people:hermann_lenhart

Dr. Hermann Lenhart

hermannlenhart.jpg

Projects

Teaching

Wintersemester 2018/2019

Sommersemester 2018

Wintersemester 2017/2018

Sommersemester 2017

Wintersemester 2016/2017

Sommersemester 2016

Wintersemester 2015/2016

Sommersemester 2015

Wintersemester 2014/2015

Sommersemester 2014

Wintersemester 2013/2014

Sommersemester 2013

Wintersemester 2012/2013

Sommersemester 2012

Wintersemester 2011/2012

Sommersemester 2011

Wintersemester 2010/2011

Sommersemester 2010

Publications

2018

  • A model–based projection of historical state of a coastal ecosystem: Relevance of phytoplankton stoichiometry (Onur Kerimoglu, Fabian Große, Markus Kreus, Hermann Lenhart, Justes E.E. van Beusekom), In Science of the Total Environment, Series: 639, pp. 1311–1323, Elsevier Science Publishers B. V. (Amsterdam, The Netherlands), ISSN: 0048-9697, 2018
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    Abstract: We employed a coupled physical-biogeochemical modelling framework for the reconstruction of the historic (H), pre-industrial state of a coastal system, the German Bight (southeastern North Sea), and we investigated its differences with the recent, control (C) state of the system. According to our findings: i) average winter concentrations of dissolved inorganic nitrogen and phosphorus (DIN and DIP) concentrations at the surface are \~70–90\% and \~50–70\% lower in the H state than in the C state within the nearshore waters, and differences gradually diminish towards off-shore waters; ii) differences in average growing season chlorophyll a (Chl) concentrations at the surface between the two states are mostly less than 50\%; iii) in the off-shore areas, Chl concentrations in the deeper layers are affected less than in the surface layers; iv) reductions in phytoplankton carbon (C) biomass under the H state are weaker than those in Chl, due to the generally lower Chl:C ratios; v) in some areas the differences in growth rates between the two states are negligible, due to the compensation by lower light limitation under the H state, which in turn explains the lower Chl:C ratios; vi) zooplankton biomass, and hence the grazing pressure on phytoplankton is lower under the H state. This trophic decoupling is caused by the low nutritional quality (i.e., low N:C and P:C) of phytoplankton. These results call for increased attention to the relevance of the acclimation capacity and stoichiometric flexibility of phytoplankton for the prediction of their response to environmental change.

2017

  • Poster: The use of ICON data within SAGA GIS for decision support in agricultural crop land utilisation (Jannek Squar, Michael Bock, Olaf Conrad, Christoph Geck, Tobias Kawohl, Michael Kuhn, Lars Landschreiber, Hermann Lenhart, Sandra Wendland, Thomas Ludwig, Jürgen Böhner), Hamburg, Germany, DKRZ user workshop 2017, 2017-10-09
    BibTeX
  • Poster: i_SSS – integrated Support System for Sustainability (Jannek Squar, Michael Bock, Olaf Conrad, Christoph Geck, Tobias Kawohl, Michael Kuhn, Lars Landschreiber, Hermann Lenhart, Sandra Wendland, Thomas Ludwig, Jürgen Böhner), Frankfurt, Germany, ISC High Performance 2017, 2017-06-20
    BibTeX URL
  • A Novel Modeling Approach to Quantify the Influence of Nitrogen Inputs on the Oxygen Dynamics of the North Sea (Fabian Große, Markus Kreus, Hermann Lenhart, Johannes Pätsch, Thomas Pohlmann), In Frontiers in Marine Science, Series: 4, pp. 383, (Editors: Christophe Rabouille), Frontiers (Avenue du Tribunal Fédéral 34, CH-1005 Lausanne, Switzerland), 2017
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    Abstract: Oxygen (O$_2$) deficiency, i.e., dissolved O$_2$ concentrations below 6\,mg\,O$_2$\,L$^{-1}$, is a common feature in the southern North Sea. Its evolution is governed mainly by the presence of seasonal stratification and production of organic matter, which is subsequently degraded under O$_2$ consumption. The latter is strongly influenced by riverine nutrient loads, i.e., nitrogen (N) and phosphorus (P). As riverine P loads have been reduced significantly over the past decades, this study aims for the quantification of the influence of riverine and non-riverine N inputs on the O$_2$ dynamics in the southern North Sea. For this purpose, we present an approach to expand a nutrient-tagging technique for physical-biogeochemical models – often referred to as ‘trans-boundary nutrient transports’ (TBNT) – by introducing a direct link to the O$_2$ dynamics. We apply the expanded TBNT to the physical-biogeochemical model system HAMSOM-ECOHAM and focus our analysis on N-related O$_2$ consumption in the southern North Sea during 2000–2014. The analysis reveals that near-bottom O$_2$ consumption in the southern North Sea is strongly influenced by the N supply from the North Atlantic across the northern shelf edge. However, riverine N sources — especially the Dutch, German and British rivers — as well as the atmosphere also play an important role. In the region with lowest simulated O2 concentrations (around 56\,$^\circ$N, 6.5\,$^\circ$E), riverine N on average contributes 39\% to overall near-bottom O$_2$ consumption during seasonal stratification. Here, the German and the large Dutch rivers constitute the highest riverine contributions (11\% and 10\%, respectively). At a site in the Oyster Grounds (around 54.5\,$^\circ$N, 4\,$^\circ$E), the average riverine contribution adds up to 41\%, even exceeding that of the North Atlantic. Here, highest riverine contributions can be attributed to the Dutch and British rivers adding up to almost 28\% on average. The atmospheric contribution results in 13\%. Our results emphasize the importance of anthropogenic N inputs and seasonal stratification for the O$_2$ conditions in the southern North Sea. They further suggest that reductions in the riverine and atmospheric N inputs may have a relevant positive effect on the O$_2$ levels in this region.

