to theoretical expectations (T = 2.05; d = 4/3). Lakes <8.5 km(2) are not power-law distributed. An independently developed regional lake census exhibits a similar transition and consistency with theoretical predictions. Small lakes deviate from the power-law distribution because smaller lakes are more susceptible to dynamical change and topographic behavior at sub-kilometer scales is not self-similar. Our results provide a robust characterization and theoretical explanation for the lake size-abundance relationship, and form a fundamental basis for understanding and predicting patterns in lake ecology at broad scales.

  • 3. Carr, J. A.
    et al.
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    D'Odorico, P.
    Inequality or injustice in water use for food?2015Ingår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 10, nr 2, artikel-id 024013Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The global distributions of water availability and population density are uneven and therefore inequality exists in human access to freshwater resources. Is this inequality unjust or only regrettable? To examine this question we formulated and evaluated elementary principles of water ethics relative to human rights for water, and the need for global trade to improve societal access to water by transferring 'virtual water' embedded in plant and animal commodities. We defined human welfare benchmarks and evaluated patterns of water use with and without trade over a 25-year period to identify the influence of trade and inequality on equitability of water use. We found that trade improves mean water use and wellbeing, relative to human welfare benchmarks, suggesting that inequality is regrettable but not necessarily unjust. However, trade has not significantly contributed to redressing inequality. Hence, directed trade decisions can improve future conditions of water and food scarcity through reduced inequality.

  • 4. Carr, Joel A.
    et al.
    D'Odorico, Paolo
    Suweis, Samir
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    What commodities and countries impact inequality in the global food system?2016Ingår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 11, nr 9, artikel-id 095013Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The global distribution of food production is unequal relative to the distribution of human populations. International trade can increase or decrease inequality in food availability, but little is known about how specific countries and commodities contribute to this redistribution. We present a method based on the Gini coefficient for evaluating the contributions of country and commodity specific trade to inequality in the global food system. We applied the method to global food production and trade data for the years 1986-2011 to identify the specific countries and commodities that contribute to increasing and decreasing inequality in global food availability relative to food production. Overall, international trade reduced inequality in food availability by 25%-33% relative to the distribution of food production, depending on the year. Across all years, about 58% of the total trade links acted to reduce inequality with similar to 4% of the links providing 95% of the reduction in inequality. Exports from United States of America, Malaysia, Argentina, and Canada are particularly important in decreasing inequality. Specific commodities that reduce inequality when traded include cereals and vegetables. Some trade connections contribute to increasing inequality, but this effect is mostly concentrated within a small number of commodities including fruits, stimulants, and nuts. In terms of specific countries, exports from Slovenia, Oman, Singapore, and Germany act to increase overall inequality. Collectively, our analysis and results represent an opportunity for building an enhanced understanding of global-scale patterns in food availability.

  • 5. D'Odorico, Paolo
    et al.
    Carr, Joel A.
    Davis, Kyle F.
    Dell'Angelo, Jampel
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Food Inequality, Injustice, and Rights2019Ingår i: BioScience, ISSN 0006-3568, E-ISSN 1525-3244, Vol. 69, nr 3, s. 180-190Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As humanity continues to grow in size, questions related to human rights and the existing unequal distribution of food resources have taken on greater urgency. Is inequality in food access unjust or a regrettable consequence of the geographic distribution of biophysical resources? To what extent are there obligations to redress inequalities in access to food? We draw from a human rights perspective to identify obligations associated with access to food and develop a quantitative framework to evaluate the fulfillment of the human right to food. We discuss the capacity of socioeconomic development to reduce inequalities in per capita food availability with respect to the distribution of biophysical resources among countries. Although, at the country level, international trade shows the capacity to reduce human rights deficits by increasing food availability in countries with limited food production, whether it actually improves the fulfillment of the right to food will depend on within-country inequality.

