Wetland Ecosystem Treatment
The Sustainability Centre has replaced the original brick Naval sewage works with a Wetland Ecosystem Treatment System to treat and purify all the waste water and sewage from the site. It was installed in May 2011 by Biologic Design and provides an effective, attractive and diverse solution that turns an unpleasant 'waste' product into clean water, a biomass yield and a diverse wetland habitat.
The WET System comprises four linear ponds and associated earth banks called Swales - these earth structures have a very high aspect ratio which maximizes the amount of water's edge available for planting of wetland species and thus for wildlife to inhabit and use.
The Centre is an upland site which is normally very dry with no natural wetland areas due to the very porous nature of the chalk substrate. The WET System has added a very valuable ecological niche to the site. The WET System swales are lined with a Geosynthetic Clay Liner in order to preclude any chance of wastewater entering the groundwater. These swales have been mulched with woodchip derived from the trees felled from the site in order to suppress weed species (nettles etc.) from germinating from the seed bank.
The swales have now been planted with 3,500 willow trees, which are all named basketry varieties and which will be managed as coppice to provide willow wands for basketry and other craft work.
In addition to the willows we have also planted 3,200 macrophytes - water plants and marginals. The species we have planted on the WET System were first checked as appropriate specifically for this site by Martin Rand, the BSBI Recorder for South Hampshire.
Species planted within the WET System
Reed Sweet Grass
Yellow Flag Iris
Lesser Pond Sedge
Reed Canary Grass
Within the first few weeks of the operation of the WET System a plethora of wildlife has come to the site (including many amphibians, birds, dragonflies etc.) and as there are still many acres of woodland remaining on this site the WET System has been a very valuable addition to the woodland and dry meadow ecotones already present at the Centre.
Dragonflies and pond skaters have been observed in the WET system within the first month of installation. The increase in invertebrates in the WET system will provide a feeding area for birds.
Increase in bird diversity - Herons and turtle doves have been observed in the WET system in the first two months of planting.
Creation of a feeding area for birds -
Creation of a foraging area for bats - The increase in insects in WET system ponds will provide a foraging ground for bats
Bees are essential for pollination and maintaining plant biodiversity. We already have 3 bee hives close to the WET system and we will put two more hives in the system itself in 2012.
There are many species of butterfly that will benefit from the short rotation coppice and woodland edge habitat that has been created in and around the WET system.
The WET system is planted with short rotation coppice willow that aids the process of evapotranspiration and waste water treatment through the system, stabilises the soil banks and produces a biomass yield of material to be used for craft projects or fuel. Short rotation coppice supports a large number of invertebrates which will lead to an increase in the number of small mammals and bird species.
The rides created between the WET system willow coppice and the surrounding secondary woodland will support a range of woodland edge species including many species of butterfly such as the silver wash fritillary. In time an ecologically beneficial ground flora will develop made up of shade tolerant plants often found within woodland and hedgerow. These will encourage the presence of small mammals and invertebrates that will in turn provide food for birds.
Through opening up an area for the WET system a woodland edge habitat has been created in the interface between trees and open ground. A structurally diverse, graduated woodland edge will enhance the diversity of species within the woodland and along rides. These areas will be allowed to regenerate naturally to preserve local provenance. These areas will also be perfect hunting ground for owls and bats as we are creating feeding corridors.
The WET system is a totally passive system that requires no energy from non-renewable sources to operate. The WET system will also produce an annual biomass yield in the form of coppice willow. This will be coppiced on an annual rotation for use in basketry, living willow structures, biomass fuel, spar gads etc. In this way the carbon is locked up in the product or for use as a carbon lean fuel.