Abstract
Investigation sites were situated on partly afforested sewage fields (six sites) and in an uncontaminated forest
(one site) north of Berlin (Germany). Field investigations were accompanied by laboratory tests concerning the
influence of soil water content and soil pH on enchytraeids. In addition, effect concentrations for mortality and
reproduction for two enchytraeid species were determined for zinc under different moisture and pH conditions.
Abundances and species composition showed relatively small differences between the examined sewage fields.
On the most contaminated site enchytraeids were found sporadically only. For the other sites no connection
seemed to exist between density of enchytraeids and heavy metal contents of the soil. The enchytraeid
population of the sewage fields only comprised six to nine species. Most dominant were r-selected species of
the genus Enchytraeus and also Henlea ventriculosa and Fridericia bulbosa. All dominant species can be
considered as indicators of slightly acid to slightly alkaline soils.
The laboratory tests were conducted with two species occurring on the investigation sites, Enchytraeus
christenseni and Enchytraeus sp. (RefB5). Test substrate was LUFA 2.2 standard soil, a commercially available
sandy soil. The reproduction of both species was significantly reduced at a water content of £ 15 % DW (= 31.4
% WHC). Further, reproduction of E. christenseni was inhibited at pH 4.2 and 4.8 in acidified LUFA 2.2.
In connection with the ecotoxicological tests zinc contents of the LUFA 2.2 soil were analysed as total contents
(aqua regia extract) and mobile fraction (ammonium nitrate extract). Effect concentrations are thus given based
on total contents as well as on mobile contents. The LC50 for zinc for E. christenseni is 271.8 mg/kg (total) and
81.4 mg/kg (mobile) respectively. For E. sp. (RefB5) the following LC50-values were determined: 423.6 mg
Zn/kg (total) and 131.5 mg Zn/kg (mobile). The reproducion test with E. christenseni produced EC50-values of
75.9 mg Zn/kg (total) and 16.7 mg Zn/kg (mobile). The corresponding effect concentrations for E. sp. (RefB5)
are on a similar level: 73.0 mg Zn/kg (total) und 15.8 mg Zn/kg (mobile).
The EC50 of acidified soil (pH 4.9) was estimated 70.6 mg/kg which is only marginally lower than without acid
(pH 5.2). The EC50 in acidified soil calculated on the basis of mobile zinc was 20.2 mg/kg.
On most sewage fields the zinc contents exceeded the EC50-values of both examined species. On one site the
zinc contents were even beyond the LC50. Further, soil moisture in the field was often below water contents that
caused considerable inhibition of reproduction under laboratory conditions. Soil acidification had negative effects
on the dominant enchytraeid species as well as on the mobility of heavy metals. In total, the habitat function of
the contaminated sewage field soils is considered seriously impaired.
Keywords: Enchytraeidae, heavy metals, zinc, soil moisture, soil pH, sewage fields |
