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Jens C Streibig - One of the best experts on this subject based on the ideXlab platform.
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an isobole based statistical model and test for synergism antagonism in binary mixture toxicity experiments
Environmental and Ecological Statistics, 2007Co-Authors: Helle Sorensen, Nina Cedergreen, Ib M Skovgaard, Jens C StreibigAbstract:Synergism and antagonism are often defined in relation to the model of Concentration Addition (CA). Hence, it is vital for the conclusion of mixture toxicity studies to be able to test whether an observed deviation from CA reflects a true deviation or whether it is simply due to random variation. In this paper we consider a non-linear regression model for the classical ray designs for binary mixture experiments. The model combines dose–response curves for each mixture in the experiment with an isobole model, describing possible deviations from CA. The method allows us to test whether the chosen isobole model is reasonable for the data and to test the hypothesis of CA. Furthermore, it provides us with a measure of the degree of synergism/antagonism. The method is flexible since both the dose–response relationships and the isobole model can be chosen arbitrarily. We demonstrate the use of the method on datasets where combinations of pesticides are tested on a Floating Plant, Lemna minor, and an algae, Pseudokirchneriella subcapitata. Furthermore, we conduct a simulation study in order to explore the power with which a specific deviation from CA can be distinguished in different test-systems.
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is mixture toxicity measured on a biomarker indicative of what happens on a population level a study with lemna minor
Ecotoxicology and Environmental Safety, 2007Co-Authors: Nina Cedergreen, Majid Abbaspoor, Helle Sorensen, Jens C StreibigAbstract:For Plants, pigment content has shown to be a remarkably consistent biomarker across chemicals with different modes of action. In this study, we evaluated the use of pigment content as endpoint in binary mixture toxicity studies compared to three growth endpoints on the Floating Plant Lemna minor. Six binary combinations of six herbicides with different mode of action were used. Data were tested against both the concentration addition (CA) and independent action (IA) reference models. For CA, two statistical approaches were used. The study showed that for some herbicide combinations the mixture toxicity measured on pigment content did not reflect the results measured on Plant population growth, emphasizing the importance of measuring growth in parallel with biomarkers. CA explained the data just as well as IA, and the two different statistical models used to test the data in relation to CA showed very similar results.
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is prochloraz a potent synergist across aquatic species a study on bacteria daphnia algae and higher Plants
Aquatic Toxicology, 2006Co-Authors: Nina Cedergreen, Anja Kamper, Jens C StreibigAbstract:Abstract Fungicides inhibiting the biosynthesis of ergostrol, such as the triazoles and imidazoles, have been shown to enhance the effect of insecticides on birds, mammals and invertebrates in the terrestrial environment. The synergy is proposed to be due to an effect on P450 monooxygenase enzymes active in pesticide metabolism in these organisms. Fungicides often enter the aquatic environment jointly with other pesticides. It is therefore possible that they could act as synergists also in the aquatic environment. In this study we tested the joint effect of the imidazole fungicide prochloraz together with the herbicides acifluorfen, diquat and terbuthylazine, the fungicide azoxystrobin and the insecticides chlorfenvinphos, dimethoate, and pirimicarb on the bacteria Vibrio fischeri (six binary mixtures), the crustacean Daphnia magna (four binary mixtures), the algae Pseudokirchneriella subcapitata (four binary mixtures) and the Floating Plant Lemna minor (three binary mixtures). All the binary mixtures were evaluated both in relation to the model of concentration addition (CA) and independent action (IA) using isobolograms. The study showed strong synergy in relation to CA between prochloraz and azoxystrobin, diquat and esfenvalerat on D. magna with sums of toxic units for the 50:50% effect mixture (∑TU50:50) as low as 0.25. The mixture with dimethoate was however antagonistic with ∑TU50:50 of 2.04. Four out of the six mixtures testes on V. fisheri showed synergy in relation to CA, but for three of the mixtures the response could be explained by IA. Only the mixture with diquat showed synergy in relation to both IA and CA with ∑TU50:50 around 0.50. There was no significant synergy for any of the combinations tested on the Plant and the algae species in relation to CA and only for diquat in the algae-test in relation to IA. Hence, prochloraz does synergise the effect of some pesticides in the aquatic environment, but not consistently across species. The organism most susceptible to synergy by prochloraz in this study was D. magna. Especially the combination with insecticides such as esfenvalerate, where the concentration needed to immobilize 50% of the daphnia was reduced from >3 μg L−1 to less than 0.5 μg L−1 when prochloraz was added, could be problematic as these concentrations are environmentally realistic. Furthermore, insecticides and ergostrol-biosynthesis-inhibitors (EBI-fungicides) are often applied together, and are therefore likely to co-exist in surface waters, enhancing the problem of the already very potent insecticides.
