Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Changes in Pig Production in China and Their Effects on Nitrogen and Phosphorus Use and Losses
    Bai, Z.H. ; Ma, L. ; Qin, W. ; Chen, Q. ; Oenema, O. ; Zhang, F.S. - \ 2014
    Environmental Science and Technology 48 (2014)21. - ISSN 0013-936X - p. 12742 - 12749.
    food-chain - integrated assessment - ammonia emission - nutrient flows - agriculture - consumption - management - performance - excretion - denmark
    China's pig production has increased manifold in the past 50 years, and this has greatly affected the nitrogen and phosphorus use and losses in the pig production sector. However, the magnitude of these changes are not well-known. Here, we provide an in-depth account of the changes in pig production-N and P use and total N and P losses in the whole pig production chain during the period 1960-2010-through simulation modeling and using data from national statistics and farm surveys. For the period of 2010-2030, we explored possible effects of technological and managerial measures aimed at improving the performances of pig production via scenario analysis. We used and further developed the NUtrient flows in Food Chains, Environment and Resources use (NUFER) model to calculate the feed requirement and consumption, and N and P losses in different pig production systems for all the years Between 1960 and 2010, pig production has largely shifted from the so-called backyard system to landless systems. The N use efficiencies at fattener level increased from 18 to 28%, due to the increased animal productivity. However, the N use efficiencies at the Whole system level decreased from 46 to 11% during this period, mainly due to the increase of landless pig farms, which rely on imported feed and have no land-base for manure disposal. The total N and P losses were 5289 and 829 Gg in 2010, which is 30 and 95 times higher than in 1960. In the business as usual scenario, the total N and P losses were projected to increase by 25 and 55% between 2010 and 2030, respectively. Analyses of other scenarios indicate that packages of technological and managerial measures can decrease total N and P losses by 64 and 95% respectively. Such improvements require major transition in the pig production sector, notably, in manure management, herd management, and feeding practices.
    Increasing eutrophication in the coastal seas of China from 1970 to 2050
    Strokal, M. ; Yang, H. ; Zhang, Y. ; Kroeze, C. ; Li, L. ; Luan, S. ; Wang, H. ; Yang, S. - \ 2014
    Marine Pollution Bulletin 85 (2014)1. - ISSN 0025-326X - p. 123 - 140.
    pearl river - future-trends - nutrient export - yangtze estuary - algal blooms - food-chain - management - nitrogen - waters - phosphorus
    We analyzed the potential for eutrophication in major seas around China: the Bohai Gulf, Yellow Sea and South China Sea. We model the riverine inputs of nitrogen (N), phosphorus (P) and silica (Si) to coastal seas from 1970 to 2050. Between 1970 and 2000 dissolved N and P inputs to the three seas increased by a factor of 2–5. In contrast, inputs of particulate N and P and dissolved Si, decreased due to damming of rivers. Between 2000 and 2050, the total N and P inputs increase further by 30–200%. Sewage is the dominant source of dissolved N and P in the Bohai Gulf, while agriculture is the primary source in the other seas. In the future, the ratios of Si to N and P decrease, which increases the risk of harmful algal blooms. Sewage treatment may reduce this risk in the Bohai Gulf, and agricultural management in the other seas.
    Enabling chain-wide transparency in meat supply chains based on the EPCIS global standard and cloud-based services
    Kassahun, A. ; Hartog, R.J.M. ; Sadowski, T. ; Scholten, H. ; Bartram, T. ; Wolfert, J. ; Beulens, A.J.M. - \ 2014
    Computers and Electronics in Agriculture 109 (2014). - ISSN 0168-1699 - p. 179 - 190.
