Tuesday, 11 September 2025, 11am   
Seminar Room 1, Brückstr. 3a, Magdeburg

Robert Lütkemeier 

Institute for Social-Ecological Research (ISOE), Head of the Research Unit Water and Land Use, Head of the Junior Research Group regulate

Shaping social ecological transformation: Interplay between infrastructure, society, and ecology on the example of the water distribution system in Saxony Anhalt

Tuesday, 16 September 2025, 11am   
Seminar Room 1, Brückstr. 3a, Magdeburg

Nelson Hairston Jr.    

Emeritus of the Cornell University, USA

Internal Waves, Internal Loading, and Infernal Cyanobacteria: Evidence from a Shallow “Bradymictic” Lake

Monday, 16 June 2025, 4pm
UFZ Leipzig, Haus 1.0, Vortragssaal (254)

M. Bayani Cardenas

2025 Birdsall-Dreiss and LaMoreaux Lecturer, Geological Society of America Hydrogeology Division

M. Bayani Cardenas is a hydrology professor in the Department of Earth and Planetary Sciences of the Jackson School of Geosciences at the Univ. of Texas at Austin. He received his education from the Univ. of the Philippines-Diliman, the Univ. of Nebraska-Lincoln, and the New Mexico Institute of Mining and Technology. His research seeks to understand flow and transport processes across different hydrologic settings, water quality and quantity problems, and scales, using a combination of theoretical, computational modeling, and observational methods.

Insights on groundwater renewability from age and residence time analysis

Groundwater is important for energy and food security, human health, and ecosystem quality. Groundwater age, the time since groundwater was recharged, is useful information for the different contexts noted above. It is also directly important for diverse geologic processes, such as chemical weathering, surface water eutrophication and climate change, for example. However, measured groundwater ages range from months to millions of years. This presentation summarizes results of collaborative efforts to globally map how much groundwater is present, the age distribution of groundwater, and the timescales for replenishment to assess groundwater renewability.

Key contributors: Tom Gleeson, Kevin Befus, Scott Jasechko, Elco Luijendijk
Suggested reading and references:
Befus, K. M., S. Jasechko, E. Luijendijk,T. Gleeson, and M. Bayani Cardenas(2017), The rapid yet uneven turnover of Earth’s groundwater, Geophys. Res. Lett.,44, 5511–5520, doi:10.1002/2017GL073322.
Cuthbert, M. O., Gleeson, T., Bierkens, M. F. P., Ferguson, G., & Taylor, R. G. (2023). Defining renewable groundwater use and its relevance to sustainable groundwater management. Water Resources Research, 59, e2022WR032831. https://doi.org/10.1029/2022WR032831
Ferguson, G., Cuthbert, M.O., Befus, K. et al. Rethinking groundwater age. Nat. Geosci. 13, 592–594 (2020). https://doi.org/10.1038/s41561-020-0629-7
Gleeson, T., Befus, K., Jasechko, S. et al. The global volume and distribution of modern groundwater. Nature Geosci 9, 161–167 (2016). https://doi.org/10.1038/ngeo2590
Jasechko, S., Perrone, D., Befus, K. et al. Global aquifers dominated by fossil groundwaters but wells vulnerable to modern contamination. Nature Geosci 10, 425–429 (2017). https://doi.org/10.1038/ngeo2943