  • 6. D'Odorico, Paolo
    et al.
    Davis, Kyle Frankel
    Rosa, Lorenzo
    Carr, Joel A.
    Chiarelli, Davide
    Dell'Angelo, Jampel
    Gephart, Jessica
    MacDonald, Graham K.
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Suweis, Samir
    Rulli, Maria Cristina
    The global Food-Energy-Water Nexus2018Ingår i: Reviews of geophysics, ISSN 8755-1209, E-ISSN 1944-9208, Vol. 56, nr 3, s. 456-531Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Water availability is a major factor constraining humanity's ability to meet the future food and energy needs of a growing and increasingly affluent human population. Water plays an important role in the production of energy, including renewable energy sources and the extraction of unconventional fossil fuels that are expected to become important players in future energy security. The emergent competition for water between the food and energy systems is increasingly recognized in the concept of the "food-energy-water nexus." The nexus between food and water is made even more complex by the globalization of agriculture and rapid growth in food trade, which results in a massive virtual transfer of water among regions and plays an important role in the food and water security of some regions. This review explores multiple components of the food-energy-water nexus and highlights possible approaches that could be used to meet food and energy security with the limited renewable water resources of the planet. Despite clear tensions inherent in meeting the growing and changing demand for food and energy in the 21st century, the inherent linkages among food, water, and energy systems can offer an opportunity for synergistic strategies aimed at resilient food, water, and energy security, such as the circular economy.

  • 7. Fader, Marianela
    et al.
    Rulli, Maria Cristina
    Carr, Joel
    Dell'Angelo, Jampel
    D'Odorico, Paolo
    Gephart, Jessica A.
    Kummu, Matti
    Magliocca, Nicholas
    Porkka, Miina
    Prell, Christina
    Puma, Michael J.
    Ratajczak, Zak
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Suweis, Samir
    Tavoni, Alessandro
    Past and present biophysical redundancy of countries as a buffer to changes in food supply2016Ingår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 11, nr 5, artikel-id 055008Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spatially diverse trends in population growth, climate change, industrialization, urbanization and economic development are expected to change future food supply and demand. These changes may affect the suitability of land for food production, implying elevated risks especially for resource-constrained, food-importing countries. We present the evolution of biophysical redundancy for agricultural production at country level, from 1992 to 2012. Biophysical redundancy, defined as unused biotic and abiotic environmental resources, is represented by the potential food production of 'spare land', available water resources (i.e., not already used for human activities), as well as production increases through yield gap closure on cultivated areas and potential agricultural areas. In 2012, the biophysical redundancy of 75 (48) countries, mainly in North Africa, Western Europe, the Middle East and Asia, was insufficient to produce the caloric nutritional needs for at least 50% (25%) of their population during a year. Biophysical redundancy has decreased in the last two decades in 102 out of 155 countries, 11 of these went from high to limited redundancy, and nine of these from limited to very low redundancy. Although the variability of the drivers of change across different countries is high, improvements in yield and population growth have a clear impact on the decreases of redundancy towards the very low redundancy category. We took a more detailed look at countries classified as 'Low Income Economies (LIEs)' since they are particularly vulnerable to domestic or external food supply changes, due to their limited capacity to offset for food supply decreases with higher purchasing power on the international market. Currently, nine LIEs have limited or very low biophysical redundancy. Many of these showed a decrease in redundancy over the last two decades, which is not always linked with improvements in per capita food availability.

  • 8. Gepharta, Jessica A.
    et al.
    Deutsch, Lisa
    Pacea, Michael L.
    Troell, Max
    Seekell, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, Arktiskt centrum vid Umeå universitet (Arcum).
    Shocks to fish production: Identification, trends, and consequences2017Ingår i: Global Environmental Change, ISSN 0959-3780, E-ISSN 1872-9495, Vol. 42, s. 24-32Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sudden disruptions, or shocks, to food production can adversely impact access to and trade of food commodities. Seafood is the most traded food commodity and is globally important to human nutrition. The seafood production and trade system is exposed to a variety of disruptions including fishery collapses, natural disasters, oil spills, policy changes, and aquaculture disease outbreaks, aquafeed resource access and price spikes. The patterns and trends of these shocks to fisheries and aquaculture are poorly characterized and this limits the ability to generalize or predict responses to political, economic, and environmental changes. We applied a statistical shock detection approach to historic fisheries and aquaculture data to identify shocks over the period 1976–2011. A complementary case study approach was used to identify possible key social and political dynamics related to these shocks. The lack of a trend in the frequency or magnitude of the identified shocks and the range of identified causes suggest shocks are a common feature of these systems which occur due to a variety, and often multiple and simultaneous, causes. Shocks occurred most frequently in the Caribbean and Central America, the Middle East and North Africa, and South America, while the largest magnitude shocks occurred in Asia, Europe, and Africa. Shocks also occurred more frequently in aquaculture systems than in capture systems, particularly in recent years. In response to shocks, countries tend to increase imports and experience decreases in supply. The specific combination of changes in trade and supply are context specific, which is highlighted through four case studies. Historical examples of shocks considered in this study can inform policy for responding to shocks and identify potential risks and opportunities to build resilience in the global food system.