2016

  • Looking beyond stratification: a model-based analysis of the biological drivers of oxygen deficiency in the North Sea (Fabian Große, Naomi Greenwood, Markus Kreus, Hermann Lenhart, Detlev Machoczek, Johannes Pätsch, Lesley A. Salt, Helmuth Thomas), In Biogeosciences, Series: 13, pp. 2511–2535, (Editors: Veronique Garçon), Copernicus Publications (Bahnhofsallee 1e, 37081 Göttingen, Germany), 2016
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    Abstract: Low oxygen conditions, often referred to as oxygen deficiency, occur regularly in the North Sea, a temperate European shelf sea. Stratification represents a major process regulating the seasonal dynamics of bottom oxygen, yet, lowest oxygen conditions in the North Sea do not occur in the regions of strongest stratification. This suggests that stratification is an important prerequisite for oxygen deficiency, but that the complex interaction between hydrodynamics and the biological processes drives its evolution. In this study we use the ecosystem model HAMSOM-ECOHAM to provide a general characterisation of the different zones of the North Sea with respect to oxygen, and to quantify the impact of the different physical and biological factors driving the oxygen dynamics inside the entire sub-thermocline volume and directly above the bottom. With respect to oxygen dynamics, the North Sea can be subdivided into three different zones: (1) a highly productive, non-stratified coastal zone, (2) a productive, seasonally stratified zone with a small sub-thermocline volume, and (3) a productive, seasonally stratified zone with a large sub-thermocline volume. Type 2 reveals the highest susceptibility to oxygen deficiency due to sufficiently long stratification periods (>  60 days) accompanied by high surface productivity resulting in high biological consumption, and a small sub-thermocline volume implying both a small initial oxygen inventory and a strong influence of the biological consumption on the oxygen concentration. Year-to-year variations in the oxygen conditions are caused by variations in primary production, while spatial differences can be attributed to differences in stratification and water depth. The large sub-thermocline volume dominates the oxygen dynamics in the northern central and northern North Sea and makes this region insusceptible to oxygen deficiency. In the southern North Sea the strong tidal mixing inhibits the development of seasonal stratification which protects this area from the evolution of low oxygen conditions. In contrast, the southern central North Sea is highly susceptible to low oxygen conditions (type 2). We furthermore show that benthic diagenetic processes represent the main oxygen consumers in the bottom layer, consistently accounting for more than 50 % of the overall consumption. Thus, primary production followed by remineralisation of organic matter under stratified conditions constitutes the main driver for the evolution of oxygen deficiency in the southern central North Sea. By providing these valuable insights, we show that ecosystem models can be a useful tool for the interpretation of observations and the estimation of the impact of anthropogenic drivers on the North Sea oxygen conditions.

