Pascal Kremer

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The role of REddyProc's friction velocity filter in determining the carbon budget of croplands

&lt;p&gt;In Poyda et al. (2019), we determined the carbon balance of six cropland sites i... more &lt;p&gt;In Poyda et al. (2019), we determined the carbon balance of six cropland sites in Southwest Germany on the basis of half-hourly net ecosystem exchange (NEE) fluxes measured with the eddy covariance (EC) method over a period of eight years from 2010 to 2017. We came up with the finding, that the sites lost on average about one ton of carbon per hectare and year. This huge loss was surprising, because the sites have been used as croplands already over several decades, and one would expect that the sites should be close to steady-state. In April 2022, we performed a soil organic carbon inventory at one of the six sites, and compared it with carbon data collected in April 2009. The soil inventory data do not give any evidence for a carbon loss in the order of one ton of carbon per hectare and year. Based on the data collected in April 2009, the carbon stock size of the plowing horizon at that time was 39.1 t C ha&lt;sup&gt;-1&lt;/sup&gt; yr&lt;sup&gt;-1&lt;/sup&gt;. The carbon stock size determined in April 2022 was in the same range and amounted 39.9 t C ha&lt;sup&gt;-1&lt;/sup&gt; yr&lt;sup&gt;-1&lt;/sup&gt; with a standard error of 1.9 t C ha&lt;sup&gt;-1&lt;/sup&gt; yr&lt;sup&gt;-1&lt;/sup&gt;, what means that these data indicate that the carbon budget of the cropland is indeed in or close to steady-state. In Poyda et al. (2019), the NEE flux data were gap-filled with the widely used software tool REddyProc. In REddyProc, the user has the option to apply or not to apply the friction velocity&amp;#160; (u*) filter before gap-filling. In Poyda et al. (2019), the u* filter was applied before gap-filling. We reprocessed the data for the year 2016, the only year with no winter time gaps, because a methanol fuel cell supplied the station with additional power, without applying the u* filter. Without applying the u* filter the cumulated annual NEE was &amp;#8209;2080 kg C ha&lt;sup&gt;-1&lt;/sup&gt;. Applying the u* filter increased the NEE by 836 kg C ha&lt;sup&gt;-1&lt;/sup&gt; to -1244 kg C ha&lt;sup&gt;-1&lt;/sup&gt;. We did the same comparison for NEE fluxes measured at the same site over the years 2019, 2020 and 2021, and we got a similar result. The application of the u* filter increased the mean NEE by +730 kg C ha&lt;sup&gt;-1&lt;/sup&gt;. The cumulated NEE was -2832 kg C ha&lt;sup&gt;-1&lt;/sup&gt; without u* filter and -2102 kg C ha&lt;sup&gt;-1&lt;/sup&gt; with u* filter. This positive bias is in the range of the EC based derived carbon loss and is able to explain a major part of the suspected positive bias. We recommend all REddyProc users to check their NEE data for this phenomena simply by processing the data once with and once without enabling the u* filter and comparing both results.&lt;/p&gt;

Auswirkungen des trockenen und heißen Sommers 2018 auf Landoberfläche-Atmosphäre-Wechselwirkungen verschiedener Ökosysteme in Deutschland

Meteorologentagung DACH 2019, 2019

Das Sommerhalbjahr 2018 brachte in weiten Teilen Mittel-, Nord- undWesteuropas Dürre- und Hitzepe... more Das Sommerhalbjahr 2018 brachte in weiten Teilen Mittel-, Nord- undWesteuropas Dürre- und Hitzeperioden mitsich, von denen Deutschland besonders betroffen war (European Drought Observatory, http://edo.jrc.ec.europa.eu).Langjährige Messnetzwerke wie TERENO (Terrestrial Environmental Observatories, teodoor.icg.kfa-juelich.de)und ICOS (European Integrated Carbon Observation System, www.icos-ri.eu, www.icos-infrastruktur.de), bietendie Gelegenheit, die Auswirkungen solcher Bedingungen auf Landoberfläche-Atmosphäre-Wechselwirkungen einschließlichGrößen des Wasser- und Kohlenstoffhaushalts zu überprüfen. Im Rahmen der hier vorgestellten Studiewerden vor allem Eddy-Kovarianz-Messungen aus verschiedenen Ökosystemen (Acker, Grünland, Wald) untersuchtund mit denen der Vorjahre verglichen. Die betrachteten Größen umfassen den Netto-CO2-Austausch(NEE), seine abgeleitete Zusammensetzung aus Photosynthese (Bruttoprimärproduktion GPP) und Atmung (RespirationTER), den fühlbaren und den latenten Wärmestrom bzw. die Verdunstung. Erste Ergebnisse zeigenein vielfältigeres Bild, als aufgrund früherer Studien zum Hitzesommer 2003 auf Basis des seinerzeit wenigerdichten Stationsnetzes zu erwarten war. Während die Wärmesummen durchgängig über- und die Niederschlägedurchgängig unterdurchschnittlich waren, blieb die CO2-Aufnahme überwiegend hinter Vergleichsjahren zurückund die Abgabe fühlbarer Wärme an die Atmosphäre war überwiegend erhöht. Verdunstung, Bruttoprimärproduktionund Atmung hingegen fielen teils höher, teils niedriger aus als üblich. Diese Größen sind in besonderem Maßesowohl positiven (Wärme und erhöhte Einstrahlung, hierdurch und durch geringere Luftfeuchte erhöhte potentielleVerdunstung vor allem an energielimitierten Standorten, z.B. im Mittelgebirge) als auch negativen (Hitzestressund Trockenheit, durch geringe Bodenfeuchte reduzierte tatsächliche Verdunstung) Auswirkungen einer trockenwarmenAnomalie ausgesetzt

