bluuebunny/crossref_metadata_2025 huggingface dataset:
Reducing impacts of systematic errors in the observation data on inversing ecosystem model parameters using different normalization methods
Authors: Zhang L. , Xu M. , Huang M. , Yu G.
Published: April 2010

Abstract. Modeling ecosystem carbon cycle on the regional and global scales is crucial to the prediction of future global atmospheric CO2 concentration and thus global temperature which features large uncertainties due mainly to the limitations in our knowledge and in the climate and ecosystem models. There is a growing body of research on parameter estimation against available carbon measurements to reduce model prediction uncertainty at regional and global scales. However, the systematic errors with the observation data have rarely been investigated in the optimization procedures in previous studies. In this study, we examined the feasibility of reducing the impact of systematic errors on parameter estimation using normalization methods, and evaluated the effectiveness of three normalization methods (i.e. maximum normalization, min-max normalization, and z-score normalization) on inversing key parameters, for example the maximum carboxylation rate (Vcmax,25) at a reference temperature of 25°C, in a process-based ecosystem model for deciduous needle-leaf forests in northern China constrained by the leaf area index (LAI) data. The LAI data used for parameter estimation were composed of the model output LAI (truth) and various designated systematic errors and random errors. We found that the estimation of Vcmax,25 could be severely biased with the composite LAI if no normalization was taken. Compared with the maximum normalization and the min-max normalization methods, the z-score normalization method was the most robust in reducing the impact of systematic errors on parameter estimation. The most probable values of estimated Vcmax,25 inversed by the z-score normalized LAI data were consistent with the true parameter values as in the model inputs though the estimation uncertainty increased with the magnitudes of random errors in the observations. We concluded that the z-score normalization method should be applied to the observed or measured data to improve model parameter estimation, especially when the potential errors in the constraining (observation) datasets are unknown.
Regional carbon dioxide and energy fluxes from airborne observations using flight-path segmentation based on landscape characteristics
Authors: Vellinga O. S. , Hutjes R. W. A. , Elbers J. A. , Holtslag A. A. M. , Kabat P.
Published: April 2010

Abstract. This paper presents an analysis of regional fluxes obtained with a small aircraft over heterogeneous terrain in the South West of France, during the large scale field experiment CERES'07. We use a method combining variable flight-path segmentation with basic airborne footprint analysis. The segmentation is based on topography, land use and soil type, using a.o. satellite imagery and digital maps. The segments are delineated using an average footprint length, based on all flights, and segment lengths, which are variable in space but not in time. The method results in segment averaged carbon and energy fluxes, which are shown to be representative of regional fluxes. Our analysis is focussed on the carbon dioxide, heat and evaporative fluxes around solar noon. We will show that spatial and seasonal variations in the fluxes can be linked to the underlying landscape. In addition, a comparison between the airborne data and ground flux data is made to support our results. However, due to the incompleteness of ground data for some predominant vegetation types (even in such a data dense context), upscaling of ground data to regional fluxes was not possible. Without the comparison, we are still able to demonstrate that aircraft can provide direct and meaningful estimates of regional fluxes of energy and carbon dioxide.
Exchange of carbonyl sulfide (COS) between the atmosphere and various soils in China
Authors: Liu J. , Geng C. , Mu Y. , Zhang Y. , Wu H.
Published: April 2010

Abstract. Using a dynamic enclosure, the exchange fluxes of carbonyl sulfide (COS) between the atmosphere and 18 soils from 10 provinces in China were investigated. The emission or uptake of COS from the soils was highly dependent on the soil type, soil temperature, soil moisture, and atmospheric COS mixing ratio. In general, with the only exception being paddy soils, the soils in this investigation acted as sinks for atmospheric COS under wide ranges of soil temperature and soil moisture. Two intensively investigated wheat soils and one forest soil, had optimal soil temperatures for COS uptake of around 15°C, and the optimal soil water content varied from 13 to 58%. The two paddy soils, exponentially COS emission fluxes increased with increasing soil temperature, and decreased COS emission fluxes with increased soil water content. However, negligible emission was found when the paddy soils were under waterlogging status. The observed compensation points for various soils were different and increased significantly with soil temperature. The laboratory simulation agreed with the preliminary field measurements for the paddy soil in Jiaxing, Zhejiang province.
The impact of Saharan dust on the particulate export in the water column of the North Western Mediterranean Sea
Authors: Ternon E. , Guieu C. , Loÿe-Pilot M.-D. , Leblond N. , Bosc E. , Gasser B. , Miquel J.-C.
Published: April 2010

