Past Research Seminars at the Dept. of Hydrogeology

Thursday, May19th, 2011, 15:00, Kubus, Room 1A

Eco-hydrology of Canadian prairie wetlands and management implications: Synthesis of a 40-year study

Speaker: Prof. Masaki Hayashi

Affiliation: Department of Geoscience, University of Calgary, Canada

Abstract: Eco-hydrology can be broadly defined as the interaction between living organisms and physical components of the hydrologic cycle. Eco-hydrological understanding of aquatic environments has far reaching implications for protection, restoration, and management of these environments. We will present a unique case study of the northern prairie wetland ecosystem in Canada, where long-term monitoring and focused experiments over the past 40 years have generated a body of fundamental scientific knowledge that is beginning to guide policy development for wetland protection and restoration. The key findings are: 1) long-term monitoring of basic hydrological and ecological variables is necessary to assess the response of wetlands to natural and anthropogenic stresses; 2) effective management of wetlands requires the consideration of wetland complexes, as opposed to individual wetlands, and the hydrological linkage between wetlands and surrounding uplands; and 3) biodiversity of prairie wetlands depends on the diversity in water regimes (e.g. ephemeral, seasonal, permanent) within a wetland complex, in other words, hydro-diversity.

For more information on Prof. Masaki Hayashi:

Monday, September 12th, 2011, 14:00, Building 1.0, Seminar Room

Recent advances and new approaches to understanding and modelling surface water groundwater interaction

Speaker: Dr. Philip Brunner

Affiliation: Stochastic Hydrogeology Group, Centre for Hydrogeology, University of Neuchâtel

Abstract: The talk covers several developments in the area of modeling surface water groundwater interactions. First, the implications of simplifying the complexity of streambeds are explored: A common approach in modeling surface water-groundwater interaction is to represent the streambed as a homogeneous geological structure with hydraulic properties obtained by means of model calibration. In reality, streambeds are among the most heterogeneous geological structures. The implications of such simplifications are explored. It is shown that the maximum error in flux can often be easily estimated, even without a numerical model.
In the second part of the talk, some additional developments associated with complex, physically based models applied to surface water groundwater interactions are explored. A new method to quantify base flow in catchments is introduced. Its application to test hydrograph separation methods is discussed. Finally, new mathematical methods to represent complex geological structures such as streambeds or aquifers are briefly introduced.

For more information on hydrogeology at the University of Neuchâtel:

Thursday, September 15th, 2011, 14:00, Kubus, Hall 2

Physics-based hydrologic response simulation: a concept development approach

Speaker: Dr. Benjamin Mirus

Affiliation: U.S. Geological Survey, Menlo Park, USA

Abstract: The latest generation of physics-based hydrologic models, coupling the equations for surface and subsurface flow, are a powerful tool. With sufficient site characterization these sophisticated models can be employed to simulate hydrologic fluxes and state variables with high spatial and temporal resolution. One of the key challenges to their more widespread use is the extensive data requirements necessary not only to parameterize, but to evaluate the plausibility of simulation results. Although successfully simulating the observed hydrologic response for a given experimental catchment is a useful endeavor, improved quantitative understanding of hydrological processes requires investigations beyond site-specific problems.

This presentation will demonstrate how physics-based simulation can be used as a concept development tool to investigate the controls on runoff generation across a broad range of environmental conditions. Successful simulations from four experimental catchments are used as starting points for a systematic exploration of a physically realistic parameter space. Simulation results illustrate the nuances of subsurface controls on runoff generation processes and highlight the importance of unsaturated storage dynamics. The connectivity between surface and subsurface fluxes is shown, in large part, to be defined by the relative rates of infiltration and the convergence of lateral drainage within the variably-saturated soil layers. The concept development approach presented here also provides a useful framework for similar studies focused on understanding surface water / groundwater interactions.

