Cefni Resevoir & Cors Bodeilio

As part of the MSc we are learning about the benefits of constructed/treatment wetlands. Natural wetlands provide many ecosystem services with a major one being natural biofilters removing excess nutrients from water ways. A treatment wetland can be developed with aims of removing pollutants from waste waters via sedimentation and uptake through the wetland plants.

This field trip started at the Cefni Reservoir, which is a small reservoir in the centre of Anglesey managed by welsh water. The small rivers and streams entering the Cefni have been identified as potential areas to create mini-constructed wetlands. These wetlands could help improve water quality entering the reservoir and also improve areas for biodiversity.

To determine where the constructed wetlands would be best placed water samples were taken from each of the inflows, where they would be taken back to the lab to be tested for pollutant levels. (This was done prior to our field field trip by experts, we also took samples to get a feel for the process).

Different constructed wetland systems would be more efficient at removing certain pollutants/excess nutrients than others...

Free water surface system (FWS)

Sandec/Eawag depiction of a FWS

A FWS constructed wetland allows water to flow above ground, exposing the water to the atmosphere and direct sunlight. Meaning there are aerobic and anaerobic zones for the complete removal of Nitrogen from the system (one of the main pollutants entering the Cefni reservoir). 

Moving to the other side of the reservoir we estimated the flow rate of one of the streams into the reservoir using a very high tech method, which involved a spade, pipe, bucket, jug and stop watch. A small dam was created with the pipe through the middle (as seen in the picture on the left), a small amount of water (around 1L) was collected from the outflow using the jug at timed intervals - which could then be used to calculate the flow rate.

Cors Bodeilio
After discussing potential treatment wetland ideas to help purify the water entering the Cefni Reservoir we travelled to Cors Bodeilio which we had previously visited during the LIFE Conference - a blog post on that can be found here. The LIFE project aimed to restore the delicate fen habitat at Cors Bodeilio with aims to restore the peatlands not only for carbon storage but also to store and purify water, before releasing it at a manageable rate to provide drinking water to Cefni reservoir.

There are a number of constructed wetlands at Cors Bodeilio that remove the nutrients from the surrounding farmlands to prevent eutrophication of the natural fen habitat. These wetlands have however been subject to subsidence and more funding is required to restore the wetlands to full working order - which is key for maintaining the delicate fen.