Author
Achim Grelle
Bio: Achim Grelle is an academic researcher from Swedish University of Agricultural Sciences. The author has contributed to research in topics: Eddy covariance & Ecosystem. The author has an hindex of 35, co-authored 62 publications receiving 13651 citations.
Papers published on a yearly basis
Papers
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Oak Ridge National Laboratory1, University of California, Berkeley2, Institut national de la recherche agronomique3, University of Amsterdam4, Carnegie Institution for Science5, Swedish University of Agricultural Sciences6, University of Göttingen7, Oregon State University8, University of Edinburgh9, University of Colorado Boulder10, San Diego State University11, University of Nebraska–Lincoln12
TL;DR: A comprehensive evaluation of energy balance closure is performed across 22 sites and 50 site-years in FLUXNET, a network of eddy covariance sites measuring long-term carbon and energy fluxes in contrasting ecosystems and climates as mentioned in this paper.
2,052 citations
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TL;DR: In this article, the authors have described the measurement system and the procedure followed for the computation of the fluxes and procedure of flux summation, including data gap filling strategy, night flux corrections and error estimation.
Abstract: Publisher Summary The chapter has described the measurement system and the procedure followed for the computation of the fluxes and the procedure of flux summation, including data gap filling strategy, night flux corrections and error estimation. It begins with the introduction of estimates of the annual net carbon and water exchange of forests using the EUROFLUX methodology. The chapter then provides us with the theory and moves on to discuss the eddy covariance system and its sonic anemometer, temperature fluctuation measurements, infrared gas analyser, air transport system, and tower instrumentation. Additional measurements are also given in the chapter. Data acquisition and its computation and correction is discussed next in the chapter by giving its general procedure, half-hourly means (co-)variances and uncorrected fluxes, intercomparison of software, and correction for frequency response losses. The chapter has also discussed about quality control and four criteria are investigated here for the same. Spatial representativeness of measured fluxes and summation procedure are reviewed. The chapter then moves on to the discussion of data gap filling through interpolation and parameterization and neural networks. Corrections to night-time data and error estimation are also explored in the chapter. Finally, the chapter closes with conclusions.
1,870 citations
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Max Planck Society1, Lund University2, Dresden University of Technology3, Gembloux Agro-Bio Tech4, University of Antwerp5, University of Helsinki6, Institut national de la recherche agronomique7, University of Göttingen8, University of Edinburgh9, University of Padua10, United States Forest Service11
TL;DR: Data of net ecosystem carbon exchange, collected between 1996 and 1998 from 15 European forests, confirm that many European forest ecosystems act as carbon sinks and indicate that, in general, ecosystem respiration determines netcosystem carbon exchange.
Abstract: Carbon exchange between the terrestrial biosphere and the atmosphere is one of the key processes that need to be assessed in the context of the Kyoto Protocol1. Several studies suggest that the terrestrial biosphere is gaining carbon2,3,4,5,6,7,8, but these estimates are obtained primarily by indirect methods, and the factors that control terrestrial carbon exchange, its magnitude and primary locations, are under debate. Here we present data of net ecosystem carbon exchange, collected between 1996 and 1998 from 15 European forests, which confirm that many European forest ecosystems act as carbon sinks. The annual carbon balances range from an uptake of 6.6 tonnes of carbon per hectare per year to a release of nearly 1 t C ha-1 yr-1, with a large variability between forests. The data show a significant increase of carbon uptake with decreasing latitude, whereas the gross primary production seems to be largely independent of latitude. Our observations indicate that, in general, ecosystem respiration determines net ecosystem carbon exchange. Also, for an accurate assessment of the carbon balance in a particular forest ecosystem, remote sensing of the normalized difference vegetation index or estimates based on forest inventories may not be sufficient.
1,636 citations
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Oregon State University1, University of Bayreuth2, University of California, Berkeley3, Climate Monitoring and Diagnostics Laboratory4, Institut national de la recherche agronomique5, University of Minnesota6, Wageningen University and Research Centre7, University of California, Davis8, University of Virginia9, Swedish University of Agricultural Sciences10, United States Department of Agriculture11, University of Antwerp12, University of Edinburgh13, Technical University of Denmark14, Duke University15, Tuscia University16, Oak Ridge National Laboratory17, University of Colorado Boulder18, Harvard University19, San Diego State University20, University of Nebraska–Lincoln21, University of Helsinki22
TL;DR: The authors compared seasonal and annual estimates of CO2 and water vapor exchange across sites in forests, grasslands, crops, and tundra that are part of an international network called FLUXNET, and investigated the responses of vegetation to environmental variables.
1,199 citations
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TL;DR: It is shown that the temporal dynamics following stand-replacing disturbances do indeed account for a very large fraction of the overall variability in forest carbon sequestration, and that mankind is ultimately controlling the carbon balance of temperate and boreal forests.