  • 9.
    Klaus, Marcus
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lidberg, William
    Department of Forest Ecology and Management, Swedish University of Agricultural Science, Umeå, Sweden.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Evaluations of Climate and Land Management Effects on Lake Carbon Cycling Need to Account Temporal Variability in CO2 Concentration2019Ingår i: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 33, nr 3, s. 243-265Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon dioxide (CO2) concentrations in lakes vary strongly over time. This variability is rarely captured by environmental monitoring but is crucial for accurately assessing the magnitude of lake CO2 emissions. However, it is unknown to what extent temporal variability needs to be captured to understand important drivers of lake carbon cycling such as climate and land management. We used environmental monitoring data of Swedish forest lakes collected in autumn (n = 439) and throughout the whole open water season (n = 22) from a wet and a dry year to assess temporal variability in effects of climate and forestry on CO2 concentrations across lakes. Effects differed depending on the season and year sampled. According to cross-lake comparisons based on autumn data, CO2 concentrations increased with annual mean air temperature (dry year) or catchment forest productivity (wet year) but were not related to colored dissolved organic matter concentrations. In contrast, open water-season averaged CO2 concentrations were similar across temperature and productivity gradients but increased with colored dissolved organic matter. These contradictions resulted from scale mismatches in input data, lead to weak explanatory power (R-2 = 9-32%), and were consistent across published data from 79 temperate, boreal, and arctic lakes. In a global survey of 144 published studies, we identified a trade-off between temporal and spatial coverage of CO2 sampling. This trade-off clearly determines which conclusions are drawn from landscape-scale CO(2 )assessments. Accurate evaluations of the effects of climate and land management require spatially and temporally representative data that can be provided by emerging sensor technologies and forms of collaborative sampling.

  • 10. Lapierre, Jean-Francois
    et al.
    Collins, Sarah M.
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Climate Impacts Research Centre, Umeå University, Abisko, Sweden.
    Cheruvelil, Kendra Spence
    Tan, Pang-Ning
    Skaff, Nicholas K.
    Taranu, Zofia E.
    Fergus, C. Emi
    Soranno, Patricia A.
    Similarity in spatial structure constrains ecosystem relationships: Building a macroscale understanding of lakes2018Ingår i: Global Ecology and Biogeography, ISSN 1466-822X, E-ISSN 1466-8238, Vol. 27, nr 10, s. 1251-1263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aim: We aimed to measure the dominant spatial patterns in ecosystem properties (such as nutrients and measures of primary production) and the multi‐scaled geographical driver variables of these properties and to quantify how the spatial structure of pattern in all of these variables influences the strength of relationships among them.

    Location and time period: We studied > 8,500 lakes in a 1.8 million km2 area of Northeast U.S.A. Data comprised 10‐year medians (2002–2011) for measured ecosystem properties, long‐term climate averages and recent land use/land cover variables.

    Major taxa studied: We focused on ecosystem properties at the base of aquatic food webs, including concentrations of nutrients and algal pigments that are proxies of pri -mary productivity.

    Methods: We quantified spatial structure in ecosystem properties and their geograph-ical driver variables using distance‐based Moran eigenvector maps (dbMEMs). We then compared the similarity in spatial structure for all pairs of variables with the cor -relation between variables to illustrate how spatial structure constrains relationships among ecosystem properties.

