TY - JOUR A1 - Wiggering, Hubert A1 - Lischeid, Gunnar A1 - Müller, Klaus A1 - Ende, Hans-Peter T1 - Ernährungssicherheit und zukünftige Landnutzungen Y1 - 2014 SN - 978-3-941880-72-6 ER - TY - JOUR A1 - Wen, Xi A1 - Unger, Viktoria A1 - Jurasinski, Gerald A1 - Koebsch, Franziska A1 - Horn, Fabian A1 - Rehder, Gregor A1 - Sachs, Torsten A1 - Zak, Dominik A1 - Lischeid, Gunnar A1 - Knorr, Klaus-Holger A1 - Boettcher, Michael E. A1 - Winkel, Matthias A1 - Bodelier, Paul L. E. A1 - Liebner, Susanne T1 - Predominance of methanogens over methanotrophs in rewetted fens characterized by high methane emissions JF - Biogeosciences N2 - The rewetting of drained peatlands alters peat geochemistry and often leads to sustained elevated methane emission. Although this methane is produced entirely by microbial activity, the distribution and abundance of methane-cycling microbes in rewetted peatlands, especially in fens, is rarely described. In this study, we compare the community composition and abundance of methane-cycling microbes in relation to peat porewater geochemistry in two rewetted fens in northeastern Germany, a coastal brackish fen and a freshwater riparian fen, with known high methane fluxes. We utilized 16S rRNA high-throughput sequencing and quantitative polymerase chain reaction (qPCR) on 16S rRNA, mcrA, and pmoA genes to determine microbial community composition and the abundance of total bacteria, methanogens, and methanotrophs. Electrical conductivity (EC) was more than 3 times higher in the coastal fen than in the riparian fen, averaging 5.3 and 1.5 mS cm(-1), respectively. Porewater concentrations of terminal electron acceptors (TEAs) varied within and among the fens. This was also reflected in similarly high intra- and inter-site variations of microbial community composition. Despite these differences in environmental conditions and electron acceptor availability, we found a low abundance of methanotrophs and a high abundance of methanogens, represented in particular by Methanosaetaceae, in both fens. This suggests that rapid (re) establishment of methanogens and slow (re) establishment of methanotrophs contributes to prolonged increased methane emissions following rewetting. Y1 - 2018 U6 - https://doi.org/10.5194/bg-15-6519-2018 SN - 1726-4170 SN - 1726-4189 VL - 15 IS - 21 SP - 6519 EP - 6536 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Webber, Heidi A1 - Lischeid, Gunnar A1 - Sommer, Michael A1 - Finger, Robert A1 - Nendel, Claas A1 - Gaiser, Thomas A1 - Ewert, Frank T1 - No perfect storm for crop yield failure in Germany JF - Environmental research letters N2 - Large-scale crop yield failures are increasingly associated with food price spikes and food insecurity and are a large source of income risk for farmers. While the evidence linking extreme weather to yield failures is clear, consensus on the broader set of weather drivers and conditions responsible for recent yield failures is lacking. We investigate this for the case of four major crops in Germany over the past 20 years using a combination of machine learning and process-based modelling. Our results confirm that years associated with widespread yield failures across crops were generally associated with severe drought, such as in 2018 and to a lesser extent 2003. However, for years with more localized yield failures and large differences in spatial patterns of yield failures between crops, no single driver or combination of drivers was identified. Relatively large residuals of unexplained variation likely indicate the importance of non-weather related factors, such as management (pest, weed and nutrient management and possible interactions with weather) explaining yield failures. Models to inform adaptation planning at farm, market or policy levels are here suggested to require consideration of cumulative resource capture and use, as well as effects of extreme events, the latter largely missing in process-based models. However, increasingly novel combinations of weather events under climate change may limit the extent to which data driven methods can replace process-based models in risk assessments. KW - crop yield failure KW - extreme events KW - support vector machine KW - process-based crop model KW - Germany Y1 - 2020 U6 - https://doi.org/10.1088/1748-9326/aba2a4 SN - 1748-9326 VL - 15 IS - 10 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Wambura, Frank Joseph A1 - Dietrich, Ottfried A1 - Lischeid, Gunnar T1 - Improving a distributed hydrological model using evapotranspiration-related boundary conditions as additional constraints in a data-scarce river basin JF - Hydrological processes N2 - Many hydrological models have been calibrated and validated using hydrographs alone. Because streamflow integrates water fluxes in space, many distributed hydrological models tend to have multiple feasible descriptions of hydrological processes. This equifinality usually leads to substantial prediction uncertainty. In this study, additional constraintsnamely, the spatial patterns of long-term average evapotranspiration (ET), shallow groundwater level, and land cover changewere used to investigate the reduction of equifinality and prediction uncertainty in the Soil and Water Assessment Tool (SWAT) in the Wami River basin in Tanzania. The additional constraints were used in the