The Land Atmosphere Feedback Observatory (LAFO): A novel sensor network to improve weather forecasting and climate models

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Multi-site, multi-crop measurements in the soil-vegetation-atmosphere continuum: A comprehensive dataset from two climatically contrasting regions in South West Germany for the period 2009–2018

We present a comprehensive, high-quality dataset characterizing soil-vegetation and land surface ... more We present a comprehensive, high-quality dataset characterizing soil-vegetation and land surface processes from continuous measurements conducted in two climatically contrasting study regions in southwestern Germany: the warmer and drier Kraichgau region with a mean temperature of 9.7 • C and annual precipitation of 890 mm and the cooler and wetter Swabian Alb with mean temperature 7.5 • C and annual precipitation of 1042 mm. In each region, measurements were conducted over a time period of nine cropping seasons from 2009 to 2018. The backbone of the investigation was formed by six eddy-covariance (EC) stations which measured fluxes of water, energy and carbon dioxide between the land surface and the atmosphere at half-hourly resolution. This resulted in a dataset containing measurements from a total of 54 site years containing observations with a multitude of crops, as well as considerable variation in local growing-season climates. The presented multi-site, multi-year dataset is composed of crop-related data on phenological development stages, canopy height, leaf area index, vegetative and generative biomass, and their respective carbon and nitrogen content. Time series of soil temperature and soil water content were monitored with 30 min resolution at Published by Copernicus Publications. 1154 T. K. D. Weber et al.: Multi-site, multi-crop and multi-year agro-ecosystem dataset various points in the soil profile, including ground heat fluxes. Moreover, more than 1200 soil samples were taken to study changes of carbon and nitrogen contents. The dataset is available at https://doi.org/10.20387/bonares-a0qc-46jc (Weber et al., 2021). One field in each region is still fully set up as continuous observatories for state variables and fluxes in intensively managed agricultural fields.

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Altered energy partitioning across terrestrial ecosystems in the European drought year 2018

Philosophical Transactions of the Royal Society B: Biological Sciences, 2020

Drought and heat events, such as the 2018 European drought, interact with the exchange of energy ... more Drought and heat events, such as the 2018 European drought, interact with the exchange of energy between the land surface and the atmosphere, potentially affecting albedo, sensible and latent heat fluxes, as well as CO 2 exchange. Each of these quantities may aggravate or mitigate the drought, heat, their side effects on productivity, water scarcity and global warming. We used measurements of 56 eddy covariance sites across Europe to examine the response of fluxes to extreme drought prevailing most of the year 2018 and how the response differed across various ecosystem types (forests, grasslands, croplands and peatlands). Each component of the surface radiation and energy balance observed in 2018 was compared to available data per site during a reference period 2004–2017. Based on anomalies in precipitation and reference evapotranspiration, we classified 46 sites as drought affected. These received on average 9% more solar radiation and released 32% more sensible heat to the atmosph...

