Aquatic Ecology, Habitat Restoration and Management Planning

The Brief

Freshwater pond in need of habitat restoration

The balance pond at the time of initial survey, a number of invasive macrophytes were present along with significant shading and organic inputs from material in the riparian zone.

Carcinus Ltd was commissioned by a Council as part of an amenity improvement drive to assess the aquatic ecology of a freshwater balance pond and produce a detailed habitat restoration and management plan. The pond was known to be suffering from a number of pre-existing ecological issues including heavy silting, lack of freshwater input and foul odours as well as excessive leaf fall, historic fish kills and infestation by invasive non-native species (INNS). The following objectives were set out to tackle the aquatic ecology issues: 

  • Assess the ponds status to identify all existing ecological stressors;
  • Undertake a baseline characterisation aquatic survey to determine the condition of the ponds habitats and fauna; and
  • Produce a comprehensive management plan to clearly set out how to restore, enhance and maintain the ponds aquatic ecosystem.
Invasive non-native aquatic macrophyte

Parrots feather Myriophyllum aquaticum, listed on Schedule 9 of the Wildlife and Countryside Act as an invasive non-native aquatic macrophyte

Our Involvement

Walkover Survey

An initial walkover survey was undertaken to identify key health and safety and access issues, inform survey planning and to undertake a high-level assessment of the aquatic ecology within the pond. It was identified that the pond was infested with New Zealand pigmyweed Crassula helmsii and parrots feather Myriophyllum aquaticum, both listed on Schedule 9 of the Wildlife and Countryside Act.

Aquatic Ecological Survey

Aquatic macro invertebrate sampling - freshwater ecology assessment

Carcinus ecologist undertaking macro invertebrate sampling using a sweep netting technique, fauna were then identified to family level for assessment purposes.

Following the walkover, an aquatic ecological survey was undertaken jointly by Carcinus Ltd and AQASS Ltd. Whilst adhering to the necessary bio-security precautions for the prevention of spread of invasive species, our ecologists assessed the current ecological status of the pond. Water chemistry parameters and habitat features such as sediment / water depth, percentage shade and the abundance / biodiversity of the macrophyte (aquatic plant) community were recorded. Aquatic invertebrate samples were also collected using net sweep sampling techniques and analysed and the water quality classified using the Average Score Per Taxa (ASPT) and the Biological Monitoring Working Party (BMWP) scoring systems.

Results indicated that the pond was ecologically stressed and in need of habitat restoration. In particular, the macroinvertebrate community was found to be representative of stress tolerant families’ indicative of a relatively low oxygenated water environment. High densities of parrots’ feather were recorded and large quantities of rotting vegetation was evident on the banks. In general, the ponds habitats were considered denuded but with the correct management recoverable.

Habitat Restoration and Management Plan

Building upon the findings of the baseline aquatic ecological survey, a comprehensive management plan was produced, which set out a series of phased habitat restoration initiatives to achieve improved ecological status and amenity value.

  • Phase I – aims to tackle the immediate ecological stressors to facilitate the restoration of the ponds aquatic habitats and its biodiversity. This is to be achieved by controlling INNS infestations, improving water flow and thinning out the tree canopy.
  • Phase II – aims to enhance the ponds habitats through native planting, riparian improvement and public awareness initiatives.
  • Phase III – focuses on the long-term management of the pond by providing advice about continued monitoring campaigns and early detection protocols for INNS management as well as building environmental awareness within the local community.


The baseline survey was well received by the Council which is currently reviewing the management plan before implementation of Phase I of the management plan.