bluuebunny/crossref_metadata_2025 huggingface dataset:
Needle age-related and seasonal photosynthetic capacity variation is negligible for modelling yearly gas exchange of a sparse temperate Scots pine forest
Authors: Op de Beeck M. , Gielen B. , Jonckheere I. , Samson R. , Janssens I. A. , Ceulemans R.
Published: April 2010

Abstract. In this study, we quantified the predictive accuracy loss involved with omitting photosynthetic capacity variation for a Scots pine (Pinus sylvestris L.) stand in Flanders, Belgium. Over the course of one phenological year, we measured the maximum carboxylation capacity at 25 °C (Vm25), the maximum electron transport capacity at 25 °C (Jm25), and the leaf area index (LAI) of different-aged needle cohorts in the upper and lower canopy. We used these measurements as input for a process-based multi-layer canopy model with the objective to quantify the difference in yearly gross ecosystem productivity (GEP) and canopy transpiration (Ecan) simulated under scenarios in which the observed needle age-related and/or seasonal variation of Vm25 and Jm25 was omitted. We compared simulated GEP with estimations obtained from eddy covariance measurements. Additionally, we measured summer needle N content to investigate the relationship between photosynthetic capacity parameters and needle N content along different needle ages. Results show that Vm25 and Jm25 were, respectively, 27% and 13% higher in current-year than in one-year old needles. A significant seasonality effect was found on Vm25, but not on Jm25. Summer needle N content was considerably lower in current-year than in one-year-old needles. As a result, the correlations between Vm25 and needle N content and Jm25 and needle N content were negative and non-significant, respectively. Some explanations for these unexpected correlations were brought forward. Yearly GEP was overestimated by the canopy model by ±15% under all scenarios. The inclusion and omission of the observed needle age-related Vm25 and Jm25 variation in the model simulations led to statistically significant but ecologically irrelevant differences in simulated yearly GEP and Ecan. Omitting seasonal variation did not yield significant simulation differences. Our results indicate that intensive photosynthetic capacity measurements over the full growing season and separate simulation of needle age classes were no prerequisites for accurate simulations of yearly canopy gas exchange. This is true, at least, for the studied stand, which has a very sparse canopy and is exposed to high N deposition and, hence, is not fully representative for temperate Scots pine stands. Nevertheless, we believe well-parameterized process-based canopy models – as applied in this study – are a useful tool to quantify losses of predictive accuracy involved with canopy simplification in modelling.
Flux and composition of settling particles across the continental margin of the Gulf of Lion: the role of dense shelf water cascading
Authors: Pasqual C. , Sanchez-Vidal A. , Zúñiga D. , Calafat A. , Canals M. , Durrieu de Madron X. , Puig P. , Heussner S. , Palanques A. , Delsaut N.
Published: April 2010

Abstract. Settling particles were collected using sediment traps deployed along three transects in the Lacaze-Duthiers and Cap de Creus canyons and the adjacent southern open slope from October 2005 to October 2006. The settling material was analyzed to obtain total mass fluxes and main constituent contents (organic matter, opal, calcium carbonate, and siliciclastics). Cascades of dense shelf water from the continental shelf edge to the lower continental slope occurred from January to March 2006. They were traced through strong negative near-bottom temperature anomalies and increased current speeds, and generated two intense pulses of mass fluxes in January and March 2006. This oceanographic phenomenon appeared as the major physical forcing of settling particles at almost all stations, and caused both high seasonal variability in mass fluxes and important qualitative changes in settling material. Fluxes during the dense shelf water cascading (DSWC) event ranged from 90.1 g m−2 d−1 at the middle Cap de Creus canyon (1000 m) to 3.2 g m−2 d−1 at the canyon mouth (1900 m). Fractions of organic matter, opal and calcium carbonate components increased seaward, thus diminishing the siliciclastic fraction. Temporal variability of the major components was larger in the canyon mouth and open slope sites, due to the mixed impact of dense shelf water cascading processes and the pelagic biological production. Results indicate that the cascading event remobilized and homogenized large amounts of material down canyon and southwardly along the continental slope contributing to a better understanding of the off-shelf particle transport and the internal dynamics of DSWC events.
Responses of soil respiration to elevated carbon dioxide and nitrogen addition in young subtropical forest ecosystems in China
Authors: Deng Q. , Zhou G. , Liu J. , Liu S. , Duan H. , Zhang D.
Published: April 2010

