Natural wetlands are well known for their biodiversity, attracting huge numbers of insects, birds and mammals as well as plant species. So how would a constructed wetland fair?
As members of the Constructed Wetland Association, we are often approached by PhD students wanting to survey our beds, studying a variety of topics from treatment performance to clogging mechanisms and more recently determining the biodiversity.
It is well known that multiple macrophyte species in a constructed wetlands have increased biodiversity, but older constructed wetlands systems typically for wastewater treatment are planted with single macrophyte species such as the common reed (Phragmites australis) Iris or cattails (Typha latifolia). How biodiverse can a reed bed be, when it is essentially a monoculture?
Over the last year, Marie Athorn, a student from Nottingham University has carried out moth, gall and mammal surveys on non-water company horizontal flow reed beds containing only the Common Reed.
Our Rugeley head office is located on an industrial estate where we treat all the wastewater from the estate in our own red beds. From our own observations, we regularly see newts, frogs, reed buntings and reed warblers as well as a plethora of invertebrates so a biodiversity survey on our reed beds was of great interest to us.
The results surprised us. On one particularly wet night, over 16 species of moth were found. On less damp occasions, in other similar constructed wetlands in the survey, that number increased to over 30 species, including the common wainscot, the mother of pearl micro-moth and flame shoulder moth, with the large yellow underwing (Noctua pronuba) topping the list of all species found.
The most exciting and unexpected find was definitely the Harvest Mice. It was really incredible to find them in such a small reed bed. Exactly the kind of thing that should boost the use of industrial reed beds, especially as harvest mice are a BAP species.
It seems that even if your treatment wetland has one dominant species, bugs and beasts will move in and make it their home. Adding different macrophyte species will only enhance the Biodiversity further.
Marie’s PhD will finish next year and we are looking forward to reading her thesis. If you are interested in following her reed bed antics, you can follow her on twitter