Investigations of annelids at soil monitoring sites in Northern Germany: reference ranges and time-series data
Soil zoological investigations at soil monitoring sites are carried out with the objective to track changes in the soil’s habitat function. At 60 soil-monitoring sites in north-western Germany, earthworms and microannelids (enchytraeids, tubificids and polychaetes) are currently being used as system indicators for the soil biota. Investigations started 1992, followed by re-investigations every 5 to 10 years. Variations in abundance, biomass and species number of annelids are assessed with respect to nondirectional fluctuations or directional changes, caused by natural variations of environmental factors or due to management practices. The sites are grouped according to land-use type and site condition into six different categories for which typical ranges of variation of the zoological parameters can be distinguished (reference ranges). Especially at sites that passed three investigations already, major changes become discernible. If the temporal variation goes in the same direction throughout the time series, it is considered a trend. When a value shifts substantially out of its reference range, a change of the system state is probable, especially if this applies for two or more parameters simultaneously. Three examples are given for considerable changes of the annelid community due to land-use change or natural succession. The detection of substantial changes of the community is based mainly on the species composition, but is supported by quantitative parameters using the reference ranges.
earthworms, enchytraeids, species composition, land use, soil properties