Monday, 16 June 2025, 3pm
Seminar Room 1, Brückstr. 3a, Magdeburg

Gregory Stryhanyuk

Spatially-Resolved Analytics: Tracing metabolism with sub-cellular resolution

Cellular metabolic activity in environmental consortia, selected microbial strains and eucaryotic tumour cells has been investigated with subcellular resolution employing the UFZ expertise in stable-isotope probing (SIP) and nanoscale secondary ion mass spectrometry (SIP-nanoSIMS). The multi-isotope tracing of nutrient metabolization in single cells of complex microbial consortia allows the differentiation between bacterial populations and reveals the interaction between inhabitants of symbiotic consortia via analysis of the interplay in their nutrition channels. For a proper decision on an optimal isotope-labelled substance, the dependence of metabolic pathways and rates on nutrient chemical and isotopic composition has to be considered to preserve intracellular homeostasis and to minimise the perturbation of native nutrition scenarios inherent to a studied ecosystem. To cope with the lability of cell nutrition, deuterium in heavy 2H216O water is considered as a substrate-independent general tracer of metabolic activity. The level of isotope labelling cannot be well defined in environmental studies when substances of natural isotopic composition are contributing to the nutrient pool. An approach to analysing the completeness of isotope-labelling in nutrient supply and to the elucidation of non-labelled substrate contribution will be discussed. Metabolic heterogeneity has been considered as an important index for the optimization of biotechnological processes, evaluating the effect of new drugs, and monitoring the changes in environmental conditions. Employing the high-sensitivity SIP-nanoSIMS for the quantitation of metabolic heterogeneity among single cells of microbial populations makes it feasible to trace microevolution processes and reveal the anthropogenically induced changes in the environment.

Monday, 28 April 2025, 3 p.m.
Seminar Room 1, Brückstr. 3a, Magdeburg

Sabine Wollrab

A trait-based approach to investigate changes in plankton phenology with global warming

Global warming leads to extended periods of summer stratification. While phytoplankton growth typically occurs during stratified periods where the warmer and shallower epilimnion layer provides enough light for growth, lake stratification also increases the risk of sinking out of the upper water column. Planktonic primary producers have developed diverse strategies to counteract sinking such as specific morphologies, flagella, or the ability to regulate cell buoyancy. A cyanobacteria with buoyancy regulation is Planktothrix rubescence, for which a strong increase has been observed in several deep stratifying lakes across Europe. One suggested reason is that they strongly profit from lengthened periods of summer stratification, with their ability to move below the thermocline giving them a unique advantage over passive sinking algae to overcome nutrient limitation in the epilimnion. So far models on phytoplankton competition and seasonal plankton succession (such as the PEG model) largely ignore vertical gradients in resource availability and specifically do not consider vertical movement strategies. This limits our ability to assess how changes in stratification regimes will impact algal growth and community composition. In this study, we theoretically investigated resource competition between two phytoplankton species along a 1D water column, contrasting passively sinking algae with taxa that can regulate buoyancy to ascend or descend along the water column according to optimal resource availability. We investigated how competition between sinking and buoyancy regulating taxa is influenced by physiological traits related to resource use efficiency of light and nutrients as well as by environmental conditions such as background turbidity and eddy diffusion. Our results show that coexistence between buoyancy-regulating and sinking algae is critically influenced by differences related to light and nutrient use efficiencies. This also applies to the occurrence of a deep chlorophyll maximum (DCM), its location along the water column as well as which species is forming the DCM.

Monday, 14 April 2025, 3 p.m.    
UFZ Leipzig, Haus 1.0, Vortragssaal (254)

Helen E. Dahlke

Helen E. Dahlke, Ph.D., is a Professor in Integrated Hydrologic Sciences at the University of California, Davis and leader of the UC ANR Water Strategic Initiative. Dr. Dahlke obtained a PhD degree in Environmental Engineering from Cornell University. Her current research interests include surface water – groundwater interaction, water resources management, vadose zone transport processes, and applications of DNA nanotechnology in hydrology. One of her main research efforts focuses on testing the feasibility of using agricultural fields as recharge sites for groundwater banking.

Agricultural Managed Aquifer Recharge (Ag-MAR) –
A Method for Sustainable Groundwater Management

More than two billion people and 40% of global agricultural production depend on unsustainable groundwater extraction. Managed Aquifer Recharge (MAR), the practice of strategically recharging water to replenish subsurface storage, is an important practice for managing groundwater more sustainably. Agricultural Managed Aquifer Recharge (Ag-MAR) is an emerging method for spreading large volume flows on agricultural lands and has the capacity for widespread global implementation. However, it is not yet reaching its full potential to counterbalance growing global groundwater demand. Knowledge gaps, synergies, and trade-offs in Ag-MAR research still exist. In this seminar, Professor Helen Dahlke describes the practice and feasibility of using agricultural land as intentional spreading basins for groundwater recharge, the opportunities to address climate change with Ag-MAR, and the benefits of Ag-MAR including groundwater storage, increased environmental flows, and domestic well support. Professor Dahlke will present the current state of research with respect to the environmental impacts of Ag-MAR on water quality (e.g., nitrate), crop health and yield, and the multidisciplinary approach needed for communication and coordination of Ag-MAR programs with stakeholders and the public. In groundwater-dependent agricultural regions, Ag-MAR provides an important approach to achieving groundwater sustainability; however, it provides one of many solutions to achieve groundwater sustainability and cannot offset the need for groundwater conservation.

