Carbon and water cycles

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The importance of tree demography and root water uptake for modelling the carbon and water cycles of Amazonia

The importance of tree demography and root water uptake for modelling the carbon and water cycles of Amazonia

Correspondence to: Emilie.joetzjer@lsce.ipsl.fr Abstract.   Amazonian forest plays a crucial role in regulating the carbon and water cycles in the global climate system. 20 However, the representation of biogeochemical fluxes and forest structure in dynamic global vegetation models (DGVMs) remains challenging. This situation has considerable implications for modelling the state and dynamics of Amazonian forest. To address these limitations, we present an adaptation of the ORCHIDEE-CAN DGVM, a second-generation DGVM that explicitly models tree demography and canopy structure with an allometry-based carbon allocation scheme and accounts for hydraulic architecture in the soil-stem-leaf continuum. We use two versions of this DGVM: the first one (CAN) includes a 25
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TADA, a mechanistic model for carbon, nitrogen and water cycles in cropland and grassland ecosystems

TADA, a mechanistic model for carbon, nitrogen and water cycles in cropland and grassland ecosystems

OBJECTIVES Based on the forest model ASPECTS 1 , the developed model, named TADA ( Terrestrial Agroecosystems Dynamics Analysis ), simulates the carbon, nitrogen and water cycles for grassland and cropland ecosystems. This unidimensional model assesses the temporal evolution of the reservoirs content which are represented by the solid line boxes in the following figure.

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Modelling carbon and water cycles in a beech forest. Part II : validation of the main processes from organ to stand scale

Modelling carbon and water cycles in a beech forest. Part II : validation of the main processes from organ to stand scale

Fig. 2. Comparison between daily measurements ( 䊉) and simulations in upper branch bag (with constant nitrogen in solid line and variable nitrogen in dotted line). (a) Daily net assimilation in gC m −2 day −1 ; (b) nocturnal respiration of leaves in gC m −2 day −1 ; (c) transpiration of leaves in mm day −1 . Considering “the lower branch bag”, both net photo- synthesis and transpiration are largely underestimated by the model ( Fig. 3 a). Using measured PAR and LMA inside the bag rather than simulated PAR and LMA, re- duces in a large extent the discrepancy between model and measure, but an underestimation persists. With the aim to understand this remaining difference, we tested the possible effects on net photosynthesis of an increase from top to bottom in the canopy of (i) measured leaf nitrogen content, and (ii) leaf absorbance (according to increase in amount of chlorophyll and leaf mass per leaf area). Both are generally observed in the deciduous canopies ( Niinemets, 1995; Niinemets and Tenhunen, 1997 ) but not considered in the model CASTANEA. However, these effects cannot explain the low simu- lated photosynthesis.
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Modelling carbon and water cycles in a beech forest Part I : model description and uncertainty analysis on modelled NEE

Modelling carbon and water cycles in a beech forest Part I : model description and uncertainty analysis on modelled NEE

erotrophic respiration. 3. In situ measurements (Hesse, France, 1997) 3.1. Site characteristics The experimental plot area is located in the State forest of Hesse (East of France; 48 ◦ 40 N, 7 ◦ 05 E), and is mainly composed of beech (Fagus sylvatica L.); un- derstorey vegetation is very sparse. The elevation is 300 m and the slope is less than 2%. The studied plot covers 0.63 ha of a pole beech forest (30 years old in 1997) with a density of 3482 trees ha −1 and a domi- nant height close to 14 m. Three towers were installed: one (18 m high) is used for eddy covariance and micro- climate measurements, the two other ones (15 m high) for physiological measurements. A hut containing the data acquisition systems is located near the first tower. Sixty sub-plots are delimited for geo-statistical studies of soil and vegetation. For more details, see Granier et al. (2000a) .
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Reviews and syntheses: Carbonyl sulfide as a multi-scale tracer for carbon and water cycles

Reviews and syntheses: Carbonyl sulfide as a multi-scale tracer for carbon and water cycles