Abstract. Simultaneous measurements of atmospheric deposition and of sinking particles at 200 m depth, were performed in the Ligurian Sea (North-Western Mediterranean) between 2003 and 2007 along with the historical time records of phytoplanktonic activity from satellite images. Atmospheric deposition of Saharan dust particles was very irregular and confirmed the importance of sporadic high magnitude events over the annual average (11.4 g m−2 yr−1 for the 4 yr). The average marine total mass flux was 31 g m−2 yr−1, the larger fraction being the lithogenic one (~37%). The marine total mass flux displayed a seasonal pattern with a maximum in winter occurring before the onset of the spring bloom. The highest POC fluxes did not occur during the spring bloom nor could they be related to any noticeable increase in the surface phytoplanktonic activity. Over the 4 yr of the study, the strongest POC fluxes were concomitant with large increases of the lithogenic marine flux, which had originated from either recent Saharan fallout events (February 2004, August 2005), or from ''old'' Saharan dust ''stored'' in the upper water column layer (March 2003, February 2005), or alternatively from lithogenic material originating from Ligurian riverine flooding (December 2003, Arno, Roya and Var rivers). These ''lithogenic events'' are believed to result from a combination of physical processes (winter mixing), the aggregation of faecal pellets resulting from zooplankton activity, and also organic-mineral aggregation inducing a ballast effect. However, such an event also occurred in August 2005 without any physical mixing, and was attributed to Saharan dust-induced biological enhancement. POC export provoked by the simultaneous occurrence of winter mixing and an extreme dust event (February 2004, 22 g m−2 deposition) was shown to represent 50% of the total annual POC export at 200 m in the water column that year, as compared to only ~25% for the bloom period. This indicates the importance of atmospheric deposition for POC fluxes in the Mediterranean Sea, which is an area strongly influenced by Saharan dust inputs.
Numerical study of surface energy partitioning on the Tibetan Plateau: comparative analysis of two biosphere models
Authors: Hong J. , Kim J.
Published: April 2010

Abstract. The Tibetan Plateau is a critical region in the research of biosphere-atmosphere interactions on both regional and global scales due to its relation to Asian summer monsoon and El Niño. The unique environment on the Plateau provides valuable information for the evaluation of the models' surface energy partitioning associated with the summer monsoon. In this study, we investigated the surface energy partitioning on this important area through comparative analysis of two biosphere models constrained by the in-situ observation data. Indeed, the characteristics of the Plateau provide a unique opportunity to clarify the structural deficiencies of biosphere models as well as new insight into the surface energy partitioning on the Plateau. Our analysis showed that the observed inconsistency between the two biosphere models was mainly related to: 1) the parameterization for soil evaporation; 2) the way to deal with roughness lengths of momentum and scalars; and 3) the parameterization of subgrid velocity scale for aerodynamic conductance. Our study demonstrates that one should carefully interpret the modeling results on the Plateau especially during the pre-monsoon period.
Effects of environmental factors and soil properties on topographic variations of soil respiration
Authors: Tamai K.
Published: April 2010

Abstract. Soil respiration rates were measured along different parts of a slope in (a) an evergreen forest with mature soil and (b) a deciduous forest with immature soil. The effects of soil temperature, soil moisture, and soil properties on soil respiration rates were estimated individually, and the magnitudes of these effects were compared between the deciduous and evergreen forests. In the evergreen forest with mature soil, soil properties had the greatest effect on soil respiration rates, followed by soil moisture and soil temperature. These results may be explained by different properties of soils that matured under different environments. Thus, we argue that the low soil respiration rates in Plot L of the evergreen forest resulted from soil properties and not from wet soil conditions. In the deciduous forest, soil respiration rates were more strongly affected by soil moisture and soil temperature than by soil properties, which were likely due to the immaturity of the forest soil.
Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development
Authors: Zhang J. , Gilbert D. , Gooday A. , Levin L. , Naqvi W. , Middelburg J. , Scranton M. , Ekau W. , Pena A. , Dewitte B. , Oguz T. , Monteiro P. M. S. , Urban E. , Rabalais N. , Ittekkot V. , Kemp W. M. , Ulloa O. , Elmgren R. , Escobar-Briones E. , Van der Plas A.
Published: April 2010

Abstract. Hypoxia has become a world-wide phenomenon in the global coastal ocean and causes deterioration of structure and function of ecosystems. Based on the collective contributions of members of SCOR Working Group #128, the present study provides an overview of the major aspects of coastal hypoxia in different biogeochemical provinces, including estuaries, upwelling areas, fjords and semi-enclosed basins, with various external forcings, ecosystem responses, feedbacks and potential impact on the sustainability of the fishery and economics. The obvious external forcings include fresh water runoff and other factors contributing to stratification, organic matter and nutrient loadings, as well as exchange between coastal and open ocean water masses; their different interactions set up mechanisms that drive the system towards hypoxia. However, whether the coastal environment becomes hypoxic or not, under the combination of external forcings, depends also on the nature of the ecosystem, e.g. physical and geographic settings. It is understood that coastal hypoxia has a profound impact on the sustainability of ecosystems, which can be seen, for example, by the change in the food-web structure and system function; other influences can be compression and loss of habitat, as well as change in life cycle and reproduction. In most cases, the ecosystem responds to the low dissolved oxygen in a non-linear way and has pronounced feedbacks to other compartments of the Earth System, hence affecting human society. Our knowledge and previous experiences illustrate that there is a need to develop new observational tools and models to support integrated research of biogeochemical dynamics and ecosystem behaviour that will improve confidence in remediation management strategies for coastal hypoxia.
Regional and temporal variability of sinking organic matter in the subtropical northeast Atlantic Ocean: a biomarker diagnosis
Authors: Alonso-González I. J. , Arístegui J. , Lee C. , Calafat A.
Published: April 2010

