Top PDF Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

include pasture conversions, rotational forestry, fires, and urbanization, results in LCLUC emissions toward the low end of the range [Jain and Yang, 2005]; and (2) the estimated LCLUC effect in this study does not include the interactive effects with changes in other environmental factors that are normally included implicitly in other calcu- lations of LCLUC effects. In the short term, the conversion of naturally occurring vegetation to croplands increases litter input to the soil that increases the overall soil decom- position rate to enhance the mineralization of N available for plant productivity. In the longer term, cropland soils lose N through agricultural harvest. While this loss of N does not generally decrease agricultural productivity because of the wide use of fertilizer N application, the loss of N from soils does affect forest regrowth on former agriculture land and on reforested land. For ISAM-NC simulations the forest regrowth and C accumulation is increasingly reduced in comparison to the ISAM-C simulation in the late 20th century (Figure 2e) in regions where N is a limiting nutrient, particularly in the southeastern United States (Figure 4e). During the 1990s global net C uptake due to land cover change estimated by ISAM-NC is 0.08 PgC yr 1 less than that estimated by ISAM-C (Table 2). It is interesting to note that the LCLUC influenced changes in vegetation and soil carbon stocks over the period 1900 – 2000 for the ISAM-C and ISAM-NC cases are quite similar, although the estimated responses of soil carbon are quit different from vegetation carbon stocks in these cases (Figure 3i). With changes in LCLUC over the period 1900 – 2000, the soil carbon stocks remained approximately constant, whereas global vegeta- tion carbon stocks decreased by about 60 PgC (Figure 3i). The ISAM estimated vegetation and soil N stocks for ISAM-NC case show generally a decreasing trend with a larger decrease in vegetation than soil N (Figure 3j).
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China's terrestrial carbon balance : contributions from multiple global change factors

China's terrestrial carbon balance : contributions from multiple global change factors

[ 27 ] The effects and relative importance of each environ- mental factor on carbon balance as simulated by DLEM and TEM also substantially varied from decade to decade (Figure 1). Throughout the study period (1961 to 2005), elevated CO 2 concentration and N deposition resulted in sustained carbon gains, whereas ozone pollution resulted in sustained carbon losses. None of the other driving forces provided monotonic responses to decadal average NECB during 1961–2005. Warmer and wetter weather during the most recent 5 years resulted in a carbon sink, instead of a source over entire China. The positive role of nitrogen fer- tilizer application to NECB reached a peak in the 1980s even though the application rate kept increasing from 1961 to 2005. In contrast to the first part of the 20th century, LCLUC effects generally increased carbon storage between 1961 and 2005. However, temporal variations in large‐scale reforestation/afforestation projects occurring since the late 1970s caused the benefits of the LCLUC effect to fluctuate over this time period. In addition, the expansion of croplands during the 1990s and large‐scale cropland abandonment in response to the recently implemented “Grain‐for‐Green” policy, which is a strategy designed to shift low‐yield farmland to forest [Liu et al., 2005a, 2005b; Liu and Tian, 2010], also contribute to the fluctuations in the LCLUC effect over this time period. As a result, the decline of carbon uptake rate in the 1990s can be attributed to the relatively higher negative impact of climate changes and ozone pol- lution along with a reduced positive contribution of LCLUC during this decade.
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A Biogeochemical analysis of Mediterranean ecosystems and the response to nitrogen deposition: an insight on the carbon and nitrogen cycle in Mediterranean Ecosystems

A Biogeochemical analysis of Mediterranean ecosystems and the response to nitrogen deposition: an insight on the carbon and nitrogen cycle in Mediterranean Ecosystems