    Results: The strength of spatial structure decreased in order for climate, land cover/use, lake ecosystem properties and lake and landscape morphometry. Having a compa -rable spatial structure is a necessary condition to observe a strong relationship be -tween a pair of variables, but not a sufficient one; variables with very different spatial structure are never strongly correlated. Lake ecosystem properties tended to have an intermediary spatial structure compared with that of their main drivers, probably be -cause climate and landscape variables with known ecological links induce spatial patterns.

    Main conclusions: Our empirical results describe inherent spatial constraints that dic -tate the expected relationships between ecosystem properties and their geographical drivers at macroscales. Our results also suggest that understanding the spatial scales at which ecological processes operate is necessary to predict the effects of multi‐scaled environmental changes on ecosystem properties.

  • 11. Lapierre, Jean-Francois
    et al.
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department ofEnvironmental Sciences, University of Virginia, Charlottesville, VA, USA.
    del Giorgio, Paul A.
    Climate and landscape influence on indicators of lake carbon cycling through spatial patterns in dissolved organic carbon2015Ingår i: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 21, nr 12, s. 4425-4435Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Freshwater ecosystems are strongly influenced by both climate and the surrounding landscape, yet the specific pathways connecting climatic and landscape drivers to the functioning of lake ecosystems are poorly understood. Here, we hypothesize that the links that exist between spatial patterns in climate and landscape properties and the spatial variation in lake carbon (C) cycling at regional scales are at least partly mediated by the movement of terrestrial dissolved organic carbon (DOC) in the aquatic component of the landscape. We assembled a set of indicators of lake C cycling (bacterial respiration and production, chlorophyll a, production to respiration ratio, and partial pressure of CO2), DOC concentration and composition, and landscape and climate characteristics for 239 temperate and boreal lakes spanning large environmental and geographic gradients across seven regions. There were various degrees of spatial structure in climate and landscape features that were coherent with the regionally structured patterns observed in lake DOC and indicators of C cycling. These different regions aligned well, albeit nonlinearly along a mean annual temperature gradient; whereas there was a considerable statistical effect of climate and landscape properties on lake C cycling, the direct effect was small and the overall effect was almost entirely overlapping with that of DOC concentration and composition. Our results suggest that key climatic and landscape signals are conveyed to lakes in part via the movement of terrestrial DOC to lakes and that DOC acts both as a driver of lake C cycling and as a proxy for other external signals.

  • 12. Lapierre, Jean-Francois
    et al.
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Filstrup, Christopher T.
    Collins, Sarah M.
    Fergus, C. Emi
    Soranno, Patricia A.
    Cheruvelil, Kendra S.
    Continental-scale variation in controls of summer CO2 in United States lakes2017Ingår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, nr 4, s. 875-885Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the broad-scale response of lake CO2 dynamics to global change is challenging because the relative importance of different controls of surface water CO2 is not known across broad geographic extents. Using geostatistical analyses of 1080 lakes in the conterminous United States, we found that lake partial pressure of CO2 (pCO(2)) was controlled by different chemical and biological factors related to inputs and losses of CO2 along climate, topography, geomorphology, and land use gradients. Despite weak spatial patterns in pCO(2) across the study extent, there were strong regional patterns in the pCO(2) driver-response relationships, i.e., in pCO(2) regulation. Because relationships between lake CO2 and its predictors varied spatially, global models performed poorly in explaining the variability in CO2 for U.S. lakes. The geographically varying driver-response relationships of lake pCO(2) reflected major landscape gradients across the study extent and pointed to the importance of regional-scale variation in pCO(2) regulation. These results indicate a higher level of organization for these physically disconnected systems than previously thought and suggest that changes in climate and land use could induce shifts in the main pathways that determine the role of lakes as sources and sinks of atmospheric CO2. Plain Language Summary In this study we show that changes in climate and terrestrial landscapes could affect which are the main mechanisms responsible for the widespread emissions of CO2 by lakes. Although mechanisms such as aquatic primary production, respiration by microorganisms, or terrestrial loadings of carbon have been studied extensively, their relative importance across broad geographic extents with different climate or land use remains unknown. Based on an analysis of 1080 lakes distributed across the continental U.S., we show that lake CO2 dynamics depend on the climate and landscape context where these lakes are found, such as precipitation, elevation, percent agriculture, or wetlands in the lakes catchments. We observed a widespread effect of in-lake primary production, while the color of water, which has often been identified as one of the main controls of lake CO2 in northern lakes, was important in only a small fraction of the lakes studied. Our results show that controls on lake CO2 dynamics vary geographically and that considering that variation will be important for creating accurate global carbon models.

