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Nitrate pollution in aquatic ecosystems is still a major problem in Germany. Although the dynamics of various nitrate-related processes in floodplains remain partially unclear, there is a great potential to permanently remove nitrate from aquatic systems through denitrification as a relevant ecosystem function. However, the controlling factors and the dimension of the denitrification potential are still not fully understood due to the high complexity of the process, various possible explanatory variables, and the high spatial and temporal heterogeneity in floodplains. This study presents the combined assessment of potential soil denitrification rates, physical and chemical soil parameters, and hydrological parameters from six floodplains of four large German rivers, namely the Rhine, the Elbe, the Weser, and the Main. Based on multivariate statistics, results show that the denitrification potential of soil was largely unaffected by hydrology but almost solely controlled by soil pH. We hypothesized that these estimates could be further specified by incorporating the duration of average inundation, as this accounts for water saturation and nutrient supply - the major controlling variables for denitrification. Results provide evidence that the denitrification potential can only be fully exploited in frequently inundated floodplains. Thus, despite favorable soil conditions for denitrification, floodplains that have suffered from anthropogenic impacts lose their importance in nitrate removal for the river system. We conclude that pH and lateral hydrological connectivity are likely to be key factors that should be considered when estimating denitrification as an ecosystem function.

Denitrification in floodplain soils is one key process that determines the buffering capacity of riparian zones in terms of diffuse nitrate pollution. One widely used approach to measure the denitrification potential is the acetylene inhibition technique that requires fresh soil samples. We conducted experiments with air-dried soils using a time series analysis to determine the optimal rewetting period. Thus, air-dried soil samples from six different floodplain areas in Germany were rewetted for 1 to 13days to 100% water-filled pore space. We analyzed nitrogen accumulated as N2O in the top of anaerobic flasks with and without acetylene by gas chromatography after four hours of incubation. We observed an overall optimal rewetting of at least seven days for complete denitrification. We also saw the strong influence of pH and field capacity on the denitrification product ratio; in soils with pH < 7, we hardly assumed complete denitrification, whereas the treatments with pH > 7 achieved stable values after seven days of rewetting. This advanced method provides the opportunity to carry out campaigns with large soil sample sizes on the landscape scale, as samples can be stored dry until measurements are taken.

River-floodplain ecosystems are long-term sinks for certain contaminants. Fluctuations between flooding and drying are major drivers of spatial and temporal changing biogeochemical processes within floodplain soils. Even small changes of the frequency, magnitude, and timing of drying and rewetting can episodically turn those ecosystems into a source for matter.To understand such changes we investigated the effects on top soils of three hydro-geomorphological units that are typical for floodplains: depression, levee, and plateau. They show distinct characteristics regarding soil type, trace element (TE) pollution level and hydrology. In the laboratory we used an automated biogeochemical microcosm set up to simulate oxidized–reduced cycles to monitor the effects of strong fluctuating redox potential (EH), on pH, iron (Fe), manganese (Mn), sulfur (S), nitrate (NO3), dissolved organic carbon (DOC) and dissolved concentrations of arsenic (As), cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn) in the soil solution.The results indicated different responses regarding the course of EH/pH and different release patterns of TEs for each hydro-geomorphological unit separately. Both could be mainly allocated to their explicit spatial characteristics; due to differences in its buffer capacities and to the interaction between pH-value and microbial activity. In particular, we could demonstrate that a combination of several biogeochemical factors may influence TE release or retention in floodplain soils by means of generalized additive models (GAMs). Using those, Fe and S were identified as most important factors that determined the dynamics of TEs in all three studied soils; concentrations of As, Cu, Cr, Ni, and Zn increased with increasing Fe-concentrations whereas Cd, Cu, Cr, Ni, and Zn seem correspondingly to be dependent on S that went along with the course of the oxidized–reduced cycle.Still, several uncertainties between environmental changes and TE release

Auen entlang großer Flüsse puffern erhebliche Schadstoffeinträge ab. Daher werden die zulässigen Gehalte für Schwermetalle und Arsen in der Bodenlösung oftmals überschritten und innovative Flächenmanagement- und Sanierungsansätze zur Lösung dieses Problems dringend benötigt. Das erfordert ein grundlegendes Verständnis der Prozesse, die die Dynamik von Schwermetallen und Arsen unter den hochdynamischen hydrologischen Bedingungen von Auen bestimmen. Mit diesem Ziel wurden adäquate Versuche an in situ Feldmessplätzen und Lysimetern durchgeführt. Für die Lysimeteruntersuchungen wurden Bodenmonolithe (Durchmesser 30 cm, Höhe 70 cm) von einem Elbauenstandort entnommen. Lysimeter und bodenhydrologische Feldmessplätze wurden mit vergleichbarer Sensorik ausgestattet. Der Grundwasserstand innerhalb des Lysimetergefäßes ist frei wählbar, wodurch hier typische saisonale Schwankungen des Grundwasserstands (schneller Wechsel zwischen Überfl utungs- und Trockenphasen) simuliert werden konnten. Die Ausstattung der Lysimeter und Feldmessplätze gestattet es, neben der Gewinnung von Bodenlösung die Parameter zu quantifizieren, die die Dynamik von Schwermetallen bestimmen (u.a. Wasserstand, EH, pH, Temperatur). Die Untersuchungen belegen auf beiden Skalenebenen signifikante Effekte des Wasserstands, des Redoxpotenzials und des pH Werts auf die Schwermetall- und Arsen-Dynamik. Zudem wirkt die Dauer und Oszillation von Hochwasserereignissen signifi kant auf die Stoffdynamik. Es kann geschlussfolgert werden, dass kombinierte Untersuchungen auf den Skalenebenen Feld und Lysimeter ein geeignetes Werkzeug zum Verständnis der in Auenböden ablaufenden biogeochemischen Prozesse darstellen.   Floodplains along great rivers buffer considerable pollutant loads in river systems. Therefore, the tolerable levels for heavy metals and arsenic in the soil solution are often exceeded and innovative land management and remediation approaches are urgently needed to solve this problem. This require

The purpose of the study was the reconstruction of palaeoclimatic conditions of the second half of the Holocene on the results of the study of floodplain soils and qualitative composition of humus in the chronological series of buried soils in the south of the East European Plain. Database palaeogeographic studies in the steppe of East European plain zone were created