Floods and drought: Response of earthworms and potworms (Oligochaeta : Lumbricidae, Enchytraeidae) to hydrological extremes in wet grassland

Enchytraeidae) were recorded in three floodplain meadows differing in soil type in Northern Germany during 2 years of contrasting hydrological extremes: 2002 with high precipitation, extended winter inundations and summer floods in two of the sites, and 2003 with an extraordinarily dry summer. In all sites, earthworms dominated the biomass of soil fauna, the dominant species being Octolasion tyrtaeum in marsh soil, Octolasion cyaneum in peat soil, Allolobophora chlorotica in gley soil, and Lumbricus rubellus in all three sites. The enchytraeid communities composed of 7-10 species, differed widely between sites. While the summer flood of 2002 reduced annelid populations in peat soil to zero, in gley soil only enchytraeids were sharply reduced. The earthworms there probably were less affected because of shorter duration of the flood, the lower air temperatures and SOM contents and the diapause of the dominant A. chlorotica. During summer drought in 2003, earthworms and enchytraeids were absent from gley soil, while they had maximum abundances in peat soil. The marsh soil, structured by a microrelief of shallow ditches and ridges, had highest densities of annelids. As it was not subjected to summer flooding in 2002, populations of both earthworms and potworms were stable. The drought in 2003 led to a sharp decrease in earthworm abundance in July, while the enchytraeids reached maximum values. Dynamics and survival strategies of different annelid species are discussed. The water holding capacity as well as the organic matter content of the soil are important factors for annelids in sites subjected to such hydrological extremes. To promote terrestrial annelids, controlled flooding should be kept short, especially in winters following natural summer floods. If possible, recovery times for annelids should be guarenteed, that is 2-3 months without inundations for enchytraeids and about half a year for earthworms. A microrelief with drier refuge sites can be judged as favourable for earthworms. An artificially raised groundwater table will favour annelids during drought periods. (c) 2005 Elsevier GmbH. All rights reserved.