Management of the invasive Nuttall’s pondweed (Elodea nuttallii) in Lough Arrow, a Natura 2000 designated lake in Western Ireland

Abstract

A benthic geotextile was used to trial the management of an invasive aquatic macrophyte Nuttall’s pondweed (Elodea nuttallii (Planch.) H. St. John, 1920) in Lough Arrow, a premier trout angling lake in the north-west of Ireland, designated as a Natura 2000 site (Special Area of Conservation (Annex I habitat, “Hard oligo-mesotrophic waters with benthic vegetation of Chara spp.”) and Special Protection Area for birdlife). The aim of this study was to manage E. nuttallii, a relatively recent arrival to this lake, while simultaneously promoting rehabilitation of native charophytes. The trial was carried out in Loughbrickbay, one of the lough’s primary boating launch sites, an area determined as highly infested with E. nuttallii. Two experimental areas covering a total of 800 m2 were treated by covering the invasive weed and substrate with jute textile, a single and double layer respectively. The trial was successful in controlling E. nuttallii for both single (P = 0) and double layer treatments (P = 0.002). The treatments applied resulted in a reduction of the mean percentage cover of the invasive species by > 60% for both treatments. Post-treatment mean percentage cover of E. nuttallii did not exceed 6% for either treatment. Furthermore, the mean percentage cover of indigenous charophyte flora present pre-treatment was not significantly impacted by the application of jute in either the single (P = 0.165) or double treatment (P = 0.353). For biosecurity purposes, the treatment areas were strategically positioned in close proximity to the bays pier and slipway. The treated transects were marked with navigational buoys to provide a corridor for boats entering and exiting the lake, which help to contain the invasive within the Natura 2000 site while reducing the spread risk via this pathway to other sites vulnerable to infestation.