For more information on Dr. Benjamin Mirus and the USGS at Menlo Park:

Tuesday, October 25th, 2011, 11:15, Building 1.0, Seminar Room

Sparkling? CO2 intrusion in freshwater aquifers at storage sites

Speaker: Sven Fahrner

Affiliation: Department of Applied Geology and Hydrogeology, University of Kiel (CAU)

Abstract: The geological storage of carbon dioxide in saline aquifers is considered as a significant option to reduce greenhouse gas emissions and thus mitigate climate change effects. However, the behaviour of the injected CO2 in the subsurface needs elucidation to meet regulative, financial and public demands for geological storage activities. The scenario modelling of HTMC processes, i.e. hydraulic, thermal, mechanical and chemical processes at virtual CO2 storage sites offers a wellestablished tool for this purpose.
In this study, the potential hydrogeochemical response to CO2 intrusion in freshwater aquifers as a consequence of leakage events is investigated. In that case, injected CO2 would by-pass existing traps in the storage complex, migrate buoyancy-driven upwards for example along faults, and intrude freshwater aquifers which may be used for drinking or industrial water supply. The intrusion results in the dissolution of gaseous CO2 in the water, a drop in the pH value and induced water-mineral-interactions, which lead to changes in the groundwater chemistry. A prediction of these
changes contributes to an impact assessment and enables the identification of suited monitoring parameters.

For more information on hydrogeology at the University of Kiel:

Monday, November 28th, 2011, 14:00, Building 1.0, Seminar Room

Reactive transport modeling of vertical flow filters used for
contaminated groundwater treatment

Speaker: Cecilia De Biase

Affiliation: Department Groundwater Remediation, UFZ, Leipzig

Abstract: Vertical flow filters are traditionally used for the treatment of domestic waste water. In the last decades, they were also used for waste water treatment of other industries as pharmacy, mining, agriculture, among others. In the frame of Safira II project, vertical filters were tested for the treatment of contaminated groundwater from Leuna. The filter was intermittently irrigated with groundwater containing mainly benzene, MTBE and ammonium. The filter operation allows the system to remain under unsaturated conditions. This facilitates the removal of the volatile compounds by aerobic biodegradation but also triggers the potential for their volatilization. Atmospheric emission of hazardous compounds due to volatilization would limit the applicability of such filter systems for volatile compounds.

The numerical model MIN3P allows for the simulation of reactive transport processes in variably saturated porous media. Simulated processes include advective-diffusive transport of dissolved and gaseous species, microbial degradation of aqueous species and their volatilization. Flow and transport processes were calibrated using measured field data and the model subsequently used to describe the removal of the main contaminants in Leuna groundwater. Field investigation used for data calibration included dissolved and gaseous tracer tests, passive emission measurements, microbial functional gene detection and compound specific stable isotope analysis. Field measurements indicated that biodegradation and volatilization have the potential to contribute to volatile compounds removal. Model results confirm experimentally observed high removal rates and, in the case of Leuna filter, biodegradation as the dominating mass removal process with volatilization contributing only to minor or negligible amounts. However, the contribution of each removal process depends on the design and operation of the filter system, the hydraulic properties of the filter material, and the degradation capacity of the microbial population. These factors have to be sufficiently well combined to avoid volatile emissions and to enhance contaminant removal by biodegradation.

For more information on the Department Groundwater Remediation at UFZ:

Monday, January 30th, 2012, 14:00, Kubus, Room 2AB

Spatial patterns of microbial respiration in streams revealed by a smart tracer

Speaker: Prof. Roy Haggerty

Affiliation: Department of Geosciences, Oregon State University, USA

Abstract: Resazurin is a microbially reactive, non-toxic, fluorescent compound that irreversibly transforms to resorufin. The transformation is proportional to aerobic respiration. Using resazurin, we show patterns of aerobic respiration in small, heterotrophic streams in Spain, Austria, and the USA. While hyporheic exchange is an important control on respiration, flow across biofilms at the sediment-water interface is also very important in some systems.

For more information on Prof. Roy Haggerty:

Wednesday, February 15th, 2012, 11:00, Bldg 1.0, Main Lecture Hall (2. Floor)

Hydrologically controlled generation of reactivity hot spots within a wetland with micro-topography: A modeling approach

