Measuring Soil Mesofauna in Green Stormwater Infrastructure

Bioretention filters (rain gardens) in urban environments that use plants are promoted as a type of green stormwater infrastructure. To better understand how these engineered controls interact with the environment, soil mesofauna extraction was performed on a variety of urban stormwater controls, including bioretention filters and other more traditional vegetated stormwater controls. Wooded areas were used as background comparisons. Soil metrics, including bulk density, loss on ignition (LOI), and soil penetrometer were performed for sampling locations and several ecological indices were calculated. Over a three-year period, 44 sites were sampled and binned into the following three groups: background (i.e., not urban stormwater controls) (10), bioretention filters (21), and other stormwater controls (13). The last grouping of other stormwater controls had statistically relevant subgroups of dry detention basins (6) and wetlands (4). The other stormwater controls group had both lower enumerations of soil fauna and lower diversity than background and bioretention filters. The lower enumerations and diversity indices of other stormwater controls was from observations in the subgroup of dry detention basins that was significantly less diverse than background, bioretention filters, and even the other subgroup of wetlands. Linear regressions of mesofauna sample enumerations and number of taxa to bulk density and LOI were poorly correlated (R2<0.09). Penetrometer tests indicated bioretention filters had the least compaction while detention basins had the highest. The relatively larger abundance of soil mesofauna (i.e., total count) and number of taxa in bioretention filters versus dry detention basins is probably because of construction practices and water holding capacity since bioretention filters are highly infiltrative and not compacted while dry detention basins are not infiltrative and highly compacted.