Abstract. Sinking particles through the pelagic ocean have been traditionally considered the most important vehicle by which the biological pump sequesters carbon in the ocean interior. Nevertheless, regional scale variability in particle flux is a major outstanding issue in oceanography. Here, we have studied the regional and temporal variability of total particulate organic matter fluxes, as well as chloropigment and total hydrolyzed amino acid (THAA) compositions and fluxes in the Canary Current region, between 20–30° N, during two contrasting periods: August 2006, characterized by warm and stratified waters, but also intense winds which enhanced eddy development south of the Canary Islands, and February 2007, characterized by colder waters, less stratification and higher productivity. We found that the eddy-field generated south of the Canary Islands enhanced by >2 times particulate organic carbon (POC) export with respect to stations (FF; far-field) outside the eddy-field influence. We also observed flux increases of one order of magnitude in chloropigment and 70% in THAA in the eddy-field relative to FF stations. Principal Components Analysis (PCA) was performed to assess changes in particulate organic matter composition between stations. At eddy-field stations, higher chlorophyll enrichment reflected "fresher" material, while at FF stations a higher proportion of pheophytin indicated greater degradation due to microbes and microzooplankton. PCA also suggests that phytoplankton community structure, particularly the dominance of diatoms versus carbonate-rich plankton, is the major factor influencing the POC export within the eddy field. In February, POC export fluxes were the highest ever reported for this area, reaching values of ~15 mmol C m−2 d−1 at 200 m depth. Compositional changes in pigments and THAA indicate that the source of sinking particles varies zonally and meridionally and suggest that sinking particles were more degraded at near-coastal stations relative to open ocean stations.
Dissolved methane during hypoxic events at the Boknis Eck Time Series Station (Eckernförde Bay, SW Baltic Sea)
Authors: Bange H. W. , Bergmann K. , Hansen H. P. , Kock A. , Koppe R. , Malien F. , Ostrau C.
Published: April 2010

Abstract. Dissolved CH4 was measured in the water column at the Boknis Eck (BE) time series station in the Eckernförde Bay (SW Baltic Sea) on a monthly basis from June 2006 to November 2008. The water column at BE was always supersaturated with CH4 and, therefore, CH4 was released to the atmosphere throughout the sampling period. A flux estimate indicates that the atmospheric CH4 emissions are balanced by the CH4 flux from the sediment. We did not detect a straightforward relationship between periods of enhanced CH4 in the bottom layer and hypoxic events at BE: The sedimentary release of CH4 seemed to be mainly triggered by sedimenting organic material from phytoplankton blooms. We conclude that future CH4 emissions from BE will be determined by both the occurrence and the intensity of phytoplankton blooms, which in turn will be influenced by eutrophication. However, hypoxic events seem to have only a modulating effect in the way that they enhance sedimentary methanogenesis.
Rainfall leads to increased pCO2 in Brazilian Coastal Lakes
Authors: Marotta H. , Duarte C. M. , Pinho L. , Enrich-Prast A.
Published: April 2010

Abstract. The variation of surface partial pressure of CO2 (pCO2), pH, salinity and dissolved organic carbon (DOC) in 12 coastal Brazilian lakes was examined following periods of contrasting rainfall. It was tested the hypothesis of a positive relationship of rainfall and the associated transport of terrestrial carbon with pCO2 in tropical lakes. High rainfall was followed by a large, almost 10 fold increase in pCO2 and a one unit decrease in pH in the lakes, whereas no consistent changes in DOC were observed. CO2 emissions to the atmosphere from the Brazilian coastal lakes studied here were enhanced, on average, almost 10 fold, from 28.5±6.0 mmol m−2 d−1 in drier periods to 245.3.1±51.5 mmol m−2 d−1 following heavy rain. Hence, precipitation and subsequent ventilation of groundwater CO2 in lakes might provide an important conduit to deliver CO2 resulting from soil respiration to the atmosphere.
Assessing variability and long-term trends in burned area by merging multiple satellite fire products
Authors: Giglio L. , Randerson J. T. , van der Werf G. R. , Kasibhatla P. S. , Collatz G. J. , Morton D. C. , DeFries R. S.
Published: April 2010

Abstract. Long term, high quality estimates of burned area are needed for improving both prognostic and diagnostic fire emissions models and for assessing feedbacks between fire and the climate system. We developed global, monthly burned area estimates aggregated to 0.5° spatial resolution for the time period July 1996 through mid-2009 using four satellite data sets. From 2001–2009, our primary data source was 500-m burned area maps produced using Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance imagery; more than 90% of the global area burned during this time period was mapped in this fashion. During times when the 500-m MODIS data were not available, we used a combination of local regression and regional regression trees to develop relationships between burned area and Terra MODIS active fire data. Cross-calibration with fire observations from the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and the Along-Track Scanning Radiometer (ATSR) allowed the data set to be extended prior to the MODIS era. With our data set we estimated the global annual area burned for the years 1997–2008 varied between 330 and 431 Mha, with the maximum occurring in 1998. We compared our data set to the recent GFED2, L3JRC, GLOBCARBON, and MODIS MCD45A1 global burned area products and found substantial differences in many regions. Lastly, we assessed the interannual variability and long-term trends in global burned area over the past 12 years. This burned area time series serves as the basis for the third version of the Global Fire Emissions Database (GFED3) estimates of trace gas and aerosol emissions.
Short scale (6 h) temporal variation of sinking fluxes of planktonic and terrigeneous lipids at 200 m in the NW Mediterranean Sea
Authors: Méjanelle L. , Dachs J.
Published: April 2010