Abstract: A study of forest ecosystems from across western Europe and the United States has settled a long-running controversy — and raised many new questions. At issue is the influence of nitrogen deposition on the global carbon cycle, particularly the part played by human activity. The new study demonstrates that via the direct effects of forest management and indirectly via the use of nitrogen fertilizers and nitrogen oxide production by cars and industry, human activities have had a profound and largely positive effect on the carbon balance or net ecosystem production. (That's the balance between ecosystem carbon fixation through photosynthesis and its subsequent release through plant and soil respiration.) The implications of these findings for practical questions such as the merits of fertilizing forests with nitrogen, are considered in the accompanying News and Views by Peter Hogberg. The profound, overwhelming effects of human activities on the carbon balance of temperate and boreal forests are demonstrated. Apart from the direct effects of forest management, they show that carbon sequestration by this important component of the biosphere is driven by the imbalance in the global nitrogen cycle determined by human activities. Temperate and boreal forests in the Northern Hemisphere cover an area of about 2 × 107 square kilometres and act as a substantial carbon sink (0.6–0.7 petagrams of carbon per year)1. Although forest expansion following agricultural abandonment is certainly responsible for an important fraction of this carbon sink activity, the additional effects on the carbon balance of established forests of increased atmospheric carbon dioxide, increasing temperatures, changes in management practices and nitrogen deposition are difficult to disentangle, despite an extensive network of measurement stations2,3. The relevance of this measurement effort has also been questioned4, because spot measurements fail to take into account the role of disturbances, either natural (fire, pests, windstorms) or anthropogenic (forest harvesting). Here we show that the temporal dynamics following stand-replacing disturbances do indeed account for a very large fraction of the overall variability in forest carbon sequestration. After the confounding effects of disturbance have been factored out, however, forest net carbon sequestration is found to be overwhelmingly driven by nitrogen deposition, largely the result of anthropogenic activities5. The effect is always positive over the range of nitrogen deposition covered by currently available data sets, casting doubts on the risk of widespread ecosystem nitrogen saturation6 under natural conditions. The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly (through forest management) or indirectly (through nitrogen deposition).
972 citations
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TL;DR: This work has suggested that several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition, causing lower observed ‘apparent’ temperature sensitivity, and these constraints may, themselves, be sensitive to climate.
Abstract: Significantly more carbon is stored in the world's soils--including peatlands, wetlands and permafrost--than is present in the atmosphere. Disagreement exists, however, regarding the effects of climate change on global soil carbon stocks. If carbon stored belowground is transferred to the atmosphere by a warming-induced acceleration of its decomposition, a positive feedback to climate change would occur. Conversely, if increases of plant-derived carbon inputs to soils exceed increases in decomposition, the feedback would be negative. Despite much research, a consensus has not yet emerged on the temperature sensitivity of soil carbon decomposition. Unravelling the feedback effect is particularly difficult, because the diverse soil organic compounds exhibit a wide range of kinetic properties, which determine the intrinsic temperature sensitivity of their decomposition. Moreover, several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition, causing lower observed 'apparent' temperature sensitivity, and these constraints may, themselves, be sensitive to climate.
5,367 citations
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TL;DR: Optimizing the need for a key human resource while minimizing its negative consequences requires an integrated interdisciplinary approach and the development of strategies to decrease nitrogen-containing waste.
Abstract: Humans continue to transform the global nitrogen cycle at a record pace, reflecting an increased combustion of fossil fuels, growing demand for nitrogen in agriculture and industry, and pervasive inefficiencies in its use. Much anthropogenic nitrogen is lost to air, water, and land to cause a cascade of environmental and human health problems. Simultaneously, food production in some parts of the world is nitrogen-deficient, highlighting inequities in the distribution of nitrogen-containing fertilizers. Optimizing the need for a key human resource while minimizing its negative consequences requires an integrated interdisciplinary approach and the development of strategies to decrease nitrogen-containing waste.
5,249 citations
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TL;DR: Interdisciplinary science that integrates knowledge of the many interacting climate services of forests with the impacts of global change is necessary to identify and understand as yet unexplored feedbacks in the Earth system and the potential of forests to mitigate climate change.
Abstract: The world's forests influence climate through physical, chemical, and biological processes that affect planetary energetics, the hydrologic cycle, and atmospheric composition. These complex and nonlinear forest-atmosphere interactions can dampen or amplify anthropogenic climate change. Tropical, temperate, and boreal reforestation and afforestation attenuate global warming through carbon sequestration. Biogeophysical feedbacks can enhance or diminish this negative climate forcing. Tropical forests mitigate warming through evaporative cooling, but the low albedo of boreal forests is a positive climate forcing. The evaporative effect of temperate forests is unclear. The net climate forcing from these and other processes is not known. Forests are under tremendous pressure from global change. Interdisciplinary science that integrates knowledge of the many interacting climate services of forests with the impacts of global change is necessary to identify and understand as yet unexplored feedbacks in the Earth system and the potential of forests to mitigate climate change.
4,541 citations
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TL;DR: An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.
Abstract: Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003.We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg Cyr21) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.
3,408 citations
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TL;DR: In this paper, the role of inland water ecosystems in the global carbon cycle has been investigated and it is shown that roughly twice as much C enters inland aquatic systems from land as is exported from land to the sea, roughly equally as inorganic and organic carbon.
Abstract: Because freshwater covers such a small fraction of the Earth’s surface area, inland freshwater ecosystems (particularly lakes, rivers, and reservoirs) have rarely been considered as potentially important quantitative components of the carbon cycle at either global or regional scales. By taking published estimates of gas exchange, sediment accumulation, and carbon transport for a variety of aquatic systems, we have constructed a budget for the role of inland water ecosystems in the global carbon cycle. Our analysis conservatively estimates that inland waters annually receive, from a combination of background and anthropogenically altered sources, on the order of 1.9 Pg C y−1 from the terrestrial landscape, of which about 0.2 is buried in aquatic sediments, at least 0.8 (possibly much more) is returned to the atmosphere as gas exchange while the remaining 0.9 Pg y−1 is delivered to the oceans, roughly equally as inorganic and organic carbon. Thus, roughly twice as much C enters inland aquatic systems from land as is exported from land to the sea. Over prolonged time net carbon fluxes in aquatic systems tend to be greater per unit area than in much of the surrounding land. Although their area is small, these freshwater aquatic systems can affect regional C balances. Further, the inclusion of inland, freshwater ecosystems provides useful insight about the storage, oxidation and transport of terrestrial C, and may warrant a revision of how the modern net C sink on land is described.
3,179 citations