Conclusions Our findings show that CO 2 effluxes emitted by Soil, BC and Soil+BC are differently driven by T s and SWC: BC respiration is mainly controlled by superficial SWC, whereas T s and SWC -20cm mostly control Soil respiration, and T s and SWC -5cm drive Soil+BC respiration. Our results complement those of previous studies highlighting the key role of the biocrust as modulator of R s in dryland ecosystems, and indicate that the biocrust has the ability to contribute to R s responding to small water pulses in periods when deeper soil layers are inactive. Thus, our results suggest that accounting for the biocrust contribution to R s and its responses to environmental drivers is highly relevant in providing accurate estimates of this key component of the C cycle at the ecosystem level. Projections based solely on bare ground and vegetated areas have been used to predict C budgets in semiarid (Rey et al., 2011) and temperate (Kim et al., 1992) grasslands. Nevertheless, the important differences observed in CO 2 efflux between Soil and Soil+BC suggest that these estimations may underestimate soil CO 2 efflux in spatially heterogeneous Mediterranean ecosystems. Given the large areas covered by biocrust, not only in drylands, but also in temperate, alpine and polar ecosystems (Belnap and Lange 2003), taking into account soil surface covered by biocrust in future modeling studies can significantly contribute to improve our understanding of the global C cycle and our ability to project the effects of global environmental change on soil CO 2 efflux.
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The importance of terrestrial weathering changes in multimillennial recovery of the global carbon cycle: a two-dimensional perspective

The importance of terrestrial weathering changes in multimillennial recovery of the global carbon cycle: a two-dimensional perspective

Terrestrial rock weathering is a complex mechanism with many variables worth considering, many of which have a high degree of interdependence (Walker et al., 1981; Berner, 1991; Lenton and Britton, 2006). In the scheme introduced in this paper for the UVic model, we considered the im- pacts of temperature, productivity and runoff (all parameters previously examined in zero-dimensional weathering mod- els), along with lithological distribution to drive spatial vari- ability. However, many other factors which affect weather- ing rates were unaccounted for that could also be relevant in the context of a spatially explicit weathering scheme. Per- haps the most meaningful of all is the consideration of sea level change. It is highly likely that the extreme warming caused by anthropogenic emissions would result in a signifi- cant melting of the Greenland and West Antarctic ice sheets (Clark et al., 2016), not only disrupting the freshwater bal- ance in the polar oceans but also providing enough of a global rise in sea levels along with the thermal expansion of seawa- ter to flood many coastal areas. Many of the low-elevation continental shelves threatened by sea level rise are situated in weathering active, tropical regions, and therefore the inter- ruption of terrestrial weathering due to the flooding of these areas could have a more than trivial effect on global weath- ering output, thus weakening the response to global warm- ing. Note that the extensive warming could also bring about a decrease in ice sheet area, especially in Greenland, which would open up some potentially very active weathering re- gions (Kump and Alley, 1994). However, the extent of this areal reduction of ice sheet cover over a few thousand years is likely to be overwhelmingly compensated for by the area of land flooded by sea level rise.
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Life-Cycle Environmental Assessment Of A1010 And Carbon Steel Girder Bridges

Life-Cycle Environmental Assessment Of A1010 And Carbon Steel Girder Bridges

This thesis presents life-cycle environmental assessment (LCEA) for carbon and A1010 steel girder bridges. This thesis setup a quantitative life-cycle environmental impacts model to help decision makers to choose the appropriate material for steel girder bridges under different environmental conditions. The overall LCEA process is structured according to ISO 14040 and ISO 14042 which are talking about the life-cycle impact assessment of structures. The LCEA process includes the product category rules development, life-cycle inventory analysis and life- cycle impact analysis. Mote-Carlo simulation is used for inventory and impact analysis and Multi Criteria Decision Aid (MCDA) method is used to determine the weighting factors for each impact category. Three inventory categories are analyzed for inventory analysis: (1) carbon dioxide, (2) sulfur dioxide, (3) nitrogen oxides. Three environmental impact categories are analyzed for life- cycle impact analysis: (1) global warming potential (GWP), (2) acidification potential (AP), and (3) Eutrophication potential (EP). The weighting factors of three impact categories are determined according to three environmental criterions: scale, duration and reversibility. By integrating the weighting factors and life-cycle impact values a weighted life-cycle environmental impact value is obtained. This weighted life-cycle environmental impact can be used to compare the
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Accounting for carbon and nitrogen interactions in the global terrestrial ecosystem model ORCHIDEE (trunk version, rev 4999): multi-scale evaluation of gross primary production