Speaker: Sven Frei

Affiliation: Department of Hydrology, University of Bayreuth

Abstract: The interaction between stream discharge and the riparian zone during high flow events is still poorly understood. Chemical data support the existence of defined flow paths controlling the exchange between riparian zone and streams. After rainfall events, waters rich in DOC, resembling the chemical composition of uppermost soil pore waters, is rapidly mobilized and mixes with waters from deeper layers and groundwater in various proportions. Monitoring and modeling of the spatial and temporal dynamics and influence of the different flow pathways on runoff generation and water quality is therefore very difficult. Chemical and hydrometric data taken for a minerotrophic fen located in North- Eastern Bavaria show that water quality and runoff generation during intensive rainfall events is controlled by complex interactions between surface flow and groundwater. Processes controlling runoff generation and water quality seem to predominantly occur within the riparian zone. The signature of runoff during intensive storm flow events often shows a similar chemical composition as the water stored in the riparian zone In this study, the hypothesis is tested that micro-topographical structures, which are typical for this types of wetlands, induce heterogeneous sub-surface flow patterns. Furthermore, they allow a complex interplay of storage and rapid mobilization of surface near pore waters. Thus, the influence of these subsurface-flow patterns on the biogeochemical processes within the wetland is investigated. Herby, a process based surface/sub-surface flow model is used which is capable of representing the interaction between precipitation, riparian zone and stream. Microtopographical structures are generated using a geostatistical approach and are integrated into the hydrological model. Along the flow paths, different biogeochemical processes are modeled, using field and literature data for initial concentrations, reaction rates, and switching points between processes. Processes were implemented as rate expressions in PhreeqC and are controlled by availability of substrates. The different flow paths with individual characteristic residence times allow for turnover of organic matter and electron acceptors, depending on rate and flow. Following field observations, we included aerobic respiration, denitrification, iron reduction, sulfate reduction, and organic matter degradation, leading also to ammonium release. All processes are resolved in high spatio-temporal resolution and cause different chemical characteristics of the waters mobilized during high flow events. Complementary to the simulations, we show field data of different soil pore water profiles. The measured data supports our hypothesis that mainly rapidly mobilized waters from the near surface layers are reflected in the chemical signature of stream water. However, there is also a chemical imprint from waters mixing in from deeper groundwater, as nitrate, sulfate, and e.g. chloride show different mixing behavior during high flow events. This supports our model hypothesis that different flow paths with different residence times contribute to the overall runoff, depending on the event and pre-event conditions.

For more information on Sven Frei:

Wednesday, March 7th, 2012, 15:30, Kubus, Room 2A

René Therrien
Département de géologie et de genie géologique
Université Laval, Québec, Canada

Recent advances in the integrated simulation of surface and subsurface flow and mass transport

Abstract: Models that simulate coupled (integrated) surface water and groundwater flow are becoming increasingly popular to address issues related to water resources, such as the impact of climate change, increased water consumption or degradation of water quality. Several coupled models have been recently presented in the literature and there is also an increasing number of published case studies demonstrating the application of such models. The current development of integrated models follows the blueprint presented by Freeze and Harlan (Journal of Hydrology, 1969), who proposed that hydrologic systems be represented by a distributed-system model in which parameters are spatially and temporally distributed. The advantage of this distributed-system approach is that a representation of the controlling physical parameters does not require simplifying assumptions with respect to the flow processes, which makes the model applicable to a potentially large range of hydrologic conditions. These integrated models should therefore be applicable to any type of river-groundwater system. This presentation will review recent developments in the simulation of coupled surface water and groundwater flow, with an emphasis on those approaches and that are based on the 3D variably-saturated groundwater flow equation. The assumptions, governing equations and numerical formulations of various models will be compared and current capabilities for simulating mass, heat and sediment transport in hydrologic systems will also be reviewed. Although models of increasing complexity have been recently developed, challenges remain with respect to the further development of integrated hydrologic system simulations. An example is the representation of water cycling in northern climates where annual freezing and thawing modify the infiltration properties of surficial soils. Another challenge is that distributed (integrated) models can become too computationally intensive for some applications, which will require faster numerical methods, such as parallelization, or will force the use of simplified models. More work is therefore needed to identify hydrologic characteristics for which more simple and less computationally demanding approaches are adequate.

Tuesday, 13th of March 2012, 10:00, Build. 1.0, VTR (2. floor)