2.2.2 Grasslands OCS observations can address the need for additional stud- ies on primary productivity in grassland ecosystems. Grass- lands generally are considered to behave as carbon sinks or be carbon-neutral but appear highly sensitive to drought and heat waves and can rapidly shift from neutrality to a carbon source (Hoover and Rogers, 2016). Currently OCS grass- land studies are scarce (Fig. 3) but indicate a significant role for soils. Theoretical deposition velocities for grasses of 0.75 mm s −1 were reported by Kuhn et al. (1999), and LRU values of 2.0 were reported by Seibt et al. (2010). Whelan and Rhew (2016) made chamber-based estimates of ecosystem fluxes from a California grassland with a dis- tinct growing and non-growing season. Total ecosystem fluxes averaged −26 pmol m −2 s −1 during the wet season and −6.1 pmol m −2 s −1 during the dry season. During the wet season, simulated rainfall increased the sink strength. Light and dark flux estimates yielded similar sinks, sug- gesting either a large role for soils in the ecosystem flux or the presence of open stomata under dark conditions. Yi and Wang (2011) undertook chamber measurements over a grass lawn in subtropical China. Ecosystem fluxes of − 19.2 pmol m −2 s −1 were observed. They noted average soil fluxes of −9.9 pmol m −2 s −1 that were occasionally greater than 50 % of the total ecosystem flux. The large contribu- tion of soils to the grassland OCS flux was attributed to at- mospheric water stress on the plants that led to significant stomatal closure and reduced midday uptake by vegetation. More recently, Gerdel et al. (2017) reported daily average ecosystem-scale OCS fluxes of −28.7±9.9 pmol m −2 s −1 for a productive managed temperate grassland.
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Valorization of anaerobic digestates in agriculture : Effects on Carbon and Nitrogen biogeochimical cycles

Valorization of anaerobic digestates in agriculture : Effects on Carbon and Nitrogen biogeochimical cycles

The digestates produced from agricultural wastes have the higher fertilizer and amending potentials. The phase separation produced a solid product which can mostly be used to maintain soil C stocks and which can be further improved by composting and a liquid product that has a greater fertilizing potential. All digestates raw, solid and liquid are characterized by a residual fraction of readily biodegradable C ranging from 23 to 91% of their organic C and related to the C content of the hot water extractable fraction. The biological stability of the digestates increases in this order: liquid <raw<solid. Taking into account the dry matter (DM) content of the digestates, only the raw ones with DM>18%, the solid and the composted digestates have an interesting amending potential. The anaerobic digestates have also a high nitrogen fertilizer value, mainly related to the fraction of ammonia N initially present in the digestate; nevertheless, the high organic C/N ratios generate relatively high nitrogen organization associated with the degradation ofdigestate organic matter.
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Impacts of Degradation on Water, Energy, and Carbon Cycling of the Amazon Tropical Forests

Impacts of Degradation on Water, Energy, and Carbon Cycling of the Amazon Tropical Forests