2015

  • The North Sea – A shelf sea in the Anthropocene (Kay-Christian Emeis, Justus van Beusekom, Ulrich Callies, Ralf Ebinghaus, Andreas Kannen, Gerd Kraus, Ingrid Kröncke, Hermann Lenhart, Ina Lorkowski, Volker Matthias, Christian Möllmann, Johannes Pätsch, Mirco Scharfe, Helmuth Thomas, Ralf Weisse, Eduardo Zorita), In Journal of Marine Systems, Series: 141, pp. 18–33, Elsevier Science Publishers B. V. (Amsterdam, The Netherlands), 2015
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    Abstract: Global and regional change clearly affects the structure and functioning of ecosystems in shelf seas. However, complex interactions within the shelf seas hinder the identification and unambiguous attribution of observed changes to drivers. These include variability in the climate system, in ocean dynamics, in biogeochemistry, and in shelf sea resource exploitation in the widest sense by societies. Observational time series are commonly too short, and resolution, integration time, and complexity of models are often insufficient to unravel natural variability from anthropogenic perturbation. The North Sea is a shelf sea of the North Atlantic and is impacted by virtually all global and regional developments. Natural variability (from interannual to multidecadal time scales) as response to forcing in the North Atlantic is overlain by global trends (sea level, temperature, acidification) and alternating phases of direct human impacts and attempts to remedy those. Human intervention started some 1000 years ago (diking and associated loss of wetlands), expanded to near-coastal parts in the industrial revolution of the mid-19th century (river management, waste disposal in rivers), and greatly accelerated in the mid-1950s (eutrophication, pollution, fisheries). The North Sea is now a heavily regulated shelf sea, yet societal goals (good environmental status versus increased uses), demands for benefits and policies diverge increasingly. Likely, the southern North Sea will be re-zoned as riparian countries dedicate increasing sea space for offshore wind energy generation – with uncertain consequences for the system's environmental status. We review available observational and model data (predominantly from the southeastern North Sea region) to identify and describe effects of natural variability, of secular changes, and of human impacts on the North Sea ecosystem, and outline developments in the next decades in response to environmental legislation, and in response to increased use of shelf sea space.
  • Looking beyond stratification: a model-based analysis of the biological drivers of oxygen depletion in the North Sea (Fabian Große, Naomi Greenwood, Markus Kreus, Hermann Lenhart, Detlev Machoczek, Johannes Pätsch, Lesley A. Salt, Helmuth Thomas), In Biogeosciences Discussions, Series: 12, pp. 12543–12610, Copernicus Publications (Bahnhofsallee 1e, 37081 Göttingen, Germany), 2015
    BibTeX URL DOI
    Abstract: The problem of low oxygen conditions, often referred to as hypoxia, occurs regularly in the North Sea, a temperate European shelf sea. Stratification represents a major process regulating the seasonal dynamics of bottom oxygen. However, lowest oxygen conditions in the North Sea do not occur in the regions of strongest stratification. This suggests that stratification is an important prerequisite for hypoxia, but that the complex interaction between hydrodynamics and the biological processes drives its development. In this study we use the ecosystem model HAMSOM-ECOHAM5 to provide a general characteristic of the different North Sea oxygen regimes, and to quantify the impact of the different physical and biological factors driving the oxygen dynamics below the thermocline and in the bottom layer. We show that the North Sea can be subdivided into three different regimes in terms of oxygen dynamics: (1) a highly productive, non-stratified coastal regime, (2) a productive, seasonally stratified regime with a small sub-thermocline volume, and (3) a productive, seasonally stratified regime with a large sub-thermocline volume, with regime 2 being highly susceptible to hypoxic conditions. Our analysis of the different processes driving the oxygen development reveals that inter-annual variations in the oxygen conditions are caused by variations in primary production, while spatial differences can be attributed to differences in stratification and water depth. In addition, we show that benthic bacteria represent the main oxygen consumers in the bottom layer, consistently accounting for more than 50 % of the overall consumption. By providing these valuable insights, we show that ecosystem models can be a useful tool for the interpretation of observations and the estimation of the impact of anthropogenic drivers on the North Sea oxygen conditions.

2014

  • Influence of large offshore wind farms on North German climate (Marita Boettcher, Peter Hoffmann, Hermann Lenhart, Heinke Schlünzen, Robert Schoetter), In Meteorologische Zeitschrift, Series: 24, pp. 465–480, Borntraeger Science Publishers (Stuttgart), ISSN: 0941-2948, 2014
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    Abstract: Wind farms impact the local meteorology by taking up kinetic energy from the wind field and by creating a large wake. The wake influences mean flow, turbulent fluxes and vertical mixing. In the present study, the influences of large offshore wind farms on the local summer climate are investigated by employing the mesoscale numerical model METRAS with and without wind farm scenarios. For this purpose, a parametrisation for wind turbines is implemented in METRAS. Simulations are done for a domain covering the northern part of Germany with focus on the urban summer climate of Hamburg. A statistical-dynamical downscaling is applied using a skill score to determine the required number of days to simulate the climate and the influence of large wind farms situated in the German Bight, about 100 km away from Hamburg.Depending on the weather situation, the impact of large offshore wind farms varies from nearly no influence up to cloud cover changes over land. The decrease in the wind speed is most pronounced in the local areas in and around the wind farms. Inside the wind farms, the sensible heat flux is reduced. This results in cooling of the climate summer mean for a large area in the northern part of Germany. Due to smaller momentum fluxes the latent heat flux is also reduced. Therefore, the specific humidity is lower but because of the cooling, the relative humidity has no clear signal. The changes in temperature and relative humidity are more wide spread than the decrease of wind speed. Hamburg is located in the margins of the influenced region. Even if the influences are small, the urban effects of Hamburg become more relevant than in the present and the off-shore wind farms slightly intensify the summer urban heat island.

2012

  • Report on “Distance to Target” Modelling Assessment by ICG-EMO (Hermann Lenhart, Xavier Desmit, Fabian Große, David Mills, Geneviève Lacroix, Hans Los, Alain Ménesguen, Johannes Pätsch, Tineke Troost, Johan van der Molen, Sonja van Leeuwen, Sarah Wakelin), Reports of OSPAR ICG-EMO Working group, OSPAR Commission (London, United Kingdom), 2012
    BibTeX

