Alexander Gröngröft

amoA-based consensus phylogeny of ammonia-oxidizing archaea and deep sequencing of amoA genes from soils of four different geographic regions

Ammonia-oxidizing archaea (AOA) play an important role in nitrification and many studies exploit their amoA genes as marker for their diversity and abundance. We present an archaeal amoA consensus phylogeny based on all publicly available sequences (status June 2010) and provide evidence for the diversification of AOA into four previously recognized clusters and one newly identified major cluster. These clusters, for which we suggest a new nomenclature, harboured 83 AOA species-level OTU (using an inferred species threshold of 85% amoA identity). 454 pyrosequencing of amoA amplicons from 16 soils sampled in Austria, Costa Rica, Greenland and Namibia revealed that only 2% of retrieved sequences had no database representative on the species-level and represented 30–37 additional species-level OTUs. With the exception of an acidic soil from which mostly amoA amplicons of the Nitrosotalea cluster were retrieved, all soils were dominated by amoA amplicons from the Nitrososphaera cluster (also called group I.1b), indicating that the previously reported AOA from the Nitrosopumilus cluster (also called group I.1a) are absent or represent minor populations in soils. AOA richness estimates on the species level ranged from 8–83 co-existing AOAs per soil. Presence/absence of amoA OTUs (97% identity level) correlated with geographic location, indicating that besides contemporary environmental conditions also dispersal limitation across different continents and/or historical environmental conditions might influence AOA biogeography in soils.

Unravelling the effects of soil properties on water infiltration : segmented quantile regression on a large data set from arid south-west Africa

Relationships were sought between infiltrability and the properties of hundreds of surface soils (pedoderms) sampled across Namibia and western South Africa. Infiltrability was determined using a laboratory method, calibrated against a rainfall simulator, which measures the passage of a suspension of soil in distilled water through a small column packed with the same soil. Other properties determined were EC, pH, water-soluble cations and anions, ammonium acetate-extractable cations, organic C, total N, a 7-fraction particle size distribution, water-dispersible silt and clay, and clay mineral composition. Our objective was to ascertain whether general principles pertaining to infiltrability can be deduced from an analysis of a wide diversity of soils. To achieve this we compared correlation analysis, generalised linear models (GLMs), and generalised additive models (GAMs) with a segmented quantile regression approach, in which parametric regression lines were fitted to the 0.9 and 0.1 quantile values of equal subpopulations based on the x variable. Quantile regression demarcated relational envelopes enclosing four-fifths of the data points. The envelopes revealed ranges for soil properties over which infiltrability is potentially maximal (spread over a wide range) or predictably minimal (confined to small values). The r2 value of the 0.9 quantile regression line was taken as an index of reliability in being able to predict limiting effects on infiltrability associated with a variety of soil properties. Prediction of infiltration was most certain from textural properties, especially the content of water-dispersible silt (r2 = 0.96, n = 581), water-dispersible clay (0.88, n = 581), very fine sand (0.86, n = 174), and medium sand (0.84, n = 174). Chemical properties such as EC, sodium status, organic C content, and clay mineralogy were less clearly related to infiltrability than was texture. The role of fine-particle dispersion in blocking pores was highlighted by the stronger prediction in all statistical analyses provided by the water-dispersible as opposed to total content of silt and clay. All the statistical analyses revealed a probable skeletal role of medium and fine sand fractions in shaping pores and a plasmic (mobile) role of finer fractions in blocking pores. A noteworthy discovery was an apparent switch in role from skeletal to plasmic at a particle diameter of about 0.1 mm (i.e. between fine and very fine sand).

Assessment of the methane oxidation capacity of compacted soils intended for use as landfill cover materials.

