Kai W. Wirtz

A Global Dynamic Model for the Neolithic Transition

During the Holocene strong gradients in the distribution of technologyincluding subsistence ways emerged on a global scale.These patterns were further amplified in historic times and are stillvisible through worldwide differences in national wealth.In order to evaluate major factors responsible for the shift fromforaging to food production we here employ quantitative methods bydeveloping a deterministic but simple model. After compiling existing maps of potential vegetation at 5000 BP theinhabited world is split into 197 regions with homogeneous environmentalconditions. Suitable variables for the macro-economic and culturaldevelopment in the Neolithic period are found to be farming to hunting-gatheringratio, number of agricultural economies and a technological development index.The model explicitly describes economic adaptation, growth and migrationof human populations together with the spread of their cultural characteristics; it accounts for over-exploitation of natural resources, crowdingmortality and the climate variability on a millennium scale.In a thorough model validation region specific trajectories are compared toarchaeological evidence revealing a high correspondence. Major parts of the knownsequence of Neolithic centers including the timing differences are robustlyreproduced. A series of known problems in prehistory is discussedcomprising the lag between domestication and full scale farming, the off-levelingof the technological boost following the transition, the emergence ofdistinct migration waves and sensitivity to climate fluctuations.Not mere population pressure but continuous innovation and competition betweensubsistence strategies is identified as a prime mover of agricultural development.The results suggest that few aspects of biogeography may have determined theobserved continental gradients in the number of domesticable species ultimatelyleading to an increasing differentiation in technology and demography.

Total oil spill costs and compensations

Although counteracting environmental programmes and policies have been strengthened, large oil spills still occur at irregular intervals. The total oil spill costs and their compensations have attracted much interest from various parties, such as local stakeholders, and state and federal governments. This paper addresses five major cost categories whose aggregations are expected to cover the overall direct and indirect costs after the release of an oil spill. Among them, research costs should not be neglected, since they tend to be high if public attention has been drawn to the case. Through an examination of the relationship between the total oil spill costs and their admissible claims, we found that: 1. admissible claims do not cover the overall costs of the oil spill, and 2. admissible claims cannot be compensated in full in the case of large spills. Clearly, a sound oil spill contingency management aims to minimize both the environmental impacts of areas most at risk and the total oil spill costs. In this paper an economic model for measuring environmental damages following an oil spill is addressed and applied to the Prestige case which happened to be the worst oil pollution in the history of Spain. The model indicates how an ideally a priori economic evaluation may intuitively help managers to make informed as well as fast decisions in contingency cases.

Control of biogeochemical cycling by mobility and metabolic strategies of microbes in the sediments: an integrated model study

An integrated modeling framework was developed to assess physical, biological and chemical processes in the sediment and at the sediment-water interface. Special focus is laid on the description of different functional groups of bacteria as defined according to their metabolic pathways, including fermentation, methanogenesis and oxidation of high and low molecular mass dissolved organic carbon, ammonium as well as other reduced compounds. The model is subjected to a new validation method which allows for an appropriate representation of remaining uncertainties. It is also able to reproduce two-dimensional gradients in all state variables induced by a pore-water velocity field typical for permeable sediments. Another improvement with respect to many classical models follows from the simulation of adaptive changes in dormancy and motility strategies. Within an extensive analysis stage, the evolutionary stability of these strategies is investigated under a variable hydrodynamical regime. The results show that optimal behavior in terms of adhesion and readiness to dormancy shifts differ between functional groups. This pattern is compared to recent empirical findings and discussed in relation to the confidence limits of the overall methodology. In the numerical experiments, also the effect of variable microbial strategies on the total carbon mineralization of the sediment is determined.

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

Abstract 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.

A generic model for changes in microbial kinetic coefficients.

Acclimation patterns in kinetic coefficients clearly demonstrate the limits of Monods theory for the mathematical description of microbial growth. Focusing on E. coli grown under variable glucose levels, these patterns turn out to be highly diverse and sometimes even contradictory. Here, a new model based on an optimisation assumption is applied to a spectrum of adaptation phenomena, which are observed at steady-state as well as during transient situations. On the level of apparent kinetic coefficients, rates of adaptation are calculated depending on differential growth benefits. The resulting dynamics is bounded since maximum growth rate and substrate affinity are related by a non-linear trade-off. Long-term effects of phenotypic and genotypic changes under glucose limitation are robustly predicted by the model and explained in terms of their adaptive significance. Equivocal short-term recovery patterns occurring after sudden substrate excess are traced back to differences in the internal physiological state of the cells which in turn can be calculated in dependence on the inoculum history. Metabolic stress is a second determinant of short-term variations in kinetic coefficients which is here quantified in relation to external conditions as well as the internal state of cells. We demonstrate that lag phenomena and oscillations in anabolic activity exercised by E. coli under continuous growth acceleration can be reproduced without formulations being explicit in lag periods, metabolite concentrations or the timing of experimental changes. The overall predictive power of the simple approach indicates that slow as well as fast adjustments in apparent kinetic characteristics are strongly related to a dynamic optimisation strategy.

