Northeast German Lowlands Research Articles

Tiefer See – a key site for lake sediment research in NE Germany

Abstract. Tiefer See formed in a subglacial gully system at the end of the last glaciation in the northeast German lowlands. The lake has been selected as a focus site within the TERENO (Terrestrial Environmental Observatory) NE German observatory because it forms annual laminations (calcite varves) providing detailed information of past climate and environmental changes. Our research integrates palaeolimnology and limnology by combining high-resolution analyses of the sediment record with a comprehensive monitoring of the lake and its sedimentation processes since 2012. This allows evaluation of the observed effects of ongoing climate change in the context of the long-term history of the lake. The lacustrine sediment profile comprises the last 13 000 years and is dated by a multiple dating approach. The sedimentation is dominated by biochemical calcite formation and algal blooms. Detrital material from the catchment forms only a minor component even during times of increased human impact. Repeated changes between well-varved, poorly varved and homogeneous sediment intervals indicate that sedimentation processes in the lake are particularly sensitive to changes in lake circulation. The research at Tiefer See is embedded in ICLEA (https://www.iclea.de, last access: 2 August 2019) and BaltRap (https://www.io-warnemuende.de/projekt/167/baltrap.html, last access: 2 August 2019) projects.

Interdisciplinary Geo‐ecological Research across Time Scales in the Northeast German Lowland Observatory (TERENO‐NE)

Core Ideas TERENO‐NE investigates the regional impact of global change. We facilitate interdisciplinary geo‐ecological research. Our data sets comprise monitoring data and geoarchives. We are able to bridge time scales from minutes to millennia. 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.

High-resolution mapping of ice-marginal landforms in the Barnim region, northeast Germany

Despite more than a 100-year-long research history, timing and position of the last glacial ice margins in the northeast German lowland are still up for debate. The Barnim region, a till plain in the northeast German young morainic landscape, is traversed by the contradictorily discussed Frankfurt ice marginal position. It is located in a key position to reassess the current state of research with help of a geographic information system (GIS) and field methods.A qualitative geomorphological analysis of a high resolution LiDAR digital elevation model (DEM) in the Barnim area uncovers a variety of landforms that were previously not described. The most prominent discovery is a set of about 10 lobe-shaped ridges in the middle Barnim area. Fieldwork and geophysical measurements were carried out to investigate the structure of the ridges. The ridges are 1000–1500m in length and their widths vary from 10 to 15km. They are raised some 6–10m from their surroundings. The Frankfurt ice marginal position can only partially be traced in the DEM. Sedimentological and geophysical investigations indicate that the ridges are composed of glacial till that was deposited on glaciofluvial sediments. Their formation most probably took place during the ice retreat of the Brandenburg phase (W1B) and hence represents the W1F phase in the region.

Groundwater–surface water interactions in a North German lowland floodplain – Implications for the river discharge dynamics and riparian water balance

Water balance and groundwater dynamics of a floodplain catchment in the Northeast German lowlands are investigated with consideration of the variable interactions between the riparian groundwater and surface water. Based on experimental and numerical investigations, evidence is given for temporally and spatially variable exchange fluxes between groundwater and surface water, which have significant impact on the riparian water balance and groundwater recharge. A coupled soil water balance–groundwater model is used for the quantification of exchange fluxes across the groundwater–surface water interface and the groundwater recharge for nested catchments in a typical floodplain representative for the Central European lowland catchments. Simulation results indicate substantial exchange fluxes between groundwater and the river, which are subjected to intensive spatial and temporal variability. The intensities and also the directions of exchange fluxes in particular stream reaches are characterised by transient alterations. Groundwater–surface water interactions are found to control the groundwater recharge dynamics in the floodplain and outweigh the influence of vertical percolation and root water uptake. Although groundwater contributions from this river stretch represent only 1% of the annual total discharge within the river its impact is much higher during low flow conditions in summer when ca. 30% of the river runoff which is generated in the catchment is originated by groundwater discharge from the riparian zone along this river stretch. The results of this study show that groundwater–surface water interactions within the investigated riparian floodplain are far too complex for the traditional classification concept distinguishing between loosing and gaining sections. The temporally variable impact of groundwater–surface water interactions furthermore highlights the necessity to consider seasonal effects when assessing the significance floodplain processes and functions.