Dr. Willem van Versefeld
Deltares-Delft, Netherlands

Hydro-biogeochemical Coupling at the Hillslope and Catchment Scale

Abstract: This presentation is about the mechanistic assessment of hydrological controls on DOC and N transport at the hillslope and catchment scale. The research site at the HJ Andrews Experimental Forest provides a somewhat controlled natural experiment for this work where debris flows in 1986 and 1996 evacuated riparian zone almost entirely. As such, hillslopes now issue directly into the stream without riparian zone modulation. This makes for potentially major research advancements whereby we can study directly how hillslope hydrological processes control stream hydro-biogeochemical response. A 10 meter wide trenched hillslope enables comparison between the single highly instrumented study hillslope and the ensemble of hillslopes that comprise the complete catchment. We use a combination of hydrometric data, natural tracers and artificial tracers to define the age, origin and flowpath of subsurface water movement and how these water fluxes control transport of dissolved constituents. A novel part of this work is the combination, for the first time that we are aware, of Specific UV absorbance SUVA (to “fingerprint” sources of dissolved organic matter), biogeochemical solutes of DOC and N (our soluble nutrients in question), and deuterium labeled water (in a controlled sprinkler experiment). We used these data to develop a conceptual model with transport modeling and end member mixing analysis. We develop a mechanistically plausible conceptual model that explains the
hydrological controls on DOC and N transport at the hillslope and catchment scale.

Tuesday, 20th of March 2012, 14:00, Build. 1.0, VTR room (2. floor)

Dr. Hannelore Waska
Max Planck Research Group for Marine Geochemistry
University of Oldenburg
Institute for Chemistry and Biology of the Marine Environment (ICBM)

Influence of groundwater-surface water interactions on aquatic biogeochemistry and ecology

Abstract: In recent years, advective groundwater discharge has been acknowledged as a source of a variety of chemical species such as nutrients, dissolved organic matter, and pollutants to surface water bodies. Likewise, surface water can impact groundwater geochemistry through intrusion into aquifers. In the presentation, examples of groundwater-surface water interactions are discussed with regards to physical, biogeochemical, and ecological impacts, current state-of-the-art methodologies, and concepts for future research directions.

Wednesday, 28th of March 2012, 15:30, Build. 1.0, VTR (2. floor)

Dr. Ype van der Velde
Hydrology, hydrogeology and water resources research group
Stockholm University
Department Physical Geography and Quarternary Geology

Groundwater surface water interactions in lowland catchments

Abstract: In general, lowland catchments are flat, have fertile soils and shallow groundwater tables, which make them ideal for intensive agriculture. However, to improve farming conditions drainage by subsurface tube drains and ditches is necessary. Together with high inputs of manure and fertilizers, this causes large nutrient fluxes to groundwater, surface waters and downstream lakes and coastal zones, impeding the ecological, recreational and consumptive functions of these waters. Key questions we asked ourselves are: what are the driving processes, hotspots and hotmoments for nutrient leaching in lowland catchments?
To find answers to these questions, we measured fluxes of water and nutrients in a small agricultural catchment (6.5 km2) in The Netherlands. At a field site we established relations between groundwater storage and fluxes from tube drains, overland flow and groundwater flow. At larger scales we focused on capturing the spatial pattern and dynamics of discharge and nutrient concentrations using passive samplers and high frequency concentration measurements. This unique dataset allowed us to propose several new concepts to describe water and nutrient fluxes at the catchment-scale. In my presentation I will give an overview of the main findings of our fieldwork and summarize our ideas for model development which include: A spatial distribution of storage-potential approach to describe fluxes of individual flow routes (tube drainage, groundwater flow and overland flow), and a dynamic travel time approach to model nutrient transport at the catchment-scale.

Tuesday, 3rd of April 2012, 10:00, Build. 1.0, VTR (2. floor)

Dr. Prabhas Yadav
Technical University Dresden
Institute for Groundwater Management

Analytical Models for Plume Length Estimations

Abstract: The presentation will demonstrate techniques that could be used for the pre-assessment of contaminated sites. The goals of the presentation is based on a simple fact that every contaminated site possesses certain potential to degrade natural resources, thus necessitating risk assessment. The talk will focus on mathematical and statistical techniques to predict the maximum length of contaminated plumes or Lmax, which is considered as a key parameter that could be used for the pre-
assessment of contaminated sites.
The first part of the presentation will introduce several processes that are active at contaminated sites. Additionally, a very brief review of analytical models that considers these processes in order to provide an estimate of Lmax will be presented. A result comparing eld and model Lmax will be shown and an excel R based tool that can be used to compare di erent analytical models will be introduced. The second part of the presentation will focus on the development of a new 3D analytical model for predicting Lmax. The usability and applicability of the 3D model will be demonstrated in addition to exploring the relationship between Lmax and other parameters of the 3D model. The third part of the presentation will introduce a new numerical approach that can be used for a rapid assessment of contaminated sites. Apart from verifying the new numerical technique, how numerical techniques can be used to improve the applicability of analytical models will be shown. Recommended research works, the most important part of the talk, for improving contaminated site assessment techniques will be presented in the last part.