Abstract. Drifting sediment trap experiments were carried out at high temporal frequency in the northwestern Mediterranean in the course of the DYNAPROC2 campaign, every 6 h at 200 m depth. Molecular biomarkers were analyzed in selected subsets of consecutive samples. Fluxes of n-alkanes, long-chain alkenones, sterols and steroid ketones show high variability between consecutive 6-h' samples, comparable in range to seasonnal variability. n-Alkane export ranges from 1.4 to 29.7 μg m−2 d−1, fluxes of C37 alkenones varies from 0 to 14.2 μg m−2 d−1. Fluxes of sterols, steroid ketones and C30 alkane diol, respectively range from 31 to 377, 2.2 to 46 and 0.3 to 9.3 μg m−2 d−1. The Biomarker composition is consistent with reworked algal and zooplanktonic organic matter with a remarkable refractory character. After a rain event ensuing the intrusion of coastal water at the study site, the relative signature of higher plant increases and corresponds to higher export fluxes of long-chain odd n-alkanes. Most phytoplanktonic biomarkers show concurrent variability in fluxes. Linear correlations between fluxes of distinct biomarkers and between fluxes of biomarkers and flux of total carbon suggest that the short term temporal variability of export fluxes depends primarily on physical constrains exerted by carrier particle dynamics. Linear correlation of their carbon-normalized concentrations explained a lower part of the variance, indicating that short-term variability in particle composition is a secondary driver of flux timing. At the end of summer stratification, export fluxes account for ca. 1% of the primary productivity. In this studied situation, biomarkers have a long residence time in the water column before they are exported at 200 m. Biomarkers exported at 200 m may thus record processes averaged over a larger period than the sampling frequency. For instance, phytoplanktonic biomarker composition of sinking particles fails to reflect the community changes occurring over the 4 weeks of study. At higher time resolution, the diel variability in primary productivity is not recorded by biomarker fluxes either. The coupling between primary productivity and biomarker export shows significant changes on time scales of days and even of 6 h.
Bioavailability of organically bound Fe to model phytoplankton of the Southern Ocean
Authors: Hassler C. S. , Schoemann V.
Published: April 2010

Abstract. Iron (Fe) is known to be mostly bound to organic ligands and to limit primary productivity in the Southern Ocean. It is thus important to investigate the bioavailability of organically bound Fe. In this study, we used four keystone phytoplankton species of the Southern Ocean (Phaeocystis sp., Chaetoceros sp., Fragilariopsis kerguelensis and Thalassiosira antarctica Comber) to measure the influence of various organic ligands on Fe solubility and bioavailability. Based on the Fe:C ratios, the strength of Fe limitation was inversely related to the surface area to volume ratio, with the chain forming Fragilariopsis being the most Fe-limited strain. The ratio of extracellular to intracellular Fe is used to discuss the relative importance of diffusive supply and uptake to control Fe bioavailability. The effect of excess of organic ligands on Fe bioavailability cannot be solely explained by their effect on Fe solubility. For all strains studied, the bioavailability of Fe can be enhanced in presence of porphyrin, cathecolate and saccharides whereas it was decreased in presence of hydroxamate and organic amine. The enhancement of Fe bioavailability in presence of saccharides is presented as the result from both the formation of bioavailable (or chemically labile) organic form of Fe and the stabilisation of Fe within the dissolved phase. Given the ubiquitous presence of saccharides in the ocean, these compounds might represent an important factor to control the basal level of soluble and bioavailable Fe. Results show that the use of model phytoplankton is promising to improve mechanistic understanding of Fe bioavailability and primary productivity in HNLC regions of the ocean.
A whole plant approach to evaluate the water use of mediterranean maquis species in a coastal dune ecosystem
Authors: Mereu S. , Salvatori E. , Fusaro L. , Gerosa G. , Muys B. , Manes F.
Published: April 2010