Abstract. Global climate change in the real world always exhibits simultaneous changes in multiple factors. Prediction of ecosystem responses to multi-factor global changes in a future world strongly relies on our understanding of their interactions. However, it is still unclear how nitrogen (N) deposition and elevated atmospheric carbon dioxide concentration [CO2] would interactively influence forest floor soil respiration in subtropical China. We assessed the main and interactive effects of elevated [CO2] and N addition on soil respiration by growing tree seedlings in ten large open-top chambers under CO2 (ambient CO2 and 700 μmol mol−1) and nitrogen (ambient and 100 kg N ha−1 yr−1) treatments. Soil respiration, soil temperature and soil moisture were measured for 30 months, as well as above-ground biomass, root biomass and soil organic matter (SOM). Results showed that soil respiration displayed strong seasonal patterns with higher values observed in the wet season (April–September) and lower values in the dry season (October–March) in all treatments. Significant exponential relationships between soil respiration rates and soil temperatures, as well as significant linear relationships between soil respiration rates and soil moistures (below 15%) were found. Both CO2 and N treatments significantly affected soil respiration, and there was significant interaction between elevated [CO2] and N addition (p<0.001, p=0.003, and p=0.006, respectively). We also observed that the stimulatory effect of individual elevated [CO2] (about 29% increased) was maintained throughout the experimental period. The positive effect of N addition was found only in 2006 (8.17% increased), and then had been weakened over time. Their combined effect on soil respiration (about 50% increased) was greater than the impact of either one alone. Mean value of annual soil respiration was 5.32 ± 0.08, 4.54 ± 0.10, 3.56 ± 0.03 and 3.53 ± 0.03 kg CO2 m−2 yr−1 in the chambers exposed to elevated [CO2] and high N deposition (CN), elevated [CO2] and ambient N deposition (CC), ambient [CO2] and high N deposition (NN), and ambient [CO2] and ambient N deposition (CK as a control), respectively. Greater above-ground biomass and root biomass was obtained in the CN, CC and NN treatments, and higher soil organic matter was observed only in the CN treatment. In conclusion, the combined effect of elevated [CO2] and N addition on soil respiration was apparent interaction. They should be evaluated in combination in subtropical forest ecosystems in China where the atmospheric CO2 and N deposition have been increasing simultaneously and remarkably.
Effects of multiple environmental factors on CO2 emission and CH4 uptake from old-growth forest soils
Authors: Fang H. J. , Yu G. R. , Cheng S. L. , Zhu T. H. , Wang Y. S. , Yan J. H. , Wang M. , Cao M. , Zhou M.
Published: April 2010

Abstract. To assess contribution of multiple environmental factors to carbon exchanges between the atmosphere and forest soils, four old-growth forests referred to as boreal coniferous forest, temperate needle-broadleaved mixed forest, subtropical evergreen broadleaved forest and tropical monsoon rain forest were selected along eastern China. In each old-growth forest, soil CO2 and CH4 fluxes were measured from 2003 to 2005 applying the static opaque chamber and gas chromatography technique. Soil temperature and moisture at the 10 cm depth were simultaneously measured with the greenhouse gas measurements. Inorganic N (NH4+-N and NO3−-N) in the 0–10 cm was determined monthly. From north to south, annual mean CO2 emission ranged from 18.09 ± 0.22 to 35.40 ± 2.24 Mg CO2 ha−1 yr−1 and annual mean CH4 uptake ranged from 0.04 ± 0.11 to 5.15 ± 0.96 kg CH4 ha−1 yr−1 in the four old-growth forests. Soil CO2 flux in the old-growth forests was mainly driven by soil temperature, followed by soil moisture and NO3−-N. Temperature sensitivity (Q10) of soil CO2 flux was lower at lower latitudes with high temperature and more precipitation, probably because of less soil organic carbon (SOC). Soil NO3− accumulation caused by environmental change was often accompanied by an increase in soil CO2 emission. In addition, soil CH4 uptake decreased with an increase in soil moisture. The response of soil CH4 flux to temperature was dependent upon the optimal value of soil temperature in each forest. Soil NH4+-N consumption tended to promote soil CH4 uptake in the old-growth forests, whereas soil NO3−-N accumulation was not conducive to CH4 oxidation in anaerobic condition. These results indicate that soil mineral N dynamics largely affects the soil gas fluxes of CO2 and CH4 in the old-growth forests, along with climate conditions.
Soil organic carbon dynamics under long-term fertilizations in arable land of northern China
Authors: Zhang W. J. , Wang X. J. , Xu M. G. , Huang S. M. , Liu H. , Peng C.
Published: April 2010

Abstract. Soil carbon sequestration is a complex process influenced by agricultural practices, climate and soil conditions. This paper reports a study of long-term fertilization impacts on soil organic carbon (SOC) dynamic from six long-term experiments. The experiment sites are located from warm-temperate zone with a double-cropping system of corn (Zea mays L.) – wheat (Triticum Aestivium L.) rotation, to mild-temperate zones with mono-cropping systems of continuous corn, or a three-year rotation of corn-wheat-wheat. Mineral fertilizer applications result in an increasing trend in SOC except in the arid and semi-arid areas with the mono-cropping systems. Additional manure application is important to maintain SOC level in the arid and semi-arid areas. Carbon conversion rate is significant lower in the warm-temperate zone with double cropping system (6.8%–7.7%) than that in the mild-temperate areas with mono-cropping systems (15.8%–31.0%). The conversion rate is significantly correlated with annual precipitation and active accumulative temperature, i.e., higher conversion rate under lower precipitation and/or temperature conditions. Moreover, soil high in clay content has higher conversion rate than soils low in clay content. Soil carbon sequestration rate ranges from 0.07 to 1.461 t ha−1 year−1 in the upland of northern China. There is significantly linear correlation between soil carbon sequestration and carbon input at most sites, indicating that these soils are not carbon-saturated thus have potential to migrate more CO2 from atmosphere.
Benthic phosphorus and iron budgets for three NW African slope sediments: a balance approach
Authors: Küster-Heins K. , de Lange G. J. , Zabel M.
Published: April 2010

