Hudson River Ecology

How does the Hudson River ecosystem respond to different types of changes over time? Are these changes permanent, and how will the ecosystem respond? Our curriculum addresses these questions through modules which combine unique and engaging Hudson River data collected by the Cary Institute and other scientists, investigations, readings, and visualizations.

Cadmium in the Cove: What happened to it?

Two class periods

Students will know the origins of cadmium in the Hudson River, and will be able to integrate information from maps and text to describe how and why distribution of cadmium changed from 1975 to 1983.




  • The tides in the Hudson River are an important abiotic factor. If your students need introduction or reinforcement of this concept, there is a lesson on Hudson River Tides in the Changing Hudson curriculum.  We have provided an engagement activity to encourage learning about this idea. 
  • You may want to do Part A of the student worksheet (color in the map) yourself before teaching the lesson.  Not only will you have a sample to show students, but you will also have a better understanding of the decision points that students will face. The maps are from different scientific papers, and are therefore not uniformly drawn but have been kept in their original formats.  It’s important to note that the ranges of cadmium levels and the coastlines are slightly different.  Decision-making and problem solving are needed to color the map to make it easy to see the changes in cadmium levels over time.
  • The associated reading with this lesson, “Cadmium in the Cove Reading,” provides background information for students and can be used as a homework assignment the night before beginning the unit or during the first few days of the unit.


Background information          

A collaborative effort among the NYS DEC, the Hudson River Foundation, and Stony Brook University yielded an online “book” that includes an incredible amount of history and background information about the site.  You can either google “Foundry Cove history” or go to   




Prompt or formative assessment: To assess students’ prior knowledge, ask:

1)What do you know about the Hudson River?  Many students may only think about the river as a place for swimming, boats, or for drinking water.  As a follow-up question, ask students:

2) What abiotic factors are important in the Hudson River?  Students might mention: dissolved oxygen, salinity, tides, sunlight, temperature. 



To focus in on tides as an important abiotic factor, use a long piece of string, yarn or rope to model the Hudson River.

  • Ask students: where does the Hudson River begin?  One student should hold the string at “the beginning” (although this simplifies the idea of a watershed and how rivers start!) and will be the source of the Hudson River at Lake Tear of the Cloud on Mt. Marcy.
  • Ask:  How high is the land where the Hudson River starts?  The mountains where the river begins are around 5,000 feet above sea level. 
  • Ask: Where does the Hudson River “end”?  Another student will hold the string at the other end to represent the mouth of the Hudson River at New York City. 
  • Ask: How high is the Hudson River at its mouth?  It may take a moment for students to realize that this end of the Hudson is at sea level (on the floor). 
  • A third student should now hold the string at the Troy Dam near Albany (roughly the middle of the string). **Ask students to guess how high above sea level the dam at Troy is – although many students will guess that it is about 2,500 feet above sea level, in reality it is actually only about 10 feet above sea level.  This allows the lower portion of the Hudson, which is relatively flat and wide, to experience tides all the way up to the Troy dam. The student should therefore squat low and hold the string just above the floor.
  • The rest of the class can now model two important characteristics of all estuaries.  Have students line up on both sides of the estuary only (to Troy).  Half of the students will say “salt water, fresh water” while making a mixing motion; the other half will say “high tide, low tide” while raising their arms up and then down.  *Note*: this has been done with students from primary grades to college. Although it may seem goofy and embarrassing, since the whole class does it together, there is no individual embarrassment, and it really helps the students remember these key concepts!