P H Taylor - One of the best experts on this subject based on the ideXlab platform.
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first and second order analysis of resonant waves between adjacent barges
Journal of Fluids and Structures, 2010Co-Authors: Eatock R Taylor, P H TaylorAbstract:Water wave diffraction by two parallel closely spaced rectangular barges is investigated, to characterise the general problem of LNG offloading from a Floating Plant into a shuttle tanker. It is well known that large free-surface motions, in the gap between the hulls, are predicted by diffraction theory; in model tests amplitudes of at least five times that of the incident wave amplitude have been observed. A second-order diffraction calculation is used, based on a quadratic boundary element method, to examine the behaviour of this characteristic configuration and to examine the influence of spacing between the hulls. The free-surface near-resonant behaviour at first and second order is interpreted in the context of simple linear analytical solutions for three-dimensional flow in an open-ended gap.
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First- and second-order analysis of resonant waves between adjacent barges
'Elsevier BV', 2010Co-Authors: Sun L, Eatock Taylor R, P H TaylorAbstract:Water wave diffraction by two parallel closely spaced rectangular barges is investigated, to characterise the general problem of LNG offloading from a Floating Plant into a shuttle tanker. It is well known that large free-surface motions, in the gap between the hulls, are predicted by diffraction theory; in model tests amplitudes of at least five times that of the incident wave amplitude have been observed. A second-order diffraction calculation is used, based on a quadratic boundary element method, to examine the behaviour of this characteristic configuration and to examine the influence of spacing between the hulls. The free-surface near-resonant behaviour at first and second order is interpreted in the context of simple linear analytical solutions for three-dimensional flow in an open-ended gap. © 2010 Elsevier Ltd
Erik Jeppesen - One of the best experts on this subject based on the ideXlab platform.
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substantial differences in littoral fish community structure and dynamics in subtropical and temperate shallow lakes
Freshwater Biology, 2009Co-Authors: Franco Teixeira De Mello, Mariana Meerhoff, Zeynep Pekcanhekim, Erik JeppesenAbstract:Summary 1. Fish play a key role in the functioning of temperate shallow lakes by affecting nutrient exchange among habitats as well as lake trophic structure and dynamics. These processes are, in turn, strongly influenced by the abundance of submerged macrophytes, because piscivorous fish are often abundant at high macrophyte density. Whether this applies to warmer climates as well is virtually unknown. 2. To compare fish community structure and dynamics in Plant beds between subtropical and temperate shallow lakes we conducted experiments with artificial submerged and free-Floating Plant beds in a set of 10 shallow lakes in Uruguay (30°–35°S) and Denmark (55°–57°N), paired along a gradient of limnological characteristics. 3. The differences between regions were more pronounced than differences attributable to trophic state. The subtropical littoral fish communities were characterised by higher species richness, higher densities, higher biomass, higher trophic diversity (with predominance of omnivores and lack of true piscivores) and smaller body size than in the comparable temperate lakes. On average, fish densities were 93 ind. m−2 (±10 SE) in the subtropical and 10 ind. m−2 (±2 SE) in the temperate lakes. We found a twofold higher total fish biomass per unit of total phosphorus in the subtropical than in the temperate lakes, and as fish size is smaller in the former, the implication is that more energy reaches the littoral zone fish community of the warmer lakes. 4. Plant architecture affected the spatial distribution of fish within each climate zone. Thus, in the temperate zone fish exhibited higher densities among the artificial free-Floating Plants while subtropical fish were denser in the artificial submerged Plant beds. These patterns appeared in most lakes, regardless of water turbidity or trophic state. 5. The subtropical littoral fish communities resembled the fish communities typically occurring in temperate eutrophic and hypertrophic lakes. Our results add to the growing evidence that climate warming may lead to more complex and omnivory-dominated food webs and higher density and dominance of smaller-sized fish. This type of community structure may lead to a weakening of the trophic cascading effects commonly observed in temperate shallow lakes and a higher risk of eutrophication.