Abstract. Despite intensive research on the different domains of the marine phosphorus (P) cycle during the last decades, frequently discussed open questions still exist especially on controlling factors for the benthic behaviour of P and its general distribution in sediment-pore water systems. Steady state or the internal balance of all relevant physical and (bio)geochemical processes are amongst the key issues. In this study we present and discuss an extended data set from surface sediments recovered from three locations on the NW African continental slope. Pore water data and results from sequential sediment extractions give clear evidence to the well-known close relationship between the benthic cycles of P and iron. Accordingly, most of the dissolved phosphate must have been released by microbially catalyzed reductive dissolution of iron (oxhydr)oxides. However, rates of release and association of P and iron, respectively, are not directly represented in profiles of element specific sediment compositions. Results from steady-state based transport-reaction modelling suggest that particle mixing due to active bioturbation, or rather a physical net downward transport of P associated to iron (oxyhydr)oxides, is an essential process for the balance of the inspected benthic cycles. This study emphasizes the importance of balancing analytical data for a comprehensive understanding of all processes involved in biogeochemical cycles.
A model-based assessment of the TrOCA approach for estimating anthropogenic carbon in the ocean
Authors: Yool A. , Oschlies A. , Nurser A. J. G. , Gruber N.
Published: April 2010

Abstract. The quantification of the amount of anthropogenic carbon (Cant) that the ocean has taken up from the atmosphere since pre-industrial times is a challenging task because of the need to deconvolute this signal from the natural, unperturbed concentration of dissolved inorganic carbon (DIC). Nonetheless, a range of techniques have been devised that perform this separation using the information implicit in other physical, biogeochemical, and man-made ocean tracers. One such method is the TrOCA approach, which belongs to a group of back-calculation techniques, but relative to other methods employs a simple parameterization for estimating the preformed, pre-industrial concentration, the key quantity needed to determine Cant. Here we examine the theoretical foundation of the TrOCA approach and test its accuracy by deconvoluting the known distribution of Cant from an ocean general circulation model (OGCM) simulation of the industrial period (1864–2004). We reveal that the TrOCA tracer reflects the air-sea exchange of both natural and anthropogenic CO2 as well as that of O2. Consequently, the determination of the anthropogenic CO2 flux component requires an accurate determination not only of the contribution of the natural (pre-industrial) CO2 flux component, but also of the O2 flux component. The TrOCA method attempts to achieve this by assuming that the concentration changes invoked by these two air-sea flux components scale with temperature and alkalinity. While observations support a strong exponential scaling of the oxygen flux component with temperature, there exists no simple relationship of the natural CO2 flux component with temperature and/or alkalinity. This raises doubts whether the sum of these two components can be adequately parameterized with a single function. The analyses of the model support this conclusion, even when Cant is deconvoluted using parameter values that were optimized on the basis of the synthetic dataset from the model. Application of an optimal, but globally uniform set of parameters for the estimation of Cant results in a global positive bias in the inventory of more than a factor of two, suggesting that a "universal" TrOCA parameterisation is not achieveable. Even the application of regionally specific sets of parameters causes, on average, a global positive bias of more than 50%. This is substantially larger than the potential positive bias of 7% identified for the ΔC* method using a similar model-based assessment method.
Exchange of carbonyl sulfide (COS) between the atmosphere and various soils in China
Authors: Liu J. , Geng C. , Mu Y. , Zhang Y. , Xu Z. , Wu H.
Published: April 2010

Abstract. Using a dynamic enclosure, the exchange rates of carbonyl sulfide (COS) between the atmosphere and 18 soils from 12 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%. COS emission rates from the two paddy soils increased exponentially with increment of the soil temperature, and decreased with increasing the 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.
Estimating mixed layer nitrate in the North Atlantic Ocean
Authors: Steinhoff T. , Friedrich T. , Hartman S. E. , Oschlies A. , Wallace D. W. R. , Körtzinger A.
Published: April 2010

Abstract. Here we present an equation for the estimation of nitrate in surface waters of the North Atlantic Ocean (40° N to 52° N, 10° W to 60° W). The equation was derived by multiple linear regression (MLR) from nitrate, sea surface temperature (SST) observational data and model mixed layer depth (MLD) data. The observational data were taken from merchant vessels that have crossed the North Atlantic on a regular basis in 2002/2003 and from 2005 to the present. It is important to find a robust and realistic estimate of MLD because the deepening of the mixed layer is crucial for nitrate supply to the surface. We compared model data from two models (FOAM and Mercator) with MLD derived from float data (using various criteria). The Mercator model gives a MLD estimate that is close to the MLD derived from floats. MLR was established using SST, MLD from Mercator, time and latitude as predictors. Additionally a neural network was trained with the same dataset and the results were validated against both model data as a "ground truth" and an independent observational dataset. This validation produced RMS errors of the same order for MLR and the neural network approach. We conclude that it is possible to estimate nitrate concentrations with an uncertainty of ±1.4 μmol L−1 in the North Atlantic.
Light effects on the isotopic fractionation of skeletal oxygen and carbon in the cultured zooxanthellate coral, Acropora: implications for coral-growth rates
Authors: Juillet-Leclerc A. , Reynaud S.
Published: April 2010

