Surveying water beetle diversity & colonisation of restored and resurrected ponds, and County Wildlife Site ponds at Brisley Green. Funded by the Norfolk Biodiversity partnership

In July 2013 the Biodiversity Partnership (NBP), awarded ENSIS funding to carry out the Ghost Ponds Project – an investigation into the conservation value of lost farmland ponds, and how their ‘resurrection’ can contribute to regional aquatic biodiversity. In September – October 2013, six new farmland ponds were restored in north Norfolk. Three of the ponds were “resurrected” ghost ponds – old ponds which had previously been filled-in for agricultural land reclamation – and three were overgrown existing ponds. While the main focus of the project has been on the role of the historic seedbank, and its' contribution to pond re-colonisation, a follow up project focused on determining how the restored ponds were colonised by actively dispersing water beetles. Alongside the restored ponds a series of 96 experimental ponds were established to further assess plant and invertebrate colonisation activity.

Objectives:

The objectives of the water beetle surveys were to;
  1. Provide data on the water beetle species colonising the six study ponds during the first year after their restoration.
  2. Help assess the importance of ghost and restored ponds for aquatic invertebrate diversity more generally, using water beetles as a proxy
  3. Help us to assess the ecological validity of the experimental mesocosms being used alongside the pond sites

Methods:

In addition to the six study ponds, 96 ‘mini-ponds’ were also established – small experimental ponds located next to the study ponds. These mini-ponds variously excluded colonisation by dispersal (fine netting), or from the sediment seed bank (plastic lining and sterile soil), allowing us to identify whether plants and invertebrates appearing in the study ponds were derived from dormant seed banks, or dispersal. These mini-ponds were been included in the water beetle surveys, both to assess their ecological validity (i.e. do they attract actively dispersing invertebrates in the same way as the six study ponds?), and also to see whether they are used by the same species of water beetle which are colonising the study ponds.

Results:

Comparing the species diversity of the ghost ponds to that of the restored ponds, despite similar chemistries and colonising plant communities, the ghost ponds supported a wider diversity of species than the restored ponds. Perhaps ghost ponds, being more exposed (no surrounding trees, high levels of disturbance), are more attractive to early colonising water beetles than the slightly more established restored ponds. There was however, a high degree of overlap in beetle species composition in ghost and restored ponds, with 51% of species occurring in both pond types.

It is sometimes argued that overgrown ponds have their own important biodiversity value, in particular for invertebrates such as water beetles. This is often the case when a pond is “overgrown” with grasses and rushes, but is rarely the case for agricultural ponds, heavily shaded by trees. In this situation ponds tend to have highly anoxic sediments, low O2 in the water and an absence of aquatic plants. In this project, to check that the ponds earmarked for restoration did not contain any rare or protected species, surveys of water chemistry, aquatic plants, and water beetles were conducted in two of the three ponds at the peak of aquatic vegetation cover and water beetle activity in the early summer

Monitoring over the course of the first year of pond colonisation has provided us with important information, not only on the species composition of water beetles within ghost and restored overgrown ponds, but also on the huge potential contribution such ponds can make to regional biodiversity in an agricultural landscape.

Links:

Ghost Ponds: Resurrecting lost ponds and species to assist aquatic biodiversity in conservation

River Mun Restoration
Surveying for water beetles at Old Hall Farm, Westfield. This species is Dytiscus marginalis (Great Diving Beetle). © Ewan Shilland