    nonfunctional requirements - food-chain - traceability - view
    Transparency in meat supply chains is necessary to guarantee the safety, quality and trust of consumers in meat products. However, transparency systems currently in place are often not adequate for sharing transparency data among food operators, providing consumers accurate transparency information, or enabling authorities to respond quickly and effectively in cases of food safety emergencies. Due to major meat crises and scandals the meat sector has in this respect attracted substantial attention. In this paper we identify regulatory, business, consumer and technological requirements for meat supply chain transparency systems and present a reference software architecture that will guide the realisation of these systems. The reference architecture is characterized by three main elements: the EPCIS standard for tracking and tracing, cloud-based realisation of transparency systems, and the provision of transparency systems as services by third-party transparency service providers (3pTSPs). Usage scenarios are presented to explain how the different types of meat supply chain actors can use transparency systems that are based on the architecture
    Key role of China and its agriculture in global sustainable phosphorus management
    Sattari, S.Z. ; Ittersum, M.K. van; Giller, K.E. ; Zhang, F. ; Bouwman, A.F. - \ 2014
    Environmental Research Letters 9 (2014)5. - ISSN 1748-9326 - 8 p.
    environmental impacts - soil-phosphorus - crop yield - food-chain - fertilizer - nitrogen - perspective - scarcity - balances - industry
    Growing global demand for food leads to increased pressure on phosphorus (P), a finite and dwindling resource. China is the largest producer and consumer of P fertilizer in the world. A mass balance analysis of historical P use on China's arable land shows that P input substantially exceeds crop P uptake leading to the accumulation of residual soil P. A Dynamic P Pool Simulator (DPPS) model is applied to estimate future P demand in China's arable land. Our simulations show that more sustainable use of P accounting for the residual P can save ca. 20% of the P fertilizer needed until 2050 in China relative to the Rio + 20 Trend scenario. This saving would be equivalent to half of the P required in Africa or sufficient for Western Europe to achieve target crop P uptake in 2050.
    Cost-effective allocation of resources for monitoring dioxins along the pork production chain
    Lascano Alcoser, V. ; Mourits, M.C.M. ; Fels-Klerx, H.J. van der; Heres, L. ; Velthuis, A.G.J. ; Hoogenboom, L.A.P. ; Oude Lansink, A.G.J.M. - \ 2014
    Food Research International 62 (2014). - ISSN 0963-9969 - p. 618 - 627.
    critical control points - dibenzo-p-dioxins - polychlorinated-biphenyls - contaminated feed - food-chain - incident - pcbs - pigs - perspective - pcdd/fs
    The pork chain has been seriously affected by dioxin incidents in recent decades. Hence, monitoring dioxins is crucial for detecting contaminations in the pork chain. This study aims to develop a decision support tool (optimization model) to determine cost-effective monitoring schemes for detecting and tracing a dioxin contamination over multiple control points along the pork production chain. The optimization model considers four control points (i.e. at the supplier of fatty feed ingredients, the feed mill, the slaughterhouse and the fat melting facility). It was applied to several hypothetical contamination scenarios involving contaminated animal fatty feed ingredients. The cost-effective allocation of resources for detecting and tracing the dioxin contamination from an integrated chain approach (i.e. considering all control points) focuses on monitoring at the feed mill, followed by the supplier of fatty feed ingredients and - to a lesser extent - by the slaughterhouse. The number of contaminated feed mills, the frequency of dioxin contaminations, the required level of effectiveness, and the cost of screening are main factors driving the total monitoring costs. Sharing the responsibility of monitoring dioxins within control points along the chain largely reduces the total monitoring costs. In each of the evaluated scenarios, the total costs of monitoring dioxins at individual control points are larger than the costs resulting from an optimal allocation of resources among all control points integrated in one overarching chain monitoring scheme. These results elicit the economic benefits of a chain approach to monitoring dioxins over an approach where each chain actor independently monitors dioxins. The developed model can be used by decision makers in the feed and food industry for determining optimal schemes for monitoring dioxins in the pork chain focusing on preventing specific contaminations
    Nitrogen and Phosphorus Use Efficiencies in Dairy Production in China
    Bai, Z.H. ; Ma, L. ; Oenema, O. ; Chen, Q. ; Zhang, F.S. - \ 2013
    Journal of Environmental Quality 42 (2013)4. - ISSN 0047-2425 - p. 990 - 1001.