Numerical models can be used to understand the links between changes in forest structure and light and water availability for different local plant communities and the overall impact on energy, water, and carbon fluxes between forests and the atmosphere. In the past, big‐leaf models have been modified to account for the long ‐term impacts of selectively logged tropical forests on the carbon cycle of tropical forests (e.g., Huang & Asner, 2010; Huang et al., 2008). However, big ‐leaf models generally do not represent the mechanisms that control access and availability of light and water in complex and heterogeneous forest structures (Fisher et al., 2018; D. Purves & Pacala, 2008) (but see Braghiere et al., 2019). Individual ‐based models can represent the changes in the population structure and microenvironments due to degradation (R. Fischer et al., 2016; Maréchaux & Chave, 2017), but the complexity and computational burden of these simulations often limit their application to single sites. Cohort ‐based models, such as the Ecosystem Demography (ED‐2.2) model (Longo, Knox, Medvigy, Levine, Dietze, Kim, et al., 2019; Medvigy et al., 2009), strike a balance between these end ‐members because they can efficiently represent the horizontal and vertical heterogeneity of for- ests. However, to represent the impact of heterogeneity in the energy, water, and carbon cycles, it is critical that these models are informed with realistic initial conditions that capture the landscape variability and they accurately represent the complex interactions between climate and the microenvironment variability. Previous studies using a variety of cohort ‐based models have demonstrated that cohort‐based models can realistically reproduce the microenvironment heterogeneity and the long ‐term dynamics of ecosystems, compared to both individual ‐based models (Moorcroft et al., 2001; Strigul et al., 2008) and observations (Koven et al., 2019; Longo, Knox, Levine, et al., 2019; D. W. Purves et al., 2008).
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Coupling of carbon, nitrogen and oxygen cycles in sediments from a Mediterranean lagoon : a seasonal perspective

Coupling of carbon, nitrogen and oxygen cycles in sediments from a Mediterranean lagoon : a seasonal perspective

cation and denitrification rates remained close to the lowest rates reported for coastal sediments (values around 0.021 to 0.35 mmol N m –2 d –1 for nitrification and 0.014 to 0.045 mmol N m –2 d –1 for denitrification). A steady-state diagenetic model closely represented the seasonal negative correla- tion of oxygen uptake, coupled nitrification–denitrification rates, the vertical distribution patterns of pore water oxygen and the solid phase distribution of organic carbon when nitrification inhibition by sulfide was included. Simulation adjusted to field data also highlighted the importance of oxygen penetration depth in the seasonal variation of nitrification. The modelling indicated that anaerobic metabolism was the most significant pathway (65 to 80%) during organic matter mineralization with a clear seasonal increase during warm periods. These warm periods were also characterized by the higher benthic demand of oxygen mostly used to re-oxidize the by-products from anaerobic reactions (from 57 to 82%), the other part being used for carbon mineralization.
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The response of marine carbon and nutrient cycles to ocean acidification: Large uncertainties related to phytoplankton physiological assumptions

The response of marine carbon and nutrient cycles to ocean acidification: Large uncertainties related to phytoplankton physiological assumptions

increased by over 100 Pg C and there was a 50% increase in the volume of suboxic water by 2100 [Oschlies et al., 2008]. However, estimating the impact of OA‐induced changes in rates or stoichiometry in OGCBMs is not straightforward and requires various assumptions to be made. Most clear‐cut is that OA enhances CO2 fixation, which raises C/N uptake ratios and that these changes are preserved in sinking organic matter [Riebesell et al., 2007; Oschlies et al., 2008]. On the other hand, it is plausible that the additional fixed DIC is lost as dissolved organic carbon (DOC) with no change in particulate organic matter ratios, with increased production of so‐called transparent exopolymer particles (TEPs) [Engel, 2002] able to enhance CEX by aggregation and coagulation of DOC [Riebesell et al., 2007; Arrigo, 2007]. In this case, spatial variability in bacterial limita- tion will be important in governing the turnover of any additional DOC [Thingstad et al., 2008] and the impact on CEX. Additionally, if additional DOC is subducted away from the sea surface, then the depth of remineralization to DIC will dictate its influence on air‐sea CO2 exchange. Regardless of the fate of the extra DIC fixation, assump- tions made about the transport into the phytoplankton cell (termed “uptake” hereafter) of other nutrients (P, Si and Fe) might also be important. If uptake of P, Si and Fe were unchanged, then C/X ratios (where X is either P, Si, or Fe) of organic matter would rise alongside C/N ratios, with N/ X ratios unchanged. Conversely, if uptake of P, Si and Fe were upregulated in response to OA, C/X ratios would remain unchanged in organic matter and decreasing N/X ratios would accompany the change in C/N ratios. Finally, modifications to N/P ratios could result from changes to the uptake of N or P. Assessing these factors requires multinutrient OGCBMs that are able to decouple the cycles of N and P from C in dissolved/particulate organic and inorganic pools, with most global OGCBMs unable to respond to these questions [e.g., Anderson and Mitra, 2010].
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Simulating the carbon cycle in a high latitude shelf sea (North Sea) — evidence for decoupled carbon and nutrient cycles

