Hudson Marshes & Climate Change

Engage:  Assess students’ prior knowledge of climate change concepts by asking a few formative assessment questions.  These can be answered on whiteboards or students can work in small groups. 

1)      Why are sea levels projected to rise if the planet continues to get warmer? 

A: Students should discuss thermal expansion of seawater and melting land-based glaciers.  Water expands as it gets warmer because the molecules move further away from one another.  Glaciers that are on top of the land and begin melting deposit their water into the oceans.  Icebergs, however, do not contribute to an increase in sea level rise because the majority of the ice is floating below the surface and thus, when it melts, the resulting water does not take up more space (consider a glass filled to the brim with water and ice – as the ice melts the glass does not overflow). 

2)      Do you agree with this statement?  Climate change will impact the Hudson River valley.

1. Strongly disagree
2. Disagree
3. Neutral
4. Agree
5. Strongly agree

If you think there will be impacts, what will they be? 

A: While there is no “right” or “wrong” answer to this question, it will help you see what students are currently thinking about climate change and how much they have thought about the possible impacts.  It will also allow you to understand whether students are thinking about the social, economic, or ecological impacts (or some combination of these).  For the purposes of this lesson, students should know something about wetlands and their importance – if they do not mention the impact of rising sea levels on wetlands, we suggest reviewing lessons 1 & 2 of the tidal marsh curriculum. 

Explore –  Hand out the student worksheet “Marshes and Climate Change”.  Ask students to read the introduction and then answer the related questions.  (This can also be done as homework the day before.)  An answer key is provided.  Before moving on to the exploration of the simulation tool, ask students to share a few of their predictions.  Specifically, pay attention to what students predict will happen to the plant community within the wetlands. 

Hand out the student worksheet “Will Hudson River Wetlands Change?”  Ask students to navigate to the correct webpage (you may want to pre-load the simulation as it can take time for the page to load if many people are trying to access it at the same time).  As a class, watch the introduction and read the text below, and discuss what the simulation is trying to show.  Then, view some of the photos in “Photo Gallery” to help students visualize what Tivoli Bays marsh looks like. 

Ask students to complete the worksheet.  An answer key is provided. 

Explain –  The vegetation community within the marshes of the Hudson River ecosystem are projected to change as a result of rising sea levels.  Wetlands generally build up over time because sediments are washed into the water system from the land, which is called “accretion”.  However, land can also subside over time, as the earth’s crustal plates move and shift.  Sedimentation rates along the Hudson River range from 0.05-2.9 cm per year, depending on the location of the wetland (Kiviat et al., 2006).  Sea level rise in the Hudson will be anywhere between 0.1 cm/year to 1.1 cm/year over the next century, so low-lying wetlands will definitely be threatened (Northeast Climate Assessment, 2007; Rosenzweig & Solecki, 2001).  The elevation of the adjacent land area is extremely important to understanding how much a wetland will be able to “migrate” to survive rising sea levels.  In Tivoli Bays, the marsh is constrained by upland geography, and the wetlands will not be able to move upland.  How much sedimentation occurs versus how much sea level rise takes place will ultimately determine whether the wetlands will persevere. 

Specifically, in Tivoli Bays, we are expecting that we will lose the graminoid vegetation, which will be replaced by the broadleaf vegetation (see model for 2080 vegetation projections).  This is due to the higher water levels which will submerge the graminoid vegetation at high tide, meaning it cannot survive.  Instead, most of the marsh will be replaced with broadleaf plants, since the marsh cannot move upland.  In a sense, the “winner” here is changing the predominant function that takes place in the ecosystem, as these marshes will no longer be able to remove a substantial amount of nitrate-nitrogen. 

Extend: Ask students to answer this challenge question: Why do you think the water level is highest in 2080, even if CO2 emissions have gone down?   Students should recognize that since CO2 has a residence time of 100-150 years in the atmosphere, its effects will be felt long after emissions are reduced. 

Evaluate: Students should be able to answer this exit ticket question: “What type of vegetation will be lost over the next 75 years in Tivoli Bays marsh?  What will be the impact of this change on ecosystem function?”  Students should highlight the ability of graminoid vegetation to remove nitrate-nitrogen, and may also discuss the organisms that rely on that type of vegetation as habitat.  Finally, ask students to return to the statement of “Climate change will impact the Hudson River valley” and revise their initial answers with specifics related to this lesson.