    nutrient flows - farming system - food-chain - management - agriculture - losses - feed - performance - industry
    Milk production has greatly increased in China recently, with significant impacts on the cycling of nitrogen (N) and phosphorus (P). However, nutrient flows within the changing dairy production system are not well quantified. The aim of this study was to increase the quantitative understanding of N and P cycling and utilization in dairy production through database development and simulation modeling. In 2010, of the entire 1987 and 346 thousand tons (Gg) of N and P input, only 188 Gg N and 31 Gg P ended up in milk. The average N and P use efficiencies were 24 and 25%, respectively, at the whole system level. Efficiencies differed significantly between the four dairy systems. Losses of N from these systems occurred via NH3 volatilization (33%), discharge (27%), denitrification (24%), NO3 leaching and runoff (16%), and N2O emission (1%). Industrial feedlots use less feed per kg milk produced than traditional systems, and rely more on high-quality feed from fertilized cropland; they have very poor recycling of manure nutrients to cropland. As industrial feedlot systems are booming, overall mean N and P use efficiencies will increase at herd level but will decrease at the whole dairy production system level unless manure N and P are used more efficiently through reconnecting China's feed and dairy production sectors.
    The critical soil P levels for crop yield, soil fertility and environmental safety in different soil types
    Bai, Z.H. ; Li, H.G. ; Yang, X.Y. ; Zhou, B.K. ; Shi, X.J. ; Wang, B.R. ; Li, D.C. ; Shen, J.B. ; Chen, Q. ; Qin, W. ; Oenema, O. ; Zhang, F.S. - \ 2013
    Plant and Soil 372 (2013)1-2. - ISSN 0032-079X - p. 27 - 37.
    silty clay loam - phosphate adsorption - calcareous soils - winter-wheat - food-chain - atr-ftir - olsen p - phosphorus - china - goethite
    Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China. Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl2-P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point. The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg(-1) to 21.4 mg kg(-1), above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg(-1) to 90.2 mg kg(-1), above which soil CaCl2-P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg(-1) to 71.8 mg kg(-1) among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content. The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field.
    Advances and Challenges for Nutrient Management in China in the 21st Century
    Sims, J.T. ; Ma, L. ; Oenema, O. ; Dou, Z. ; Zhang, F.S. - \ 2013
    Journal of Environmental Quality 42 (2013)4. - ISSN 0047-2425 - p. 947 - 950.
    food-chain - world
    Managing agricultural nutrients to provide a safe and secure food supply while protecting the environment remains one of the great challenges for the 21st century. The fourth International Nutrient Management Symposium (INMS), held in 2011 at the University of Delaware, addressed these issues via presentations, panel sessions, and field tours focused on latest technologies and policies available to increase nutrient use efficiency. Participants from the United States, Europe, Canada, and China discussed global trends and challenges, balancing food security and the environment in countries with struggling and emerging economics, nutrient management and transport at the catchment scale, new technologies for managing fertilizer and manure nutrients, and adaptive nutrient management practices for farm to watershed scales. A particular area of interest at the fourth INMS was nutrient management progress and challenges in China over the past 40 years. China's food security challenges and rapidly growing economy have led to major advances in agricultural production systems but also created severe nutrient pollution problems. This special collection of papers from the fourth INMS gives an overview of the remarkable progress China has made in nutrient management and highlights major challenges and changes in agri-environmental policies and practices needed today. Lessons learned in China are of value to both developing and developed countries facing the common task of providing adequate food for an expanding world population, while protecting air and water quality and restoring damaged ecosystems.