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Die Zuckerrübe im Klimawandel -Eine empirisch-statistische Analyse der Auswirkungen der Witterung und des Klimas auf die Ertragsentwicklung in ausgewählten Regionen von Rheinland-Pfalz

Sugar Industry, 2012

Die Zuckerrübenerträge auf den landwirtschaftlichen Flächen der kreisfreien Städte Mainz, Worms u... more Die Zuckerrübenerträge auf den landwirtschaftlichen Flächen der kreisfreien Städte Mainz, Worms und Frankenthal aus den Jahren 1951–2003 wurden mit ausgewählten Witterungsparametern korreliert. Für das Untersuchungsgebiet konnte ein signifikanter Zusammenhang zwischen Zuckerrübenertrag und Witterung nachgewiesen werden. Um den Einfluss des Faktors Züchtung, welcher maßgeblich für den Produktionsfortschritt verantwortlich ist und somit den Zusammenhang zwischen Ertrag und Witterung bzw. Klima verfälschen würde, auszublenden, wurden die Erträge von diesem bereinigt. Die züchtungsfortschrittsbereinigten Erträge korrelieren durchweg deutlich höher mit den Witterungsparametern als die real erzielten Erträge. Vor allem die Witterungsparameter der Monate Juni bis August, während der Hauptwachstumsphase der Zuckerrübe, klären einen großen Teil der Ertragsvarianz auf. Hohe Niederschlagssummen haben einen positiven, hohe Temperatursummen hingegen einen negativen Einfluss auf den erzielten Ert...

Downscaling of agricultural market impacts under bioeconomy development to the regional and the farm level—An example of Baden‐Wuerttemberg

GCB Bioenergy, 2019

The expansion of the bioeconomy sector will increase the competition for agricultural land regard... more The expansion of the bioeconomy sector will increase the competition for agricultural land regarding biomass production. Furthermore, the particular path of the expansion of the bioeconomy is associated with great uncertainty due to the early stage of technology development and its dependency on political framework conditions. Economic models are suitable tools to identify tradeoffs in agricultural production and address the high uncertainty of the bioeconomy expansion. We present results from the farm model EFEM of four bioeconomy scenarios in order to evaluate impacts and tradeoffs of different potential bioeconomy developments and the corresponding uncertainty at regional and farm level in Baden-Wuerttemberg, Germany. The demand-side effects of the bioeconomy scenarios are based on downscaling EU level results of a separate model linkage between an agricultural sector and an energy sector model. The general model results show that the expanded use of agricultural land for the bioeconomy sector, especially for the cultivation of perennial lignocellulosic biomass crops (PBC), reduces biomass production for established value chains, especially for food and feed. The results also show differences between regions and farm types in Baden-Wuerttemberg. Fertile arable regions and arable farms profit more from the expanded use of biomass in the bioeconomy than farms that focus on cattle farming. Latter farms use the arable land to produce feed for the cattle, whereas arable farms can expand feedstock production for new value chains. Additionally, less intensive production systems like extensive grassland suffer from economic losses, whereas the competition in fertile regions further increases. Hence, if Accepted Article This article is protected by copyright. All rights reserved. the extensive production systems are to be preserved, appropriate subsidies must be provided. This emphasizes the relevance of downscaling aggregated model results to higher spatial resolution, even as far as to the decision maker (farm), to identify possible contradicting effects of the bioeconomy as well as policy implications.

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Carbon fluxes and budgets of intensive crop rotations in two regional climates of southwest Germany

Agriculture, Ecosystems & Environment, 2019

The carbon (C) sequestration potential of croplands has recently become a subject of debate becau... more The carbon (C) sequestration potential of croplands has recently become a subject of debate because it may contribute significantly to global climate change mitigation. By contrast, carbon dioxide (CO 2) emissions from German croplands have continuously increased over the past decades as a result of soil organic carbon (SOC) losses. Contrasting results, however, have been obtained on the C sink or source function of European croplands based on long-term experiments and rather recent eddy covariance (EC) measurements. Over a period of eight years (2010-2017), we measured the net ecosystem exchange (NEE) of CO 2 on six intensively managed cropland sites in two climatically different regions of southwest Germany (Kraichgau (KR) and Swabian Jura (SJ)) using the EC technique. Additionally, we measured aboveground crop biomass at three development stages and estimated management-related C inputs and exports. The inter-annual on-site variability of cumulated annual NEE was large, and neither the region nor the different sites significantly affected NEE budgets. Winter rapeseed showed the lowest CO 2 uptake capacity among the observed crops, and the mean annual NEE in the years with winter rapeseed harvest was significantly lower compared to winter wheat, silage maize and winter barley. On average over 46 site-years, annual NEE showed a distinct CO 2 uptake of −2580 kg CO 2-C ha −1 yr −1. Considering management-related C fluxes, the resulting net biome productivity (NBP) indicated a C source function of the study sites with mean annual losses of 1190 kg C ha −1 yr −1. Due to high C removals after whole plant harvests, silage maize cropping resulted in significantly higher C losses of 4280 kg C ha −1 yr −1 compared to winter rapeseed, winter wheat and winter barley, with mean annual NBPs of 1430, −188 and −1340 kg C ha −1 yr −1 , respectively. Consequently, a higher share of exported C in annual NBP resulted in higher C losses. We conclude that the recently increased importance of silage maize in crop rotations destabilizes SOC stocks, threatening the efforts in enhancing soil C sequestration. This calls for further investigations on the C sequestration potentials of more diverse crop rotations including perennial phases. nature with frequent disturbances of the soil-plant system. In Germany, 33% of the land area was covered by croplands in 2016, corresponding to 71% of the total agriculturally utilized area (Destatis, 2017). Estimated CO 2 emissions from German croplands reported under the