2010

  • Modellbasierte Bewertung der Auswirkungen von Offshore-Windkraftanlagen auf die ökologische Integrität der Nordsee (Benjamin Burkhard, Silvia Opitz, Hermann Lenhart, Kai Ahrendt, Stefan Garthe, Bettina Mendel, Petra Nerge, Wilhelm Windhorst), In Forschung für ein integriertes Küstenzonenmanagement: Fallbeispiele Odermündungsregion und Offshore-Windkraft in der Nordsee (A. Kannen, G. Schernewski, I. Krämer, M. Lange, H. Janßen, N. Stybel), Series: 15 (2010), pp. 15–29, Coastline Reports (EUCC - Die Küsten Union Deutschland e. V., c/o Leibniz-Institut für Ostseeforschung Warnemünde, Seestr. 15, 18119 Rostock, Germany), ISBN: 978-3-9811839-7-9, 2010
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  • Wake Effects (Petra Nerge, Hermann Lenhart), In Analyzing Coastal and Marine Changes: Offshore Wind Farming as a Case Study. Zukunft Küste - Coastal Futures Synthesis Report. (Marcus Lange, Benjamin Burkhard, Stefan Garthe, Kira Gee, Andreas Kannen, Hermann Lenhart, Wilhelm Windhorst), Series: No. 36, Chapters: 5.3, pp. 68–73, LOICZ Research and Studies (GKSS Research Center, Geesthacht, Germany), 2010
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  • Predicting the consequences of nutrient reduction on the eutrophication status of the North Sea (Hermann Lenhart, David K. Mills, Hanneke Baretta-Bekker, Sonja M. van Leeuwen, Johan van der Molen, Job W. Barettad, Meinte Blaase, Xavier Desmite, Wilfried Kühna, Geneviève Lacroixf, Hans J. Lose, Alain Ménesgueng, Ramiro Nevesh, Roger Proctori, Piet Ruardijj, Morten D. Skogenk, Alice Vanhoutte-Brunierg, Monique T. Villarse, Sarah L. Wakelini), In Journal of Marine Systems, Series: 81 (1-2), pp. 148–170, Elsevier B.V (Amsterdam, Netherlands), ISSN: 0924-7963, 2010
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    Abstract: In this paper the results from a workshop of the OSPAR Intersessional Correspondence Group on Eutrophication Modelling (ICG-EMO) held in Lowestoft in 2007 are presented. The aim of the workshop was to compare the results of a number of North Sea ecosystem models under different reduction scenarios. In order to achieve comparability of model results the participants were requested to use a minimum spin-up time, common boundary conditions which were derived from a wider-domain model, and a set of common forcing data, with special emphasis on a complete coverage of river nutrient loads. Based on the OSPAR requirements river loads were derived, taking into account the reductions already achieved between 1985 and 2002 for each country. First, for the year 2002, for which the Comprehensive Procedure was applied, the different horizontal distributions of net primary production are compared. Furthermore, the differences in the net primary production between the hindcast run and the 50% nutrient reduction runs are displayed. In order to compare local results, the hindcast and reduction runs are presented for selected target areas and scored against the Comprehensive Procedure assessment levels for the parameters DIN, DIP and chlorophyll. Finally, the temporal development of the assessment parameter bottom oxygen concentration from several models is compared with data from the Dutch monitoring station Terschelling 135. The conclusion from the workshop was that models are useful to support the application of the OSPAR Comprehensive Procedure. The comparative exercise formulated specifically for the workshop required models to be evaluated for pre-defined target areas previously classified as problem areas according to the first application of the Comprehensive Procedure. The responsiveness of the modelled assessment parameters varied between different models but in general the parameter showed a larger response in coastal rather than in offshore waters, which in some cases lead to the goal to achieve a non-problem status. Therefore, the application of the Comprehensive Procedure on model results for parameter assessment opens a new potential in testing eutrophication reduction measures within the North Sea catchment. As a result of the workshop further work was proposed to confirm and bolster confidence in the results. One general field of difficulty appeared to be the model forcing with SPM data in order to achieve realistic levels of light attenuation. Finally, effects of the prescribed spin-up procedure are compared against a long-term run over many years and consequences on the resulting initial nutrient concentrations are highlighted

2009

  • Ecosystem based modeling and indication of ecological integrity in the German North Sea - Case study offshore wind parks (Benjamin Burkhard, Silvia Opitz, Hermann Lenhart, Kai Ahrendt, Stefan Garthe, Bettina Mendel, Wilhelm Windhorst), In Ecological Indicators, Series: 11-1, pp. 168–174, Elsevier B.V (Amsterdam, Netherlands), ISSN: 1470-160X, 2009
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    Abstract: Human exploitation and use of marine and coastal areas are apparent and growing in many regions of the world. For instance, fishery, shipping, military, raw material exploitation, nature protection and the rapidly expanding offshore wind power technology are competing for limited resources and space. The development and implementation of Integrated Coastal Zone Management (ICZM) strategies could help to solve these problems. Therefore, suitable spatial assessment, modeling, planning and management tools are urgently needed. These tools have to deal with data that include complex information on different spatial and temporal scales. A systematic approach based on the development of future scenarios which are assessed by combining different simulation models, GIS methods and an integrating set of ecological integrity indicators, was applied in a case study in the German North Sea. Here, the installation of huge offshore wind parks within the near future is planned. The aim was to model environmental effects of altered sea-use patterns on marine biota. Indicators of ecological integrity were used to assess altering conditions and possible ecosystem shifts ranging from systems' degradations to the development of highly productive and diverse artificial reef systems. The results showed that some ecosystem processes and properties and related indicators are sensitive to changes generated by offshore wind park installations while others did not react as hypothesized

