Once a pond in time: employing palaeoecology to inform farmland pond restoration

The restoration of highly terrestrialized farmland ponds that combines the removal of woody vegetation and pond sediment greatly enhances aquatic biodiversity. Nonetheless, questions remain regarding the historical precedent of pond restoration, and particularly if post-restoration aquatic macrophyte communities resemble pre-terrestrialization assemblages. We used a paleoecological approach to address these questions for a typical, recently restored farmland pond in Norfolk, eastern England. Plant and animal remains in pond sediment cores were used to infer decadal-centennial scale changes to pond communities and to identify past pond management events. We then evaluated the resemblance of restored and historical assemblages by comparisons with contemporary post-restoration vegetation data. Based on changes in the abundance of terrestrial leaf remains and other indicators (increases followed by declines of aquatic organisms), the study pond appears to have a long history (going back to the early-1800s) of canopy management (at least three inferred management events), but after the mid-1970s, steady and substantial increases in terrestrial indicators, suggest cessation of management resulting in uninterrupted terrestrialization. Aquatic macrophyte communities arising after restoration showed some similarities with historical assemblages, but also contained apparently new species. This study demonstrates how paleolimnological methods can improve understanding of pond ecological histories to better inform restoration targets and practices. Implications for Practice Paleolimnological methods can be successfully employed at small, human-made ponds to assess past biological communities and trajectories of ecological change. Restoration of heavily terrestrialized farmland ponds through major woody vegetation and sediment removal mimics periodic management activities undertaken over past centuries and is essential to the maintenance of open canopy conditions and biodiversity conservation. Caution must be taken when setting restoration targets for farmland ponds as rare macrophyte species indicative of high water quality may not necessarily return to restored pond habitats due to fragmentation effects associated with the loss of local populations and/or in-pond eutrophication development