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  • 1
    Language: English
    In: Biogeosciences, Jan 10, 2018, Vol.15(1), p.187
    Description: Modeling net ecosystem exchange (NEE) at the regional scale with land surface models (LSMs) is relevant for the estimation of regional carbon balances, but studies on it are very limited. Furthermore, it is essential to better understand and quantify the uncertainty of LSMs in order to improve them. An important key variable in this respect is the prognostic leaf area index (LAI), which is very sensitive to forcing data and strongly affects the modeled NEE. We applied the Community Land Model (CLM4.5-BGC) to the Rur catchment in western Germany and compared estimated and default ecological key parameters for modeling carbon fluxes and LAI. The parameter estimates were previously estimated with the Markov chain Monte Carlo (MCMC) approach DREAM.sub.(zs) for four of the most widespread plant functional types in the catchment. It was found that the catchment-scale annual NEE was strongly positive with default parameter values but negative (and closer to observations) with the estimated values. Thus, the estimation of CLM parameters with local NEE observations can be highly relevant when determining regional carbon balances. To obtain a more comprehensive picture of model uncertainty, CLM ensembles were set up with perturbed meteorological input and uncertain initial states in addition to uncertain parameters. C.sub.3 grass and C.sub.3 crops were particularly sensitive to the perturbed meteorological input, which resulted in a strong increase in the standard deviation of the annual NEE sum (#xCF;#x83;.sub. #xE2;#x88;#x91; NEE) for the different ensemble members from #xE2;#x88;#xBC; 2 to 3 g C m.sup.-2 yr.sup.-1 (with uncertain parameters) to #xE2;#x88;#xBC; 45 g C m.sup.-2 yr.sup.-1 (C.sub.3 grass) and #xE2;#x88;#xBC; 75 g C m.sup.-2 yr.sup.-1 (C.sub.3 crops) with perturbed forcings. This increase in uncertainty is related to the impact of the meteorological forcings on leaf onset and senescence, and enhanced/reduced drought stress related to perturbation of precipitation. The NEE uncertainty for the forest plant functional type (PFT) was considerably lower (#xCF;#x83;.sub. #xE2;#x88;#x91; NEE #xE2;#x88;#xBC; 4.0-13.5 g C m.sup.-2 yr.sup.-1 with perturbed parameters, meteorological forcings and initial states). We conclude that LAI and NEE uncertainty with CLM is clearly underestimated if uncertain meteorological forcings and initial states are not taken into account.
    Keywords: Carbon Cycle – Environmental Aspects ; Terrestrial Ecosystems – Models
    ISSN: 1726-4170
    ISSN: 17264189
    E-ISSN: 17264189
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  • 2
    Language: English
    In: Biogeosciences, March 9, 2017, Vol.14(5), p.1153
    Description: Phosphorus (P) species in colloidal and dissolved soil fractions may have different distributions. To understand which P species are potentially involved, we obtained water extracts from the surface soils of a gradient from Cambisol, Stagnic Cambisol to Stagnosol from temperate grassland in Germany. These were filtered to 450 nm, and divided into three procedurally defined fractions: small-sized colloids (20-450 nm), nano-sized colloids (1-20 nm), and dissolved P ( 1 nm), using asymmetric flow field-flow fractionation (AF4), as well as filtration for solution .sup.31 P-nuclear magnetic resonance (NMR) spectroscopy. The total P of soil water extracts increased in the order Cambisol Stagnic Cambisol Stagnic Cambisol Stagnosol. Across all soil types, elevated proportions of inositol hexakisphosphate (IHP) species (e.g., myo-, scyllo- and D-chiro-IHP) were associated with soil mineral particles (i.e., bulk soil and small-sized soil colloids), whereas other orthophosphate monoesters and phosphonates were found in the dissolved P fraction. We conclude that P species composition varies among colloidal and dissolved soil fractions after characterization using advanced techniques, i.e., AF4 and NMR. Furthermore, stagnic properties affect P speciation and availability by potentially releasing dissolved inorganic and ester-bound P forms as well as nano-sized organic matter-Fe/Al-P colloids.
    Keywords: Nuclear Magnetic Resonance ; Nuclear Magnetic Resonance Spectroscopy
    ISSN: 1726-4170
    ISSN: 17264189
    E-ISSN: 17264189
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  • 3
    Language: English
    In: Biogeosciences, March 19, 2019, Vol.16(6), p.1111
    Description: pFor an assessment of the roles of soil and vegetation in the climate system, a further understanding of the flux components of H.sub.2 O and CO.sub.2 (e.g., transpiration, soil respiration) and their interaction with physical conditions and physiological functioning of plants and ecosystems is necessary. To obtain magnitudes of these flux components, we applied source partitioning approaches after Scanlon and Kustas (2010; SK10) and after Thomas et al. (2008; TH08) to high-frequency eddy covariance measurements of 12 study sites covering different ecosystems (croplands, grasslands, and forests) in different climatic regions. Both partitioning methods are based on higher-order statistics of the H.sub.2 O and CO.sub.2 fluctuations, but proceed differently to estimate transpiration, evaporation, net primary production, and soil respiration. We compared and evaluated the partitioning results obtained with SK10 and TH08, including slight modifications of both approaches. Further, we analyzed the interrelations among the performance of the partitioning methods, turbulence characteristics, and site characteristics (such as plant cover type, canopy height, canopy density, and measurement height). We were able to identify characteristics of a data set that are prerequisites for adequate performance of the partitioning methods. SK10 had the tendency to overestimate and TH08 to underestimate soil flux components. For both methods, the partitioning of CO.sub.2 fluxes was less robust than for H.sub.2 O fluxes. Results derived with SK10 showed relatively large dependencies on estimated water use efficiency (WUE) at the leaf level, which is a required input. Measurements of outgoing longwave radiation used for the estimation of foliage temperature (used in WUE) could slightly increase the quality of the partitioning results. A modification of the TH08 approach, by applying a cluster analysis for the conditional sampling of respiration-evaporation events, performed satisfactorily, but did not result in significant advantages compared to the original method versions developed by Thomas et al. (2008). The performance of each partitioning approach was dependent on meteorological conditions, plant development, canopy height, canopy density, and measurement height. Foremost, the performance of SK10 correlated negatively with the ratio between measurement height and canopy height. The performance of TH08 was more dependent on canopy height and leaf area index. In general, all site characteristics that increase dissimilarities between scalars appeared to enhance partitioning performance for SK10 and TH08.
    Keywords: Turbulence (Fluid Dynamics) – Physiological Aspects ; Turbulence (Fluid Dynamics) – Analysis ; Ecosystems – Physiological Aspects ; Ecosystems – Analysis
    ISSN: 1726-4170
    E-ISSN: 17264189
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