Abstract. Skeletal isotopic and metabolic measurements of the branching coral Acropora cultured in constant conditions and subjected to two light intensities were revisited. We individually compared the data recorded at low light (LL) and high light (HL) for 24 colonies, all derived from the same parent colony. Metabolic and isotopic responses to the different light levels were highly variable. High light led to productivity enhancement, reduction of surface extension, doubling of aragonite deposited weight and increased δ18O levels in all nubbins; responses in respiration and δ13C were not clear. The partitioning of the colonies cultured at HL into two groups, one showing a δ13C enrichment and the other a δ13C decrease revealed common behaviors. Samples showing an increase in δ13C were associated with the co-variation of low surface extension and high productivity while samples showing a decrease in δ13C were associated with the co-variation of higher surface extension and limited productivity. This experiment, which allowed for the separation of temperature and light effects on the coral, highlighted the significant light influences on both skeletal δ18O and δ13C. The high scattering of inter-colony δ18O observed at one site could be due to the differing photosynthetic responses of symbiotic algal assemblages. We compared our results with observations by Gladfelter on Acropora cervicornis (1982). Both set of results highlight the relationships between coral-growth rates, micro-structures and photosynthetic activity. It appears that extension growth and skeleton thickening are two separate growth modes, and thickening is light-enhanced while extension is light-suppressed. There are multiple consequences of these findings for paleoclimatic reconstructions involving corals.
Simulating carbon and water cycles of larch forests in East Asia by the BIOME-BGC model with AsiaFlux data
Authors: Ueyama M. , Ichii K. , Hirata R. , Takagi K. , Asanuma J. , Machimura T. , Nakai Y. , Ohta T. , Saigusa N. , Takahashi Y. , Hirano T.
Published: April 2010

Abstract. Larch forests are widely distributed across many cool-temperate and boreal regions, and they are expected to play an important role in global carbon and water cycles. Model parameterizations for larch forests still contain large uncertainties owing to a lack of validation. In this study, a process-based terrestrial biosphere model, BIOME-BGC, was tested for larch forests at six AsiaFlux sites and used to identify important environmental factors that affect the carbon and water cycles at both temporal and spatial scales. The model simulation performed with the default deciduous conifer parameters produced results that had large differences from the observed net ecosystem exchange (NEE), gross primary productivity (GPP), ecosystem respiration (RE), and evapotranspiration (ET). Therefore, we adjusted several model parameters in order to reproduce the observed rates of carbon and water cycle processes. This model calibration, performed using the AsiaFlux data, substantially improved the model performance. The simulated annual GPP, RE, NEE, and ET from the calibrated model were highly consistent with observed values. The observed and simulated GPP and RE across the six sites were positively correlated with the annual mean air temperature and annual total precipitation. On the other hand, the simulated carbon budget was partly explained by the stand disturbance history in addition to the climate. The sensitivity study indicated that spring warming enhanced the carbon sink, whereas summer warming decreased it across the larch forests. The summer radiation was the most important factor that controlled the carbon fluxes in the temperate site, but the VPD and water conditions were the limiting factors in the boreal sites. One model parameter, the allocation ratio of carbon between belowground and aboveground, was site-specific, and it was negatively correlated with the annual climate of annual mean air temperature and total precipitation. Although this study substantially improved the model performance, the uncertainties that remained in terms of the sensitivity to water conditions should be examined in ongoing and long-term observations.
CO2 air-sea exchange due to calcium carbonate and organic matter storage: pre-industrial and Last Glacial Maximum estimates
Authors: Lerman A. , Mackenzie F. T.
Published: April 2010

Abstract. Release of CO2 from surface ocean water owing to precipitation of CaCO3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface water to sedimentary storage was studied by means of a model that gives the quotient θ=(CO2 released to the atmosphere)/(CaCO3 precipitated). The surface ocean layer is approximated by a euphotic zone, 50 m thick, that includes the shallower coastal area and open ocean. θ depends on water temperature, CaCO3 and organic carbon mass formed, and atmospheric CO2 concentration. At temperatures between 5 and 25°C, and three atmospheric CO2 pressures – 195 ppmv corresponding to the Last Glacial Maximum, 280 ppmv for the end of pre-industrial time, and 375 ppmv for the present – θ varies from a fraction of 0.38 to 0.79, increasing with decreasing temperature, increasing atmospheric CO2 content, and increasing CaCO3 precipitated mass (up to 45% of the DIC concentration in surface water). For a surface ocean layer that receives input of inorganic and organic carbon from land, the calculated CO2 flux to the atmosphere at the Last Glacial Maximum is 20 to 22×1012 mol/yr and in pre-industrial time it is 45 to 49×1012 mol/yr. In addition to the environmental factors mentioned above, flux to the atmosphere and increase of atmospheric CO2 depend on the thickness of the surface ocean layer. The significance of these fluxes and comparisons with the estimates of other investigators are discussed. Within the imbalanced global carbon cycle, our estimates are in agreement with the conclusions of others that the global ocean prior to anthropogenic emissions of CO2 to the atmosphere was losing carbon, calcium, and total alkalinity owing to precipitation of CaCO3 and consequent emission of CO2. Other pathways of CO2 exchange between the atmosphere and land organic reservoir and rock weathering may reduce the imbalances in the carbon cycle on millenial time scales.
Hydroxylamine (NH2OH) in the Baltic Sea
Authors: Gebhardt S. , Walter S. , Nausch G. , Bange H. W.
Published: April 2010