Friday, 20th of April 2012, 10:00, Build. 1.0, VTR (2. floor)

Marieke Oosterwoud
University of Wageningen, Netherlands
Soil Physics, Ecohydrology and Groundwater Management Group

DOC - from soils to surface water

Abstract: Large amounts of organic C have been accumulated in tundra and taiga ecosystems of the northern hemisphere. Dissolved organic carbon (DOC) represents the most mobile, dynamic, and reactive component of the soil C pool. In view of climate change and the expected permafrost thawing, there is a growing interest in the transfer of C between soil and surface waters. Besides biological transformations, chemical interactions are recognized as key processes that are involved in DOC dynamics. We hypothesise that sorption mechanism influence the size of the DOC pool by means of equilibrium between solution and sorbed phases of the potentially water soluble organic carbon (WSOC). We found that DOC solubility is influenced by the soils Al and Fe oxide content, which determine the sorption capacity, by the composition of the material, which determine the sorption affinity, and by soil properties like pH and cation content, which determine the type of complexes that are formed. With the use of the LCD (Ligand and Charge Distribution) model we are able to describe the partitioning of WSOC and cations over a mineral surface based on equilibrium reactions taking into account electrostatic effects, sites competition, and the formation of specific surface complexes. Together with DOC production and degradation models, our results provide a more balanced instrument to address changes in DOC loading to surface waters.

Tuesday, 22nd of May 2012, 10:00, Build. 1.0, VTR (2. floor)

Gunnar Lischeid
Leibniz Centre for Agricultural Landscape Research, Institute of Landscape Hydrology, and University of Potsdam, Institute for Earth and Environmental Sciences

How Landscapes Organise Hydrological Processes

Abstract: The Institute of Landscape Hydrology at ZALF investigates hydrological and hydrochemical processes and their linkages to biological processes, especially in small streams and lakes. Humans have been modifying European landscapes and corresponding hydrological and biogeochemical processes for millennia, resulting in a confusing interplay of various processes. However, landscapes are not random ensembles of single landscape elements, but highly structured systems with many linkages and feedback loops at various scales. For example, landscapes organise themselves in a way to ensure that the annual surplus water is discharging to receiving waters and is exported from the landscape. Vegetation cover not only adapts to existing conditions but even alters soils and hydrological processes to facilitate long-term vegetation cover. Consequently, the intrinsic dimensionality of hydrological and associated biogeochemical processes often is rather low: The total number of observed system states usually is much smaller compared to what our theories and models would allow.
Based on this perception of landscape functioning innovative methods have been developed to better understand how landscapes organise hydrological and biogeochemical processes. The basic idea is, that data of system “behaviour”, e.g., time series of groundwater heads, soil matrix potential or discharge, measured at different sites, can be used to extract information about number and nature of prevailing processes as well as about the intrinsic dimensionality of the observed heterogeneities. Different approaches will be presented to assess the intrinsic dimensionality of hydrological processes at different scales. It was often found that functional heterogeneity was much less compared to structural heterogeneities, e.g., spatial patterns of soil physical properties or aquifer transmissivity. That information can be used to identify anthropogenic effects on the observed dynamics as well as to optimise the structure of process-based models in a systematic way. Examples will be presented addressing heterogeneities of soil hydrological processes, anthropogenic effects on groundwater heads and lake water level, multivariate trends in soil solution quality, and the effects of near-surface atmospheric water vapour exchange processes.

Monday 19th of August 2013, 3 PM, Building 1.0, VTR (2. floor)

Daniel Partington
School of Civil, Environmental and Mining Engineering
The University of Adelaide, Australia

Quantifying in-stream and overland flow generation mechanisms using fully integrated flow models

Abstract: Surface water and groundwater systems exhibit important feedbacks that influence the hydrologic response, water quality and ecology of catchments. Understanding surface and subsurface flow processes and the interactions at their interface requires that the physics driving the interactions/processes are well understood. Fully integrated surface-subsurface flow models (i.e. simultaneously solving the surface and subsurface flow equations) play an important role in helping to understand and quantify flow generation processes and surface-subsurface interactions. However, current analysis and interpretation of outputs from fully integrated surface-subsurface flow models does not exploit the wealth of spatiotemporal information provided. A key shortcoming of current methods is the inability to use model outputs to interpret both in-stream and overland flow generation mechanisms and surface water-groundwater interactions with respect to the streamflow hydrograph. In this talk, a method which allows for quantifying in-stream and overland flow generation mechanisms within fully integrated models of surface-subsurface flow is described. This method was used to in a series of tests to investigate the flow generation mechanisms in hypothetical and real catchments. The analysis elucidated the dynamics of overland and in-stream flow generation processes as simulated by the model. This allows for new ways of analysing and interpreting flows within catchments using fully integrated surface-subsurface flow models.

