Influence of Enchytraeidae (Enchytraeus albidus) and compaction on nutrient mobilization in an urban soil

Soil compaction is an often-recorded characteristic of degraded soils, and—along with soil sealing and contamination—frequently found in urban habitats. Knowledge about the impact of soil degradation on the ecosystem functioning in urban environments is limited, although urbanization is the major ongoing land use change worldwide. Since urban soils are a potential habitat for soil animals, and burrowing soil fauna exerts a profound impact on the structure and functioning of soils, we studied the impact of increased bulk densities on the ability of Enchytraeus albidus (Enchytraeidae: Oligochaeta) to penetrate compacted soils. Moreover, it was our aim to characterize the influence of the worms on the mobilization of nutrients in urban soils. E. albidus was able to enter compacted sandy loamy soil columns with a bulk density of up to approx. 1.4 g cm⁻³, but only up to approx. 1.0 g cm⁻³ in pure sandy soil columns. Soil compaction increased the amounts of water-extractable sodium (7.5%) and magnesium (13.4%) compared to the non-compacted soil. Presence of E. albidus in the non-compacted soil resulted in higher water-extractable concentrations of sodium (17.4%), potassium (16.8%), calcium (11.3%), magnesium (13.2%), dissolved organic carbon (DOC, 14.5%) and nitrate (20.4%) in soil extracts. In the compacted soil, however, the enhanced nutrient availability due to the activity of the enchytraeids was less pronounced than in the non-compacted soil. Although the concentrations of DOC (13.5%), nitrate (15.6%), calcium (5.8%) and magnesium (4.0%) were significantly higher in the presence of E. albidus than in the columns without animals, the performance of the animals was partly impaired. This was most likely due to the higher penetration resistance of the compacted soils. The degree of compaction investigated in this study was relatively low-chosen to allow for the colonization of the soils by E. albidus. We conclude that the observed negative effects of increased bulk densities on the activity of soil enchytraeids can occur in any more frequented city park, thereby decreasing turnover rates and the supply of soil nutrients in urban ecosystems.