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Evaluating multi-year, multi-site data on the energy balance closure of eddy-covariance flux measurements at cropland sites in southwestern Germany

Biogeosciences, 2019

The energy balance of eddy-covariance (EC) measurements is typically not closed, resulting in one... more The energy balance of eddy-covariance (EC) measurements is typically not closed, resulting in one of the main challenges in evaluating and interpreting EC flux data. Energy balance closure (EBC) is crucial for validating and improving regional and global climate models. To investigate the nature of the gap in EBC for agroecosystems, we analyzed EC measurements from two climatically contrasting regions (Kraichgau-KR-and Swabian Jura-SJ) in southwestern Germany. Data were taken at six fully equipped EC sites from 2010 to 2017. The gap in EBC was quantified by ordinary linear regression, relating the energy balance ratio (EBR), calculated as the quotient of turbulent fluxes and available energy, to the residual energy term. In order to examine potential reasons for differences in EBC, we compared the EBC under varying environmental conditions and investigated a wide range of possible controls. Overall, the variation in EBC was found to be higher during winter than summer. Moreover, we determined that the site had a statistically significant effect on EBC but no significant effect on either crop or region (KR vs SJ). The time-variable footprints of all EC stations were estimated based on data measured in 2015, complimented by micro-topographic analyses along the prevailing wind direction. The smallest mean annual energy balance gap was 17 % in KR and 13 % in SJ. Highest EBRs were mostly found for winds from the prevailing wind direction. The spread of EBRs distinctly narrowed under unstable atmospheric conditions, strong buoyancy, and high friction velocities. Smaller footprint areas led to better EBC due to increasing homogeneity. Flow distortions caused by the back head of the anemometer negatively affected EBC during corresponding wind conditions.

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Evaluating multi-year, multi-site data on the energy balance closure of eddy-covariance flux measurements at cropland sites in southwest Germany

Biogeosciences Discussions, 2018

The energy balance of eddy covariance (EC) measurements is typically not closed. This so-called e... more The energy balance of eddy covariance (EC) measurements is typically not closed. This so-called energy balance closure (EBC) problem has been a long-standing issue in micrometeorology. It is a main challenge in evaluating and interpreting EC flux data. EBC is crucial for validating and improving regional and global climate models. To investigate the reasons behind EBC more closely for agro-ecosystems, we analysed EC measurements from two climatically contrasting regions (Kraichgau (KR) and Swabian Jura (SJ)) in southwest Germany. Data were taken at six fully equipped EC sites from 2010 to 2017. The gap in EBC was quantified by ordinary linear regression, by the energy balance ratio (EBR) between turbulent fluxes and available energy, and by the residual energy term. In order to examine potential reasons for differences in EBC, we compared the EBC under varying environmental conditions and investigated a wide range of possible controls. Statistical analyses were conducted for the whole data set to test the effects of different regions, years, sites and crops on EBC. We also investigated whether EBC was a function of buoyancy, friction velocity, or atmospheric stability. The timevariable footprints of all EC stations were estimated based on data measured in 2015, complemented by micro-topographic analyses along the prevailing wind direction. The lowest mean annual energy balance gap was 17 % in KR and 13 % in SJ. Highest EBRs were commonly measured for winds originating from the prevailing wind direction. The variation of EBC was higher in winter than in summer. The measurement site exerted a statistically significant effect on EBC, but not crop or region. The spread of EBR distinctly narrowed under unstable atmospheric conditions, strong buoyancy, and high friction velocities. Smaller footprint areas led to better EBC due to increasing homogeneity. Flow distortions of winds that first travelled past the back head of the anemometer affected EBC negatively.

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Einfluss des Klimawandels auf das Auftreten und den Epidemieverlauf der Cercospora beticola Blattfleckenkrankheit an Zuckerrüben in Anbauregionen in Rheinland-Pfalz und Südhessen

Sugar beet growth in a changing climate: past, present and future trends in southwest Germany

Possible impact of climate change on the occurrence and the epidemic development of cercospora leaf spot disease (Cercospora beticola sacc.) in sugar beets for Rhineland-Palatinate and the southern part of Hesse

Climatic Change, 2016

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