Accounting for carbon and nitrogen interactions in the global terrestrial ecosystem model ORCHIDEE (trunk version, rev 4999): multi-scale evaluation of gross primary production

GPP but only indirectly through changes in vegetation green- ness. This conceptual limitation may explain the absence of trends in the GPP signal from MTE-GPP and restricts the domain of validity of this product to the period over which it has been trained. The aforementioned limitation may also ex- plain part of the spatial disagreement between ORCHIDEE and MTE-GPP. Nevertheless, GPP appears significantly bi- ased – against MTE-GPP – over the tropical regions, with positive biases in central Africa and negative ones in Ama- zonia. One may note that these biases do not show such con- trast in the original ORCHIDEE version without the nitrogen cycle (r3977; see Fig. 8c). Further analyses showed that the GPP biases over tropical forest regions are driven by different leaf C/N ratios across regions. However, it remains unclear what are the primary drivers of the spatial variation of the leaf C/N ratio and consequently of GPP. One of the drivers is likely to be NO x deposition, which is lower in Amazonia
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Rain Attenuation Prediction for Terrestrial Microwave Link in Bangladesh

Rain Attenuation Prediction for Terrestrial Microwave Link in Bangladesh

This paper presents the rain attenuation for terrestrial microwave link for the major cities in Bangladesh. The rain rate is maximum at Sylhet among the concerned cities, which is followed by Chittagong, Dhaka, Khulna, and Rajshahi, respectively. The difference between the ITU predicted rain rate and the measured value is about 20%. The highest rainfall amount in a particular month is found at Sylhet, which is almost double of the other cities except Chittagong. The specific attenuation of the mentioned cities remains very close up to 25 GHz, followed by significant difference for higher frequencies. The rain attenuation for longer distance is found comparatively less affected than shorter link length because of noQ- uniform rain distribution across the link. It is also found that the horizontally polarized signal is more affected by the precipitation than the circularly and vertically polarized signal. Thus, using vertical polarization in highly rain\ area like Sylhet is more economical. The fade margin of horizontally polarized signal required for Rajshahi is smaller than the fade margin for vertically polarized signal at Sylhet. In addition, the amount of fade margin required at Rajshahi to ensure the availability of 99.99 % is almost equal to that for Sylhet to ensure 99.95% availability. Thus, the more availability of terrestrial microwave link can be ensured in Rajshahi, Khulna than the higher rainy areas like Sylhet and Chittagong. The predicted attenuation given in appendix can facilitate engineers in designing terrestrial point-to-point link. All the predicted data can be used to apply frequency diversity technique for
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Environmental heterogeneity amplifies behavioural response to a temporal cycle

Environmental heterogeneity amplifies behavioural response to a temporal cycle

doi: 10.1111/oik.05579 00 1–12 Resource acquisition is integral to maximise fitness, however in many ecosystems this requires adaptation to resource abundance and distributions that seldom stay constant. For predators, prey availability can vary at fine spatial and temporal scales as a result of changes in the physical environment, and therefore selection should favour individuals that can adapt their foraging behaviour accordingly. The tidal cycle is a short, yet predictable, temporal cycle, which can influence prey availability at temporal scales relevant to movement decisions. Here, we ask whether black-legged kittiwakes Rissa tridactyla can adjust their foraging habitat selection according to the tidal cycle using GPS tracking studies at three sites of differing environmental heterogeneity. We used a hidden Markov model to classify kittiwake behaviour, and analysed habitat selection during foraging. As expected for a central-place forager, we found that kittiwakes preferred to forage nearer to the breeding colony. However, we also show that habitat selection changed over the 12.4-h tidal cycle, most likely because of changes in resource availability. Furthermore, we observed that environmental heterogeneity was associated with amplified changes in kittiwake habitat selection over the tidal cycle, potentially because environmental heterogeneity drives greater resource variation. Both predictable cycles and environmental heterogeneity are ubiquitous. Our results therefore suggest that, together, predictable cycles and environmental heterogeneity may shape predator behaviour across ecosystems.
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GOLUM-CNP v1.0: a data-driven modeling of carbon, nitrogen and phosphorus cycles in major terrestrial biomes