    Risks associated with the transfer of toxic organo-metallic mercury from soils into the terrestrial feed chain
    Henriques, B. ; Rodrigues, S.M. ; Coelho, C. ; Cruz, N. ; Duarte, A.C. ; Romkens, P.F.A.M. ; Pereira, E. - \ 2013
    Environment International 59 (2013). - ISSN 0160-4120 - p. 408 - 417.
    oryza-sativa-l. - atomic-absorption-spectrometry - inorganic mercury - heavy-metals - chloralkali plant - asturias spain - food-chain - part i - rice - methylmercury
    Although the transfer of organo-metallic mercury (OrgHg) in aquatic foodwebs has long been studied, it has only been recently recognized that there is also accumulation in terrestrial systems. There is still however little information about the exposure of grazing animals to OrgHg from soils and fHenriqueseed as well as on risks of exposure to animal and humans. In this study we collected 78 soil samples and 40 plant samples (Lolium perenne and Brassica juncea) from agricultural fields near a contaminated industrial area and evaluated the soil-to-plant transfer of Hg as well as subsequent trophic transfer. Inorganic Hg (IHg) concentrations ranged from 0.080 to 210 mg kg-1 d.w. in soils, from0.010 to 84 mg kg-1 d.w. in roots and from0.020 to 6.9 mg kg-1 d.w. in shoots.OrgHg concentrations in soils varied between 0.20 and 130 µg kg-1 d.w. representing on average 0.13% of the total Hg (THg). In root and shoot samples OrgHg comprised on average 0.58% (roots) and 0.66% (shoots) of THg. Average bioaccumulation factors (BAFs) for OrgHg in relation to soil concentrations were 3.3 (for roots) and 1.5 (for shoots). The daily intake (DI) of THg in 33 sampling sites exceeded the acceptable daily intake (ADI) of THg of both cows (ADI = 1.4 mg d-1) and sheep (ADI = 0.28 mg d-1), in view of food safety associated with THg in animal kidneys. Estimated DI of OrgHg for grazing animals were up to 220 µg d-1 (for cows) and up to 33 µg d-1 (for sheep). This study suggested that solely monitoring the levels of THg in soils and feedmay not allow to adequately taking into account accumulation of OrgHg in feed crops and properly address risks associatedwith OrgHg exposure for animals and humans. Hence, the inclusion of limits for OrgHg in feed quality and food safety legislation is advised.
    Colloidal properties of nanoparticular biogenic selenium govern environmental fate and bioremediation effectiveness
    Buchs, B. ; Evangelou, M.H.W. ; Winkel, L. ; Lenz, M. - \ 2013
    Environmental Science and Technology 47 (2013)5. - ISSN 0013-936X - p. 2401 - 2407.
    ray-absorption spectroscopy - anaerobic sludge - aquatic systems - food-chain - removal - selenate - ecotoxicology - reactors - water - se
    Microbial selenium (Se) bioremediation is based on conversion of water soluble, toxic Se oxyanions to water insoluble, elemental Se. Formed biogenic elemental Se is of nanometer size, hampering straightforward separation from the aqueous phase. This study represents the first systematic investigation on colloidal properties of pure biogenic Se suspensions, linking electrophoretic mobility (¿-potential) to column settling behavior. It was demonstrated that circumneutral pH, commonly applied in bioremediation, is not appropriate for gravitational separation due to the negative ¿-potential preventing agglomeration. Mono/di/trivalent counter cations and acidity (protons) were used to screen efficiently the intrinsic negative charge of biogenic Se suspensions at circumneutral pH. Fast settling was induced by La3+ addition in the micromolar range (86.2 ± 3.5% within 0.5 h), whereas considerably higher concentrations were needed when Ca2+ or Na+ was used. Colloidal stability was furthermore studied in different model waters. It was demonstrated that surface waters as such represent a fragile system regarding colloidal stability of biogenic Se suspensions (¿-potential -30 mV), whereas dissolved organic matter increases colloidal stability. In marine waters, biogenic Se is colloidally destabilized and is thus expected to settle, representing a potential sink for Se during transport in the aquatic environment
    Derivation of soil to plant transfer functions for metals and metalloids: impact of contaminant's availability
    Rodrigues, S.R. ; Pereira, E. ; Duarte, A.C. ; Römkens, P.F.A.M. - \ 2012
    Plant and Soil 361 (2012)1-2. - ISSN 0032-079X - p. 329 - 341.