Short‐Lived Tree Species and Their Role as Indicators for Plant Diversity in the Restoration of Natural Forests

Abstract Anthropogenic forests, particularly conifer monocultures, today constitute a large proportion of Central European woodland. Conversion of such forest stands into abundantly structured mixed‐species woodland is within the focus of ecosystem restoration and is considered to affect forest biodiversity. Short‐lived tree species play an important role in such conversion processes and may serve as focal species. However, not much is known about their relationship with forest biodiversity. In this study, the short‐lived tree species, European mountain ash (Sorbus aucuparia L.), European white birch (Betula pendula Roth), Downy birch (B. pubescens Ehrh.), and Glossy buckthorn (Frangula alnus P. Mill.), commonly occurring throughout Central Europe, are investigated with regard to their relationship with plant diversity. The focus is on their occurrences in Scots pine (Pinus sylvestris L.)–dominated forests in the Northeast German lowlands. A significant increase in vascular plant diversity is revealed in stands with the selected species’ presence, in comparison to stands without them. Increase in plant species numbers is highest where the respective species occurs in the tree and/or shrub layer, compared with their presence only in the herb layer. For bryophyte species, there is a less strong inverse relationship. An analysis of different species groups, such as threatened, woody, and typical forest species of higher plants, reveals no decrease in species numbers in these groups if short‐lived tree species are present. It is concluded that short‐lived tree species can be indicators for plant diversity assessment within forest restoration processes. As to causal explanations, effects of differing site conditions, assessed by use of Ellenberg indicator values, are discussed as well as possible active effects of the tree species changing their environment.

The derivation of grassland vegetation types on the basis of site and land use characteristics

This study derives grassland communities from site, climate and land use characteristics, allowing yield estimation within the framework of model scenarios. Based on the dominant species, about 450 relevés, primarily of extensively used grassland from four regions of the North-East German lowlands, were classified into vegetation types using a cluster analysis. These types were then reclassified to known phytosociological communities. The relationship between the vegetational composition and the abiotic explanatory variables were verified by a discriminant analysis. The water supply level proved to be the most important factor influencing grassland vegetation. The impact of historical land use (especially the persistence of formerly sown species) reduced prognostic quality.

Application of multiple regression and neural network approaches for landscape-scale assessment of soil microbial biomass

Previous soil surveys across the north-east German lowland have reported significant correlations of soil microbial biomass (SMB) contents and organic carbon and total nitrogen contents as well as texture. Using these data sets obtained from 89 arable sites along a regional-scale transect, a linear full-factorial regression model and a neural network model were constructed and evaluated for landscape-scale assessment of SMB. The validation by means of an additional data set consisting of 30 long-term soil observation sites located in the federal state of Brandenburg was within a confidence range of 95%. Using existing models from other regions with our data sets resulted in underestimation of SMB, while using data sets from another region with our model led to overestimation of SMB. It was concluded that a linear full-factorial regression model approach, as well as neural network modelling are promising tools for the prediction of SMB at the landscape scale but need to be validated for the respective region.

Bodenhydrologische untersuchungen im Nordostdeutschen tiefland als grundlage des vorsorgenden bodenschutzes: Investigations in hydrological properties of soils in North-East Germany as a basis of soil conservation

Methodological developments and findings are presented on the quantification of the water balance of soils in the North-East German Lowland. The unsaturated hydraulic conductivity and the water retention function of representative soils are measured by means of the evaporation method. From these findings typical hydraulic conductivity and water retention functions for soil types of different parent material and hydromorphy were derived, and differentiated for arable, grassland and forest locations. Soil hydrological field measurements were used to quantify the dynamics of soil water storage and deep seepage as well as of solute transport under typical soil, climate, land use and management conditions. The effect of soil, land use and management on discharge and nitrate leaching are discussed.

Application of Two Forest Succession Models at Sites in North East Germany

In order to simulate potential impacts of climate change on forests, two succession models were applied to sites in the north east German lowlands. The models, which had been developed for alpine (FORECE) and boreal (FORSKA) forests differ from each other in the way they represent tree growth processes and the impact of environmental factors on establishment and growth. Both models were adjusted and compared with each other at sites that are situated along an ecological gradient from maritime to subcontinental climate. These sites are extending the former environmental space of model application towards water-limited conditions, which under a predicted climatic change may have increasing importance for European forests. First results showed that FORECE was unrealistically sensitive to changes in soil moisture. On the other hand, FORSKA generally simulated very low biomasses. Since the structure of