Brian Kronvang

A new era of agro-environmental nutrient management in Danish catchments

Denmark has world record in reducing nitrogen and phosphorus pollution of surface waters from both point sources and diffuse sources during the period 1985-2005. Since then, climate normalized N and P emissions to surface waters have been relatively constant even though Water Framework Directive goals for Danish coastal waters still demanded a further reduction of especially nitrogen emissions (ca. 25%). Denmark introduced a new targeted way of combating nutrient pollution in 2015 – a year where Danish farmers were allowed again to fertilize to the Nitrates Directive levels (1.7 animal units) after a nearly 20-year period with 10-20% below economic optimum fertilization for all Danish farmers. The new targeted approach included especially demands for catch crops with a percentage for each coastal water, and heavily use of different types of constructed wetlands and restoration of wetlands and lakes. June last year a ‘The Green Tripartite’ was agreed after ½- year negotiations between Danish Society for Nature Conservation, Danish Agricultural and Food Council and three Danish Labor Unions and the Government of Denmark. A broad majority in the Danish Parliament supports the Green Tripartite Agreement in its entirety and has entered into a political framework agreement in November 2024 with formation of a Ministry for The Green Tripartite that includes the largest land reform in Denmark in 150 year – including afforestation of 250,000 ha of agricultural land before 2045 and rewetting of 140,000 ha low-lying organic soils before 2030 at a cost of ca. 6 billion €. The agreement also includes the first tax on CO2 emissions from Danish agricultural production to be phased in from 2030. The targeted approach from 2015 with its different management measures as well as this new multifunctional approach of the Danish regulation will be highlighted.

Dominik Zak

Insights into peatland restoration: a biogeochemical perspective

Currently, significant efforts are underway to restore peatlands in response to a range of environmental challenges, including biodiversity loss, rising greenhouse gas levels in the atmosphere, and ongoing eutrophication of both terrestrial and aquatic ecosystems. These challenges have emerged due to globalization and contemporary land use practices. Over the past few decades, our comprehension of the biogeochemical processes within rewetted peatlands has grown substantially. This increased understanding has allowed us to establish robust scientific principles that aid in comprehending the consequences of our actions and optimizing restoration strategies. Factors such as water table levels, water sources, chemical composition of outflowing water, physico-chemical soil characteristics, and the dominant vegetation have all been identified as crucial drivers of wetland biogeochemistry and thus influence the restoration outcome. A thorough grasp of these drivers is essential for modeling nutrient removal in rewetted peatlands and, ultimately, for prioritizing, planning, and successfully executing restoration initiatives while ensuring their long-term sustainability. Nevertheless, the substantial spatial and temporal heterogeneity in soil properties, intricate hydrological dynamics, and knowledge gaps pertaining to microbial activities and functions continue to introduce significant uncertainties in assessing and forecasting nutrient cycling across all types of wetlands. In this presentation, I aim to provide a concise overview of biogeochemistry and nutrient cycling in rewetted riparian peatlands and eventually discuss different restoration strategies.

Tuesday, 21 November 2025, 10 am
Seminar Room 1, Brückstr. 3a, Magdeburg   

Monday, 20 July 2025, 10 a.m.
Seminar Room 1, Brückstr. 3a, Magdeburg

Dietmar Straile

Effects of multiple stressors
on plankton dynamics in a deep lake ecosystem

Ecosystems are affected by multiple stressors, which simultaneous occurrence might strongly influence ecosystem functioning, and might also limit our ability to detect, disentangle and finally predict their effects on these ecosystems. Lake Constance, one of the best-studied lakes in the world has been affected during the last decades by major changes in nutrient concentrations, climate warming, and invasions of neobiota. In my talk, I will present analyses on how these stressors affected long-term and seasonal plankton dynamics using paleolimnological and long-term data. I will show what we have learned from our analyses, but will also point to difficulties in disentangling multiple stressors and to unexpected changes (“ecological surprises”) that have been observed in recent decades.