2008

  • Ecological risk as a tool for evaluating the effects of offshore wind farm construction in the North Sea (Corinna Nunneri, Hermann Lenhart, Benjamin Burkhard, Wilhelm Windhorst), In Regional Environmental Change, Series: 8-1, pp. 31–43, Springer (Berlin / Heidelberg, Germany), ISSN: 1436-3798, 2008-03
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    Abstract: Offshore wind power generation represents a chance to supply energy in a more sustainable way; however, the ecological risks associated with the construction and operation of offshore wind farms are still largely unknown. This paper uses the concept of ecological risk for analysing ecological changes during construction of offshore wind farms. “Ecological risk” is defined as the potentially reduced ability of providing ecosystem services. The ERSEM ecosystem model allows assessing ecological risk based on a number of selected variables (integrity indicators) and under the assumption that increased suspended matter concentration during construction of wind farms affects ecosystem functioning. We conclude that ecological risk is adequate to describe the effects of wind farm constructions, although the computation procedure still needs to be refined and the choice of indicators further optimised. In this context, the choice of indicators available in modelling as well as in monitoring time-series may offer the way forward
  • The use of 'ecological risk' for assessing effects of human activities: an example including eutrophication and offshore wind farm construction in the North Sea (Corinna Nunneri, Hermann Lenhart, Benjamin Burkhard, Franciscus Colijn, Felix Müller, Wilhelm Windhorst), In Landscape online, Series: 5, ISSN: 1865-1542, 2008
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    Abstract: This paper takes the move from the uncertainty surrounding ecosystem thresholds and addresses the issue of ecosystem-state assessment by means of ecological integrity indicators and ‘ecological risk‘. The concept of ‘ecological risk‘ gives a measure of the likelihood of ecosystem failure to provide the level of natural ecological goods and services expected/desired by human societies. As a consequence of human pressures (use of resources and discharge into the environment), ecosystem thresholds can be breached thus resulting in major threats to human health, safety and well-being. In this study we apply the concept of ‘ecological risk‘ to two case-studies in the German exclusive economic zone: eutrophication and construction of offshore wind farms. The effects of different future scenarios for single-uses upon ecosystem integrity are analysed as well as the effects of one combined scenario. We conclude that in the short term construction of offshore wind farms can influence some processes to a much larger degree than eutrophication, however, combined impacts deriving from eutrophication and offshore wind farm construction need a more detailed analysis. Due to non-linear ecosystem processes, effects of combined or multiple uses of marine resources in terms of ‘ecological risk‘, cannot be extrapolated from single-use scenarios

2007

  • Nutrient emission reduction scenarios in the North Sea: An abatement cost and ecosystem integrity analysis (Corinna Nunneri, Wilhelm Windhorst, R. Kerry Turner, Hermann Lenhart), In Ecological Indicators, Series: 7-4, pp. 776–792, Elsevier B.V (Amsterdam, Netherlands), ISSN: 1470-160X, 2007
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    Abstract: Economic cost–benefit appraisal (and its sub-set cost-effectiveness) of ecosystem conservation and/or pollution abatement strategies have proved to be powerful decision-making aids. But the monetary economic valuation of ecosystem goods and services (gains and losses) can only provide a good indication of social welfare impacts under certain conditions and in selective contexts. The values derived through this appraisal process will, for a number of measures, be underestimates of the full total system value [Turner, R.K., Paavola, J., Cooper, P. Farber, S., Jessamy, V., Georgiou, S., 2003. Valuing nature: lessons learned and future research directions. Ecol. Econ. 46, 493–510]. The economic analysis is best suited to assessing the value of ‘marginal’ gains and losses in ecosystem goods/services and not the total destruction of whole systems (including life support systems, the value of which is not commensurate with monetary values and/or is infinitely high). In this study economic costs and what we call 'ecological risk' analysis are used to appraise the implementation costs and ecological benefits of selected measures for combating eutrophication. Ecological risk is expressed in terms of ecosystem integrity and resilience. The paper presents three regional case studies dealing with the issue of nutrient emission reduction to the southern North Sea, namely the catchments/estuaries of the Humber (UK), the Rhine (Germany and The Netherlands) and the Elbe (Czech Republic and Germany). On the basis of these comparative regional examples, wider implications in the light of international management of the North Sea are presented. A range of nutrient reduction scenarios have been deployed within the overall OSPAR target agreement of 50% nitrogen and phosphorous reduction compared with 1985 levels. Each scenario assumes pollution reduction measures, characterised in terms of their overall implementation costs and nutrient-reduction effects. Specific policy instruments analysed were: the creation of more intertidal habitat via managed coastal realignment in the Humber area, farm-based land cover changes in the Rhine catchment and a mix of agricultural regime and wastewater treatment plant (WWTP) improvements in the Elbe area. The ecological consequences associated with each reduction scenario have been modelled [using the ERSEM model, see Baretta, J.W., Ebenhöh, W., Ruardij, P., 1995. An overview over the European Regional Sea Ecosystem Model, a complex marine ecosystem model. Neth. J. Sea Res. 33 (3/4), 233–246] for the coastal zones supplied from the rivers Elbe, Humber and Rhine. The modelled ecological quality indicators, which describe scenario effects on the coastal zone ecosystem, are then aggregated in terms of ecosystem integrity and ecological risk. The results are presented in terms of two selected key-indicators: implementation costs of the abatement measures and changes in ecological risk status, across the different catchments and assuming different scenarios. They thus provide a possible basis for international agreement negotiations at the North Sea scale