Simulating the carbon cycle in a high latitude shelf sea (North Sea) — evidence for decoupled carbon and nutrient cycles

balanced by an export of carbon into the deep waters of the North Atlantic, confirm- ing observations suggesting the efficient removal of CO 2 from the atmosphere via the continental shelf pump mechanism. The simulated net community production (NCP) and net primary production (NPP) reveal the biological controls of this transport: de- spite the higher NPP in the southern North Sea, NCP, i.e. net carbon fixation, and the NCP/NPP ratio are small because of high remineralization of organic matter in the continuously mixed water column. In contrast, in the surface layers of the northern North Sea, NCP, net carbon fixation and the NCP/NPP ratio are high because of the high export of organic matter into the deeper layer of the seasonally stratified system, preventing organic matter remineralization in the surface layer. The implementation of overflow production releasing semi–labile dissolved organic carbon under nutrient limited conditions enables the model to reproduce the observed pCO 2 and DIC draw-
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Coupling of carbon, nitrogen and oxygen cycles in sediments from a Mediterranean lagoon: a seasonal perspective

Coupling of carbon, nitrogen and oxygen cycles in sediments from a Mediterranean lagoon: a seasonal perspective

ABSTRACT: Experimental data and simulations were used to investigate the seasonal coupling between carbon, nitrogen and oxygen cycles in marine sediments from a eutrophic shallow lagoon in the Mediterranean Sea area. A negative seasonal correlation was observed between oxygen con- sumption and coupled nitrification–denitrification rates in surface sediments. Elevated values of oxy- gen consumption rates were reached during warm periods (up to 87.7 mmol m –2 d –1 ) whereas nitrifi- cation and denitrification rates remained close to the lowest rates reported for coastal sediments (values around 0.021 to 0.35 mmol N m –2 d –1 for nitrification and 0.014 to 0.045 mmol N m –2 d –1 for denitrification). A steady-state diagenetic model closely represented the seasonal negative correla- tion of oxygen uptake, coupled nitrification–denitrification rates, the vertical distribution patterns of pore water oxygen and the solid phase distribution of organic carbon when nitrification inhibition by sulfide was included. Simulation adjusted to field data also highlighted the importance of oxygen penetration depth in the seasonal variation of nitrification. The modelling indicated that anaerobic metabolism was the most significant pathway (65 to 80%) during organic matter mineralization with a clear seasonal increase during warm periods. These warm periods were also characterized by the higher benthic demand of oxygen mostly used to re-oxidize the by-products from anaerobic reactions (from 57 to 82%), the other part being used for carbon mineralization.
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Applications of stable water and carbon isotopes in watershed research: Weathering, carbon cycling, and water balances

Applications of stable water and carbon isotopes in watershed research: Weathering, carbon cycling, and water balances

Research on rivers has traditionally involved concentration and flux measurements to better understand weathering, transport and cycling of materials from land to ocean. As a relatively new tool, stable isotope measurements complement this type of research by providing an extra label to characterize origin of the transported material, its transfer mechanisms, and natural versus anthropogenic influences. These new stable isotope techniques are scalable across a wide range of geographic and temporal scales. This review focuses on three aspects of hydrological and geochemical river research that are of prime importance to the policy issues of climate change and include utilization of stable water and carbon isotopes: (i) silicate and carbonate weathering in river basins, (ii) the riverine carbon and oxygen cycles, and (iii) water balances at the catchment scale. Most studies at watershed scales currently focus on water and carbon balances but future applications hold promise to integrate sediment fluxes and turnover, ground and surface water interactions, as well as the understanding of contaminant sources and their effects in river systems.
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Seasonal dynamics of atmospheric and river inputs of black carbon, and impacts on biogeochemical cycles in Halong Bay, Vietnam