The microbial oxidation of methane in engineered cover soils is considered a potent option for the mitigation of emissions from old landfills or sites containing wastes of low methane generation rates. A laboratory column study was conducted in order to derive design criteria that enable construction of an effective methane oxidising cover from the range of soils that are available to the landfill operator. Therefore, the methane oxidation capacity of different soils was assessed under simulated landfill conditions. Five sandy potential landfill top cover materials with varying contents of silt and clay were investigated with respect to methane oxidation and corresponding soil gas composition over a period of four months. The soils were compacted to 95% of their specific proctor density, resulting in bulk densities of 1.4-1.7 g cm(-3), reflecting considerably unfavourable conditions for methane oxidation due to reduced air-filled porosity. The soil water content was adjusted to field capacity, resulting in water contents ranging from 16.2 to 48.5 vol.%. The investigated inlet fluxes ranged from 25 to about 100g CH(4)m(-2)d(-1), covering the methane load proposed to allow for complete oxidation in landfill covers under Western European climate conditions and hence being suggested as a criterion for release from aftercare. The vertical distribution of gas concentrations, methane flux balances as well as stable carbon isotope studies allowed for clear process identifications. Higher inlet fluxes led to a reduction of the aerated zone, an increase in the absolute methane oxidation rate and a decline of the relative proportion of oxidized methane. For each material, a specific maximum oxidation rate was determined, which varied between 20 and 95 g CH(4)m(-2)d(-1) and which was positively correlated to the air-filled porosity of the soil. Methane oxidation efficiencies and gas profile data imply a strong link between oxidation capacity and diffusive ingress of atmospheric air. For one material with elevated levels of fine particles and high organic matter content, methane production impeded the quantification of methane oxidation potentials. Regarding the design of landfill cover layers it was concluded that the magnitude of the expected methane load, the texture and expected compaction of the cover material are key variables that need to be known. Based on these, a column study can serve as an appropriate testing system to determine the methane oxidation capacity of a soil intended as landfill cover material.

Temporal variability of soil gas composition in landfill covers.

In order to assess the temporal variability of the conditions for the microbial oxidation of methane in landfill cover soils and their driving variables, gas composition at non-emissive and strongly emissive locations (hotspots) was monitored on a seasonal, daily and hourly time scale on an old, unlined landfill in northern Germany. Our study showed that the impact of the various environmental factors varied with the mode of gas transport and with the time scale considered. At non-emissive sites, governed by diffusive gas transport, soil gas composition was subject to a pronounced seasonal variation. A high extent of aeration, low methane concentrations and a high ratio of CO(2) to CH(4) were found across the entire depth of the soil cover during the warm and dry period, whereas in the cool and moist period aeration was less and landfill gas migrated further upward. Statistically, variation in soil gas composition was best explained by the variation in soil temperature. At locations dominated by advective gas transport and showing considerable emissions of methane, this pattern was far less pronounced with only little increase in the extent of aeration during drier periods. Here, the change of barometric pressure was found to impact soil gas composition. On a daily scale under constant conditions of temperature, gas transport at both types of locations was strongly impacted by the change in soil moisture. On an hourly scale, under constant conditions of temperature and moisture, gas migration was impacted most by the change in barometric pressure. It was shown that at diffusion-dominated sites complete methane oxidation was achieved even under adverse wintry conditions, whereas at hotspots, even under favorable dry and warm conditions, aerobic biological activity can be limited to the upper crust of the soil.

Impact of Land Use Management and Soil Properties on Denitrifier Communities of Namibian Savannas

We studied potential denitrification activity and the underlying denitrifier communities in soils from a semiarid savanna ecosystem of the Kavango region in NE Namibia to help in predicting future changes in N2O emissions due to continuing changes of land use in this region. Soil type and land use (pristine, fallow, and cultivated soils) influenced physicochemical characteristics of the soils that are relevant to denitrification activity and N2O fluxes from soils and affected potential denitrification activity. Potential denitrification activity was assessed by using the denitrifier enzyme activity (DEA) assay as a proxy for denitrification activity in the soil. Soil type and land use influenced C and N contents of the soils. Pristine soils that had never been cultivated had a particularly high C content. Cultivation reduced soil C content and the abundance of denitrifiers and changed the composition of the denitrifier communities. DEA was strongly and positively correlated with soil C content and was higher in pristine than in fallow or recently cultivated soils. Soil type and the composition of both the nirK- and nirS-type denitrifier communities also influenced DEA. In contrast, other soil characteristics like N content, C:N ratio, and pH did not predict DEA. These findings suggest that due to greater availability of soil organic matter, and hence a more effective N cycling, the natural semiarid grasslands emit more N2O than managed lands in Namibia.

