Macro-invertebrate survey

On 9th August 2001 a macro-invertebrate survey of the Watercress-beds Local Nature Reserve was undertaken to assess the richness of the aquatic fauna and whether any species of conservation value were present.

The watercress beds were heavily overgrown with no or little water visible. Large growths of Reed Sweet Grass (Glyceria maxima), Water mint (Mentha aquatica) and Fools Water Cress (Apium nodiflorum) were present. Small amounts of Bulrush (Typha sp.) and Yellow Flag Iris (Iris pseudocorus) were also present around the margins of the channel. The following three photographs show the habits present within the cress beds.

Photo 1

Watercress Beds Nature Reserve - Small Bed Overgrown Channel

Photo 2

Watercress Beds Nature Reserve - Small Bed Overgrown Channel

Photo 3

Watercress Beds Nature Reserve - Large Open Pond Area

Macro-invertebrates were was collected following the standard Agency methodology, of a combination of kick and sweep sampling with a pond net. In addition there was a hand search of boulders and other movable material present within the cress-beds.

Results:

All samples were then returned to the laboratory in Hatfield for sorting and identification to species. The results are summarised below and listed in Table 1. Macroinvertebrates taxa were identified as far as available keys would allow with the exception of Chironomidae (midge larvae), families of Oligochaeta (worms) and Hydracarina (water mites) which were not identified further. For the remaining groups all were identified to species, although certain identification was not possible for several closely related species which cannot be readily separated as larvae (eg Caenis luctosa group and Pericoma sp.).

In total 40 taxa were recorded from 28 families with a BMWP score of 90. The site recorded two local species. The soldier fly larvae (Oxycera nigricornis) is typical of fens and marshes or sedge margins of old silted up pools. The crawling water beetle (Haliplus wehnckei are found in many lowland water areas.

The Nationally Notable B Crawling Water Beetle (Haliplus laminatus), a small brown beetle was also recorded during the survey. This beetle is typically found in lowland areas in slow-moving parts of rivers and base-rich pools and canals with restricted vegetation. The adults feed on filamentous algae, worms (Oligochaeta) and non-biting midge (Chironomidae) larvae.

The species of conservation interest recorded within this survey are associated with areas of still and slow flowing water. Any enhancement proposals for the sites should ensure that some areas of slack and slow flowing water are retained. The proposals to create a low flow channel withing the cress-beds to create areas of habitat diversity and flow variation would increase the habitat types available to the aquatic macro-invertebrates and increase the richness of the community within the nature reserve.

Table 1 - species list