What are Freshwater Tidal Wetlands?

Engage:

Write the following questions on the board and ask students to answer them in their journal, on a whiteboard, or as a discussion in pairs.  What is a wetland, and what is a tidal marsh?  How are these two types of ecosystems different?  Are they important?  Have they ever seen one?  Where might they find one?  Share students’ responses.  Expect a range of “I don’t know, swamps, a place to fish;” some may have them in their back yard.

Ask students to create a list in their notes of the benefits of & threats to wetlands, and to keep track of each as they watch one (or more) of the videos.  Afterwards, revisit the question: “Are wetlands important?”

Explore:

Working in small groups, hand out the Marsh Cards (laminate them for longevity) and challenge students to complete the chart using the Marsh Field Guide and Info Cards.  There are 25 organisms. Ask each student to identify 4-8 organisms (depending on the size of your groups) and share with the rest of the small group.  Responses will be checked as a class.  Once students have identified all the organisms, project the Marsh Zone picture and ask students to place the organisms in the appropriate zone (either use a Smartboard or have students tape the laminated pictures in the correct place).  Students should create a sketch of the vegetation zones with organisms in their notes. 

Explain: 

A marsh is a type of wetland.  In general, wetlands have high biodiversity values, protect shorelines from flooding and erosion, and filter pollutants.  Threats include land conversion, sea level rise, pollution, and invasive species.  In this series of lessons, we focus on freshwater tidal wetlands, which are a unique, globally rare ecosystem type found in the Hudson River.  They are affected by the tides but, since they are above the salt front, experience only freshwater tides and thus contain only freshwater organisms.  There are more than 200 freshwater tidal marshes along the Hudson River estuary.  Although they make up only 8% of the Hudson River area, each molecule of water that travels down the river from the Troy Dam to the mouth of the estuary goes in and out of a marsh 3 times (during the summer months).  Consequently, what happens to the water within the marshes can be very important for the River’s overall water quality.

There are three major ecosystem “zones” within a freshwater tidal marsh.  Each zone receives different amounts of water, depending on the elevation, and different organisms tend to live in each of the different zones.  Inundation by water is the driver of the differences.  Different plants tolerate, or are adapted to, the different amounts of water and exposure within the zones of the marsh.  For example, plants that live underneath the water like water celery cannot live in the higher parts of the marsh because they cannot survive outside of the water for long periods of time.  Similarly, graminoid plants like cattails cannot be submerged.  Plants that live in the broadleaf portion of the wetland can tolerate being submerged or being exposed. 

The three main zones are called: submerged aquatic vegetation (S), broadleaf vegetation (B), and graminoid vegetation (G).  In the lowest zone (submerged), you will find water celery and water milfoil, and often there are water chestnut plants floating on top.  In the middle zone (broadleaf), you will find plants like spatterdock and pickerelweed, which have their roots under the water for part of the day, and above the water at other times, depending on the tides.  The tallest vegetation includes common reed and cattails (graminoid).  These plants are never covered with water. 

Extend: 

Reading from Changing Tides, by Esther Kiviat.  This reading is filled with scientific vocabulary and Common Core Tier II vocabulary.  It is a rich description of the complexity of a Hudson River Tidal Marsh and also provides a link to the local aspect of wetlands.  Scientific vocabulary has been highlighted in bold print and Tier II words have been underlined.   Have students read the article, circling things that they don’t understand.  Address words that students circled and have them verbally summarize each paragraph. 

Evaluate:  Using exit slips, ask students to answer the following question using a Venn diagram: How are tidal wetlands along the Hudson River similar to other wetlands, and how are they different?