Seasonal dynamics of atmospheric and river inputs of black carbon, and impacts on biogeochemical cycles in Halong Bay, Vietnam

were blank-corrected by subtracting the machine blank obtained at the beginning of each sample run. Samples for DBC analyses were collected and prepared according to the solid-phase extraction (SPE) method (Dittmar et al., 2008). This method allows concentrating DOM molecules (including DBC) in salt-free methanol extracts. Briefly, for each sampling occasion, 500 mL of SML and 500 mL of ULW samples were filtered through pre-combusted (450°C overnight) 47-mm diameter GF/F filters, directly into acid-washed polycarbonate bottles and immediately acidified with hydrochloric acid 37% to reach a pH of 2. The bottles were stored in a cool box filled with ice (< 4°C) until SPE procedure in the laboratory. Solid phase extractable DOM is referred to as SPE-DOM in the following. Cartridges filled with Varian Bond Elut sorbents (PPL) were used to concentrate DOM. PPL sorbent consists of a styrene divinyl copolymer and is made for the retention of highly polar to non-polar substances from large volumes of water. The cartridges were rinsed with methanol (HPLC grade) immediately before use. The filtered and acidified samples were gravity-processed through the cartridges at a flow rate of < 15 mL min –1 . Immediately after extraction, remaining
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Coupling of carbon, nitrogen and oxygen cycles in sediments from a Mediterranean lagoon: a seasonal perspective

Coupling of carbon, nitrogen and oxygen cycles in sediments from a Mediterranean lagoon: a seasonal perspective

cation and denitrification rates remained close to the lowest rates reported for coastal sediments (values around 0.021 to 0.35 mmol N m –2 d –1 for nitrification and 0.014 to 0.045 mmol N m –2 d –1 for denitrification). A steady-state diagenetic model closely represented the seasonal negative correla- tion of oxygen uptake, coupled nitrification–denitrification rates, the vertical distribution patterns of pore water oxygen and the solid phase distribution of organic carbon when nitrification inhibition by sulfide was included. Simulation adjusted to field data also highlighted the importance of oxygen penetration depth in the seasonal variation of nitrification. The modelling indicated that anaerobic metabolism was the most significant pathway (65 to 80%) during organic matter mineralization with a clear seasonal increase during warm periods. These warm periods were also characterized by the higher benthic demand of oxygen mostly used to re-oxidize the by-products from anaerobic reactions (from 57 to 82%), the other part being used for carbon mineralization.
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Endogenous Retirement and Monetary Cycles

Endogenous Retirement and Monetary Cycles

vidual life span. In case of uncertain life span, an increase in longevity can reduce the age at retirement. The effect of an increase of the elasticity of inter-temporal substitution on retirement is negative. Indeed, at the monetary steady state where the interest rate is zero, the elasticity does not influence the individual consump- tion growth rate. It only modifies the arbitrage between consumption and leisure in favor of the second one, which ultimately means less human wealth and less consumption. The effect of the elasticity on aggregate wealth is the opposite of the effect of the age at retirement on wealth.
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Cycles, derived categories, and rationality

Cycles, derived categories, and rationality

rdim(X) ≤ max{dim(Y ), d}. It then follows that to study rcodim(X) we should focus on A X/Y and its representability. 10 8.1. Motivic measures and a rational defect. Let us quickly recall some general motivation for Question 8.0.4 . Bondal, Larsen, and Lunts [ 49 ] defined the Grothendieck ring P T (k) of (dg enhanced) triangulated k-linear categories, by considering the free Z-module generated by equivalence classes of such categories, denoted by I(−), and introducing a scissor-type relation: I(T) = I(A) + I(B) if there is a semiorthogonal decomposition T = hA, Bi. The product of this ring is a convolution product, in such a way that the product of I(D b (X)) and I(D b (Y )) coincides with I(D b (X × Y )). See [ 49 ] for more details. We notice that the unit e of P T (k) is the class of D b (k) and that if T is generated by r k-exceptional objects, then I(T) = re.
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Innovation Cycles and Urban Dynamics