Abstract. The vertical distribution of dissolved hydroxylamine (NH2OH) was measured for the first time at 10 stations in the western, southern and central Baltic Sea during a cruise in February 2004. The distribution of dissolved NH2OH was complex due to the interplay of in-situ production in the shallow western and southern Baltic Sea and the hydrographical setting in the central Baltic Sea caused by the major North Sea water inflow event in January 2003. We conclude that nitrification might be the major source of NH2OH, whereas anaerobic ammonium oxidation (anammox) appeared to be negligible. We suggest that a "fresh" nitrifying system, in which the NH+4-oxidation rates exceeded the NO−2-oxidation rates, favoured the build-up of NH2OH.
Profiles of C- and N-trace gas production in N-saturated forest soils
Authors: Butterbach-Bahl K. , Berger U. , Brüggemann N. , Duyzer J.
Published: April 2010

Abstract. This study provides for the first time data on the stratification of NO and N2O production with soil depth under aerobic and anaerobic incubation conditions for different temperate forest sites in Germany (spruce, beech, clear-cut) and the Netherlands (Douglas fir). Results show that the NO and N2O production activity is highest in the forest floor and decreases exponentially with increasing soil depth. Under anaerobic incubation conditions NO and N2O production was in all soil layers up to 2-3 orders of magnitude higher then under aerobic incubation conditions. Furthermore, significant differences between sites could be demonstrated with respect to the magnitude or predominance of NO and N2O production. These were driven by stand properties (beech or spruce) or management (clear-cut versus control). With regard to CH4 the most striking result was the lack of CH4 uptake activity in soil samples taken from the Dutch Douglas fir site at Speulderbos, which is most likely a consequence of chronically high rates of atmospheric N deposition. In addition, we could also demonstrate that CH4 fluxes at the soil surface are obviously the result of simultaneously occurring uptake and production processes, since even under aerobic conditions a net production of CH4 in forest floor samples was found. The provided dataset will be very useful for the development and testing of process oriented models, since for the first time activity data stratified for several soil layers for N2O, NO, and CH4 production/oxidation activity for forest soils are provided.
Sources of nitrous oxide emitted from European forest soils
Authors: Ambus P. , Zechmeister-Boltenstern S. , Butterbach-Bahl K.
Published: April 2010

Abstract. Forest ecosystems may provide strong sources of nitrous oxide (N2O), which is important for atmospheric chemical and radiative properties. Nonetheless, our understanding of controls on forest N2O emissions is insufficient to narrow current flux estimates, which still are associated with great uncertainties. In this study, we have investigated the quantitative and qualitative relationships between N-cycling and N2O production in European forests in order to evaluate the importance of nitrification and denitrification for N2O production. Soil samples were collected in 11 different sites characterized by variable climatic regimes and forest types. Soil N-cycling and associated production of N2O was assessed following application of 15N-labeled nitrogen. The N2O emission varied significantly among the different forest soils, and was inversely correlated to the soil C:N ratio. The N2O emissions were significantly higher from the deciduous soils (13 ng N2O-N cm-3d-1) than from the coniferous soils (4 ng N2O-N cm-3d-1). Nitrate (NO3-) was the dominant substrate for N2O with an average contribution of 62% and exceeding 50% at least once for all sites. The average contribution of ammonium (NH4+) to N2O averaged 34%. The N2O emissions were correlated with gross nitrification activities, and as for N2O, gross nitrification was also higher in deciduous soils (3.4 μ g N cm-3d-1) than in coniferous soils (1.1 μ g N cm-3d-1). The ratio between N2O production and gross nitrification averaged 0.67% (deciduous) and 0.44% (coniferous). Our study suggests that changes in forest composition in response to land use activities and global change may have implications for regional budgets of greenhouse gases. From the study it also became clear that N2O emissions were driven by the nitrification activity, although the N2O was produced per se mainly from denitrification. Increased nitrification in response to accelerated N inputs predicted for forest ecosystems in Europe may thus lead to increased greenhouse gas emissions from forest ecosystems.
Emission of monoterpenes from European beech (Fagus sylvatica L.) as a function of light and temperature
Authors: Dindorf T. , Kuhn U. , Ganzeveld L. , Schebeske G. , Ciccioli P. , Holzke C. , Köble R. , Seufert G. , Kesselmeier J.
Published: April 2010

