arXiv subjects

Carsten Lemmen

Publications and source records attributed to Carsten Lemmen.

14 recordsLinked to original sources

arXiv2026

OxyPOM: a biogeochemical model for Oxygen and Particulate Organic Matter dynamics with detailed temperature sensitivity

Periods of low dissolved oxygen concentration -- hypoxia and anoxia -- threaten the health of aquatic ecosystems and the services they provide.Hypoxia is strongly influenced by temperature, but the different sensitivities and response functions of oxygen removal and production processes to temperature are not regarded in most models. Here we present OxyPOM -- Oxygen and Particulate Organic Matter, a nuanced temperature-aware process-based biogeochemical model. OxyPOM incorporates nuanced temperature sensitivities for the key oxygen-related processes photosynthesis, re-aeration, respiration, mineralization, and nitrification. Further sensitive variables like optimal light intensity, winter grazing inhibition, and pathogenesis are also represented. Our model was tested in an idealized water column experiment, representing a typical estuarine seasonal low-oxygen environment. Differences between nuanced and uniform temperature sensitivities affect seasonal patterns of oxygen-related processes, resulting in under- or overestimation during different times of the year, particularly with higher differences in summer. While these changes may balance in the overall annual oxygen budget, uniform sensitivities underestimate particulate organic carbon production by up to a factor of four along the year and overestimate nutrient concentrations. This nuanced approach to temperature sensitivity allows us to explore and test new hypotheses related to climate warming and heatwaves, addressing the ecosystem changes demanded by climate change models.

q-bio.OT↗

arXiv2025

Disentangling peri-urban river hypoxia

Episodes of low dissolved oxygen concentration--hypoxia--threaten the functioning of and the services provided by aquatic ecosystems, particularly those of urban rivers. Here, we disentangle oxygen-related processes in the highly modified Elbe River flowing through the major German city of Hamburg, where low oxygen levels are frequently observed. We use a process-based biochemical model that describes particulate and dissolved organic matter, micro-algae, their pathogens, and the key reactions that produce or consume oxygen: photosynthesis, re-aeration, respiration, mineralization, and nitrification. The model analysis reveals pronounced spatial variability in the relative importance of these processes. Photosynthesis and respiration are more prominent upstream of the city, while mineralization, nitrification, and re-aeration prevail downstream. The city, characterized by rapid changes in bathymetry, marks a transitional area: pathogen-related micro-algal lysis may increase organic material, explaining the shift towards heterotrophic processes downstream. As the primary driver of seasonal changes, the model analysis reveals a differential temperature sensitivity of biochemical rates. These results may be extrapolated to other urban rivers, and also provide valuable information for estuarine water quality management.

q-bio.OT↗

arXiv2024

Good modelling software practices

Frequently in socio-environmental sciences, models are used as tools to represent, understand, project and predict the behaviour of these complex systems. Along the modelling chain, Good Modelling Practices have been evolving that ensure - amongst others - that models are transparent and their results replicable. Whenever such models are represented in software, Good Modelling meet Good Software Practices, such as a tractable development workflow, good code, collaborative development and governance, continuous integration and deployment; and they meet Good Scientific Practices, such as attribution of copyrights and acknowledgement of intellectual property, publication of a software paper and archiving. Too often in existing socio-environmental model software, these practices have been regarded as an add-on to be considered at a later stage only; modellers have shied away from publishing their model as open source out of fear that having to add good practices is too demanding. We here argue for making a habit of following a list of simple and not so simple practices early on in the implementation of the model life cycle. We contextualise cherry-picked and hands-on practices for supporting Good Modelling Practice, and we demonstrate their application in the example context of the Viable North Sea fisheries socio-ecological systems model.

