Radiation measurements at ICOS ecosystem stations

Solar radiation is a key driver of energy and carbon fluxes in natural ecosystems. Radiation measurements are essential for interpreting ecosystem scale greenhouse gases and energy fluxes as well as many other observations performed at ecosystem stations of the Integrated Carbon Observation System (ICOS). We describe and explain the relevance of the radiation variables that arc monitored continuously at ICOS ecosystems stations and define recommendations to perform these measurements with consistent and comparable accuracy. The measurement methodology and instruments are described including detailed technical specifications. Guidelines for instrumental set up as well as for operation, maintenance and data collection arc defined considering both ICOS scientific objectives and practical operational constraints. For measurements of short-wave (solar) and long wave (infrared) radiation components, requirements for the ICOS network are based on available well-defined state-of-the art standards (World Meteorological Organization, International Organization for Standardization). For photosynthetically active radiation measurements, some basic instrumental requirements are based on the performance of commercially available sensors. Since site specific conditions and practical constraints at individual ICOS ecosystem stations may hamper the applicability of standard requirements, we recommend that ICOS develops mid-tern coordinated actions to assess the effective level of uncertainties in radiation measurements at the network scale.Peer reviewe

Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe's terrestrial ecosystems : a review

Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.Peer reviewe

Analyzing the major drivers of NEE in a Mediterranean alpine shrubland

Two years of continuous measurements of net ecosystem exchange (NEE) using the eddy covariance technique were made over a Mediterranean alpine shrubland. This ecosystem was found to be a net source of CO2 (+ 52±7 g C m−2 and + 48±7 g C m−2 for 2007 and 2008) during the two-year study period. To understand the reasons underlying this net release of CO2 into the atmosphere, we analysed the drivers of seasonal variability in NEE over these two years. We observed that the soil water availability – driven by the precipitation pattern – and the photosynthetic photon flux density (PPFD) are the key factors for understanding both the carbon sequestration potential and the duration of the photosynthetic period during the growing season. Finally, the effects of the self-heating correction to CO2 and H2O fluxes measured with the open-path infrared gas analyser were evaluated. Applying the correction turned the annual CO2 budget in 2007 from a sink (−135±7 g C m−2) to a source (+ 52±7 g C m−2). The magnitude of this change is larger than reported previously and is shown to be due to the low air density and cold temperatures at this high elevation study site

Can flux tower research neglect geochemical **CO2** exchange?

This study examines the hypothesis that surface-atmosphere exchange of CO2 in terrestrial ecosystems always can be interpreted purely in terms of biological processes, neglecting geochemical cycling by karst systems that characterize 22 million km2 in the world [Yuan Daoxian, G., 1997. The carbon cycle in karst, Zeitschrift für Geomorphologie 108 (Supplementbände), 91-102]. Eddy covariance data of net CO2 fluxes are examined for two ecosystems over karstic substrates in contrasting climates in the North and South of Spain. A semi-arid matorral is found to behave similarly to previously studied ecosystems when well watered, but sizeable mid-day CO2 emissions during extended drought and plant senescence are found to be incompatible with ecophysiological interpretations of the flux. For a temperate pasture overlying an accessible cave, afternoon CO2 emissions in summer are likewise inexplicable in a biological context, but coincide with periods when ventilation is observed inside the subterranean cavity. These results suggest direct linkages at times in CO2 exchanges among atmosphere, ecosystems, and carbonate substrates which represent more than a tenth of the Earth's land surface. © 2008 Elsevier B.V. All rights reserved.This work was funded by Spanish National R&D (CICYT) water resources program projects RECLISE (REN2002-04517-C02-02/HID) and CANOA (CGL2004-04919-C02-01/HID), by Science Ministry projects BTE2002-04492-C02-02, CGL2006-11561/BTE, and CGL2006-26147-E/CLI, by regional government (Junta de Andalucía) projects BACAEMÁ (RNM 332) and IRASEM (Instituto del Agua), and by the Sierra Nevada National Park.Peer reviewe

Analysis of shape using Delaunay triangulations

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