Abstract. Using a dynamic branch enclosure technique European beech (Fagus sylvatica L.) was characterised as a strong emitter of monoterpenes, with sabinene being the predominant compound released. Since monoterpene emission was demonstrated to be a function of light and temperature, application of light and temperature dependent algorithms resulted in reasonable agreement with the measured data. Furthermore, during high temperature periods the depression of net CO2 exchange during midday (midday depression) was accompanied by a depression of monoterpene emission on one occasion. The species dependent standard emission factor and the light and temperature regulated release of monoterpenes is of crucial importance for European VOC emissions. All measurements were performed within the framework of the ECHO project (Emission and CHemical transformation of biogenic volatile Organic compounds) during two intensive field campaigns in the summers of 2002 and 2003.
Nitrogen oxides emission from two beech forests subjected to different nitrogen loads
Authors: Kitzler B. , Zechmeister-Boltenstern S. , Holtermann C. , Skiba U. , Butterbach-Bahl K.
Published: April 2010

Abstract. We analysed nitrogen oxides (N2O, NO and NO2) and carbon dioxide (CO2) emissions from two beech forest soils close to Vienna, Austria, which were exposed to different nitrogen input from the atmosphere. The site Schottenwald (SW) received 22.6 kg N y-1 and Klausenleopoldsdorf (KL) 13.5 kg N y-1 through wet and dry deposition. Nitrogen oxide emissions from soil were measured hourly with an automatic dynamic chamber system. Daily N2O measurements were carried out by an automatic gas sampling system. Measurements of nitrous oxide (N2O) and CO2 emissions were conducted over larger areas on a biweekly (SW) or monthly (KL) basis by manually operated chambers. We used an autoregression procedure (time-series analysis) for establishing time-lagged relationships between N-oxide emissions and different climate, soil chemistry and N-deposition data. It was found that changes in soil moisture and soil temperature significantly effected CO2 and N-oxide emissions with a time lag of up to two weeks and could explain up to 95% of the temporal variations of gas emissions. Event emissions after rain or during freezing and thawing cycles contributed significantly (for NO 50%) to overall N-oxides emissions. In the two-year period of analysis the annual gaseous N2O losses at SW ranged from 0.65 to 0.77 kg N ha-1 y-1 and NO losses were 0.18 to 0.67 kg N ha-1 per vegetation period. In KL significantly lower annual N2O emissions (0.52 kg N2O-N kg ha-1 y-1) as well as considerably lower NO-losses were observed. During a three-month measurement campaign NO losses at KL were 0.02 kg, whereas in the same time period significantly more NO was emitted in SW (0.32 kg NO-N ha-1). Higher N-oxide emissions, especially NO emissions from the high N-input site (SW) indicate that atmospheric deposition had a strong impact on losses of gaseous N from our forest soils. At KL there was a strong correlation between N-deposition and N-emission over time, which shows that low N-input sites are especially responsive to increasing N-inputs.
Group additivity calculation of the standard molal thermodynamic properties of aqueous amino acids, polypeptides and unfolded proteins as a function of temperature, pressure and ionization state
Authors: Dick J. M. , LaRowe D. E. , Helgeson H. C.
Published: April 2010

Abstract. Thermodynamic calculation of the chemical speciation of proteins and the limits of protein metastability affords a quantitative understanding of the biogeochemical constraints on the distribution of proteins within and among different organisms and chemical environments. These calculations depend on accurate determination of the ionization states and standard molal Gibbs free energies of proteins as a function of temperature and pressure, which are not generally available. Hence, to aid predictions of the standard molal thermodynamic properties of ionized proteins as a function of temperature and pressure, calculated values are given below of the standard molal thermodynamic properties at 25°C and 1 bar and the revised Helgeson-Kirkham-Flowers equations of state parameters of the structural groups comprising amino acids, polypeptides and unfolded proteins. Group additivity and correlation algorithms were used to calculate contributions by ionized and neutral sidechain and backbone groups to the standard molal Gibbs free energy (Δ G°), enthalpy (Δ H°), entropy (S°), isobaric heat capacity (C°P), volume (V°) and isothermal compressibility (κ°T) of multiple reference model compounds. Experimental values of C°P, V° and κ°T at high temperature were taken from the recent literature, which ensures an internally consistent revision of the thermodynamic properties and equations of state parameters of the sidechain and backbone groups of proteins, as well as organic groups. As a result, Δ G°, Δ H°, S° C°P, V° and κ°T of unfolded proteins in any ionization state can be calculated up to T~-300°C and P~-5000 bars. In addition, the ionization states of unfolded proteins as a function of not only pH, but also temperature and pressure can be calculated by taking account of the degree of ionization of the sidechain and backbone groups present in the sequence. Calculations of this kind represent a first step in the prediction of chemical affinities of many biogeochemical reactions, as well as of the relative stabilities of proteins as a function of temperature, pressure, composition and intra- and extracellular chemical potentials of O2 and H2, NH3, H2PO4 and CO2.
Land-surface modelling in hydrological perspective
Authors: Overgaard J. , Rosbjerg D. , Butts M. B.
Published: April 2010

