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Water Chestnut
The water chestnut (scientific name Trapa natans) is an aquatic plant called a "macrophyte", which literally means large plant. It is a native of Eurasia that was introduced to the US as an ornamental plant in the 1800's. It first appeared in the Hudson River in the 1930's. It favors quiet, non-moving waters like bays and inlets and near docks. Its leaves float on the surface of the water thus blocking light to water below. In blocking light and reducing dissolved oxygen in the water column, it out-competes native species like water celery (Vallisneria americana) and alters the conditions for macroinvertebrate species. It was identified as a nuisance plant in the 1950's and there have been many attempts to eradicate it, none successful. Perhaps its most distinctive feature is its hard, spiny seed pod that can cause great pain if stood upon. In these lessons, students will learn how this very important invasive aquatic plant has changed the Hudson River ecosystem in many unforeseen ways.
Lesson 1- Simulated Aquatic Plant Invasion
In this 1-2 week lesson, students will simulate an invasion of an aquatic plant and study its effects on the dissolved oxygen levels in the water. Using Elodea, students will measure dissolved oxygen levels after their microcosms have been left in the dark and again after plants have been placed in the light. They will simulate a mat similar to the mats of water chestnut that block sunlight and measure the effects of that on the dissolved oxygen levels.
Lesson 2- Graphing Water Chestnut Data
Using Hudson River data that IES scientists have collected, students will graph and analyze the effects of zebra mussels on very important zooplankton species. If students are unfamiliar with Microsoft Excel, it will be worthwhile asking them to first complete the Excel Tutorial in the Hudson River Ecosystem module (link to excel tutorial). Data for this lesson are provided on the lab sheet as well as below in an Excel spreadsheet.
Lesson 3- The Effect of Invasive Species on Macroinvertebrates
In this lesson, students will compare invertebrate data collected in Water Chestnut beds with invertebrates collected in Water Celery beds in the Hudson River. They will compare the total biomass of water chestnut and water celery on macroinvertebrate numbers and species diversity. Accelerated students can create their own graphs using the Excel Data; beginning students can use the prepared graphs.
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