2005

  • Catchment-coastal zone interaction based upon scenario and model analysis: Elbe and the German Bight case study (J. Hofmann, H. Behrendt, A. Gilbert, R. Jannssen, A. Kannen, Hermann Lenhart, W. Lise, Corinna Nunneri, Wilhelm Windhorst), In Regional Environmental Change, Series: 5 (2-3), Springer (Berlin / Heidelberg, Germany), ISSN: 1436-378X, 2005
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    Abstract: This paper presents a holistic strategy on the interaction of activities in the Elbe river basin and their effects on eutrophication in the coastal waters of the German Bight. This catchment–coastal zone interaction is the main target of the EUROCAT (EUROpean CATchments, catchment changes and their impact on the coast) research project, with the Elbe being one of eight case studies. The definition of socio-economic scenarios is linked with the application of models to evaluate measures in the catchment by estimation of nutrient emissions with MONERIS (MOdelling Nutrient Emissions in RIver Systems), and their effects on coastal waters with the ecosystem model ERSEM (European Regional Seas Ecosystem Model). The cost effectiveness of reduction measures will then be evaluated by application of the CENER model (Cost-Effective Nutrient Emission Reduction) and a multi-criteria analysis. Finally, the interpretation of ecological integrity is used as a measure to describe ecological impacts in an aggregated form
  • Defining a good ecological status of coastal waters - a case study for the Elbe plume (Wilhelm Windhorst, Franciscus Colijn, Saa Kabuta, Remi Laane, Hermann Lenhart), In Managing European Coasts (Jan Vermaat, Wim Salomons, Laurens Bouwer, Kerry Turner), pp. 59–74, Springer (Berlin / Heidelberg, Germany), ISBN: 978-3-540-23454-8, 2005
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    Abstract: The definition of a good ecological status of coastal waters requires a close cooperation between sciences (natural and socio-economic) and decision makers. An argument is presented for the use of ecosystem integrity assessment based on indicators of function and state. Ecosystem integrity is understood to be reflected in exergy capture (here expressed as net primary production), storage capacity (as nutrient input/outut balances for coastal sediments), cycling (turn-over of winter nutrient stocks), matter losses (into adjacent water), and heterogeneity (here the diatom/non-diatom ratio of planktonic algae is used). Its feasibility is assessed using ERSEM, an ecosystem model of the North Sea, for the Elbe plume, after prior satisfactory calibration. Three scenarios were applied corresponding to 80, 70 and 60% reduction of the riverine nutrient load into the German Bight, compared to a reference situation of 1995. The modelling effort suggested that drastic nutrient load reduction from the Elbe alone would have a limited effect on the larger German Bight: even a 60% reduction scenario would only lead to moderate changes in all five indicators. In conclusion, application of functional integrity indicators appears feasible for coastal seas at larger spatial scales (i.e. the German Bight), and, for the coast, would form a useful addition to the indicators presently proposed in the Water Framework Directive (WFD)

2004

  • North Sea Hydrodynamic Modelling: A Review (Hermann Lenhart, Thomas Pohlmann), In Senckenbergiana maritima, Series: 34-(1/2), pp. 53–88, (Editors: Ingrid Kröncke, Michael Türkay, Jürgen Sündermann), 2004
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2002

  • Nährstoffe und Eutrophierung (Uwe Brockmann, Hermann Lenhart, Heinke Schlünzen, Dilek Topcu), In Warnsignale aus Nordsee und Wattenmeer - Eine aktuelle Umweltbilanz (Jose L. Lozan, Eike Rachor, Karsten Reise, Jürgen Sündermann, Hein Westernhagen), pp. 61–76, ISBN: 978-3000101663, 2002
    BibTeX

2000

  • Effects of river nutrient load reduction on the eutrophication of the North Sea, simulated with the ecosystem model ERSEM (Hermann Lenhart), In Senckenbergiana maritima, Series: 31-2, pp. 299–311, (Editors: Ingrid Kröncke, Michael Türkay, Jürgen Sündermann), 2000
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    Abstract: The results of the ecosystem model ERSEM showed, that a reduction in the nutrient load by 50% for N and P cannot be linearly transferred to a similar reduction in primary production in comparison to the standard run for the year 1988. While the reduction scenario results in decreased winter concentrations of nitrogen and phosphorus of up to 40%, the decrease in net primary production reached only up to 20% in small areas in the coastal zone. The phytoplankton groups indicated different reactions to the changed nutrient availability. Generally, there were significant changes in the strength and timing of the nutrient limitation in all phytoplankton groups in the model, but the diatom concentration did not change much. Differences did occur for the flagellates, with sporadically higher flagellate concentration in comparison to the standard run. This result is important, because the increase in algal biomass due to eutrophication was related mainly to an increase in flagellates, which are not decreasing accordingly in the reduction scenario. The reduction scenarios demonstrated that changes in the discharges of the major rivers hardly affect the central North Sea, but lead to significant regional differences in the net primary production. Greatest differences with regard to primary production were found downstream of the river Rhine and Elbe. This leads to changes in the mass flows in the coastal area with an increased importance of the microbial loop. One possible reason for the muted reaction of primary production to decreasing nutrient inputs can be seen in the temporal coincidence of maximum river inputs and the phytoplankton spring bloom. Due to the high nutrient uptake during the spring bloom, inorganic nutrients are bound in the phytoplankton and form a potential for remineralisation. With a more efficient microbial loop, the system becomes less dependent on riverine nutrient inputs in summer