GOLUM-CNP v1.0: a data-driven modeling of carbon, nitrogen and phosphorus cycles in major terrestrial biomes

A growing number of data sets in recent decades have addressed many aspects of the nutrient cycles and their interactions with C dynamics. For example, Zechmeister- Boltenstern et al. (2015) synthesized the stoichiometry in different ecosystem compartments and highlighted the lati- tudinal gradients of plant, litter, and soil stoichiometry. Liu et al. (2017) evaluated soil net N mineralization among dif- ferent ecosystems at the global scale and found that net N mineralization decreased with increasing latitude. They also found that the N mineralization at higher latitudes is more sensitive to temperature changes than at lower latitudes, in- dicating potential alleviation of N limitation for plants’ pro- ductivity at boreal regions under global warming. Yang et al. (2013) provided spatially explicit estimates of different forms of soil P globally and thus made it possible to assess the P content that is available for plant uptake. These data help to improve the understanding of the global terrestrial biogeochemical cycles across large climatic and ecological gradients and can in principle be combined to provide an in- tegrated analysis of terrestrial C, N, and P cycles. Estimates of C, N, and P cycles consistent with all these data sets, how- ever, have not yet been successfully provided due to the diffi- culties in combining these data sets with different uncertain- ties and inconsistent spatiotemporal representations.
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The nitrogen cycle in the sea

The nitrogen cycle in the sea

The metabolism has been discussed of the following sources of nitrogen available to plants in sea water: mono-, di- and trimethylamine, trimethylamine oxide, urea, amino-acids, ammonia, [r]

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The impact of spatiotemporal variability in atmospheric CO2 concentration on global terrestrial carbon fluxes

The impact of spatiotemporal variability in atmospheric CO2 concentration on global terrestrial carbon fluxes

seen in the tropics for Catchment-CN are not surprising given that higher values were also found for CLM4 (Bonan et al., 2011), the parent model of Catchment-CN’s carbon code. Also note that because the MTE-GPP dataset is more reliable in regions with denser observations, and because measure- ment stations in the tropics are limited, MTE-GPP estimates in the tropics are subject to particular uncertainty (Anav et al., 2015). Outside the tropics, the model produces higher GPP values in southeastern China, southeastern Brazil and the North American boreal region but slightly lower values in western Europe. The zonal means of the simulated GPP data and the MTE-GPP product in fact agree well (Fig. 2c), though the seasonal mean of the simulated GPP is slightly more evenly distributed over the year than the MTE-GPP (Fig. 2d). The zonal means of the Catchment-CN GPP for each season agree reasonably well with the MTE-GPP prod- uct (Fig. S1 in the Supplement).
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A new synthesis for terrestrial nitrogen inputs

