Water Chestnut: Field Observations, Competition, and Seed Germination and Viability in Lake Ontario Coastal Wetlands

Abstract

Water chestnut (Trapa natans L.) has recently invaded an increasing number of sites in New York State, particularly Lake Ontario coastal wetlands. It can severely inhibit ecosystem functioning and can be costly to control. To understand this exotic invasive plant more thoroughly, field observations and experiments were performed. The field observations were made in Lake Ontario coastal wetlands during the 2014 growing season. Percent coverage, time of flowering, time of seed production, and co-occurring species were noted. A competition experiment was performed using water chestnut and white water lily (Nymphaea odorata Aiton). They were planted together and in monocultures of differing densities. A greenhouse germination experiment in aquaria was conducted on water chestnut seeds using light and temperature as treatments, and seed-viability was examined to assess development stage and cold-stratification requirements. Water lily was the better competitor of the two, but water chestnut had very high germination success. Water chestnut germination does not seem to be inhibited by temperature or by exposure to shade. The seeds do, however, need to be mature and cold-stratified (subjected to a period of cold temperatures for dormancy) to germinate. Water chestnut’s tolerance to temperature, shade, and water depth has serious implications for Great Lakes wetlands if not controlled. There are a few control methods that could prove to be useful, but more research is needed before they are used in field settings. Early detection and manually pulling small patches of plants is a viable option at present.