    potentially toxic elements - halimione-portulacoides - mercury contamination - chemical-extraction - chloralkali plant - risk-assessment - organic-matter - trace-elements - food-chain - cadmium
    Background Soil to plant transfer models (SPT) are needed to predict levels of potentially toxic elements (PTE’s) in crops in view of risk assessment. Methods Here we developed a field study to test the suitability of empirical SPT models based on the reactive soil content in combination with soil properties versus a 0.01 M CaCl2 extraction to predict levels of metals and metalloids in ryegrass (Lolium perenne). Results Both empirical SPT models and the 0.01 M CaCl2 extraction explained between 14 and 68 % of the variation of Cd, Zn, Pb, Cu, Hg, As, Co and Ba in the ryegrass. Organic carbon and pH were the main variables explaining levels of elements in ryegrass. For Hg and Pb, amorphous aluminium oxides (Alox) played a significant role. For B, Cr, Mo, Ni, Sb and U no significant relationship could be derived. Conclusions Despite a range in the predictive quality of empirical SPT models reasonable to good estimates of As, Ba, Cd, Co, Cu, Hg, Pb and Zn in ryegrass could be obtained. The main advantage of SPT models is that they allow to account for differences in the availability of PTE’s. Ultimately either SPT’s or fixed crop levels can be the basis of a more realistic risk assessment framework addressing the transfer of contaminants from soil into the food chain
    Contaminant exposure in relation to spatio-temporal variation in diet composition: A case study of the little owl (Athene noctua)
    Schipper, A.M. ; Wijnhoven, S. ; Baveco, J.M. ; Brink, N.W. van den - \ 2012
    Environmental Pollution 163 (2012). - ISSN 0269-7491 - p. 109 - 116.
    river floodplains - small mammals - risk-assessment - cadmium accumulation - metal concentrations - food-chain - soil - predators - birds - heterogeneity
    We assessed dietary exposure of the little owl Athene noctua to trace metal contamination in a Dutch Rhine River floodplain area. Diet composition was calculated per month for three habitat types, based on the population densities of six prey types (earthworms, ground beetles and four small mammal species) combined with the little owl’s functional response to these prey types. Exposure levels showed a strong positive relationship with the dietary fraction of earthworms, but also depended on the dietary fraction of common voles, with higher common vole fractions resulting in decreasing exposure levels. Spatio-temporal changes in the availability of earthworms and common voles in particular resulted in considerable variation in exposure, with peaks in exposure exceeding a tentative toxicity threshold. These findings imply that wildlife exposure assessments based on a predefined, average diet composition may considerably underestimate local or intermittent peaks in exposure. --------------------------------------------------------------------------------
    Soil-plant-animal transfer models to improve soil protection guidelines: A case study from Portugal
    Rodrigues, S.M. ; Pereira, M.E. ; Duarte, A.C. ; Römkens, P.F.A.M. - \ 2012
    Environment International 39 (2012)1. - ISSN 0160-4120 - p. 27 - 37.
