No abstract

The Northeast German Lowland Observatory (TERENO-NE) was established to investigate the regional impact of climate and land use change. TERENO-NE focuses on the Northeast German lowlands, for which a high vulnerability has been determined due to increasing temperatures and decreasing amounts of precipitation projected for the coming decades. To facilitate in-depth evaluations of the effects of climate and land use changes and to separate the effects of natural and anthropogenic drivers in the region, six sites were chosen for comprehensive monitoring. In addition, at selected sites, geoarchives were used to substantially extend the instrumental records back in time. It is this combination of diverse disciplines working across different time scales that makes the observatory TERENO-NE a unique observation platform. We provide information about the general characteristics of the observatory and its six monitoring sites and present examples of interdisciplinary research activities at some of these sites. We also illustrate how monitoring improves process understanding, how remote sensing techniques are fine-tuned by the most comprehensive ground-truthing site DEMMIN, how soil erosion dynamics have evolved, how greenhouse gas monitoring of rewetted peatlands can reveal unexpected mechanisms, and how proxy data provides a long-term perspective of current ongoing changes.

No abstract

Soil water retention is frequently described by unique main drying curves measured in the laboratory on intact soil cores. In the field, however, soil pore structure changes as a result of swelling and shrinkage, wetting and drying, or tillage operations. For erosion-affected arable soils characterized by truncated profiles, water retention dynamics could be even more complex. The objective of this study was to separate shorter term hysteretic from longer term seasonal dynamics in field-measured water retention data of eroded Luvisols. Soil water content and matric potential data were from tensiometers and time-domain reflectometry sensors of six lysimeter soil monoliths from two sites. For 2012 through 2014, drying and wetting periods were identified and fitted with the van Genuchten (VG) retention function. The results confirmed that drying water retention curves were steeper than those obtained in the laboratory. Steepness increased and fitted VG parameter values of saturated water content decreased within seasons, indicating that rewetting rates successively declined after each dry-wet cycle. Drying water retention curves returned to a similar level in each spring except for soils of transferred monoliths, where drying water retention tended to increase. Results suggested that water retention dynamics of eroded Luvisols was affected by continual incorporation of subsoil material in the Ap horizon and crop management practices in addition to hysteresis and seasonal dynamics. The disentangling of dry-wet cycles from time series of soil water content and matric potential was found useful for identifying the processes responsible for water retention dynamics and could eventually help improve flow and transport models.

Agricultural soil landscapes of hummocky ground moraines are characterized by 3D spatial patterns of soil types that result from profile modifications due to the combined effect of water and tillage erosion. We hypothesize that crops reflect such soil landscape patterns by increased or reduced plant and root growth. Root development may depend on the thickness and vertical sequence of soil horizons as well as on the structural development state of these horizons at different landscape positions. The hypotheses were tested using field data of the root density (RD) and the root lengths (RL) of winter wheat using the minirhizotron technique. We compared data from plots at the CarboZALF‐D site (NE Germany) that are representing a non‐eroded reference soil profile (Albic Luvisol) at a plateau position, a strongly eroded profile at steep slope (Calcaric Regosol), and a depositional profile at the footslope (Anocolluvic Regosol). At each of these plots, three Plexiglas access tubes were installed down to approx. 1.5 m soil depth. Root measurements were carried out during the growing season of winter wheat (September 2014–August 2015) on six dates. The root length density (RLD) and the root biomass density were derived from RD values assuming a mean specific root length of 100 m g−1. Values of RD and RLD were highest for the Anocolluvic Regosol and lowest for the Calcaric Regosol. The maximum root penetration depth was lower in the Anocolluvic Regosol because of a relatively high and fluctuating water table at this landscape position. Results revealed positive relations between below‐ground (root) and above‐ground crop parameters (i.e., leaf area index, plant height, biomass, and yield) for the three soil types. Observed root densities and root lengths in soils at the three landscape positions corroborated the hypothesis that the root system was reflecting erosion‐induced soil profile modifications. Soil landscape position dependent root growth should be considered when attempting to quantify landscape scale water and element balances as well as agricultural productivity.