Innovation Cycles and Urban Dynamics

Commonplace widespread technologies (diffusion stage): ␤ = 1 Mature technologies (decay or substitution stage): ␤ < 1 This model was applied to three urban systems. Our first test of the theory is based on the distribution of the labor force in 276 French urban areas (the largest “aires urbaines”, 1 which are roughly equivalent to the American Metropolitan Stan- dard Areas). Inevitably, the official nomenclatures used for economic activity (32 categories of the NES – Nomenclature Economique de Synth`ese) do not always correspond exactly to historical innovation cycles: they were not designed for this purpose, even if they are revised from time to time to provide a more apt descrip- tion of current economic activities (Desrosi`eres, 1993). Because of the somewhat arbitrary aggregation of activity sectors that they give, it would be hazardous to interpret the value of scaling parameters in absolute terms. Moreover, it is obvious that the content of activities that we classify as “mature” at the level of aggregated economic sectors can be just as up-to-date, in terms of technological and managerial processes, as the diffusing or even leading activities, at the level of individual firms. What the model seeks to express is an aggregated spatio-temporal view of the whole system of cities and over very long periods.
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Carbon emissions and business cycles

Carbon emissions and business cycles

Carbon Emissions and Business Cycles January 8, 2019 Abstract Carbon emissions and real GDP are strongly correlated over the U.S. business cycle. This relationship suggests that macroeconomic shocks inducing cyclical fluctuations in output should also account for the cyclical behavior of emissions and motivates our analysis. We begin by expanding the set of technology shocks in a popular emissions- augmented dynamic stochastic general equilibrium model from the literature, and show that the model generates positive emissions-GDP comovements to each shock through distinct channels. We then estimate the emissions’ response to empirically identified technology shocks using structural vector autoregressions (SVARs). Using the SVARs, we also rank the shocks in terms of explaining the emissions’ forecast error variation. While emissions tend to rise gradually after most shocks, consistent with their theoret- ical counterparts, the impulse responses are not statistically significant. Unanticipated technology shocks account for less than 10 percent of the variation in emissions. By contrast, anticipated investment technology shocks account for 25 percent of the varia- tion. Government spending and monetary policy shocks account for less than 1 percent. Importantly, close to two thirds of the variation in emissions appears to be due to a structural shock not yet identified in the literature.
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Exploring the water and carbon monoxide shell around Betelgeuse with VLTI/AMBER

Exploring the water and carbon monoxide shell around Betelgeuse with VLTI/AMBER

u (m) v (m) Fig. 1. Left: Fit of the continuum squared visibilities. The black points represent the data. The red continous line is the best fit uniform disk model and the green dashed line is the best fit limb-darkened disk model. Right: (u, v) coverage of our AMBER data for the first and second lobes. The blue dashed line represents the average position angle of 73 ◦ .

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Molecular dynamics study of ionomer and water adsorption at carbon support materials

Molecular dynamics study of ionomer and water adsorption at carbon support materials

Molecular dynamics simulations were applied to unravel the microscopic structure of Nafion ionomer and water adsorbed at graphitized carbon sheets. The considered molecular model resembles microscopic interfaces at which current generation proceeds in catalyst layers of polymer electrolyte fuel cells. The analysis of equilibrated interfacial configurations shows that Nafion ionomer forms a thin adhesive film on the graphite sheet. At low water content, water molecules form clusters around sulfonic acid groups. At high water content, a continuous water film wets the ionomer surface. The structural analysis of this model did not provide any evidence for interconnected water clusters existing inside the ionomer film, which implies that hydronium ion transport will occur mainly along hydrated ionomer surfaces.
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