Vegetation management and benthic macroinvertebrate communities in urban stormwater ponds: implications for regional biodiversity

Designed ecosystems (e.g., gardens or engineered ponds) are increasingly common components of urban landscapes and contribute valuable ecosystem services. However, management of designed ecosystems is typically vegetation-centric and often does not consider associated fauna. Urban ponds typify this relationship as their vegetation is managed to improve ecosystem services, such as aesthetics and stormwater runoff mitigation, but it is unclear how pond management affects associated organisms. Here, we used urban stormwater ponds as a study system to determine how vegetation management related to benthic macroinvertebrate communities in these systems. We compared macroinvertebrates across a range of actively managed to unmanaged stormwater ponds and differentiated direct relationships with vegetation structure from indirect relationships of vegetation modulating pond chemistry. Pond vegetation and chemistry had little influence on macroinvertebrate abundance or diversity but did explain substantial variability in community composition (34%). Actively managed stormwater ponds with simpler vegetation structure were dominated by Amphipoda (scuds) and Diptera (primarily midges), unmanaged ponds with more complex structure were dominated by Oligochaeta (worms), and ponds with intermediate structure were dominated by a variety of macroinvertebrates. These community associations with vegetation management primarily occurred indirectly via changes in pond chemistry, such as unmanaged ponds with higher tree and shrub cover harboring macroinvertebrates characteristic of low oxygen environments. Additionally, variation in management maximized community differences because different macroinvertebrate orders dominated at different management intensities. Variability in the management intensity of plant communities in stormwater ponds may therefore be a feasible strategy to enhance regional benthic macroinvertebrate biodiversity in urban landscapes.