Abstract. An integrated approach has been used to analyse the water relations of three Mediterranean species, A. unedo L., Q. ilex L. and P. latifolia L. co-occurring in a coastal dune ecosystem. The approach considered leaf level gas exchange, sap flow measurements and structural adaptations between 15 May and 31 July 2007, and was necessary to capture the different response of the three species to the same environment. The complexity of the response was proportional to the complexity of the system, characterized by a sandy soil with a low water retention capacity and the presence of a water table. The latter did not completely prevent the development of a drought response, and species differences in this responses have been partially attributed to a different root distribution. Sap flow of A. unedo decreased rapidly in response to the decline of Soil Water Content, while that of Q. ilex decreased only moderately. Midday leaf water potential of P. latifolia and A. unedo was between 2.2 and 2.7 MPa through the measuring period, while in Q. ilex it reached a value of 3.4 MPa at the end of the season. A. unedo was the only species to decrease the leaf area to sapwood area ratio from 23.9±1.2 (May) to 15.2±1.5 (July), as a response to drought. A. unedo also underwent an almost stepwise loss on hydraulic conductivity, such a loss didn't occur for Q. ilex, while P. latifolia was able to slightly increase hydraulic conductivity, showing how different plant compartments coordinate differently between species as a response to drought. Such different coordination affects the gas exchange between vegetation and the atmosphere, and has implications for the response of the Mediterranean coastal dune ecosystems to climate change.
Factors governing the pH in a heterotrophic, turbid, tidal estuary
Authors: Hofmann A. F. , Meysman F. J. R. , Soetaert K. , Middelburg J. J.
Published: April 2010

Abstract. A method to quantify the influence of kinetically modelled biogeochemical processes on the pH of an ecosystem with time variable acid-base dissociation constants is presented and applied to the heterotrophic, turbid Scheldt estuary (SW Netherlands, N Belgium). Nitrification is identified as the main process governing the pH profile of this estuary, while CO2 degassing and advective-dispersive transport "buffer" the effect of nitrification. CO2 degassing accounts for the largest proton turnover per year in the whole estuary. There is a clear inverse correlation between oxygen turnover and proton turnover. The main driver of long-term changes in the mean estuarine pH from 2001 to 2004 is a changing freshwater flow which influences the pH "directly" via [∑CO2] and [TA] and to a significant amount also "indirectly" via [∑NH4+] and the nitrification rates in the estuary.
Influence of landscape heterogeneity on spatial patterns of wood productivity, wood specific density and above ground biomass in Amazonia
Authors: Anderson L. O. , Malhi Y. , Ladle R. J. , Aragão L. E. O. C. , Shimabukuro Y. , Phillips O. L. , Baker T. , Costa A. C. L. , Espejo J. S. , Higuchi N. , Laurance W. F. , López-González G. , Monteagudo A. , Núñez-Vargas P. , Peacock J. , Quesada C. A. , Almeida S. , Vásquez R.
Published: April 2010

Abstract. Long-term studies using the RAINFOR network of forest plots have generated significant insights into the spatial and temporal dynamics of forest carbon cycling in Amazonia. In this work, we map and explore the landscape context of several major RAINFOR plot clusters using Landsat ETM+ satellite data. In particular, we explore how representative the plots are of their landscape context, and test whether bias in plot location within landscapes may be influencing the regional mean values obtained for important forest biophysical parameters. Specifically, we evaluate whether the regional variations in wood productivity, wood specific density and above ground biomass derived from the RAINFOR network could be driven by systematic and unintentional biases in plot location. Remote sensing data covering 45 field plots were aggregated to generate landscape maps to identify the specific physiognomy of the plots. In the Landsat ETM+ data, it was possible to spectrally differentiate three types of terra firme forest, three types of alluvial terrain forest, two types of bamboo-dominated forest, palm forest, Heliconia monodominant vegetation, swamp forest, disturbed forests and land use areas. Overall, the plots were generally representative of the forest physiognomies in the landscape in which they are located. Furthermore, the analysis supports the observed regional trends in those important forest parameters. This study demonstrates the utility of landscape scale analysis of forest physiognomies for validating and supporting the finds of plot based studies. Moreover, the more precise geolocation of many key RAINFOR plot clusters achieved during this research provides important contextual information for studies employing the RAINFOR database.
Spatial trends in leaf size of Amazonian rainforest trees
Authors: Malhado A. C. M. , Malhi Y. , Whittaker R. J. , Ladle R. J. , ter Steege H. , Aragão L. E. O. C. , Quesada C. A. , Araujo-Murakami A. , Phillips O. L. , Peacock J. , Lopez-Gonzalez G. , Baker T. R. , Butt N. , Anderson L. O. , Arroyo L. , Almeida S. , Higuchi N. , Killeen T. J. , Monteagudo A. , Neill D. , Pitman N. , Prieto A. , Salomão R. P. , Silva N. , Vásquez-Martínez R. , Laurance W. F.
Published: April 2010