cs.SE↗

arXiv2023

Interactive effects of multiple stressors in coastal ecosystems

Coastal ecosystems are increasingly experiencing anthropogenic pressures such as climate heating, CO2 increase, metal and organic pollution, overfishing and resource extraction. Some resulting stressors are more direct like fisheries, others more indirect like ocean acidification, yet they jointly affect marine biota, communities and entire ecosystems. While single-stressor effects have been widely investigated, the interactive effects of multiple stressors on ecosystems are less researched. In this study, we review the literature on multiple stressors and their interactive effects in coastal environments across organisms. We classify the interactions into three categories: synergistic, additive, and antagonistic. We found phytoplankton and mollusks to be the most studied taxonomic groups. The stressor combinations of climate warming, ocean acidification, eutrophication, and metal pollution are the most critical for coastal ecosystems as they exacerbate adverse effects on physiological traits such as growth rate, basal respiration, and size. Phytoplankton appears to be most sensitive to interactions between metal and nutrient pollution. In nutrient-enriched environments, the presence of metals considerably affects the uptake of nutrients, and increases respiration costs and toxin production in phytoplankton. For mollusks, warming and low pH are the most lethal stressors. The combined effect of heat stress and ocean acidification leads to decreased growth rate, shell size, and acid-base regulation capacity in mollusks. However, for a holistic understanding of how coastal food webs will evolve with ongoing changes, we suggest more research on ecosystem-level responses. This can be achieved by combining in-situ observations from controlled environments (e.g. mesocosm experiments) with modelling approaches.

q-bio.QM↗

arXiv2017

The large scale impact of offshore wind farm structures on pelagic primary productivity in the southern North Sea

The increasing demand for renewable energy is projected to result in a 40-fold increase in offshore wind electricity in the European Union by 2030. Despite a great number of local impact studies for selected marine populations, the regional ecosystem impacts of offshore wind farm structures are not yet well assessed nor understood. Our study investigates whether the accumulation of epifauna, dominated by the filter feeder Mytilus edulis (blue mussel), on turbine structures affects pelagic primary productivity and ecosystem functioning in the southern North Sea. We estimate the anthropogenically increased potential distribution based on the current projections of turbine locations and reported patterns of M. edulis settlement. This distribution is integrated through the Modular Coupling System for Shelves and Coasts to state-of-the-art hydrodynamic and ecosystem models. Our simulations reveal non-negligible potential changes in regional annual primary productivity of up to 8% within the offshore wind farm area, and induced maximal increases of the same magnitude in daily productivity also far from the wind farms. Our setup and modular coupling are effective tools for system scale studies of other environmental changes arising from large-scale offshore wind-farming such as ocean physics and distributions of pelagic top predators.

q-bio.PE↗

arXiv2017

Modular System for Shelves and Coasts (MOSSCO v1.0) - a flexible and multi-component framework for coupled coastal ocean ecosystem modelling

Shelf and coastal sea processes extend from the atmosphere through the water column and into the sea bed. These processes are driven by physical, chemical, and biological interactions at local scales, and they are influenced by transport and cross strong spatial gradients. The linkages between domains and many different processes are not adequately described in current model systems. Their limited integration level in part reflects lacking modularity and flexibility; this shortcoming hinders the exchange of data and model components and has historically imposed supremacy of specific physical driver models. We here present the Modular System for Shelves and Coasts (MOSSCO, http://www.mossco.de), a novel domain and process coupling system tailored---but not limited--- to the coupling challenges of and applications in the coastal ocean. MOSSCO builds on the existing coupling technology Earth System Modeling Framework and on the Framework for Aquatic Biogeochemical Models, thereby creating a unique level of modularity in both domain and process coupling; the new framework adds rich metadata, flexible scheduling, configurations that allow several tens of models to be coupled, and tested setups for coastal coupled applications. That way, MOSSCO addresses the technology needs of a growing marine coastal Earth System community that encompasses very different disciplines, numerical tools, and research questions.

physics.ao-ph↗

arXiv2017

The Diffusion of Humans and Cultures in the Course of the Spread of Farming

The most profound change in the relationship between humans and their environment was the introduction of agriculture and pastoralism. [....] For an understanding of the expansion process, it appears appropriate to apply a diffusive model. Broadly, these numerical modeling approaches can be catego- rized in correlative, continuous and discrete. Common to all approaches is the comparison to collections of radiocarbon data that show the apparent wave of advance of the transition to farming. However, these data sets differ in entry density and data quality. Often they disregard local and regional specifics and research gaps, or dating uncertainties. Thus, most of these data bases may only be used on a very general, broad scale. One of the pitfalls of using irregularly spaced or irregularly documented radiocarbon data becomes evident from the map generated by Fort (this volume, Chapter 16): while the general east-west and south-north trends become evident, some areas appear as having undergone anomalously early transitions to farming. This may be due to faulty entries into the data base or regional problems with radiocarbon dating, if not unnoticed or undocumented laboratory mistakes.

