NATURAL AQUATIC PLANT COLONIZATION IN A NEWLY CONSTRUCTED IRISH CANAL

In January 1989 a major breach in a section of the Grand Canal occurre d. As a consequence, a 2.5 km long section required reconstruction. Th e 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 To lypella glomerata, which appeared in September 1990. This occurred wit h low abundance until April 1991, when it disappeared. Between Septemb er 1991 and April 1992 charophytes, mainly T. glomerata and Chara vulg aris, proliferated. Their abundance diminished significantly during th e summer of 1992. It was not until August 1991, 18 months after rewate ring, that the first naturally colonising phanerogams were recorded. P rincipal among these was Myriophyllum verticillatum. In September of t hat year an aggressive coloniser in Irish canal and river habitats, Po tamogeton pectinatus, was first observed. This became a permanent cons tituent of the flora and ultimately dominated the vegetation at the si te. In total, 28 plant species were recorded from the newly constructe d section. Nine of these species were either purposely or accidentally introduced during bankside stabilisation operations when live roots a nd rhizomes were planted along the exposed canal margins. By the end o f the study period an abundant and diverse macroinvertebrate community had colonised the vegetation.