Abstract. Leaf size influences many aspects of tree function such as rates of transpiration and photosynthesis and, consequently, often varies in a predictable way in response to environmental gradients. The recent development of pan-Amazonian databases based on permanent botanical plots (e.g. RAINFOR, ATDN) has now made it possible to assess trends in leaf size across environmental gradients in Amazonia. Previous plot-based studies have shown that the community structure of Amazonian trees breaks down into at least two major ecological gradients corresponding with variations in soil fertility (decreasing south to northeast) and length of the dry season (increasing from northwest to south and east). Here we describe the results of the geographic distribution of leaf size categories based on 121 plots distributed across eight South American countries. We find that, as predicted, the Amazon forest is predominantly populated by tree species and individuals in the mesophyll size class (20.25–182.25 cm2). The geographic distribution of species and individuals with large leaves (>20.25 cm2) is complex but is generally characterized by a higher proportion of such trees in the north-west of the region. Spatially corrected regressions reveal weak correlations between the proportion of large-leaved species and metrics of water availability. We also find a significant negative relationship between leaf size and wood density.
Intercomparison and assessment of turbulent and physiological exchange parameters of grassland
Authors: Nemitz E. , Hargreaves K. J. , Neftel A. , Loubet B. , Cellier P. , Dorsey J. R. , Flynn M. , Hensen A. , Weidinger T. , Meszaros R. , Horvath L. , Dämmgen U. , Frühauf C. , Löpmeier F. J. , Gallagher M. W. , Sutton M. A.
Published: April 2010

Abstract. Commonly, the micrometeorological parameters that underline the calculations of surface atmosphere exchange fluxes (e.g. friction velocity and sensible heat flux) and parameters used to model exchange fluxes with SVAT-type parameterisations (e.g. latent heat flux and canopy temperature) are measured with a single set of instrumentation and are analysed with a single methodology. This paper evaluates uncertainties in these measurements with a single instrument, by comparing the independent results from nine different institutes during the international GRAMINAE integrated field experiment over agricultural grassland near Braunschweig, Lower Saxony, Germany. The paper discusses uncertainties in measuring friction velocity, sensible and latent heat fluxes, canopy temperature and investigates the energy balance closure at this site. Although individual 15-min flux calculations show a large variability between the instruments, when averaged over the campaign, fluxes agree within 2% for momentum and 11% for sensible heat. However, the spread in estimates of latent heat flux (λE) is larger, with standard deviations of averages of 18%. While the dataset averaged over the different instruments fails to close the energy budget by 30%, if the largest turbulent fluxes are considered, near perfect energy closure can be achieved, suggesting that most techniques underestimate λE in particular. The uncertainty in λE feeds results in an uncertainty in the bulk stomatal resistance, which further adds to the uncertainties in the estimation of the canopy temperature that controls the exchange. The paper demonstrated how a consensus dataset was derived, which is used by the individual investigators to calculate fluxes and drive their models.
Above- and below-ground net primary productivity across ten Amazonian forests on contrasting soils
Authors: Aragão L. E. O. C. , Malhi Y. , Metcalfe D. B. , Silva-Espejo J. E. , Jiménez E. , Navarrete D. , Almeida S. , Costa A. C. L. , Salinas N. , Phillips O. L. , Anderson L. O . , Baker T. R. , Goncalvez P. H. , Huamán-Ovalle J. , Mamani-Solórzano M. , Meir P. , Monteagudo A. , Peñuela M. C. , Prieto A. , Quesada C. A. , Rozas-Dávila A. , Rudas A. , Silva Junior J. A. , Vásquez R.
Published: April 2010

Abstract. The net primary productivity (NPP) of tropical forests is one of the most important and least quantified components of the global carbon cycle. Most relevant studies have focused particularly on the quantification of the above-ground coarse wood productivity, and little is known about the carbon fluxes involved in other elements of the NPP, the partitioning of total NPP between its above- and below-ground components and the main environmental drivers of these patterns. In this study we quantify the above- and below-ground NPP of ten Amazonian forests to address two questions: (1) How do Amazonian forests allocate productivity among its above- and below-ground components? (2) How do soil and leaf nutrient status and soil texture affect the productivity of Amazonian forests? Using a standardized methodology to measure the major elements of productivity, we show that NPP varies between 9.3±1.3 Mg C ha−1 yr−1 (mean±standard error), at a white sand plot, and 17.0±1.4 Mg C ha−1 yr−1 at a very fertile Terra Preta site, with an overall average of 12.8±0.9 Mg C ha−1 yr−1. The studied forests allocate on average 64±3% and 36±3% of the total NPP to the above- and below-ground components, respectively. The ratio of above-ground and below-ground NPP is almost invariant with total NPP. Litterfall and fine root production both increase with total NPP, while stem production shows no overall trend. Total NPP tends to increase with soil phosphorus and leaf nitrogen status. However, allocation of NPP to below-ground shows no relationship to soil fertility, but appears to decrease with the increase of soil clay content.
Historical records of coastal eutrophication-induced hypoxia
Authors: Gooday A. J. , Jorissen F. , Levin L. A. , Middelburg J. J. , Naqvi S. W. A. , Rabalais N. N. , Scranton M. , Zhang J.
Published: April 2010