A new synthesis for terrestrial nitrogen inputs

Beyond the atmosphere, geobiological controls in the or- ganism factor are widely known to influence the physical and chemical weathering of rock-derived elements. This occurs though direct and indirect mechanisms mediated by plant– microbe interactions. “Rock-eating fungi” have been shown to directly accelerate the weathering of calcium (Ca 2+ )- and potassium (K + )-bearing lithologies in forests (Jongmans et al., 1997; van Scholl et al., 2008). Past work points to my- corrhizal fungi (i.e., root symbionts) in the weathering of feldspar minerals via the production of various organic acids and chelates, such as succinate, citrate, oxalate, formate, and malate (Jongmans et al., 1997; Hoffland et al., 2004; van Scholl et al., 2006, 2008). Other mechanisms include the production of siderophores, particularly via ectomycor- rhizae (ECM), which bind iron and thereby accelerate soil mineral weathering and horizon development (Taylor et al., 2009). Indirectly, biomass allocations to belowground root and hyphal networks increase reactive mineral surfaces, pro- vide C for microbial decomposition, and contribute to in- creased soil acidity. Together, these factors are thought to en- hance chemical-weathering rates by a factor of 2–10 (Drever, 1994; Andrews and Schlesinger, 2001). Such vegetation- driven weathering rates in upland ecosystems have been sug- gested to vary with atmospheric CO 2 concentrations over the
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Stable carbon isotope discrimination by rubisco enzymes relevant to the global carbon cycle

Stable carbon isotope discrimination by rubisco enzymes relevant to the global carbon cycle

1 Chapter One: Introduction Phytoplankton and their importance for the marine carbon cycle Carbon dioxide (CO 2 ) is the main form of carbon in the atmosphere, where as in the oceans the major form is bicarbonate (HCO 3 − ; Zeebe and Wolf-Gladrow 2003). In the ocean, the approximate ratio of the forms of dissolved inorganic carbon (DIC: CO 2 :HCO 3 – :CO 3 2– ) are respectively 1:100:10 (Zeebe and Wolf-Gladrow 2003). A combination of physical and biological processes, such as carbon fixation by autotrophic organisms and the production of CaCO 3 shells, influences the distribution of CO 2 in ocean surface waters. The production of CaCO 3 shells by marine organisms releases CO 2; however, calcification also sequesters DIC, as CaCO 3 particles can sink and become buried in sediments before they undergo dissolution (Jansen et al., 2002). Autotrophic organisms are able to fix inorganic carbon into particulate organic carbon (POC), which, like CaCO 3 , may be exported into the deep-ocean and sediment through sinking via the biological pump, taking carbon out of contact with the atmosphere for hundreds to millions of years, influencing atmospheric CO 2 and climate (Volk and Hoffert, 1985). The POC which is not exported to the ocean floor is oxidized back to DIC by
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The Global Terrestrial Carbon Stocks, Status of Carbon in Forest and Shrub Land of Nepal, and Relationship between Carbon Stock and Diversity

The Global Terrestrial Carbon Stocks, Status of Carbon in Forest and Shrub Land of Nepal, and Relationship between Carbon Stock and Diversity

formulate policies and facilitate ‘REDD readiness’ activities which received financing from the World Bank’s Forest Carbon Partnership Facility (FCPF). In Nepal, handover of national forest to community forest user groups (CFUGs) as community managed forests evolved in the late 1970’s through an interaction of multiplicity of factors such as deforestation, excessive dependence of the people over forest resources, political turmoil, population growth, regulatory enforcement and adjustments, and a paradigmatic shift in global development thinking. In Nepalese context, community forest has received highest priority of all the programs of Nepal’s forestry sector since 1978 and constitutes more than 18,000 community forests occupying 1.65 million ha (about 4 2.6% of total forest area). It has been renowned worldwide as a very successful community based forest management system in terms of decreasing deforestation, conservation of forest and biodiversity and supply of forest produce. The sustainable management of community forest has carbon sequestration rate of 2.79 t ha-1yr-1 (Banskota, Karki, & Skutsch, 2007) which shows greater potentiality of the carbon sink in the community forests instead of providing tangible benefits. Thus, community forest of Nepal has greater potentiality to gain monetary benefits through carbon credits from REDD + mechanism. The promotion of carbon stock, sustainable forest management and carbon enhancement are necessary for getting benefit from REDD+ for reducing emission. A broad set of management actions such as various forms of forest restoration, reforestation, afforestation, enrichment planting and another proper management practices are necessary to maximize benefits from REDD+ mechanism. While any or all of these actions may potentially form part of REDD+ programs and strategies, selection of appropriate management practices in existing national and community forests are key to minimizing negative impacts, and ensuring positive outcomes for both carbon and biodiversity. The monetary benefits from carbon
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Assigning hydrogen, carbon, and nitrogen isotope values for phytoplankton and terrestrial detritus in aquatic food web studies