  • 13. MacDonald, Graham K
    et al.
    D'Odorico, Paolo
    Seekell, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Pathways to sustainable intensification through crop water management2016Ingår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 11, nr 9, artikel-id 025002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    How much could farm water management interventions increase global crop production? This is the central question posed in a global modelling study by Jägermeyr et al (2016 Environ. Res. Lett. 11 025002). They define the biophysical realm of possibility for future gains in crop production related to agricultural water practices—enhancing water availability to crops and expanding irrigation by reducing non-productive water consumption. The findings of Jägermeyr et al offer crucial insight on the potential for crop water management to sustainably intensify agriculture, but they also provide a benchmark to consider the broader role of sustainable intensification targets in the global food system. Here, we reflect on how the global crop water management simulations of Jägermeyr et al could interact with: (1) farm size at more local scales, (2) downstream water users at the river basin scale, as well as (3) food trade and (4) demand-side food system strategies at the global scale. Incorporating such cross-scale linkages in future research could highlight the diverse pathways needed to harness the potential of farm-level crop water management for a more productive and sustainable global food system.

  • 14. Marchand, Philippe
    et al.
    Carr, Joel A.
    Dell'Angelo, Jampel
    Fader, Marianela
    Gephart, Jessica A.
    Kummu, Matti
    Magliocca, Nicholas R.
    Porkka, Miina
    Puma, Michael J.
    Ratajczak, Zak
    Rulli, Maria Cristina
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Suweis, Samir
    Tavoni, Alessandro
    D'Odorico, Paolo
    Reserves and trade jointly determine exposure to food supply shocks2016Ingår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 11, nr 9, artikel-id 095009Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    While a growing proportion of global food consumption is obtained through international trade, there is an ongoing debate on whether this increased reliance on trade benefits or hinders food security, and specifically, the ability of global food systems to absorb shocks due to local or regional losses of production. This paper introduces a model that simulates the short-term response to a food supply shock originating in a single country, which is partly absorbed through decreases in domestic reserves and consumption, and partly transmitted through the adjustment of trade flows. By applying the model to publicly-available data for the cereals commodity group over a 17 year period, we find that differential outcomes of supply shocks simulated through this time period are driven not only by the intensification of trade, but as importantly by changes in the distribution of reserves. Our analysis also identifies countries where trade dependency may accentuate the risk of food shortages from foreign production shocks; such risk could be reduced by increasing domestic reserves or importing food from a diversity of suppliers that possess their own reserves. This simulation-based model provides a framework to study the short-term, nonlinear and out-of-equilibrium response of trade networks to supply shocks, and could be applied to specific scenarios of environmental or economic perturbations.