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can warm climate related structure of littoral predator assemblies weaken the clear water state in shallow lakes
Global Change Biology, 2007Co-Authors: Mariana Meerhoff, Carlos Iglesias, Juan M Clemente, Franco Teixeira De Mello, Asger Roer Pedersen, Erik JeppesenAbstract:Shallow lakes, the most abundant lake type in the world, are very sensitive to climatic changes. The structure and functioning of shallow lakes are greatly impacted by submerged Plants, and these may be affected by climate warming in various, contrasting, ways. Following a space-for-time substitution approach, we aimed to analyse the role of aquatic (submerged and free-Floating) Plants in shallow lakes under warm climates. We introduced artificial submerged and free-Floating Plant beds in five comparable lakes located in the temperate zone (Denmark, 55–57 °N) and in the subtropical zone (Uruguay, 30–35 °S), with the aim to study the structure and dynamics of the main associated communities. Regardless of differences in environmental variables, such as area, water transparency and nutrient status, we found consistent patterns in littoral community dynamics and structure (i.e. densities and composition of fish, zooplankton, macroinvertebrates, and periphyton) within, but substantial differences between, the two regions. Subtropical fish communities within the macrophyte beds exhibited higher diversity, higher density, smaller size, lower relative abundance of potentially piscivores, and a preference for submerged Plants, compared with otherwise similar temperate lakes. By contrast, macroinvertebrates and cladocerans had higher taxon richness and densities, and periphyton higher biomass, in the temperate lakes. Several indicators suggest that the fish predation pressure was much stronger among the Plants in the subtropical lakes. The antipredator behaviour of cladocerans also differed significantly between climate zones. Submerged and free-Floating Plants exerted different effects on the spatial distribution of the main communities, the effects differing between the climate zones. In the temperate lakes, submerged Plants promoted trophic interactions with potentially positive cascading effects on water transparency, in contrast to the free-Floating Plants, and in strong contrast to the findings in the subtropical lakes. The higher impact of fish may result in higher sensitivity of warm lakes to external changes (e.g. increase in nutrient loading or water level changes). The current process of warming, particularly in temperate lakes, may entail an increased sensitivity to eutrophication, and a threat to the high diversity, clear water state.
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restoration of shallow lakes by nutrient control and biomanipulation the successful strategy varies with lake size and climate
Hydrobiologia, 2007Co-Authors: Erik Jeppesen, Jens Peder Jensen, Mariana Meerhoff, B A Jacobsen, R S Hansen, Martin Sondergaard, Torben L Lauridsen, Nestor Mazzeo, Christina W C BrancoAbstract:Major efforts have been made world-wide to improve the ecological quality of shallow lakes by reducing external nutrient loading. These have often resulted in lower in-lake total phosphorus (TP) and decreased chlorophyll a levels in surface water, reduced phytoplankton biomass and higher Secchi depth. Internal loading delays recovery, but in north temperate lakes a new equilibrium with respect to TP often is reached after <10–15 years. In comparison, the response time to reduced nitrogen (N) loading is typically <5 years. Also increased top-down control may be important. Fish biomass often declines, and the percentage of piscivores, the zooplankton:phytoplankton biomass ratio, the contribution of Daphnia to zooplankton biomass and the cladoceran size all tend to increase. This holds for both small and relatively large lakes, for example, the largest lake in Denmark (40 km2), shallow Lake Arreso, has responded relatively rapidly to a ca. 76% loading reduction arising from nutrient reduction and top-down control. Some lakes, however, have proven resistant to loading reductions. To accelerate recovery several physico-chemical and biological restoration methods have been developed for north temperate lakes and used with varying degrees of success. Biological measures, such as selective removal of planktivorous fish, stocking of piscivorous fish and imPlantation or protection of submerged Plants, often are cheap versus traditional physico-chemical methods and are therefore attractive. However, their long-term effectiveness is uncertain. It is argued that additional measures beyond loading reduction are less cost-efficient and often not needed in very large lakes. Although fewer data are available on tropical lakes these seem to respond to external loading reductions, an example being Lake Paranoa, Brazil (38 km2). However, differences in biological interactions between cold temperate versus warm temperate-subtropical-tropical lakes make transfer of existing biological restoration methods to warm lakes difficult. Warm lakes often have prolonged growth seasons with a higher risk of long-lasting algal blooms and dense Floating Plant communities, smaller fish, higher aggregation of fish in vegetation (leading to loss of zooplankton refuge), more annual fish cohorts, more omnivorous feeding by fish and less specialist piscivory. The trophic structures of warm lakes vary markedly, depending on precipitation, continental or coastal regions locations, lake age and temperature. Unfortunately, little is known about trophic dynamics and the role of fish in warm lakes. Since many warm lakes suffer from eutrophication, new insights are needed into trophic interactions and potential lake restoration methods, especially since eutrophication is expected to increase in the future owing to economic development and global warming.
Baoshan Xing - One of the best experts on this subject based on the ideXlab platform.
