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In contrast to TME, that are meant to be soil cores usually transported to and stored in an ex- perimental environment after coring, mesocosms were defined as enclosed outdoor systems partially permeable to their surroundings, according to ODUM (1984). They should contain the

full complexity of biotic and abiotic components of natural systems and provide replicable units. They are invented to overcome the simplicity of many small-scaled TME (in other words ‘microcosms’), based on the prerequisite that realism is seen as a crucial feature of mesocosms (KAMPICHLER et al. 1999). For the purposes of ecotoxicological test systems,

mesocosms were designed to validate the predictions from standard laboratory tests in a semi- field situation (SVENDSEN & WEEKS 1997). The category ‘mesocosm’ was subdivided into

two classes of mesocosm studies, which were frequently found in the literature. On the one hand, a more realistic approach dealt with intact soil mainly replanted undisturbed after ma- nipulation directly at the study site. It accepted a relatively high natural variability of soil conditions and an inhomogeneous distribution pattern of the soil fauna. Some experiments were conducted with homogenized soil; this feature defines here the second class of meso- cosms. In the following, the setup, objectives of research and some results of exemplified studies are presented.

I-3.9.1

Homogenised mesocosms

The first division of this category was marked by a relative homogenous quality of the soil. Homogenous conditions were introduced by sieving (and occasionally defaunating through deep freezing) of the soil before the start of the experiments. SMIT et al. (2002) cross-

inoculated their mesocosms additionally with living nematodes from fresh soil to further im- prove the homogeneity of the distribution of organisms between the mesocosm-experimental units. They found a high persistence of total numbers after application of zinc while analysing various community related parameters and the community as a whole (analysed by Principal

Scope, aim and purpose of TME studies

Response Curves) was the most sensitive endpoint. GREVILLE &MORGAN (1991) conducted

another experiment concerning the effects of metals on various biotas. They transplanted un- loaded slug species to a heavily polluted, former Pb/Zn mine site and compared the bioaccu- mulation of heavy metals with residential slugs. It became obvious that the adapted slugs built up a metal tolerance or a phenotypically reduction of accumulation, which could lead to mis- interpretations of monitoring measurements. Experimenters using mesocosms asked often non-ecotoxicological questions. TEUBEN (1991) examined the functional roles of the fun- givorous collembolan Tomocerus minor and the detritivorous isopod Philoscia muscorum during the decomposition of Pinus nigra needles. They concluded a new mechanism from their study: A buffering effect on the microbial activity of soil was attributed to both species. In cases where the control abundances of the soil fauna were high, the microbial activities and decomposition rates decreased and vice versa.

I-3.9.2

Intact mesocosms

In the previous chapter, semi-field enclosures with sieved soil were focused. Historically, much more effort was put into the development of systems containing intact soil cores that were replanted to the field. KAMPICHLER and his working group at the Federal Forest Office

in Austria conducted many of the studies that are available in the literature. The most im- portant aspects of theirs and other approaches and the related results are presented in the fol- lowing. FRAMPTON & WRATTEN (2000) applied systemic fungicides (propiconazole, car-

bendazim and triadimenol) on open and barrier-enclosed wheat-crop plots. They found no effects on the activity of surface-dwelling collembolans, but negative effects were found on the overall abundance, using two different sampling methods (pitfall traps and suction sam- pling). The ecology of soil organisms was investigated by NIEMINEN &SETÄLÄ (1998). They concluded by the results of their experiments with enclosed and open natural ecosystems, which they compared with the field situation that the diversity of microarthropods was not affected by reducing the space for a single growing season. However, in a long term, the de- composer food web structure would be changed. BRUCKNER et al. (1993) first described the above-cited construction of mesocosms. They examined the re-immigration of microarthro- pods in previously defaunated soil cores, exposed under natural outdoor conditions. In further experiments, KAMPICHLER et al. (1995), BRUCKNER et al. (1995) and KAMPICHLER et al.

(1999) evaluated the side effects occurring in intact soil monoliths in the field by treatments of deep-freezing, wrapping in nets of different mesh-sizes and replanting the soil cores into the field. Most groups of the soil fauna investigated (ciliates, collembolans, tardigrades, nematodes) were not affected by the treatments, but oribatid mites were reduced by 30 % of

Scope, aim and purpose of TME studies

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the control abundance, six month after incubation. In order to overcome the low recovery po- tential of oribatid mites, the authors recommended an artificially reintroduction of this group into the defaunated soil monoliths. ZECHMEISTER-BOLTENSTERN et al.(1998) used an identi- cal approach as KAMPICHLER to investigate the effects of meso- and macrofauna on the nutri- ent availability in forest soils. They inoculated fauna of different complexity into defaunated soil and detected an increase of exchangeable base cations and a decrease of exchangeable acidic cations with increasing complexity of fauna. They explained these effects with an indi- rect enhancement of humification processes in the presence of fauna, causing a rise of ion- binding sites in the soil. KANDELER et al.(1999), coming from the same group of soil ecol-

ogists, supplemented these findings by detecting an enhancing effect of the mesofauna on the microbial activity. This result was in contrast to the findings of SOUSA et al.(2004) who could

not explain statistically the changes of microbial activity by the feeding activity of the soil fauna.