Assigning hydrogen, carbon, and nitrogen isotope values for phytoplankton and terrestrial detritus in aquatic food web studies

between estimated and measured values among lakes was not significantly different from 1. For Method B, however, the intercept was significantly <0. Because the range of the data is far from the intercept, this bias is of less concern than a departure from unity in the slope. There is evidence that organic matter C:N changes during decom- position (e.g., Melillo et al. 1982), so that using the C:N value of live leaves in the watershed may present a bias in the calculation of the end member for the degraded terrestrial material in aquatic ecosystems. Because Method B was able to adequately reproduce the measured values, the introduced error is likely minimal.
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A new model of the coupled carbon, nitrogen, and phosphorus cycles in the terrestrial biosphere (QUINCY v1.0; revision 1996)

A new model of the coupled carbon, nitrogen, and phosphorus cycles in the terrestrial biosphere (QUINCY v1.0; revision 1996)

The predicted GPP and NPP across a large range of climatic and biogeographic situations are in good agree- ment with observations and so is the average of the CUE (NPP / GPP). However, the model does not reproduce the observed range in CUE in temperate and boreal forests, and the analysis of the main drivers of CUE shows that in the current model version, CUE is mostly a function of mean annual temperature. Vicca et al. (2012) suggested that this variance is associated with altered carbon partitioning and in particular increased belowground carbon allocation in re- sponse to nutrient shortage. The QUINCY v1.0 model sim- ulates an increase of the root-to-shoot ratio with response to nutrient stress. However, the effect of this change on CUE is small, as increased root allocation not only decreases biomass production through increased allocation to higher turnover tissues, but also whole-plant-mass-specific respira- tion, given the implicit model assumption that mass-specific fine root respiration is smaller than leaf-mass-specific respi- ration. This inference is consistent with detailed observations at the FLUXNET site FI-Hyy (Ilvesniemi et al., 2009; Ko- rhonen et al., 2013), where the QUINCY v1.0 model suc- cessfully simulated GPP and vegetation C storage (simu- lated/observed 7.0/6.8 kgC m −2 , Ilvesniemi et al., 2009) but substantially overestimated the NPP (simulated/observed: 536/242 gC m −2 yr −1 ). Additionally, the N uptake by the vegetation in addition to the N losses was in the same or- der of magnitude as the observations (Korhonen et al., 2013), suggesting that C partitioning rather than N availability is the source of the underestimation. Further causes of this model–data mismatch include alternative pathways of carbon partitioning not represented in the model (e.g. exudation),
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Biochemical and physiological bases for the use of carbon and nitrogen isotopes in environmental and ecological studies

Biochemical and physiological bases for the use of carbon and nitrogen isotopes in environmental and ecological studies

In 1967, Y. Miyake and E. Wada first reported that mar- ine animals incorporate dietary 15 N in preference to 14 N (Miyake and Wada 1967). Later, several seminal papers provided robust data on the 15 N-enrichment that occurs during heterotrophic processes, based on diet-controlled laboratory culture experiments (e.g., DeNiro and Epstein 1981; Minagawa and Wada 1984). This 15 N-enrichment is a reflection of biochemical processes that accompany significant isotopic fractionation. The carbon isotopic composition of an organism mainly reflects its dietary signature (DeNiro and Epstein 1978), and coordinated isotopic measurements of organisms provide a unique approach to describing the dietary habits of animals, a macroscale ecological phenomenon. Such macroscale functions in the biosphere strongly influence the Earth's surface environment via the population dynamics of eco- systems (Begon et al. 2006). In this review, we summarize our current knowledge on the theoretical background underlying this approach. To achieve this, we consider the processes sequentially, first describing the isotopic rela- tionships between substrates and autotrophs. We also present original datasets to address two related topics, compound-specific and organ-level isotopic compositions, which are helpful in achieving this goal.
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A carbon balance of Norway: terrestrial and aquatic carbon fluxes