Thursday, 17th of July, 2014, 14:00, Kubus Lecture Hall 1A

Dr. Benjamin Gilfedder
Department of Hydrology
University of Bayreuth

Towards real-time quantitative groundwater surface water interactions: Rn as a continuous tracer

Abstract: Currently, groundwater and surface water are managed as two separate resources, ignoring the complex exchange of water and solutes across the groundwater-surface water interface. This can lead to ‘double accounting’ of water budgets, over allocation and use of water resources and unexpected surface water contamination. Even within the scientific community groundwater discharge is often considered to change slowly in response to seasonal and longer-term variations in water balances. This stems partly from the lack of methods for quantifying long-term high temporal resolution exchange. The aim of this talk is to determine how dynamic groundwater - surface water interactions are, with a particular focus on transient events such as storms and floods. I will present a system for high resolution Rn measurement to quantify groundwater-surface water exchange in (1) a gaining wetland ecosystem and (2) bank storage in a river system. The Rn data will be compared to more conventional electrical conductivity measurements and discuss the benefits and disadvantages of the new system.

Monday, 6th of October, 2014, 11:00, Meeting Room, Building 1, 2nd floor

Dr. Christopher T. Green
National Research Program
U.S. Geological Survey
Menlo Park, CA, USA

Reactive transport of nitrate in groundwater in the USA

Abstract: Nitrate flux in the subsurface is an issue of global importance, yet little is known about the extents and rates of reactions (e.g. denitrification) affecting concentrations in groundwater. The US Geological Survey has conducted studies to better understand the fluxes and reactions of nitrate in groundwater in a range of settings in the USA. Monitoring wells were sampled and sediment cores collected in flow-transects between agricultural fields and streams. Groundwater samples were analyzed for atmospheric tracers of groundwater age, stable isotopes of N and O in nitrate, and dissolved gases to characterize reaction progress. Sediments were analyzed for solid phase electron donors that promote denitrification. Modeling methods included detailed numerical models for understanding processes in heterogeneous aquifers, and analytical solutions to allow systematic comparisons among many sites across the USA. Among the key findings of these studies are that mixing in heterogeneous aquifers reduces the apparent rates of reactions and isotope fractionations, denitrification depends on solid phase electron donors, denitrification rates are often too low to substantially mitigate contamination before reaching receptors, and most shallow aquifers are at or near equilibrium with respect to the depth of nitrate. These findings indicate, in general, that extensive nitrate contamination will persist under current agricultural practices and may worsen if labile, solid-phase electron donors are depleted in aquifers.

Friday, 10th of October, 2014, 10:00, Meeting Room, Building 1, 2nd floor

Dr. Christopher T. Green
National Research Program
U.S. Geological Survey
Menlo Park, CA, USA

US Geological Survey’s National Water Quality Assessment (NAWQA)

Abstract: Evaluating regional water quality requires approaches that are sufficiently complex to represent realistic hydrologic processes, yet sufficiently simple to be applied at very large scales (e.g. thousands of km2). This challenge is central to the mission of the National Water Quality Assessment (NAWQA) Program of the US Geological Survey which began in 1991 with the goals of (1) providing insight into the quality of the nation’s waters and (2) increasing the understanding of local factors and processes that affect water quality. This presentation will address issues of appropriate model complexity and will provide examples of NAWQA activities at large scales including (1) forecasting of nitrate concentrations in groundwater and (2) evaluating trends in surface water nitrate concentrations. In one study, we used numerical experiments and actual tracer data to evaluate the suitability of simple analytical models to estimate travel time distributions of groundwater samples and to forecast nitrate concentrations in groundwater in the Central Valley, California. Numerical experiments indicated that analytical estimates tended to give more accurate predictions of nitrate concentrations than detailed numerical models. Analytical models applied to regional tracer data predicted a continued increase of nitrate concentrations in Central Valley groundwater. Another study addressed long-term trends in nitrate concentrations in large catchments in Iowa. The USGS model EGRET (Exploration and Graphics for RivEr Trends) was used to develop weighted regressions that revealed N concentration trends independent of flow variations. Flow-normalized N concentrations decreased in Iowa Rivers from 2000 to 2012. A multi-model analysis with varying conceptual and mathematical representations of N processes indicated that these trends resulted from extreme flows interacting with hydrogeochemistry and land use rather than stemming directly from changes in agricultural practices. These studies illustrate that hypothesis-driven adaptations of parsimonious models can lead to new insights about water quality issues at large scales.