Abstract. A comprehensive review of energy-based land-surface modelling, as seen from a hydrological perspective, is provided. We choose to focus on energy-based approaches, because in comparison to the traditional potential evapotranspiration models, these approaches allow for a stronger link to remote sensing and atmospheric modelling. New opportunities for evaluation of distributed land-surface models through application of remote sensing are discussed in detail, and the difficulties inherent in various evaluation procedures are presented. Remote sensing is the only source of distributed data at scales that correspond to hydrological modelling scales. Finally, the dynamic coupling of hydrological and atmospheric models is explored, and the future perspectives of such efforts are discussed.
Control of phytoplankton production by physical forcing in a strongly tidal, well-mixed estuary
Authors: Desmit X. , Vanderborght J. P. , Regnier P. , Wollast R.
Published: April 2010

Abstract. A model for phytoplanktonic production in turbid, macro-tidal estuaries is proposed. It is based on the description of light-dependent algal growth, phytoplankton respiration and mortality. The model is forced by solar irradiance, mixing depth and light penetration. The extinction coefficient is directly related to the dynamics of suspended particulate matter. Model results show that the description of phytoplankton growth must operate at a time resolution sufficiently high to describe the interference between solarly and tidally driven physical forcing functions. It also demonstrates that in tidal and turbid estuaries, the short-term variation of the euphotic depth to mixing depth ratio has to be resolved for production estimates and that net positive phytoplankton production can be achieved in areas of high turbidity. The model is used to explain the typical phytoplankton decay observed along the longitudinal gradient of salinity in turbid estuaries, using the Western Scheldt as an example.
Coupled carbon-water exchange of the Amazon rain forest, II. Comparison of predicted and observed seasonal exchange of energy, CO2, isoprene and ozone at a remote site in Rondônia
Authors: Simon E. , Meixner F. X. , Rummel U. , Ganzeveld L. , Ammann C. , Kesselmeier J.
Published: April 2010

Abstract. A one-dimensional multi-layer scheme describing the coupled exchange of energy and CO2, the emission of isoprene and the dry deposition of ozone is applied to a rain forest canopy in southwest Amazonia. The model was constrained using mean diel cycles of micrometeorological quantities observed during two periods in the wet and dry season 1999. Predicted net fluxes and concentration profiles for both seasonal periods are compared to observations made at two nearby towers. The predicted day- and nighttime thermal stratification of the canopy layer is consistent with observations in dense canopies. The observed and calculated net fluxes above and H2O and CO2 concentration profiles within the canopy show a good agreement. The predicted net carbon sink decreases from 2.5 t C ha-1yr-1 for wet season conditions to 1 t C ha-1yr-1 for dry season conditions, whereas observed and predicted midday Bowen ratio increases from 0.5 to 0.8. The evaluation results confirmed a seasonal variability of leaf physiological parameters, as already suggested in the companion study. The predicted midday canopy net flux of isoprene increased from 7.1 mg C m-2h-1 during the wet season to 11.4 mg C m-2h-1 during the late dry season. Applying a constant emission capacity in all canopy layers, resulted in a disagreement between observed and simulated profiles of isoprene concentrations, suggesting a smaller emission capacity of shade adapted leaves and deposition to the soil or leaf surfaces. Assuming a strong light acclimation of emission capacity, equivalent to a 66% reduction of the standard emission factor for leaves in the lower canopy, resulted in a better agreement of observed and calculated concentration profiles and a 30% reduction of the canopy net flux. The mean calculated ozone flux for dry season condition at noontime was ≈12 nmol m-2s-1, agreeing well with observed values. The corresponding deposition velocity increased from 0.8 cm s-1 to >1.6 cm s-1 in the wet season, which can not be explained by increased stomatal uptake. Considering reasonable physiological changes in stomatal regulation, the predicted value was not larger than 1.05 cm s-1. Instead, the observed fluxes could be explained with the model by decreasing the cuticular resistance to ozone deposition from 5000 to 1000 s m-1. For doubled atmospheric CO2 concentrations the model predicts a strong increase of surface temperatures (0.1–1°C) and net assimilation (22%), a considerable shift in the energy budget (≈25% decreasing transpiration and increasing sensible heat), a slight increase of isoprene emissions (10%) and a strong decrease of ozone deposition (35%).
Nitrous oxide emissions from a beech forest floor measured by eddy covariance and soil enclosure techniques
Authors: Pihlatie M. , Rinne J. , Ambus P. , Pilegaard K. , Dorsey J. R. , Rannik Ü. , Markkanen T. , Launiainen S. , Vesala T.
Published: April 2010