Abstract. Under certain conditions, sediment cores from coastal settings subject to hypoxia can yield records of environmental changes over time scales ranging from decades to millennia, sometimes with a resolution of as little as a few years. A variety of biological and geochemical proxies derived from such cores have been used to reconstruct the development of eutrophication and hypoxic conditions over time. Proxies based on 1) the preserved remains of benthic organisms (mainly foraminiferans and ostracods), 2) sedimentary features (e.g. laminations) and 3) sediment chemistry and mineralogy (e.g. presence of sulphides and redox-sensitive trace elements) reflect conditions at or close to the seafloor. Those based on 4) the preserved remains of planktonic organisms (mainly diatoms and dinoflagellates), 5) pigments and lipid biomarkers derived from prokaryotes and eukaryotes and 6) organic C, N and their isotope values reflect conditions in the water column. However, the interpretation of these proxies is not straightforward. A central difficulty concerns the fact that hypoxia is strongly correlated with, and often induced by, organic enrichment (eutrophication), making it difficult to separate the effects of these phenomena in sediment records. The problem is compounded by the enhanced preservation in anoxic and hypoxic sediments of organic microfossils and biomarkers indicating eutrophication. The use of hypoxia-specific indicators, such as the trace metals molybdenum and rhenium and the bacterial biomarker isorenieratene, which have not been used often in historical studies, may provide a way forward. All proxies of bottom-water hypoxia are basically qualitative; their quantification presents a major challenge to which there is currently no satisfactory solution. Finally, it is important to separate the effects of natural ecosystem variability from anthropogenic effects. Despite these problems, in the absence of historical data for dissolved oxygen concentrations, the analysis of sediment cores can provide plausible reconstructions of the temporal development of human-induced hypoxia, and associated eutrophication, in vulnerable coastal environments.
Phosphatase activity and organic phosphorus turnover on a high Arctic glacier
Authors: Stibal M. , Anesio A. M. , Blues C. J. D. , Tranter M.
Published: April 2010

Abstract. Arctic glacier surfaces harbor abundant microbial communities consisting mainly of heterotrophic and photoautotrophic bacteria. The microbes must cope with very low concentrations of nutrients and with the fact that both the dissolved and debris-bound nutrient pools are dominated by organic phases. Here we provide evidence that phosphorus (P) is deficient and limiting in the supraglacial environment on a Svalbard glacier, we show how the microbial community responds to the P stress and we quantify the contribution of the microbes to the cycling of the dominant organic P in the supraglacial environment. Incubation of cryoconite debris revealed significant phosphatase activity in the samples (19–67 nmol MUP g−1 h−1), which was controlled by the concentration of inorganic P during incubations and had its optimum at around 30°C. The phosphatase activity rates measured at near-in situ temperature and substrate concentration imply that the available dissolved organic P can be turned over by microbes within ~3–11 h on the glacier surface. By contrast, the amount of potentially bioavailable debris-bound organic P is sufficient for a whole ablation season. However, it is apparent that some of this potentially bioavailable debris-bound P is not accessible to the microbes.
Applying biomass and stem fluxes to quantify temporal and spatial fluctuations of an old-growth forest in disturbance
Authors: Liu S. , Li Y. -L. , Zhou G. -Y. , Wenigmann K. O. , Luo Y. , Otieno D. , Tenhunen J.
Published: April 2010

Abstract. A subtropical old-growth forest was analyzed over a twelve year period to investigate temporal and spatial fluctuations of biomass and stem fluxes under disturbances. Vegetations were categorized into three types caused by biotic factors and abiotic factors, including Castanopsis chinensis population, insect direct-influenced population, and insect indirect-influenced population according to disturbance scenarios. The biomass fluxes (including biomass growth and mortality) and stem fluxes (including stem recruitment and mortality) were used to quantify the fluctuation of population. The results showed that annual average biomass growth rate was stable throughout the three periods, 1992–1994, 1994–1999, and 1999–2004, while annual biomass mortality and stem fluxes kept increasing through the three periods. Castanopsis chinensis population contributed the most in biomass fluxes of the community. Biomass and stem mortalities of insect direct-influenced population increased significantly during the whole study period (1992–2004). Dynamics of indirect-influenced population were compared by dominate species, diameter classes, and spatial patterns of subplots, respectively. Results of indirect-influenced population showed that (1) the increase of biomass of the dominant species was well correlated between different intervals. Similar relationships were found in stem fluxes; (2) higher stem mortality was observed when DBH ranged from 1 to 10 cm as compared with individuals in other DBH classes; (3) stem fluxes in the canopy gaps were remarkably higher than those in closed canopy. The biomass growth rate in gaps increased remarkably after the formation of the gaps.
Effect of land use on carbon dioxide, water vapour and energy exchange over terrestrial ecosystems in Southwestern France during the CERES campaign
Authors: Jarosz N. , Béziat P. , Bonnefond J. M. , Brunet Y. , Calvet J. C. , Ceschia E. , Elbers J. A. , Hutjes R. W. A. , Traullé O.
Published: April 2010

