Natural aquatic plant colonisation in a newly constructed Irish Canal

Abstract

AbstractIn January 1989 a major breach in a section of the Grand Canal occurred. As a consequence, a 2.5 km long section required reconstruction. The channel was built up using peat material, lined with an impermeable membrane and overlayed with Puddle Clay. The section was rewatered in March 1990. For the next 30 months the course of natural aquatic plant colonisation was monitored. The first coloniser was the charophyte Tolypella glomerata, which appeared in September 1990. This occurred with low abundance until April 1991, when it disappeared. Between September 1991 and April 1992 charophytes, mainly T. glomerata and Chara vulgaris, proliferated. Their abundance diminished significantly during the summer of 1992. It was not until August 1991, 18 months after rewatering, that the first naturally colonising phanerogams were recorded. Principal among these was Myriophyllum verticillatum. In September of that year an aggressive coloniser in Irish canal and river habitats, Potamogeton pectinatus, was first observed. This became a permanent constituent of the flora and ultimately dominated the vegetation at the site. In total, 28 plant species were recorded from the newly constructed section. Nine of these species were either purposely or accidentally introduced during bankside stabilisation operations when live roots and rhizomes were planted along the exposed canal margins. By the end of the study period an abundant and diverse macroinvertebrate community had colonised the vegetation.