1997

  • The effects of river input on the ecosystem dynamics in the continental coastal zone of the North Sea using ERSEM (Hermann Lenhart, Günther Radach, Piet Ruardij), In Journal of Sea Research, Series: 38 (3-4), pp. 249–274, Elsevier B.V (Amsterdam, Netherlands), ISSN: 1385-1101, 1997
    BibTeX DOI
    Abstract: The general characteristics of the continental coastal zone, with nutrient concentrations, primary production and biomass high near the coast but decreasing with distance from the coast, are simulated by a box-refined version of the ecosystem model ERSEM. Aggregated model results compared to the literature as well as to two different three-dimensional models show a good agreement in the coastal region. The dynamical interactions as simulated by the ecosystem model are presented in the form of N/P ratios, the limitation by various nutrients and changes in the pathways of the flow of matter in the boxes; e.g. while the silicate limitation stops the spring bloom offshore, near the coast it is terminated by zooplankton
    grazing. When the river load was reduced by 50%, the largest effect was observed in the coastal boxes with 15% reduction of the net primary production. The discharges of the major rivers hardly affect the central North Sea, but lead to significant changes in nutrient limitations and mass flows in the coastal area. The realistic forcing, which was adopted for this setup, allows a higher net primary production in the southern North Sea in 1989 than in 1988, even though the nutrient river loads in 1989 were lower. The reason appears to be a higher solar energy input in 1989, by about 10 W m^−2 d-^-1, compared to 1988
  • The ICES-boxes approach in relation to results of a North Sea circulation model (Hermann Lenhart, Thomas Pohlmann), In Tellus, Series: 49 A, pp. 139–160, Blackwell (Oxford, United Kingdom), ISSN: 0280-6495, 1997
    BibTeX
    Abstract: Based on the division of the North Sea into the ICES boxes, often used as a tool to present data aggregated from measurements, the results of a 3-D baroclinic model for 11 years of simulation are presented. Since the information on the ICES boxes from the 3-D model is available as synoptic property, a comprehensive description of the water budget, the transport through the boxes as well as the flushing times is attained. Moreover, the results of the 3-D model allows for a quantification of the horizontal diffusion acting between the ICES boxes. Integrated properties of the boxes are obtained from comparing the depth of the thermocline derived by vertical diffusion and by the gradient in the temperature profile. Considerable changes can be observed for the period of stratification within the boxes from the gradient in the temperature profile compared to potential energy calculations. The properties of the ICES boxes as the basis for a box model are presented by means of the ecosystem model ERSEM. A tracer study, using freshwater as a conservative tracer, compares the results of the ERSEM box model with the results aggregated from a gridded dispersion model, using the same physical forcing. From this comparison, an appropriate transport representation for the box model is derived. Furthermore the results of ERSEM demonstrate that a modification of the boxes, i.e., by introducing a vertical separation for those boxes which are stratified in summer, can improve the representation of the biological processes influenced by the thermocline dynamics

1996

  • Influence of variability in water transport on phytoplankton biomass and composition in the southern North Sea: a modelling approach (FYFY) (A. J. Van Den Berg, H. Ridderinkhof, R. Riegman, P. Ruardij, Hermann Lenhart), In Continental Shelf Research, Series: 16-7, pp. 907–917, Elsevier B.V (Amsterdam, Netherlands), ISSN: 0278-4343, 1996
    BibTeX DOI
    Abstract: A model for phytoplankton composition and succession coupled to a transport model for the southern North Sea is presented. This model is used to examine the time and spatial variability in phytoplankton biomass and succession. Long term time variability due to the variability in horizontal water transport is studied by using daily varying transport fields for the period 1970-1981. These transport fields result from simulations with a circulation model driven by realistic wind fields for this period. Selective factors for phytoplankton are resource competition and zooplankton grazing. This leads to a general abundance of edible phytoplankton groups in the whole southern North Sea, while poorly edible groups mainly occur in the eutrophicated coastal areas. Apart from this, phytoplankton groups which are specialized in growth under nitrogen-limited conditions are selected in open sea while, near the Dutch coast and the German Bight, phosphate-specialized groups are selected. From a comparison of simulations with yearly averaged and daily varying transport fields, it is concluded that differences with respect to the annual mean phytoplankton biomass are negligible. However, large differences are found for the distribution and abundance of specific phytoplankton groups. A simulation for the period 1970-1981 shows that part of the observed variability in spring biomass as well as the variability in the duration of dominance and abundance of species near the Dutch coast can be attributed to the variability in the horizontal water transport