set-up, parameter emulation and calibration of the SWAT model termed an improved hydrological model (IHM). The IHM was then compared with a classical hydrological model (CHM) that was also developed using the SWAT model but without additional constraints. In the calibration, the CHM used only the hydrograph, but the IHM used the hydrograph and the spatial pattern of long-term average ET as an additional constraint. The IHM produced a single, unique behavioural simulation, whereas the CHM produced many behavioural simulations that resulted in prediction uncertainty. The performance of the IHM with respect to the hydrograph was more consistent than that of the CHM, and the former clearly captured the mean behaviour of ET in the river basin. Therefore, we conclude that additional constraints substantially reduce equifinality and prediction uncertainty in a distributed hydrological model. KW - data scarcity KW - equifinality KW - evapotranspiration KW - parameter emulation KW - prediction uncertainty KW - SWAT Y1 - 2018 U6 - https://doi.org/10.1002/hyp.11453 SN - 0885-6087 SN - 1099-1085 VL - 32 IS - 6 SP - 759 EP - 775 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Wambura, Frank Joseph A1 - Dietrich, Ottfried A1 - Lischeid, Gunnar T1 - Evaluation of Spatio-Temporal Patterns of Remotely Sensed Evapotranspiration to Infer Information about Hydrological Behaviour in a Data-Scarce Region JF - Water N2 - Information about the hydrological behaviour of a river basin prior to setting up, calibrating and validating a distributed hydrological model requires extensive datasets that are hardly available for many parts of the world due to insufficient monitoring networks. In this study, the focus was on prevailing spatio-temporal patterns of remotely sensed evapotranspiration (ET) that enabled conclusions to be drawn about the hydrological behaviour and spatial peculiarities of a river basin at rather high spatial resolution. The prevailing spatio-temporal patterns of ET were identified using a principal component analysis of a time series of 644 images of MODIS ET covering the Wami River basin (Tanzania) between the years 2000 and 2013. The time series of the loadings on the principal components were analysed for seasonality and significant long-term trends. The spatial patterns of principal component scores were tested for significant correlation with elevations and slopes, and for differences between different soil texture and land use classes. The results inferred that the temporal and spatial patterns of ET were related to those of preceding rainfalls. At the end of the dry season, high ET was maintained only in areas of shallow groundwater and in cloud forest nature reserves. A region of clear reduction of ET in the long-term was related to massive land use change. The results also confirmed that most soil texture and land use classes differed significantly. Moreover, ET was exceptionally high in natural forests and loam soil, and very low in bushland and sandy-loam soil. Clearly, this approach has shown great potential of publicly available remote sensing data in providing a sound basis for water resources management as well as for distributed hydrological models in data-scarce river basins at lower latitudes. KW - evapotranspiration KW - hydrological behaviour KW - land cover change KW - MODIS ET KW - principal component analysis KW - shallow groundwater Y1 - 2017 U6 - https://doi.org/10.3390/w9050333 SN - 2073-4441 VL - 9 SP - 297 EP - 315 PB - MDPI CY - Basel ER - TY - GEN A1 - Vyse, Stuart Andrew A1 - Semiromi, Majid Taie A1 - Lischeid, Gunnar A1 - Merz, Christoph T1 - Characterizing hydrological processes within kettle holes using stable water isotopes in the Uckermark of northern Brandenburg, Germany T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Understanding the hydrologic connectivity between kettle holes and shallow groundwater, particularly in reaction to the highly variable local meteorological conditions, is of paramount importance for tracing water in a hydro(geo)logically complex landscape and thus for integrated water resource management. This article is aimed at identifying the dominant hydrological processes affecting the kettle holes' water balance and their interactions with the shallow groundwater domain in the Uckermark region, located in the north-east of Germany. For this reason, based on the stable isotopes of oxygen (delta O-18) and hydrogen (delta H-2), an isotopic mass balance model was employed to compute the evaporative loss of water from the kettle holes from February to August 2017. Results demonstrated that shallow groundwater inflow may play the pivotal role in the processes taking part in the hydrology of the kettle holes in the Uckermark region. Based on the calculated evaporation/inflow (E/I) ratios, most of the kettle holes (86.7%) were ascertained to have a partially open, flow-through-dominated system. Moreover, we identified an inverse correlation between E/I ratios and the altitudes of the kettle holes. The same holds for electrical conductivity (EC) and the altitudes of the kettle holes. In accordance with the findings obtained from this study, a conceptual model explaining the interaction between the shallow groundwater and the kettle holes of Uckermark was developed. The model exhibited that across the highest altitudes, the recharge kettle holes are dominant, where a lower ratio of E/I and a lower EC was detected. By contrast, the lowest topographical depressions represent the discharge kettle holes, where a higher ratio of E/I and EC could be identified. The kettle holes existing in between were categorized as flow-through kettle holes through which the recharge takes place from one side and discharge from the other side. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1392 KW - evaporation KW - groundwater inflow KW - kettle hole KW - stable water isotope KW - surface–groundwater interactions Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-514453 SN - 1866-8372 IS - 8 ER - TY - JOUR A1 - Vyse, Stuart Andrew A1 - Semiromi, Majid Taie A1 - Lischeid, Gunnar A1 - Merz, Christoph T1 - Characterizing hydrological processes within kettle holes using stable water isotopes in the Uckermark of northern Brandenburg, Germany JF - Hydrological Processes N2 - Understanding the hydrologic connectivity between kettle holes and shallow groundwater, particularly in reaction to the highly variable local meteorological conditions, is of paramount importance for tracing water in a hydro(geo)logically complex landscape and thus for integrated water resource management. This article is aimed at identifying the dominant hydrological processes affecting the kettle holes' water balance and their interactions with the shallow groundwater domain in the Uckermark region, located in the north-east of Germany. For this reason, based on the stable isotopes of oxygen (delta O-18) and hydrogen (delta H-2), an isotopic mass balance model was employed to compute the evaporative loss of water from the kettle holes from February to August 2017. Results demonstrated that shallow groundwater inflow may play the pivotal role in the processes taking part in the hydrology of the kettle holes in the Uckermark region. Based on the calculated evaporation/inflow (E/I) ratios, most of the kettle holes (86.7%) were ascertained to have a partially open, flow-through-dominated system. Moreover, we identified an inverse correlation between E/I ratios and the altitudes of the kettle holes. The same holds for electrical conductivity (EC) and the altitudes of the kettle holes. In accordance with the findings obtained from this study, a conceptual model explaining the interaction between the shallow groundwater and the kettle holes of Uckermark was developed. The model exhibited that across the highest altitudes, the recharge kettle holes are dominant, where a lower ratio of E/I and a lower EC was detected. By contrast, the lowest topographical depressions represent the discharge kettle holes, where a higher ratio of E/I and EC could be identified. The kettle holes existing in between were categorized as flow-through kettle holes through which the recharge takes place from one side and discharge from the other side. KW - evaporation KW - groundwater inflow KW - kettle hole KW - stable water isotope KW - surface–groundwater interactions Y1 - 2020 U6 - https://doi.org/10.1002/hyp.13699 SN - 0885-6087 SN - 1099-1085 VL - 34 IS - 8 SP - 1868 EP - 1887 PB - Wiley CY - New York ER - TY - JOUR A1 - Thomas, Björn A1 - Lischeid, Gunnar A1 - Steidl, Jörg A1 - Dietrich, Ottfried T1 - Long term shift of low flows predictors in small lowland catchments of Northeast Germany JF - Journal of hydrology N2 - Runoff, especially during summer months, and low flows have decreased in Central and Eastern Europe during the last decades. A detailed knowledge on predictors and dependencies between meteorological forcing, catchment properties and low flow is necessary to optimize regional adaption strategies to sustain minimum runoff. The objective of this study is to identify low flow predictors for 16 small catchments in Northeast Germany and their long-term shifts between 1965 and 2006. Non-linear regression models (support vector machine regression) were calibrated to iteratively select the most powerful low flow predictors regarding annual 30-day minimum flow (AM(30)). The data set consists of standardized precipitation (SPI) and potential evapotranspiration (SpETI) indices on different time scales and lag times. The potential evapotranspiration of the previous 48 and 3 months, as well as the precipitation of the previous 3 months and last year were the most relevant predictors for AM(30). Pearson correlation (r(2)) of the final model is 0.49 and if for every year the results for all catchments are averaged r(2) increases to 0.80 because extremes are smoothing out. Evapotranspiration was the most important low flow predictor for the study period. However, distinct long-term shifts in the predictive power of variables became apparent. The potential evapotranspiration of the previous 48 months explained most of the variance, but its relevance decreased during the last decades. The importance of precipitation variables increased with time. Model performance was higher at catchments with a more damped discharge behavior. The results indicate changes in the relevant processes or flow paths generating low flows. The identified predictors, temporal patterns and patterns between catchments will support the development of low flow monitoring systems and determine those catchments where adaption measures should