Spatial and temporal variability of urban soil water dynamics observed by a soil monitoring network

PurposeUrban soils’ variability in the vertical direction presumably affects hydrological parameters at the timescale. Moreover, horizontal soil alterations at small spatial scales are common in urban areas. This spatio-temporal variability and heterogeneity of soil moisture and the possible influencing factors were to be described and quantified, using data of a soil monitoring network in the city of Hamburg, Germany.Materials and methodsSoil moisture data from ten observation sites within the project HUSCO was evaluated for two different years. The sites were located within districts with different mean groundwater table depths and characteristic urban soil properties. Soil hydrological simulations with SWAP were calculated for a selected site.Results and discussionThe temporal evolution of soil water content and tension for the sites was very distinct, related to soil substrate, organic matter content, and groundwater table depth. Impacts of different vegetation rooting depths, the soil substrates’ type, and to some extent the degree of disturbance on soil water dynamics could be identified. An impact of groundwater table depth on the water content of the topsoil during low-precipitation periods could be assumed. The comparison of the results of soil hydrological simulations with empirical data indicated an overestimation of infiltration and percolation for the given soil substrates.ConclusionsWhile soil properties are mainly determinant for the long-term progression of soil hydrology, local site factors affect the short-term regime. A shallow groundwater table contributes to more constant water dynamics while the relative decrease of water during a dry phase is diminished.

Charakterisierung und Wasserhaushalt typischer Böden im Überschwemmungsbereich der unteren Mittelelbe

Das heutige Bild des Elbtales als naturnah zu bezeichnen, fallt angesichts der zahlreichen anthropogenen Eingriffe schwer. Gab es beispielsweise 1776 im Bereich der unteren Mittelelbe von Stromkilometer 475–583 noch 55 Elbinseln und nur 27 Buhnen, so hat sich dieses Verhaltnis in den vergangenen 200 Jahren vollkommen gewandelt. Fur das Jahr 1992 konnten keine Inseln, dafur aber 1680 Buhnen in diesem Flusabschnitt registriert werden (Harms 1999). Ungefahr wahrend desselben Zeitraumes ist das direkt hochwasserbeeinfluste Vordeichsareal aufgrund des Deichbaus stark zuruckgegangen. Im Jahr 1994 waren 86,4 % des ursprunglichen Vordeichslandes verschwunden (Simon 1994). Oftmals wird der verbleibende Rest der rezenten Aue mehr oder weniger stark landwirtschaftlich genutzt. Grosere, vom Menschen unberuhrte Auwaldreste sind entlang der Elbe sehr rar geworden. Unter anderem aus diesem Grund wurde von der Europaischen Union ein Wiederaufforstungsprogramm (EU-Life-Projekt, Lilje 1996) und werden z.Zt. noch vom Bundesministerium fur Bildung und Forschung (BMBF) seit August 1996 zahlreiche Projekte entlang der Elbe finanziell unterstutzt (Bornhoft u. Gruber 1998, Gruber 1999).

Influence of Oil-Contamination on N-Mineralisation in Soils

The mineralisation of soil organic matter depends on the activity of fungi and bacteria. The different organisms degrade and transform the organic matter by various processes resulting in an availability of nutrients as part natural nutrient cycles. The activity of microorganisms, and thus the intensity of mineralisation, is strongly related to the physicochemical environment (pH, temperature, water content a.o.) and the existence of appropriate substrate and energy sources. As the natural degradation of organic matter includes various hydrocarbons, microorganisms are used to purify soils and wastewater on a technical scale. Investigations of these techniques mostly focus on the degree of mineralisation caused by the activity of heterotrophic microorganisms neglecting those autotrophic organisms (e.g. nitrifying bacteria) that are not directly involved in mineralisation. The strongly increased activity of heterotrophic microorganisms in oil contaminated soil may result in a considerable change of environmental conditions for the anaerobic autotrophic nitrifying bacteria, especially with regard to oxygen supply and the availability of NH3 as electron donator for the first step of nitrification.