Abstract. Spring time soil nitrous oxide (N2O) fluxes were measured in an old beech (Fagus sylvatica L.) forest with eddy covariance (EC) and chamber techniques. The aim was to compare the two techniques and to test whether EC can be used in the trunk-space of the forest to measure N2O. Mean N2O fluxes over the five week measurement period were 5, 10 and 16 μg N m-2h-1 from EC, automatic chamber and manual chambers, respectively. When data from one hot spot chamber was excluded the mean N2O flux of 8 μg N m-2h-1 from the soil chambers nearly equaled to the mean flux of 7 μg N m-2h-1 measured with EC from the direction were soil chambers located. Spatial variability in the N2O emissions was high in soil chamber measurements, while the EC integrated over this spatial variability and suggested that N2O emissions were uniform within the footprint area. The highest emissions measured with the EC occurred during the first week of May when the trees were leafing and when soil moisture content was at its highest. To our knowledge, this is the first study to demonstrate that the EC technique can be used to measure N2O fluxes in the trunk-space of a forest. If chamber techniques are used to estimate ecosystem level N2O emissions from forest soils, placing of the chambers should be considered carefully to cover the heterogeneity in the soil N2O emissions.
On the available evidence for the temperature dependence of soil organic carbon
Authors: Knorr W. , Prentice I. C. , House I. J. , Holland E. A.
Published: April 2010

Abstract. Two recent papers by Knorr et al. (2005) and Fang et al. (2005) provide variations of model fitting conducted in the former study. Knorr et al. (2005) suggested that more recalcitrant fractions of soil organic carbon (SOC) could be more sensitive to temperature. Fang et al. (2005) argue that this is an implication of the choice of model used. Further, Reichstein et al. (2005) point out that the evidence for a stronger temperature sensitivity of recalcitrant soil carbon mainly rests on an analysis of data provided by Kätterer et al. (1998) and argue for a different selection criterion to exclude short-term incubations. Here, we explain why the model used by Knorr et al. (2005) is the simplest multi-pool model that can fit the available data and is at the same time fully consistent with the concept of "pools", as opposed to some of the model formulations proposed by Fang et al. (2005). It is also pointed out that the criterion proposed by Reichstein et al. (2005) uses posterior information to determine inclusion of experimental data, a practice that should be avoided. We conclude that the original analysis of Knorr et al. (2005) as well as the one added by Fang et al. (2005) indicate that there is a serious possibility that recalcitrant SOC reacts more to temperature changes than labile SOC.
Pollen transport to southern Greenland: new evidences of a late spring long distance transport
Authors: Rousseau D.-D. , Schevin P. , Duzer D. , Cambon G. , Ferrier J. , Jolly D. , Poulsen U.
Published: April 2010

Abstract. New observations of long distance transport of pollen to southern Greenland are recorded during two consecutive weeks, 19 May until 1 June 2003. These new results indicate again Northeastern America as the source area of the transported pollen grains. Backward trajectories studies indicate that transport occurred twice during the first week, which corresponds to the interval of maximum pollen flux emitted in the atmosphere. This is indicated by the large percentage of exotic pollen grains identified, about 11% of the total counted including the local vegetation. Conversely, the transport observed during the second week occurred during a single day, at a time of reduced pollen emission into the atmosphere in the source area, and experienced severe wash out and thus is indicated by a lower percentage of exotic grains, 1% of the total identified ones. The trajectories modeled by the HYSPLIT application show different patterns to those previously identified in 2002. Although air volumes passing over southern Greenland at 3000 m carried out the main transport, additional transport occurred at a much lower altitude leading producing a more complicated pattern of modeling than previously considered.
Seasonal dynamics of Pseudocalanus minutus elongatus and Acartia spp. in the southern Baltic Sea (Gdańsk Deep) – numerical simulations
Authors: Dzierzbicka-Głowacka L. , Bielecka L. , Mudrak S.
Published: April 2010

Abstract. A population dynamics model for copepods is presented describing a seasonal dynamics of Pseudocalanus minutus elongatus and Acartia spp. in the southern Baltic Sea (Gdansk Deep). The copepod model was coupled with an one-dimensional physical and biological upper layer model for nutrients (total inorganic nitrogen, phosphate), phytoplankton, microzooplankton and an early juvenile of herring as predator. In this model, mesozooplankton (herbivorous copepods) has been introduced as animals having definite patterns of growth in successive stages, reproduction and mortality. The populations are represented by 6 cohorts in different developmental stages, thus assuming, that recruitment of the next generation occurs after a fixed period of adult life. The copepod model links trophic processes and population dynamics, and simulates individual growth within cohorts and the changes in biomass between cohorts. The simulations of annual cycles of copepods contain one complete generation of Pseudocalanus and two generations of Acartia in the whole column water, and indicate the importance of growth of older stages of 6 cohorts each species to total population biomass. The peaks of copepods biomass, main, at the turn of June and July for Pseudocalanus and smaller, in July for Acartia, lag that phytoplankton by ca. two mouths due to growth of cohorts in successive stages and egg production by females. The numerical results show that the investigated species could not be the main factor limiting the spring phytoplankton bloom in the Gdansk Deep, because the initial development was slow for Acartia and faster for Pseudocalanus, but main development formed after the bloom, in both cases. However, the simulated microzooplankton biomass was enough high to conclude, in our opinion, that, in this case, it was major cause limiting phytoplankton bloom. Model presented here is a next step in understanding how the population dynamics of a dominant species in the southern Baltic Sea interact with the environment.