A carbon balance of Norway: terrestrial and aquatic carbon fluxes

obtained by simply subtracting riverine OC export from NEP, drainage basin NEP is reduced by between 10% and 23%. This is lower than the DOC flux correction of NEP in peatlands (Yu 2012), similar to Lake Torneträsk in northern Sweden) (Christensen et al. 2007), and much higher than the NHL District in northern US (Buffam et al. 2011) and Öreälven catchment (Jonsson et al. 2007). NEP would be reduced even more if we had used headwater OC export, instead of coastal OC inputs. As river OC originates from soils, we might correct the soil carbon sink by subtracting riverine OC fluxes. This results in a circa 50% reduction of the soil sink in southeast and subarctic Norway, and a switch of the soil in western Norway from sink to source of carbon. The latter appears to be an unreasonable result, from which it may be concluded that either 1) NEP should not be corrected by subtracting riverine OC fluxes, 2) the estimate for the soil sink is too low, or 3) the soil sink should be at least equal to the riverine OC flux to compensate for lateral losses of OC. The latter point might be considered as a way to contribute to validation of regional scale soil carbon sink estimates. For this, better estimates of headwater OC export would be extremely useful. For better quantification and understanding of the role of northern landscapes in the carbon cycle, there is a clear need for
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Rain type classification for rain attenuation models in terrestrial link

Rain type classification for rain attenuation models in terrestrial link

3 Earth-based communication that covered data transmission within geographical areas. However, satellite communications is the communication between the Earth station and the space station. Today, commonly used wireless communication includes Global Positioning System (GPS), television broadcasting industry and Internet usage around the world. History of wireless communications has begun since World War I and World War II. The army then began to invent a system such as wireless telegraph in year 1913.

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A model using marginal efficiency of investment to analyze carbon and nitrogen interactions in terrestrial ecosystems (ACONITE Version 1)

A model using marginal efficiency of investment to analyze carbon and nitrogen interactions in terrestrial ecosystems (ACONITE Version 1)

Abstract. Carbon (C) and nitrogen (N) cycles are coupled in terrestrial ecosystems through multiple processes includ- ing photosynthesis, tissue allocation, respiration, N fixation, N uptake, and decomposition of litter and soil organic mat- ter. Capturing the constraint of N on terrestrial C uptake and storage has been a focus of the Earth System Modeling com- munity. However, there is little understanding of the trade- offs and sensitivities of allocating C and N to different tis- sues in order to optimize the productivity of plants. Here we describe a new, simple model of ecosystem C–N cycling and interactions (ACONITE), that builds on theory related to plant economics in order to predict key ecosystem properties (leaf area index, leaf C : N, N fixation, and plant C use effi- ciency) based on the outcome of assessments of the marginal change in net C or N uptake associated with a change in allo- cation of C or N to plant tissues. We simulated and evaluated steady-state ecosystem stocks and fluxes in three different forest ecosystems types (tropical evergreen, temperate decid- uous, and temperate evergreen). Leaf C : N differed among the three ecosystem types (temperate deciduous < tropical evergreen < temperature evergreen), a result that compared well to observations from a global database describing plant traits. Gross primary productivity (GPP) and net primary pro- ductivity (NPP) estimates compared well to observed fluxes at the simulation sites. Simulated N fixation at steady-state, calculated based on relative demand for N and the marginal return on C investment to acquire N, was an order of mag- nitude higher in the tropical forest than in the temperate for- est, consistent with observations. A sensitivity analysis re- vealed that parameterization of the relationship between leaf
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