  • 15. Rusak, J. A.
    et al.
    Tanentzap, A. J.
    Klug, J. L.
    Rose, K. C.
    Hendricks, S. P.
    Jennings, E.
    Laas, A.
    Pierson, D.
    Ryder, E.
    Smyth, R. L.
    White, D. S.
    Winslow, L. A.
    Adrian, R.
    Arvola, L.
    de Eyto, E.
    Feuchtmayr, H.
    Honti, M.
    Istvánovics, V.
    Jones, I. D.
    McBride, C. G.
    Schmidt, S. R.
    Seekell, David A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Staehr, P. A.
    Zhu, G.
    Wind and trophic status explain within and among‐lake variability of algal biomass2018Ingår i: Limnology and Oceanography Letters, ISSN 2378-2242, Vol. 3, nr 6, s. 409-418Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phytoplankton biomass and production regulates key aspects of freshwater ecosystems yet its variability and subsequent predictability is poorly understood. We estimated within‐lake variation in biomass using high‐frequency chlorophyll fluorescence data from 18 globally distributed lakes. We tested how variation in fluorescence at monthly, daily, and hourly scales was related to high‐frequency variability of wind, water temperature, and radiation within lakes as well as productivity and physical attributes among lakes. Within lakes, monthly variation dominated, but combined daily and hourly variation were equivalent to that expressed monthly. Among lakes, biomass variability increased with trophic status while, within‐lake biomass variation increased with increasing variability in wind speed. Our results highlight the benefits of high‐frequency chlorophyll monitoring and suggest that predicted changes associated with climate, as well as ongoing cultural eutrophication, are likely to substantially increase the temporal variability of algal biomass and thus the predictability of the services it provides.

  • 16.
    Seekell, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    ECOLOGY AND ENVIRONMENT: Passing the point of no return2016Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 354, nr 6316, s. 1109-Artikel i tidskrift (Refereegranskat)
  • 17.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Byström, Pär
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lake morphometry moderates the relationship between water color and fish biomass in small boreal lakes2018Ingår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, nr 5, s. 2171-2178Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lake morphometry may moderate the effects of water color on fish biomass in boreal lakes, but empirical evidence is scarce because there are a limited number of lakes for which both water color and bathymetry have been measured. We evaluated variations in catch-per-unit-effort (CPUE), an indicator of fish biomass, across orthogonal gradients of light extinction and mean depth in 16 small Swedish lakes (mean depth 1.7-4.8 m, surface area 1-10 ha). Multiple regression coefficients indicated that the effect of light extinction on CPUE was negative, and that the relationship was more negative for deeper lakes than it was for shallower lakes. The pattern was strongest for lakes with mean depths between 2.1 m and 3.5 m. We estimated that 26% of small lakes in boreal Sweden fall within this mean depth range. These results contribute to the growing understanding of how variations in water color and lake morphometry influence patterns of fish biomass across the boreal landscape.

  • 18.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA.
    Carr, Joel A.
    Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA.
    Gudasz, Cristian
    Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Upscaling carbon dioxide emissions from lakes2014Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, nr 21, s. 7555-7559Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantifying CO2 fluxes from lakes to the atmosphere is important for balancing regional and global-scale carbon budgets. CO2 emissions are estimated through statistical upscaling procedures that aggregate data from a large number of lakes. However, aggregation can bias flux estimates if the physical and chemical factors determining CO2 exchange between water and the atmosphere are not independent. We evaluated the magnitude of aggregation biases with moment expansions and pCO(2) data from 5140 Swedish lakes. The direction of the aggregation bias depends on lake size; mean flux was overestimated by 4% for small lakes (0.01-0.1 km(2)) but underestimated by 13% for large lakes (100-1000 km(2)). Simple covariance-based correction factors were generated to adjust for upscaling biases. These correction factors represent an easily interpretable and implemented approach to improving the accuracy of regional and global estimates of lake CO2 emissions.

  • 19.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dakos, Vasilis
    Heteroskedasticity as a leading indicator of desertification in spatially explicit data2015Ingår i: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 5, nr 11, s. 2185-2192Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Regime shifts are abrupt transitions between alternate ecosystem states including desertification in arid regions due to drought or overgrazing. Regime shifts may be preceded by statistical anomalies such as increased autocorrelation, indicating declining resilience and warning of an impending shift. Tests for conditional heteroskedasticity, a type of clustered variance, have proven powerful leading indicators for regime shifts in time series data, but an analogous indicator for spatial data has not been evaluated. A spatial analog for conditional heteroskedasticity might be especially useful in arid environments where spatial interactions are critical in structuring ecosystem pattern and process. We tested the efficacy of a test for spatial heteroskedasticity as a leading indicator of regime shifts with simulated data from spatially extended vegetation models with regular and scale-free patterning. These models simulate shifts from extensive vegetative cover to bare, desert-like conditions. The magnitude of spatial heteroskedasticity increased consistently as the modeled systems approached a regime shift from vegetated to desert state. Relative spatial autocorrelation, spatial heteroskedasticity increased earlier and more consistently. We conclude that tests for spatial heteroskedasticity can contribute to the growing toolbox of early warning indicators for regime shifts analyzed with spatially explicit data.