aim more at increasing groundwater recharge. (C) 2014 Elsevier B.V. All rights reserved. KW - Low flow indicator KW - Post-glacial landscape KW - Catchment classification KW - Support vector machine regression KW - Annual 30-day minimum flow KW - Standardized precipitation index Y1 - 2015 U6 - https://doi.org/10.1016/j.jhydrol.2014.12.022 SN - 0022-1694 SN - 1879-2707 VL - 521 SP - 508 EP - 519 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Thomas, Björn A1 - Lischeid, Gunnar A1 - Steidl, Jörg A1 - Dannowski, Ralf T1 - Regional catchment classification with respect to low flow risk in a Pleistocene landscape JF - Journal of hydrology N2 - The classification of small catchments with respect to low flow risk is needed by water and environmental managers to plan adaptation measures for freshwater streams. In this study a new approach is presented to assess the risk of seasonal low flow in the Pleistocene landscape of the Federal State of Brandenburg in Germany. Seasonal low flow and drought in small streams is very common in this region and is predicted to increase due to climate change within the next decades. Data of 15 years (1991-2006) of daily discharge at 37 small catchments (<500 km(2)) and rainfall data from the same region were used. Principal component analyses were applied to the two data sets separately. The first five principal components of the discharge data, principal components of a precipitation data set covering the same catchments and catchment characteristics were used to explain the patterns found. The first five discharge components explained 72.9% of the total variance in the data set. The first component reflected the general regional discharge pattern. Components 2 and 3 of the discharge data could be related to spatial patterns of precipitation. Components 4 and 5 of the discharge data reflected geohydrologic processes within the catchments. In order to identify catchments with high risk with respect to low flows, component three and five were important as they both identified catchments with faster decrease of flows during summer. These components were used to estimate low flow risk. Catchments located in the northeast of Brandenburg, especially those in the Barnim highlands north and east of Berlin, were identified to be prone to seasonal low flow. There water management measures to adapt to climate change are needed the most. KW - Catchment classification KW - Principal component analysis KW - Catchment characteristics KW - Precipitation pattern KW - Regional scale Y1 - 2012 U6 - https://doi.org/10.1016/j.jhydrol.2012.10.020 SN - 0022-1694 SN - 1879-2707 VL - 475 IS - 2 SP - 392 EP - 402 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Steidl, Jörg A1 - Lischeid, Gunnar A1 - Engelke, Clemens A1 - Koch, Franka T1 - The curse of the past BT - What can tile drain effluent tell us about arable field management? JF - Agriculture, Ecosystems & Environment N2 - One challenge for modern agricultural management schemes is the reduction of harmful effects on the envi-ronment, e.g. in terms of the emission of nutrients. Sampling the effluent of tile drains is a very efficient way to sample seepage water from larger areas directly underneath the main rooting zone. Time series of solute con-centration in tile drains can be linked to agricultural management data and thus indicate the efficacy of individual management measures. To that end, the weekly runoff and solute concentration were determined in long-term measurement campaigns at 25 outlets of artificial tile drains at 19 various arable fields in the German federal state of Mecklenburg-Vorpommern. The study sites were distributed within a 23,000 km(2) region and were deemed representative of intense arable land use. In addition, comprehensive meteorological and man-agement data were provided. To disentangle the different effects, monitoring data were subjected to a principal component analysis. Loadings on the prevailing principal components and spatial and temporal patterns of the component scores were considered indicative of different processes. Principal component scores were then related to meteorological and management data via random forest modelling. Hydrological conditions and weather were identified as primary driving forces for the nutrient discharge behaviour of the drain plots, as well as the nitrogen balance. In contrast, direct effects of recent agricultural management could hardly be identified. Instead, we found clear evidence of the long-term and indirect effects of agriculture on nearly all solutes. We conclude that tile drain effluent quality primarily reflected the soil-internal mobilisation or de-mobilisation of nutrients and related solutes rather than allowing inferences to be drawn about recent individual agricultural management measures. On the other hand, principal component analysis revealed a variety of indirect and long-term effects of fertilisation on solutes other than nitrogen or phosphorus that are still widely overlooked in nutrient turnover studies. KW - Agricultural management KW - Tile drains KW - Nitrate KW - Phosphorus KW - Water KW - pollution KW - Multivariate statistics KW - Random forest modelling Y1 - 2021 U6 - https://doi.org/10.1016/j.agee.2021.107787 SN - 0167-8809 SN - 1873-2305 VL - 326 PB - Elsevier CY - Amsterdam ER -