Second order up-scaling : theory and an exercise with a complex photosynthesis model

Model objectives related to higher levels of description in general require the application of aggregation methods which shorten computation time but preserve the effect of fine scale variability. It is shown that in particular temporal up-scaling problems can be solved through a second order approximation of a statistical expectation operator. For the application of the second order up-scaling method one has to evaluate estimates of second order derivatives of the model functions as well as variances of fluctuating boundary conditions. Here, we propose to calculate second order derivatives on the base of look-up tables, which significantly reduces computational effort. This technique, however, should be used with care since round-offs of the model output largely affect second order terms. In order to obtain values of fine scale variances in external conditions one can simply correlate these with longer-term averages. The correctness of the correlation method is demonstrated for different irradiance and temperature time-series. After a more general derivation, the combination of methods is tested by aggregating a complex photosynthesis model in time. This exercise shows that computation time can be reduced by many orders of magnitude using the combined second order up-scaling technique. Other potentials as well as limitations of look-up tables, second order moment approximations and the statistical representation of daily climate fluctuations are discussed.

Willingness to pay among households to prevent coastal resources from polluting by oil spills: A pilot survey

In many coastal regions oil spills can be considered to be one of the most important risks for the coastal environment. Efficient contingency management in responding to oil spills is critically important. Strategic priorities in contingency management highly depend upon the importance attributed to different economic and ecological resources such as beaches or birds. Due to the lack of a market for natural resources in the real world, these resources cannot be directly measured in monetary terms. This increases the risk that natural resources and their services are neglected in contingency decision making. This paper evaluates these natural resources in a hypothetical market by using the methodology of stated choice experiments. Results from a pilot survey show that according to the perspective of individuals, an oil spill combat process should focus on the protection of coastal waters, beaches and eider ducks.

The economy of oil spills: Direct and indirect costs as a function of spill size

As a rational basis for addressing both ecological and economic consequences of oil spills, a combination of simulating and estimating methods is proposed in this paper. An integration of the state-of-the-art oil spill contingency simulation system OSCAR with economic assessment method leads to realistic oil spill scenarios including their biological and economic impacts and the effort taken for combat as well as to an estimate for the total oil spill costs. In order to derive a simple function of total costs depending on few spill characteristics such as size, a number of hypothetical scenarios are simulated and evaluated for the German North Sea area. Results reveal that response costs of per unit oil spilled as well as integrated costs of oil released are simply characterized as two particular power-law functions of spill size. Such relationships can be straightforward transferred into decision making for efficient prevention and combat strategy in the study area.

Linear understanding of a huge aquatic ecosystem model using a group-collecting sensitivity analysis

Abstract Huge complex ecosystem models with several hundred parameters and large input data sets escape standard attempts at integral assessment. We introduce the concept of group-collecting sensitivity analysis in which related model parameters or forcing coefficients are combined into subsets. Since means and standard deviations of subsets are varied instead of individual coefficients, the method is numerically efficient and produces a condensed amount of results. Application to the Aquatic Ecosystem Model (AQEM) is presented. AQEM is a descendant of the European Regional Seas Ecosystem Model (ERSEM) with a finer process and spatial resolution with respect to the Wadden Sea. A two-dimensional sub-structured sensitivity table, which is the major result of this approach, enables an immediate perception of sensitive functional relationships and dependencies between individual parameters and the relevant characteristics of a near-shore aquatic ecosystem. Special emphasis is placed on differences in average and seasonal behaviour. The response of selected result variables to the variations of the majority of group parameters is correlated, i.e. result variables show a similar sensitivity to variations in a specific parameter group. We show that exceptions to this rule lead to a deeper insight into the model system.

Strategies for transforming fine scale knowledge to management usability

Simulation tools used for management purposes should fulfill several conditions by being computationally fast, user-friendly, realistic, generic and reliable. These traits are often counteracting since they simultaneously demand for model complexity as well as simplicity. Here we develop a strategy to overcome this general problem of environmental modelling for management use. Major ingredients are model analysis and reduction as new core components of the modelling process. In detail, a set of combined methods is proposed. Within a large class of models the set allows for automatically exploring model behaviour and for aggregating fine scale process knowledge together with spatio temporal resolution. Applications to a huge aquatic European regional seas ecosystem model (ERSEM), a complex photosynthesis model (PGEN) as well as a simple diagenetic model are presented. The analysis and aggregation methods provide first steps towards a new generation of decision support tools able to cope with an increase in scientific knowledge as well as management demands.