Biodiversity Northern Ireland

Tackling Aquatic Invasives at Glastry Ponds

Glastry Ponds, Ard's peninsula is a major site of Hydrocotyle ranunculoides (Floating Pennywort) in Northern Ireland first recorded from the site in 2002. 

Originating as a 19th Century brick works, the pits were flooded creating a network of interlinking ponds. Other aquatic invasives, Crassula helmsii (New Zealand Pigmyweed), Azolla filiculoides (Water Fern) and Myriophyllum aquaticum (Parrot's Feather) are also known to occur or have been present at the site in the recent past.  

Hydrocotyle ranunculoides is native to North America and was brought to Britain & Ireland in the 1980's as a plant for garden ponds.  The plant is a stoloniferous, perennial aquatic plant which colonises shallow eutrophic water bodies such as ditches, ponds and lakes where it is generally rooted in soft sediments. The plant is known to block water bodies which may lead to an increased risk of flooding, deoxygenate the water body it colonises with effects on native fauna, and out-competes native aquatic plants.

Experiment removal of Floating Pennywort from two ponds at the site began in January 2008 removing 30 tonnes of plant material with follow up removal in early 2009. Mechanical removal was achieved by cutting the mats of vegetation with hand saws into smaller fragments from a boat. The blocks of vegetation were then dragged to shore and removed with a modified bucket on a tracked digger located on the bank side. A similar programme of control is taking place this year also. In addition to mechanical removal, areas of the floating pennywort mat were covered with black polythene sheets (10m x 5m) fixed to the surface and bottom excluding light from the plant underneath.  

There were many lessons learnt from this project, the pro and cons of the methods used, and the implications for pond fauna and future management options will be presented at the upcoming Invasive Species Ireland Conference in April. This project was a joint partnership between NIEA, Rivers Agency and The National Trust.