Tuesday, 30th of June, 2015, 2PM, Meeting Room, Building 1, 2nd floor

Prof. Dr. A.I. Packman
Department of Civil and Environmental Engineering
Northwestern University
Evanston, IL, USA

Combined effects of hyporheic exchange and metabolism on reach-scale nutrient uptake

Abstract: Microbial metabolism in rivers substantially transforms terrestrially-derived nutrients and carbon during passage through watersheds. Co-injections of conservative tracers and nutrients are commonly used to assess net reach-scale nutrient transformation rates and associated benthic and hyporheic uptake parameters. Whole-stream injections are conventionally believed to capture hyporheic exchange processes and nutrient uptake processes independently, and parameters obtained from conservative tracer injections are used directly to interpret nutrient uptake rates. However, in reality hyporheic exchange and metabolism are coupled, and little information is available on spatial patterns of metabolism in the benthic and hyporheic regions. We used numerical simulations to explore the effects of spatial patterns in metabolism on estimates of reach-scale nutrient uptake rates. Within the hyporheic zone, metabolism locally depletes nutrient concentrations relative to conservative tracers, causing concentration profiles of injected nutrients and conservative tracers to diverge. At slow rates of hyporheic exchange relative to rates of metabolism, overall hyporheic nutrient uptake is limited by delivery from the stream, and effective reach-scale nutrient uptake parameters will be controlled by the hyporheic exchange rate. At high rates of hyporheic exchange, the injected tracer can propagate beyond regions of high microbial activity, which commonly occur near the streambed surface. In this case, the injected tracer may not adequately capture timescales of nutrient replenishment in the most bioactive regions (periphyton, biofilms). I will present results from simulations at multiple scales to show how these interactions between hyporheic exchange and metabolism control the relationship between local- and reach-scale biogeochemical transformation rates.

Friday, 28th of August, 2015, 10 AM, Kubus, Room 1A

Prof. Hjalmar Laudon
Department of Forest Ecology and Management
Swedish University of Agricultural Sciences

Linking the terrestrial and aquatic system across scales: The role of connectivity, landscape organization and catchment size for the dynamics of DOC

Abstract: While the production and export of DOC - dissolved organic carbon - from the terrestrial landscape has been extensively studied during the past decades, mechanistic understanding of processes that control stream water quality at the soil/water interface, across different spatial scales, are still at its infancy. To improve the process description of DOC regulation, I will use data and understanding from three decades of research that has been conducted within the interdisciplinary, multi-scale Krycklan Catchment Study (KCS) in northern Sweden ( KCS consists of 17 intensively long-term monitored catchments ranging over three orders of magnitude in size, from 3 ha to over 6780 ha, to elucidate the dominate hydrobiogeophysical processes regulating the concentration and export of nutrients, metals and organic pollutants. By combining the use of detailed catchment information with natural isotopes and the dynamics of stream biogeochemistry we can directly link variability in hydrological flow pathways, catchment characteristics and scale with the spatial and temporal dynamics of DOC. Our results suggest that the contrasting spatial variability in the flow pathways among the different landscape types has a first order control on the DOC. As a result, large variations in the dynamics of DOC and its quality are observed that varies with changes in hydrological connectivity, landscape organization and catchment size.

We have the pleasure to announce that Dr. Diederik Jaques, SCK•CEN Belgium, is giving a talk within the

IP Catchment Dynamics Colloquium

"HPx - a tool for simulating interactive biohydrogeochemical processes in soil systems"


Date: 20 October 2016
Time: 10 am
Venue: UFZ Leipzig, Lecture Hall, Main Building with video transmission to UFZ Magdeburg and Halle