Abstract. Eddy fluxes were measured over different ecosystems, winter and summer crops, a maritime pine forest at different stages of development and grassland, from 17 May to 26 June 2005 in the southwestern region of France. During the experiment, summer crops started growing whereas winter crops and grassland achieved their senescence. Comparatively, the other ecosystems had a much slower growth emphasized by soil water deficit at forest sites. The ten ecosystems showed different partitioning of available energy. Net radiation was the highest above the maritime pine forest, followed, in decreasing order, by the crops, the vineyard and the grassland. Over the whole campaign period, the Bowen ratio (β=H/LE) was larger above the forest sites than for the other sites. The various vegetation types also showed contrasting net ecosystem exchange (NEE) dynamics following their growth status and respective behaviour in response to drought. Both the clearcut and summer crops before irrigation and plant growth behaved as sources of CO2, whereas the vineyard, the mature forest and winter crops acted as sinks. However the maize crops became substantial sinks of CO2 after the start of irrigation and canopy growth, with fluxes twice as large as for the mature pine forest. Finally, throughout the experiment, forest, grassland and crops sequestrated from about 50 gC m−2 to 230 gC m−2, while the cleacut and the beans crop rejected about 30 gC m−2. These results support the idea that converting a mature forest to a clearcut or bare soil available to agricultural use enhances the sensible heat flux and shifts the ecosystem from a sink to a source of carbon.
Direct contribution of phytoplankton-sized particles to optical backscattering in the open ocean
Authors: Dall'Olmo G. , Westberry T. K. , Behrenfeld M. J. , Boss E. , Slade W. H.
Published: April 2010

Abstract. Light scattering properties of oceanic particles have been suggested as an alternative index of phytoplankton biomass than chlorophyll-a concentration (chl-a), with the benefit of being less sensitive to physiological forcings (e.g., light and nutrients) that alter the intracellular pigment concentrations. The drawback of particulate scattering is that it is not unique to phytoplankton. Nevertheless, field studies have demonstrated that, to first order, the particulate beam-attenuation coefficient (cp) can track phytoplankton abundance. The relationship between cp and the particulate backscattering coefficient (bbp), a property retrievable from space, has not been fully evaluated, largely due to a lack of open-ocean field observations. Here, we present extensive data on inherent optical properties from the Equatorial Pacific surface waters and demonstrate a remarkable coherence in bbp and cp. Coincident measurements of particle size distributions (PSDs) and optical properties of size-fractionated samples indicate that this covariance is due to both the conserved nature of the PSD and a greater contribution of phytoplankton-sized particles to bbp than theoretically predicted. These findings suggest that satellite-derived bbp could provide similar information on phytoplankton biomass in the open ocean as cp.
Testing the relationship between the solar radiation dose and surface DMS concentrations using high resolution in situ data
Authors: Miles C. J. , Bell T. G. , Lenton T. M.
Published: April 2010

Abstract. We tested the recently proposed, strong positive relationship between dimethylsulphide (DMS) concentrations and the solar radiation dose (SRD) received into the surface ocean. We utilised in situ daily data sampled concurrently with DMS concentrations from the Atlantic Meridional Transect (AMT) programme for the component variables of the SRD; mixed layer depth (MLD), surface insolation (I0) and a light attenuation coefficient (k), to calculate SRDin situ. We find a significant correlation (ρ=0.53) but the slope of the relationship is approximately half that previously proposed. The correlation is improved (ρ=0.76) by replacing the in situ data with an estimated I0 (which assumes a constant 50% removal of the top of atmosphere value; 0.5×TOA), a MLD climatology and a fixed value for k following a previously described methodology. Equally significant, but non-linear relationships are also found between DMS and both in situ MLD (ρ=0.73) and the estimated I0 (ρ=0.76) alone. The DMS data shows an interesting relationship to an approximated UV attenuation depth profile. Using a cloud adjusted, satellite climatology of surface UVA irradiance to calculate a UV radiation dose (UVRD) provides an equivalent correlation (ρ=0.73) to DMS. With this data, MLD appears the dominant control upon DMS concentrations and remains a useful shorthand to prediction without fully resolving the biological processes involved. However, the implied relationship between incident solar/ultraviolet radiation dose and sea surface DMS concentrations (modulated by MLD) is critical for closing a climate feedback loop.
Liana infestation impacts tree growth in a lowland tropical moist forest
Authors: van der Heijden G. M. F. , Phillips O. L.
Published: April 2010

Abstract. Stand-level estimates of the effect of lianas on tree growth in mature tropical forests are needed to evaluate the functional impact of lianas and their potential to affect the ability of tropical forests to sequester carbon, but these are currently lacking. Using data collected on tree growth rates, local growing conditions and liana competition in five permanent sampling plots in Amazonian Peru, we present the first such estimates of the effect of lianas on above-ground productivity of trees. By constructing a multi-level linear mixed effect model to predict individual tree diameter growth model using individual tree growth conditions, we were able to estimate stand-level above-ground biomass (AGB) increment in the absence of lianas. We show that lianas, mainly by competing above-ground with trees, reduce tree annual above-ground stand-level biomass by ~10%, equivalent to 0.51 Mg dry weight ha−1 yr−1 or 0.25 Mg C ha−1 yr−1. AGB increment of lianas themselves was estimated to be 0.15 Mg dry weight ha−1 yr−1 or 0.07 Mg C ha−1 yr−1, thus only compensating ~29% of the liana-induced reduction in stand-level AGB increment. Increasing liana pressure on tropical forests may therefore not only reduce their carbon storage capacity, by indirectly promoting tree species with low-density wood, but also their rate of carbon uptake, with potential consequences for the rate of increase in atmospheric carbon dioxide.