Ecosystem experiments

Maund SJ, Van Wijngaarden R, Roessink I et al (2008) Aquatic fate and effects of lambda-cyhalothrin in model ecosystem experiments. In Gan J, Spurlock F, Hendley P et al (eds) Synthetic pyrethroids occurrence and behavior in aquatic environments. ACS Symposium Series 991, American Chemical Society, Washington DC... 

Schachtman DP, Reid RJ, Ayling SM (1998) Phosphorus uptake by plants from soil to cell. Plant Physiol 116 447-453. doi http //www.plantphysiol.org Schindler DW (1974) Eutrophication and recovery in experimental lakes implications for lake management. Science 184 897-899. doi http //www.sciencemag.org/cgi/content/abstract/184/4139/897 Schindler DW, Hecky RE, Findlay DL, Stainton MP, Parker BR, Paterson MJ, Beaty KG, Lyng M, Kasian SEM (2008) Eutrophication of lakes cannot be controlled by reducing nitrogen input results of a 37-year whole-ecosystem experiment. Proc Natl Acad Sci USA 105 11254-11258. doi http //www.pnas.org/content/105/32/l 1254.abstract Scott JT, Condron LM (2003) Dynamics and availability of phosphorus in the rhizosphere of a temperate silvopastoral system. Biol Fert Soils 39 65-73 Shane MW, Lambers H (2005) Cluster roots a curiosity in context. Plant Soil 274 101-125. doi http //dx.doi.org/10.1007/s 11104-004-2725-7... 

Hertel O, Geels C, Frohn LM, Ellermann T, Skjoth CA, Lofstrom P, Christensen JH, Andersen, HV, Peel RG (2012) Assessing atmospheric nitrogen deposition to natural and semi-natural ecosystems experience from Danish studies using the DAMOS system. Atmos Environ, in press, http //dx.doi.Org/10.1016/j.atmosenv.2012.02.071... 

Single species tests and tests using bioassay batteries are called lower-tier tests.19 But in order to carry out a more stringent examination of the complex interactions between potentially toxic chemical compounds and organisms inhabiting specific ecosystems, experiments are sometimes carried out in microcosms and mesocosms the literature describes these as higher-tier tests.19... 

The time schedule of aquatic model ecosystem experiments and the size of the system itself favor population growth of small organisms with short generation times... 

The Community-Level Aquatic Systems Studies Interpretation Studies (CLASSIC) guidance document, which deals with the interpretation of results of microcosm and mesocosm tests in the risk assessment procedure of pesticides, recommends that regulatory model ecosystem experiments be conducted in spring to midsummer (Giddings et al. 2002). On the basis of the limited number of model ecosystem experiments described above, it seems that threshold concentrations for effects observed in early-season studies are reasonably predictive for threshold concentrations later in the season. Above these threshold concentrations, however, the intensity and duration of the responses (direct and indirect effects) may vary during different periods of the year. Consequently, the extrapolation of NOECcommunity values from one season to another seems to be possible with lower uncertainty than hazard estimates of higher concentrations in which both direct and indirect effects are involved. 

For most pesticides evaluated, an uncertainty factor of 10 to 15 seems to suffice to extrapolate a median acute HC5 to a median chronic HC5, at least when based on toxicity data of sensitive taxonomic groups. In addition, it appears from model ecosystem experiments with pesticides that threshold concentrations for chronic exposures are approximately a factor of 10 lower than those for acute exposure. For a wider generalization, however, more data are required on compounds that differ in toxic mode of action (Section 6.2.4). 

When evaluating the influence of the time of year on responses of aquatic communities to chemical stress, it is convenient to make a distinction in threshold concentrations of direct toxic effects, and in the magnitude of effects that occur above these threshold concentrations. Only a limited number of (model) ecosystem experiments are available that allow a comparison of responses due to treatment with the same chemical in the same type of test system at different periods of the year. These studies indicate that, in freshwater communities, threshold concentrations for direct toxic effects may vary little with the season (within a factor of 2). At higher exposure concentrations, however, the intensity and duration of the responses (direct and indirect effects) may vary considerably between different periods of the year (Section 6.3.2). 

Experimental aquatic ecosystems have become widely used tools in ecotoxicology because they allow for a greater degree of control, replication, and repeatability than is achievable in natural ecosystems. The test systems in use vary from small indoor microcosms to large and complex outdoor experimental ecosystems. However, natural freshwater systems may also vary considerably in size and ecological complexity. Before addressing the spatial extrapolation of results of model ecosystem experiments that were conducted on different localities, the possible influence of the size and ecological complexity of test systems on responses to chemical stress will be discussed. 

These examples described above indicate that certain properties of model ecosystems may affect the fate and exposure concentrations of a chemical and, consequently, the treatment-related effects observed. However, an important question remains Can responses of model ecosystem experiments be extrapolated between different types of experimental ecosystems if exposure concentrations are similar ... 

It appears from several model ecosystem experiments with insecticides, where exposure concentrations are similar, that threshold concentrations for effects may be very similar between different types of test systems, at least when they contain representatives of sensitive taxonomic groups (in this case, arthropod populations). For... 

Computer models that simulate the dynamics of food webs might be used to extrapolate results of model ecosystem experiments to systems differing in size and ecological complexity. In principle, food-web models such as IFEM (Bartell et al. 1988), AQUATOX (Park 1999), and C-COSM (Traas 2004) can be adapted to do this, at least when detailed information on the ecology and ecotoxicology of the species and functional groups of concern is available. 

Threshold concentrations for direct toxic effects of the most sensitive endpoints (responses of populations of crustaceans and insects) in model ecosystem experiments that studied the ecological impact of short term exposure to the insecticide chlorpyrifos... 

Recently 2 reviews of model ecosystem experiments with herbicides (Brock et al. 2000a) and insecticides were performed (Brock et al. 2000b van Wijngaarden et al. 2005b). The following criteria were applied in the selection of the studies ... 

In aquatic risk assessment, an important question at stake is how unique model ecosystem experiments are in their threshold concentrations for direct toxic effects. When comparing chemicals for which at least 5 aquatic NOECeco values are available, it appears that geographical extrapolation of model ecosystem experiments is possible. The proposed geographical uncertainty factor (spread) for threshold concentrations was in the range of 1.4 to 5.4 (Section 7.2.5). 

Effects classes aim to facilitate an objective interpretation of model ecosystem experiments performed for regulatory purposes. Effect Class 1 = effects could not be demonstrated Class 2 = slight effects. ... 

Wright R. E. and Rasmussen L. (eds.) (1998) The whole ecosystem experiments of the NITREX and EXMAN projects. Forest Ecol. Manage. 101, 1-363. 

P.D. Delorme. The effects of toxaphene, chlordane and 2,3,4,7,8-pentachlorodibenzofuran on lake trout and white sucker in an ecosystem experiment and the distribution and effects of 2,3,4,7,8-pentachlorodibenzo-furan on white suckers and broodstock rainbow trout in laboratory experiments. PhD Thesis, University of Manitoba, Winnipeg, Man., 1995. 

These data are from multispecies ecosystem experiments (Lu and Metcalf 1975) and the calculations assume there is no uptake or loss of metabolites by the Physa sp. 

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