    potentially toxic elements - available pools - risk-assessment - food-chain - part ii - cadmium - mercury - lead - metals - sheep
    Food chain models are essential tools to assess risks of soil contamination in view of product quality including fodder crops and animal products. Here we link soil to plant transfer (SPT) models for potentially toxic elements (PTEs) including As, Ba, Cd, Co, Cu, Hg, Ni, Pb, Sb, U and Zn with models describing accumulation in animal organs. Current EU standards for food products and acceptable daily intake levels (ADI) for humans were used as critical limits. The combined model is used to assess the impact of soil contamination on animal health, product quality and human health using data from 100 arable fields. Results indicate that 42 existing arable fields near industrial and mining sites are unsuitable for animal grazing in view of food safety due to elevated intake of Cd, Cu, Hg and Pb by cows and sheep. At 10 sites daily intake levels of As by cows exceeded threshold concentrations regarding the quality of animal products. The food chain model also was used inversely to derive soil threshold concentrations in view of EU fodder standards. Calculated threshold levels in soil for As, Cd, Cu, Pb, Hg and Zn appear to be in line with those proposed or used in other EU countries. As such the approach applied here can form a conceptual basis for a more harmonized risk assessment strategy regarding the protection of animal and human health. --------------------------------------------------------------------------------
    Efficient Estimation of the Robustness Region of Biological Models with Oscillatory Behavior
    Apri, M. ; Molenaar, J. ; Gee, M. de; Voorn, G.A.K. van - \ 2010
    PLoS ONE 5 (2010)4. - ISSN 1932-6203
    biochemical network models - food-chain - cells
    Robustness is an essential feature of biological systems, and any mathematical model that describes such a system should reflect this feature. Especially, persistence of oscillatory behavior is an important issue. A benchmark model for this phenomenon is the Laub-Loomis model, a nonlinear model for cAMP oscillations in Dictyostelium discoideum. This model captures the most important features of biomolecular networks oscillating at constant frequencies. Nevertheless, the robustness of its oscillatory behavior is not yet fully understood. Given a system that exhibits oscillating behavior for some set of parameters, the central question of robustness is how far the parameters may be changed, such that the qualitative behavior does not change. The determination of such a “robustness region” in parameter space is an intricate task. If the number of parameters is high, it may be also time consuming. In the literature, several methods are proposed that partially tackle this problem. For example, some methods only detect particular bifurcations, or only find a relatively small box-shaped estimate for an irregularly shaped robustness region. Here, we present an approach that is much more general, and is especially designed to be efficient for systems with a large number of parameters. As an illustration, we apply the method first to a well understood low-dimensional system, the Rosenzweig-MacArthur model. This is a predator-prey model featuring satiation of the predator. It has only two parameters and its bifurcation diagram is available in the literature. We find a good agreement with the existing knowledge about this model. When we apply the new method to the high dimensional Laub-Loomis model, we obtain a much larger robustness region than reported earlier in the literature. This clearly demonstrates the power of our method. From the results, we conclude that the biological system underlying is much more robust than was realized until now.
    Toxicological risks for small mammals in a diffusely and moderately polluted floodplain
    Wijnhoven, S. ; Leuven, R.S.E.W. ; Velde, G. van der; Eijsackers, H.J.P. - \ 2008
    Science of the Total Environment 406 (2008)3. - ISSN 0048-9697 - p. 401 - 406.
    metal accumulation - river floodplains - heavy-metals - food-chain - cadmium - exposure - liver - lead - mice - bioaccumulation
    The ecotoxicological risk of heavy metal pollution in diffusely polluted floodplains is largely unclear, as field-based data are scarce. This study investigated cadmium (Cd) and lead (Pb) accumulation in the liver and kidneys of small mammal species (voles, mice and shrews) from a moderately polluted Dutch floodplain. The Cd and Pb concentrations were compared with effect concentrations (ECs). Reported ECs in literature varied considerably, with the lowest values frequently exceeded by our values, whereas the highest values were encountered only occasionally. Cd and Pb levels were highest in the shrew species, particularly in Sorex araneus. Although toxicological effects at the specimen level were present in these floodplains, effects at population level are thought to be limited, as a result of the animals' relatively short life expectancies (due to recurrent floods) and the rapid maturation of small mammals. Exceptionally high tissue metal concentrations in some specimens of all species indicated local hotspots with peaks in metal concentrations. Sanitizing such local hotspots might reduce toxicological risks. (C) 2008 Published by Elsevier B.V.