Charakterisierung des Wasser- und Stoffhaushalts der Böden im Projektgebiet „Deichrückverlegung an der Elbe bei Lenzen“

Um die Veranderungen der naturlichen Bodenfunktionen ‘Lebensraum fur Bodenorganismen’, ‘Standort fur hohere Pflanzen’ und ‘Speicher und Transformator fur eingetragene Stoffe’ nach einer Deichruckverlegung prognostizieren zu konnen, ist es notwendig, zunachst die Eigenschaften der unterschiedlichen Standorte des Projektgebietes zu charakterisieren. Im Zentrum der Untersuchungen stehen die physikalischen Eigenschaften (Lagerungsdichte, Wasserspannungskurve, Wasserleitfahigkeit) und der Wasserhaushalt der betroffenen Auenboden. Diese Untersuchungen werden erweitert durch Bestimmungen von Nahrstoffvorraten und in der Bodenlosung zeitabhangig vorhandenen Nahrstoffgehalten. Zusammen mit den biologischen Untersuchungen soll aus der Wechselwirkung abiotischer und biotischer Prozesse ein Prognoseverfahren fur die Auengebiete entwikkelt werden. Im folgenden werden einige der bisherigen Ergebnisse zur Ist-Zustands-Erfassung zusammengefast. Die Eigenschaften der Auenboden werden primar von der Verbreitung der bodenbildenden Substrate Auensande, Auenlehme und rezenter Auen-schlamme bestimmt, in Randlagen der Auen auch von Torfen und Mudden. Wie Transektkartierungen durch das uberwiegend eingedeichte Plangebiet gezeigt haben (Grongroft et al. 1997), kommt im Normalfall auf dem machtigen sandigen Untergrund eine im Mittel 1.5 m machtige Schicht von Auenlehm vor. Bei diesem Substrat variiert die Bodenart von sandigem Lehm zu Ton. In der heutigen Gelandemorphologie lassen sich zwar noch Rinnen und Walle erkennen, die liegenden Sandschichten weisen jedoch eine wesentlich bewegtere Oberflache auf, die im Zuge der Lehm-Sedimentation eingeebnet wurde.

Standorteigenschaften von Böden der Mittelelbe I. Einfluß von Eindeichungen auf den Nährstoffhaushalt

Naturliche Auenokosysteme verdanken ihren Artenreichtum extremen abiotischen Bedingungen im Einflusbereich der Flusse. Im Verlauf seiner Entwicklungsgeschichte hat der Flus durch Verlagerung seines Bettes und daraus folgend im Wechselspiel von Sedimentation und Erosion ein kleinraumlich variierendes Standortmosaik aus feuchten, tonverfullten Rinnen, trockenen, sandigen Uferwallen, nassen Boden am Rande von Altarmen und wechselfeuchten Ebenen aus Auenlehm geschaffen. Dieses Mosaik wird auch heute noch (in Bereichen geringer anthropogener Beeinflussung) durch den Flus umgestaltet. Mit dem Hochwasser gelangen in die nicht eingedeichten Bereiche der Aue, abhangig von der Topographie, Nahr- und Schadstoffe. Infolge von Eindeichungen und der damit ausbleibenden Uberflutungen versiegt dieser partikulare Stoffeintrag. Bodenbildende Prozesse (Entwasserung, Oxidation, Redoximorphose, Verbraunung, Verlehmung) setzen ein, Nahrstoffe konnen ausgewaschen oder dem Boden durch landwirtschaftliche Nutzung entzogen werden. Langandauerndes Ausbleiben des Stoffeintrages fuhrt demzufolge zu einer Veranderung der Nahrstoffgehalte und einer Verschiebung der Elementverhaltnisse. Die in der Tab. 1 aufgefuhrten Ergebnisse entstammen dem Bereich der unteren Mittelelbe (Stromkilometer 438 und 480). Es handelt sich um Hochflutsedimente des Jahres 1996–97 (n = 25) und um Oberbodenproben. Diese unterteilen sich einerseits in ausendeichs gelegene Auenboden (n = 43) und andererseits in eingedeichte Bereiche (n = 83). Insgesamt ist eine gute Nahrstoffversorgung bei einem fur landwirtschaftliche Zwecke geeigneten pH-Wert zu verzeichnen. Lediglich der pflanzenverfugbare Anteil des Phosphors ist auf den eingedeichten Bereichen stark erniedrigt.