  • 20.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Gudasz, Cristian
    Department of Ecology and Genetics/Limnology, Uppsala University, Uppsala, Sweden.
    Long-term pCO(2) trends in Adirondack Lakes2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 5109-5115Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lakes are globally significant sources of CO2 to the atmosphere. However, there are few temporally resolved records of lake CO2 concentrations and long-term patterns are poorly characterized. We evaluated annual trends in the partial pressure of CO2 (pCO2) based on chemical measurements from 31 Adirondack Lakes taken monthly over an 18 year period. All lakes were supersaturated with CO2 and were sources of CO2 to the atmosphere. There were significant pCO2 trends in 29% of lakes. The median magnitude of significant positive trends was 32.1 µatm yr−1. Overall, 52% of lakes had pCO2 trends greater than those reported for the atmosphere and ocean. Significant trends in lake pCO2 were attributable to regional recovery from acid deposition and changing patterns of ice cover. These results illustrate that lake pCO2 can respond rapidly to environmental change, but the lack of significant trend in 71% of lakes indicates substantial lake-to-lake variation in magnitude of response.

  • 21.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lapierre, Jean-Francois
    East Lansing, Michigan.
    Ask, Jenny
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bergström, Ann-Kristin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Deininger, Anne
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rodriguez, Patricia
    Tierra del Fuego, Argentina.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    The influence of dissolved organic carbon on primary production in northern lakes2015Ingår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, nr 4, s. 1276-1285Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dissolved organic carbon (DOC) concentrations in lakes are changing globally, but little is known about potential ecosystem impacts.We evaluated the relationship between DOC and whole-lake primary production in arctic and boreal lakes. Both light extinction (inhibits primary production) and nutrient availability (stimulates primary production) are positively and nonlinearly related to DOC concentration. These nonlinearities create a threshold DOC concentration (4.8mg L-1), below which the DOC-primary production relationship is positive, and above which the relationship is negative. DOC concentration varies maximally between regions, creating a unimodal relationship between primary production and DOC that emerges at broader scales because arctic lakes largely fall below the threshold DOC concentration, but boreal lakes fall above it. Our analysis suggests that the impact of DOC trends on lake primary production will vary across lakes and regions as a result of contrasting baseline conditions relative to the DOC threshold.

  • 22.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia.
    Lapierre, Jean-Francois
    Pace, Michael L.
    Gudasz, Cristian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey.
    Sobek, Sebastian
    Tranvik, Lars J.
    Regional-scale variation of dissolved organic carbon concentrations in Swedish lakes2014Ingår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, nr 5, s. 1612-1620Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We assessed spatial variability in dissolved organic carbon (DOC) concentrations measured in nearly 2000 Swedish lakes. Inter-lake variance peaked at two different scales, representing within-region and between-region variability. The variation between regions was greater than the variation among lakes within regions. We tested relationships between DOC and runoff, drainage ratio, and altitude for spatial heterogeneity using geographically weighted regression. Relationships varied geographically, but cluster analysis delineated two contiguous regions of similar relationships. Altitude had a significant inverse relationship with DOC in the highlands, and drainage ratio had a significant positive relationship with DOC in the lowlands. These heterogeneous relationships explained regional patterns in DOC concentrations. We conclude that regions, rather than individual lakes, are a key, emergent scale of spatial variability for DOC concentrations. This scale of variability reflects the intersection of environmental gradients (e.g., altitude) with spatially heterogeneous relationships (e.g., DOC-drainage ratio relationship). Regional-scale structure in limnological patterns indicates that individual lakes are not independent from one another, but are emergent groups where DOC concentrations are a function of similar environmental patterns and processes.