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interaction of cuo nanoparticles with duckweed lemna minor l uptake distribution and ros production sites
Environmental Pollution, 2018Co-Authors: Le Yue, Jian Zhao, Zhenyu Wang, Baoshan XingAbstract:Abstract CuO engineered nanoparticles (NPs) are of increasing concern due to their extensive use in daily life and adverse effect on aquatic organisms. The investigations on the toxicity of CuO NPs to aquatic Plants through uptake from roots versus fronds are limited. This paper discusses the interactions of CuO NPs with Lemna minor, a Floating Plant. After CuO NPs (150 μg L−1) exposure for 7 days, the frond number, frond surface area and dry weights of whole Plants significantly decreased by 32%, 47% and 33%; the responses were dose-dependent. Microscopy imaging showed that the epidermis was severely damaged in fronds, edges were severely sloughed off and cell integrity was damaged in roots. Shrinkage of both chloroplast and starch grains were observed in the frond cells. Internalization of CuO NPs in root and frond cells during CuO NPs (1 mg L−1) exposure was confirmed with the root Cu levels of Lemna minor being three times higher than the fronds by using transmission electron microscopy and flame atomic absorption spectrophotometry. Reactive oxygen species, mainly H2O2 (increased by 56%) and ·OH (increased by 57%), accumulated in Lemna minor tissues in response to CuO NPs exposure. Moreover, chloroplasts were confirmed as a site of ROS production. These findings are helpful for better understanding the biological responses of aquatic Plants upon NPs exposure.
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uptake distribution and transformation of cuo nps in a Floating Plant eichhornia crassipes and related stomatal responses
Environmental Science & Technology, 2017Co-Authors: Jian Zhao, Wenting Ren, Yanhui Dai, Lijiao Liu, Zhenyu Wang, Junzhe Zhang, Xiangke Wang, Baoshan XingAbstract:Engineered nanoparticles (NPs) are being released into aquatic environments with their increasing applications. In this work, we investigated the interaction of CuO NPs with a Floating Plant, water hyacinth (Eichhornia crassipes). CuO NPs (50 mg/L) showed significant growth inhibition on both roots and shoots of E. crassipes after 8-day exposure, much higher than that of the bulk CuO particles (50 mg/L) and their corresponding dissolved Cu2+ ions (0.30 mg/L). Scanning electron and light microscopic observations showed that the root caps and meristematic zone of E. Crassipes were severely damaged after CuO NP exposure, with disordered cell arrangement and a destroyed elongation zone of root tips. It is confirmed that CuO NPs could be translocated to shoot from both roots and submerged leaves. As detected by X-ray absorption near-edge spectroscopy analysis (XANES), CuO NPs were observed in roots, submerged leaves, and emerged leaves. Cu2S and other Cu species were also detected in these tissues, providing s...
Michael Opoku Adomako - One of the best experts on this subject based on the ideXlab platform.
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effects of fragmentation of clones compound over vegetative generations in the Floating Plant pistia stratiotes
Annals of Botany, 2021Co-Authors: Michael Opoku Adomako, Peter AlpertAbstract:Background and aims Clonal Plants dominate many Plant communities, especially in aquatic systems, and clonality appears to promote invasiveness and to affect how diversity changes in response to disturbance and resource availability. Understanding how the special physiological and morphological properties of clonal growth lead to these ecological effects depends upon studying the long-term consequences of clonal growth properties across vegetative generations, but this has rarely been done. This study aimed to show how a key clonal property, physiological integration between connected ramets within clones, affects the response of clones to disturbance and resources in an aquatic, invasive, dominant species across multiple generations. Methods Single, parental ramets of the Floating stoloniferous Plant Pistia stratiotes were grown for 3 weeks, during which they produced two or three generations of offspring; connections between new ramets were cut or left intact. Individual offspring were then used as parents in a second 3-week iteration that crossed fragmentation with previous fragmentation in the first iteration. A third iteration yielded eight treatment combinations, zero to three rounds of fragmentation at different times in the past. The experiment was run once at a high and once at a low level of nutrients. Results In each iteration, fragmentation increased biomass of the parental ramet, decreased biomass of the offspring and increased number of offspring. These effects persisted and compounded from one iteration to another, though more recent fragmentation had stronger effects, and were stronger at the low than at the high nutrient level. Fragmentation did not affect net accumulation of mass by groups after one iteration but increased it after two iterations at low nutrients, and after three iterations at both nutrient levels. Conclusions Both the positive and negative effects of fragmentation on clonal performance can compound and persist over time and can be stronger when resource levels are lower. Even when fragmentation has no short-term net effect on clonal performance, it can have a longer-term effect. In some cases, fragmentation may increase total accumulation of mass by a clone. The results provide the first demonstration of how physiological integration in clonal Plants can affect fitness across generations and suggest that increased disturbance may promote invasion of introduced clonal species via effects on integration, perhaps especially at lower nutrient levels.