1995

  • Simulations of the North Sea circulation, its variability, and its implementation as hydrodynamical forcing in ERSEM (Hermann Lenhart, Günther Radach, Jan O. Backhaus, Thomas Pohlmann), In Netherlands Journal of Sea Research, Series: 33 (3-4), pp. 271–299, Elsevier B.V (Amsterdam, Netherlands), ISSN: 0077-7579, 1995
    BibTeX DOI
    Abstract: The rationale is given of how the gross physical features of the circulation and the stratification of the North Sea have been aggregated for inclusion in the ecosystem box model ERSEM. As the ecosystem dynamics are to a large extent determined by small-scale physical events, the ecosystem model is forced with the circulation of a specific year rather than using the long-term mean circulation field. Especially the vertical exchange processes have been explicitly included, because the primary production strongly depends on them. Simulations with a general circulation model (GCM), forced by three-hourly meteorological fields, have been utilized to derive daily horizontal transport values driving ERSEM on boxes of sizes of a few 100 km. The daily vertical transports across a fixed 30-m interface provide the necessary short-term event character of the vertical exchange. For the years 1988 and 1989 the properties of the hydrodynamic flow fields are presented in terms of trajectories of the flow, thermocline depths, of water budgets, flushing times and diffusion rates. The results of the standard simulation with ERSEM show that the daily variability of the circulation, being smoothed by the box integration procedure, is transferred to the chemical and biological state variables to a very limited degree only
  • Nutrient dynamics in the North Sea: Fluxes and budgets in the water column derived from ERSEM (Günther Radach, Hermann Lenhart), In Netherlands Journal of Sea Research, Series: 33 (3-4), Elsevier B.V (Amsterdam, Netherlands), ISSN: 0077-7579, 1995
    BibTeX DOI
    Abstract: Nutrient dynamics for phosphate, nitrate, ammonium and silicate have been simulated with ERSEM, the European Regional Seas Ecosystem Model. From the model results budgets for the dissolved inorganic nutrients and the corresponding particulate fractions have been calculated. The annual cycles of the nutrients phosphate and silicate compare quite well with the observed ranges of variability. This does not hold for ammonium and nitrate. Biologically mediated transformations such as nutrient uptake and pelagic and benthic mineralization are the dominant processes in changing the nutrient concentrations with the horizontal advective contributions playing a minor role during the productive season. Vertical advection and vertical diffusion have a clear seasonal signal, with a maximum in February. The decay of the advective nutrient transport in summer is caused by the depletion of the upper layer of dissolved inorganic nutrients by algal uptake. The inflow of nutrients in the northwest is almost balanced by the outflow in the northeast, without causing large nutrient transports into the shallower areas from the north. However, from the coastal areas there is a nutrient flow towards the central North Sea, enhancing primary production in the central area

1990

  • Nährstoffe in der Nordsee - Eutrophierung, Hypertrophierung und deren Auswirkungen (G. Radach, W. Schönfeld, Hermann Lenhart), In Warnsignale aus der Nordsee (José .L. Lozan, Walter Lenz, Eike Rachor, Burkard Watermann, Heinz v. Westernhagen), pp. 48–65, Paul Parey Verlagsbuchhandlung (Hamburg / Berlin), 1990
    BibTeX

Talks

2018

  • Assessing trans-boundary nutrient modelling results including WFD reduction scenario within an OSPAR frame (Hermann Lenhart, Fabian Große), 4th International Symposium on Research and Management of Eutrophication in Coastal Ecosystems (EUTRO2018), Nyborg, Denmark, 2018-06-18

2017

  • Riverine nitrogen and oxygen deficiency in the North Sea: Extending trans-boundary nutrient transports for the ecological management of low oxygen conditions (Fabian Große, Markus Kreus, Hermann Lenhart, Johannes Pätsch), Advances in Marine Ecosystem Modelling Research (AMEMR), Plymouth, UK, 2017-07-04
  • WFD-compliant nitrogen reductions within the OSPAR framework: A source-oriented approach for the North Sea (Fabian Große, Hermann Lenhart), Innovative modelling in support of MSFD implementation, Brussels, Belgium, 2017-03-22

2016

  • The influence of riverine nitrogen on the North Sea oxygen minimum zone (Fabian Große, Markus Kreus, Hermann Lenhart, Johannes Pätsch), EGU General Assembly 2016, Vienna, Austria, 2016-04-20

2014

  • Looking beyond stratification: A model-based analysis of the biological drivers of oxygen depletion in the North Sea (Fabian Große, Hermann Lenhart, Uwe Brockmann), 46th International Liège Colloquium, Liègei, Belgium, 2014-05-06

2010

  • Auswirkungen von Windfeldänderungen durch Offshore-Windparks auf das marine Umfeld (Hermann Lenhart, Petra Nerge), Abschlusssymposium Zukunft Küste - Coastal Futures, Hamburg, Deutschland, 2010-03-04 Presentation

Supervised Theses

2016

people/hermann_lenhart.txt · Last modified: 2018-02-07 15:31 (external edit)