Agricultural pond restoration enhances species richness in non‐biting midges (Diptera: Chironomidae)

Agricultural ponds are biodiversity hotspots, especially when restored to open‐canopy conditions. Studies comparing pre‐ and post‐restoration pond diversity are rare, however, and have widely focused on “easy‐to‐identify” taxa. Chironomids have so far been neglected in pond restoration studies, but are a highly speciose group critical to aquatic ecosystem functioning. This makes them good potential indicators of ecological change. Despite a reputation for being taxonomically challenging, the final molts of chironomid pupae, the exuviae, can be reliably sampled and identified using the Chironomid Pupal Exuvial Technique (CPET). For a lowland farmland pond landscape in eastern England, we used CPET sampling in a Before‐After Control‐Impact study encompassing nine ponds restored by major removal of woody vegetation and sediment, four terrestrialized control ponds and two open‐canopy control ponds. Species richness was significantly greater in the restored and open‐canopy control ponds compared to the terrestrialized ponds, likely due to structurally complex plant communities in the former. Few chironomid species preferred the wood and organic matter‐dominated conditions afforded by the terrestrialized ponds, while the restoration of these ponds to open‐canopy, macrophyte‐dominated condition strongly increased chironomid diversity. To maximize landscape‐scale chironomid diversity, agricultural landscapes should ideally contain ponds at different stages of succession, including a high proportion of ponds restored to an early successional macrophyte‐filled state. As for many other taxonomic groups, we show that pond restoration is essential to the maintenance of species‐rich chironomid communities in farmland pondscapes.