  • 23.
    Seekell, David A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Climate Impacts Research Centre, Umeå University, Umeå, Sweden.
    Lapierre, Jean‐François
    Cheruvelil, Kendra S.
    A geography of lake carbon cycling2018Ingår i: Limnology and Oceanography Letters, ISSN 2378-2242, Vol. 3, nr 3, s. 49-56Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon cycling in lakes is highly variable among lakes within regions, and across regions and continents, but the underlying causes of this variation among lakes and regions are not well understood. In this essay, we propose two main mechanisms that operate at the regional scale and contribute to broad‐scale interlake variation in carbon cycling. This essay sets the foundation for a geographic understanding of lake carbon cycling, which facilitates developing testable hypotheses to improve estimates of the role of inland waters in global elemental cycles.

  • 24.
    Seekell, David A
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lapierre, Jean-François
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Trade-offs between light and nutrient availability across gradients of dissolved organic carbon concentration in Swedish lakes: implications for patterns in primary production2015Ingår i: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533, Vol. 72, nr 11, s. 1663-1671Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dissolved organic carbon (DOC) limits primary production in lakes when present at high concentrations by reducing light availability, but stimulates primary production at lower concentrations by releasing nutrients through photolysis. These dual influences create the potential for threshold relationships between DOC and primary production, but empirical tests for the prevalence of thresholds are scarce. We used Box–Cox regression and environmental monitoring data from 703 subarctic and boreal lakes to assess patterns and potential threshold relationships between light and nutrient availability along gradients of DOC in northern Sweden’s six major watersheds. We found consistent patterns of increasing nutrient concentration and light attenuation with DOC. Further, we identified thresholds (mean = 5.96 mg·L−1) below which nutrient concentrations increased more rapidly than light extinction and above where the opposite occurred. These results suggest consistent patterns in primary production with shifts from nutrient to light limitation with increasing DOC. Accordingly, the thresholds agree with the vertex of the curvilinear relationship between lake primary production and DOC. We estimated that most lakes in Sweden are within ±3 mg·L−1 of the threshold, indicating high potential for changes from positive to negative influences of DOC on primary production if forecasted increases in DOC concentrations due to climate and land cover change are realized.

  • 25.
    Seekell, David
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Carr, Joel
    Dell'Angelo, Jampel
    D'Odorico, Paolo
    Fader, Marianela
    Gephart, Jessica
    Kummu, Matti
    Magliocca, Nicholas
    Porkka, Miina
    Puma, Michael
    Ratajczak, Zak
    Rulli, Maria Cristina
    Suweis, Samir
    Tavoni, Alessandro
    Resilience in the global food system2017Ingår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 12, nr 2, artikel-id 025010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ensuring food security requires food production and distribution systems function throughout disruptions. Understanding the factors that contribute to the global food system's ability to respond and adapt to such disruptions (i.e. resilience) is critical for understanding the long-term sustainability of human populations. Variable impacts of production shocks on food supply between countries indicate a need for national-scale resilience indicators that can provide global comparisons. However, methods for tracking changes in resilience have had limited application to food systems. We developed an indicator-based analysis of food systems resilience for the years 1992-2011. Our approach is based on three dimensions of resilience: socio-economic access to food in terms of income of the poorest quintile relative to food prices, biophysical capacity to intensify or extensify food production, and the magnitude and diversity of current domestic food production. The socio-economic indicator has a large variability, but with low values concentrated in Africa and Asia. The biophysical capacity indicator is highest in Africa and Eastern Europe, in part because of a high potential for extensification of cropland and for yield gap closure in cultivated areas. However, the biophysical capacity indicator has declined globally in recent years. The production diversity indicator has increased slightly, with a relatively even geographic distribution. Few countries had exclusively high or low values for all indicators. Collectively, these results are the basis for global comparisons of resilience between countries, and provide necessary context for developing generalizations about resilience in the global food system.

  • 26.
    Seekell, David
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Climate Impacts Research Centre, Umeå University, Abisko, Sweden.
    D'Odorico, Paolo
    MacDonald, Graham K.
    Food, trade, and the environment2018Ingår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 13, nr 10, artikel-id 100201Artikel i tidskrift (Övrigt vetenskapligt)
1 - 26 av 26
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