q-bio.PE↗

arXiv2015

Cultural and Demic Diffusion of First Farmers, Herders, and their Innovations Across Eurasia

Was the spread of agropastoralism from the Eurasian founder regions dominated by demic or by cultural diffusion? This study employs a mathematical model of regional sociocultural development that includes different diffusion processes, local innovation and societal adaptation. Simulations hindcast the emergence and expansion of agropastoral life style in 294 regions of Eurasia and North Africa. Different scenarios for demic and diffusive exchange processes between adjacent regions are contrasted and the spatiotemporal pattern of diffusive events is evaluated. This study supports from a modeling perspective the hypothesis that there is no simple or exclusive demic or cultural diffusion, but that in most regions of Eurasia a combination of demic and cultural processes were important. Furthermore, we demonstrate the strong spatial and temporal variability in the balance of spread processes. Each region shows sometimes more demic, and at other times more cultural diffusion. Only few, possibly environmentally marginal, areas show a dominance of demic diffusion. This study affirms that diffusion processes should be investigated in a diachronic fashion and not from a time-integrated perspective.

q-bio.PE↗

arXiv2014

Bricks and urbanism in the Indus Valley rise and decline

The Indus Civilization, often denoted by its major city Harappa, spanned almost two millennia from 3200 to 1300 BC. Its tradition reaches back to 7000 BC: a 5000 year long expansion of villages and towns, of trading activity, and of technological advancements culminates between 2600 and 1900 BC in the build-up of large cities, writing, and political authority; it emerges as one of the first great civilizations in history. During the ensuing 600 years, however, key technologies fall out of use, urban centers are depopulated, and people emigrate from former core settlement areas. Although many different hypotheses have been put forward to explain this deurbanization, a conclusive causal chain has not yet been established. We here combine literature estimates on brick typology, and on urban area for individual cities. In the context of the existing extensive data on Harappan artifact find sites and put in their chronological context, the combined narratives told by bricks, cities, and spatial extent can provide a new point of departure for discussing the possible reasons for the mysterious "decline".

physics.hist-ph↗

arXiv2012

On the sensitivity of the simulated European Neolithic transition to climate extremes

Was the spread of agropastoralism from the Fertile Crescent throughout Europe influenced by extreme climate events, or was it independent of climate? We here generate idealized climate events using palaeoclimate records. In a mathematical model of regional sociocultural development, these events disturb the subsistence base of simulated forager and farmer societies. We evaluate the regional simulated transition timings and durations against a published large set of radiocarbon dates for western Eurasia; the model is able to realistically hindcast much of the inhomogeneous space-time evolution of regional Neolithic transitions. Our study shows that the consideration of climate events improves the simulation of typical lags between cultural complexes, but that the overall difference to a model without climate events is not significant. Climate events may not have been as important for early sociocultural dynamics as endogenous factors.

q-bio.PE↗

arXiv2012

Malthusian assumptions, Boserupian response in models of the transitions to agriculture

In the many transitions from foraging to agropastoralism it is debated whether the primary drivers are innovations in technology or increases of population. The driver discussion traditionally separates Malthusian (technology driven) from Boserupian (population driven) theories. I present a numerical model of the transitions to agriculture and discuss this model in the light of the population versus technology debate and in Boserup's analytical framework in development theory. Although my model is based on ecological -Neomalthusian- principles, the coevolutionary positive feedback relationship between technology and population results in a seemingly Boserupian response: innovation is greatest when population pressure is highest. This outcome is not only visible in the theory-driven reduced model, but is also present in a corresponding "real world" simulator which was tested against archaeological data, demonstrating the relevance and validity of the coevolutionary model. The lesson to be learned is that not all that acts Boserupian needs Boserup at its core.