    Heavy-metal concentrations in small mammals from a diffusely polluted floodplain: Importance of species- and location-specific characteristics
    Wijnhoven, S. ; Leuven, R.S.E.W. ; Velde, G. van der; Jungheim, G. ; Koelemij, E.I. ; Vries, F.T. de; Eijsackers, H.J.P. ; Smits, A.J.M. - \ 2007
    Archives of Environmental Contamination and Toxicology 52 (2007)4. - ISSN 0090-4341 - p. 603 - 613.
    ecological risk-assessment - river floodplains - food-chain - spatial variability - apodemus-sylvaticus - cadmium - accumulation - netherlands - grassland - shrews
    The soil of several floodplain areas along large European rivers shows increased levels of heavy metals as a relict from past sedimentation of contaminants. These levels may pose risks of accumulation in food webs and toxicologic effects on flora and fauna. However, for floodplains, data on heavy-metal concentrations in vertebrates are scarce. Moreover, these environments are characterised by periodical flooding cycles influencing ecologic processes and patterns. To investigate whether the suggested differences in accumulation risks for insectivores and carnivores, omnivores, and herbivores are reflected in the actual heavy-metal concentrations in the species, we measured the current levels of Zn, Cu, Pb, and Cd in 199 specimens of 7 small mammal species (voles, mice, and shrews) and in their habitats in a diffusely polluted floodplain. The highest metal concentrations were found in the insectivorous and carnivorous shrew, Sorex araneus. Significant differences between the other shrew species, Crocidura russula, and the vole and mouse species was only found for Cd. The Cu concentration in Clethrionomys glareolus, however, was significantly higher than in several other vole and mouse species. To explain the metal concentrations found in the specimens, we related them to environmental variables at the trapping locations and to certain characteristics of the mammals. Variables taken into account were soil total and CaCl2-extractable metal concentrations at the trapping locations; whether locations were flooded or nonflooded; the trapping season; and the life stage; sex; and fresh weight of the specimens. Correlations between body and soil concentrations and location or specimen characteristics were weak. Therefore; we assumed that exposure of small mammals to heavy-metal contamination in floodplains is significantly influenced by exposure time, which is age related, as well as by dispersal and changes in foraging and feeding patterns under influence of periodic flooding.
    Why plankton communities have no equilibrium: solutions to the paradox
    Scheffer, M. ; Rinaldi, S. ; Huisman, J. ; Weissing, F.J. - \ 2003
    Hydrobiologia 491 (2003)1. - ISSN 0018-8158 - p. 9 - 19.
    time-series analysis - resource competition - intermediate disturbance - laboratory experiments - strange attractors - food-chain - prey model - chaos - dynamics - phytoplankton
    In a classical paper, Hutchinson (1961) argued that the large number of species in most plankton communities is remarkable in view of the competitive exclusion principle, which suggests that in homogeneous, well-mixed environments species that compete for the same resources cannot coexist. Few ideas in aquatic ecology have evoked more research than this `paradox of the plankton'. This review is an effort to put the main solutions to the paradox that have been proposed over the years into perspective. Hutchinson himself already suggested that the explanation could be that plankton communities are not in equilibrium at all due to weather-driven fluctuations. Subsequent research confirmed that such externally imposed variability can allow many species to coexist. Another important point is that in practice the homogeneous well-mixed conditions assumed in the competitive exclusion principle hardly exist. Even the open ocean, for instance, has a spatial complexity resulting from meso-scale vortices and fronts that can facilitate coexistence of species. Perhaps most excitingly, theoretical work on species interactions has given a counter-intuitive new dimension to the understanding of diversity. Various competition and predation models suggest that even in homogeneous and constant environments plankton will never settle to equilibrium. Instead, interactions between multiple species may give rise to oscillations and chaos, with a continuous wax and wane of species within the community. Long-term laboratory experiments support this view. This chaotic behavior implies among other things that plankton dynamics are intrinsically unpredictable in the long run when viewed in detail. Nonetheless, on a higher aggregation level, indicators such as total algal biomass may show quite regular patterns.
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