q-bio.PE↗

arXiv2012

A simulation of the Neolithic transition in the Indus valley

The Indus Valley Civilization (IVC) was one of the first great civilizations in prehistory. This bronze age civilization flourished from the end of the fourth millennium BC. It disintegrated during the second millennium BC; despite much research effort, this decline is not well understood. Less research has been devoted to the emergence of the IVC, which shows continuous cultural precursors since at least the seventh millennium BC. To understand the decline, we believe it is necessary to investigate the rise of the IVC, i.e., the establishment of agriculture and livestock, dense populations and technological developments 7000--3000 BC. Although much archaeological information is available, our capability to investigate the system is hindered by poorly resolved chronology, and by a lack of field work in the intermediate areas between the Indus valley and Mesopotamia. We thus employ a complementary numerical simulation to develop a consistent picture of technology, agropastoralism and population developments in the IVC domain. Results from this Global Land Use and technological Evolution Simulator show that there is (1) fair agreement between the simulated timing of the agricultural transition and radiocarbon dates from early agricultural sites, but the transition is simulated first in India then Pakistan; (2) an independent agropastoralism developing on the Indian subcontinent; and (3) a positive relationship between archeological artifact richness and simulated population density which remains to be quantified.

q-bio.PE↗

arXiv2011

Different mechanisms shaped the transition to farming in Europe and the North American Woodland

The introduction and emergence of agriculture into Eastern North America (ENA) and Europe proceeded very differently in both subcontinents: it varied in timing, speed, and mechanism. Common to both regions, agricultural subsistence profited from the introduction of major staple crops which had been domesticated elsewhere; in both regions, the temperate climate and originally predominant forest vegetation provided an environmental context conducive to agriculture. To understand the different paths to agricultural subsistence, an integrated view of technological innovation, domestication and exchange of domesticates, migration and trade is required within the constraints imposed by the environmental context and geography. This study makes use of a numerical model of regional socio-technological evolution which builds on adaptation of important characteristics of prehistoric societies such as technology and subsistence diversity. With this Global Land Use and Technological Evolution Simulator (GLUES), regional transitions from foraging to agropastoralism, and associated land use and demographic changes are realistically hindcasted. I show that the model is capable of explaining the different timing, speed, and transition mechanisms: Europe received a large package of foreign domesticates and converted rapidly to agriculture, this fast transition can be best explained with demic and cultural diffusion followed by fast adoption by resident foragers. In contrast, ENA trajectories show a more gradual transition. Hunting-gathering and agropastoral life style coexisted for a long time and agriculture was adopted slowly into the existing subsistence scheme.

nlin.AO↗

arXiv2011

A simulation of the Neolithic transition in Western Eurasia

Farming and herding were introduced to Europe from the Near East and Anatolia; there are, however, considerable arguments about the mechanisms of this transition. Were it people who moved and outplaced the indigenous hunter- gatherer groups or admixed with them? Or was it just material and information that moved-the Neolithic Package-consisting of domesticated plants and animals and the knowledge of its use? The latter process is commonly referred to as cultural diffusion and the former as demic diffusion. Despite continuous and partly combined efforts by archaeologists, anthropologists, linguists, paleontologists and geneticists a final resolution of the debate has not yet been reached. In the present contribution we interpret results from the Global Land Use and technological Evolution Simulator (GLUES), a mathematical model for regional sociocultural development embedded in the western Eurasian geoenvironmental context during the Holocene. We demonstrate that the model is able to realistically hindcast the expansion speed and the inhomogeneous space-time evolution of the transition to agropastoralism in Europe. GLUES, in contrast to models that do not resolve endogenous sociocultural dynamics, also describes and explains how and why the Neolithic advanced in stages. In the model analysis, we uncouple the mechanisms of migration and information exchange. We find that (1) an indigenous form of agropastoralism could well have arisen in certain Mediterranean landscapes, but not in Northern and Central Europe, where it depended on imported technology and material, (2) both demic diffusion by migration or cultural diffusion by trade may explain the western European transition equally well, (3) [...]

cs.MA↗