  1. Use the “Cadmium in the Cove” PowerPoint to introduce students to cadmium contamination in Foundry Cove.  The powerpoint notes have been provided to help you with the content. 
  2. After introducing students to the contamination story, hand out the student packets “Cadmium in the Cove.” Ask students to answer the first question, which is the same question as in slide #5: How could scientists find out where the cadmium went after it left the Marathon Battery outfall?  Students should suggest testing for cadmium in the soil and the water around the outfall and into the marsh and river.   
  3. Guide students to understand the two maps (from 1975 and 1983) showing cadmium contamination in the surfacesediments of the cove. Use slides #6-8.  Walk through the details of the maps as students follow along with the maps in their packets.  
    1. Orient them to the major features of the map: locations of water and land, the Hudson River, Foundry Cove, the Marathon Battery plant outfall (where toxic metals were released into the cove), the railroad trestle, land, and the key.
    2. Note that the cadmium contamination is reported as ppm.  
    3. Encourage students to look at the map similarly to a topo map, where there is not an ‘immediate’ transition of elevation—or cadmium contamination—between lines. These are just guidelines to help see boundaries between values. **For example, the samples with squares around them from 1975 and 1983 were measured at 2000ppm and 750 ppm, respectively. If you have a Smart Board or similar screen, you can help students understand the map by coloring in parts of the map as you go along. 




For a quick formative assessment, ask students to estimate the ppm cadmium at different spots on the map. Since most of the samples are taken in approximately the same spots in the marsh, one can estimate how much the cadmium level decreased in that particular spot.  Depending on the map skills of your students, students may work on their own, in groups, or as a whole class to color their maps. You might suggest that students think about how they can use color to make it easier to see how the cadmium levels changed over time. Since the maps use different ppm ranges and show slightly different shorelines, students will need to look at both maps to figure out how to color code their maps. In addition, there are some places in which cadmium level is ambiguous, so students may make different decisions about these parts of the map. An example of a completed map is shown at right. 



  1. After students have completed the mapping section, return to the powerpoint (slide 9).  Ask students to explain what happened to the cadmium levels between 1979 and 1983.   
  2. Students should now move on to Part B in their packets, focusing on the question:  Where did the cadmium pollution go? 
  3. After students have completed Part B of the worksheet, bring the class back together to discuss the remaining slides in the powerpoint (10&11).  Ask: What is the difference between biotic and abiotic factors?  What are some examples of things that are biotic factors and abiotic factors in the Hudson River?  As a class, discuss how these factors might influence the location and movement of cadmium in Foundry Cove.



The following information is provided to students in Part B of their worksheet to assist them in thinking about what abiotic factors can influence the pathways cadmium follows in the cove. 


Additional Information

  1. On the maps above, all cadmium levels shown are at the surface of the mud in the cove.
  2. Between 1975 and 1983, there were no cleanup projects at Foundry Cove.
  3. Batteries continued to be produced until 1979.
  4. Freshwater in the form of natural run-off, storm water, and snowmelt enters Foundry Cove from Foundry Cove Creek and other sources.
  5. Foundry Cove is a tidal cove, so Hudson River water flows in and out about twice a day, mostly under the train trestle.
  6.  In 1983, scientists also sampled cadmium levels in the sediments below the surface of the mud in the cove, but these data are not shown on the maps. 
  7.  In some locations in Foundry Cove, the highest cadmium levels were found 20 cm or more below the surface. 


The two maps look slightly different, because that is how they were originally published, each in a different scientific paper. Some of the samples were collected in different locations, as shown by the black dots on the maps.  It is important to note that these data are for surface sediments only.

Since Foundry Cove is part of the estuarine portion of the river, it experiences two high and two low tides every day, which over time redistribute cadmium sediments within the cove.  In addition, the receding tide carries some cadmium out to the Hudson.  Though some is washed back in with the next tide, scientists found that the overall net effect is that cadmium is very slowly leaving the cove with the tides.

Further, Foundry Cove Creek and other sources of freshwater bring sediments into the cove.  Over time, the incoming sediments slowly cover the older, cadmium-laden mud.  Scientists discovered evidence of this when they collected and tested sediment samples from different depths below the surface.  Depth of sediment coverage varied. In some sample sites, the most contaminated sediment was found 20 cm below the surface, indicating that 20 cm of sediments had settled over the cadmium in less than ten years!    

Abiotic and biotic factors contribute to the movement of cadmium within and outside the cove. Abiotic environmental factors such as tides, freshwater runoff, snowmelt, and sedimentation play significant roles in the movement and location of cadmium.  Biota such as benthic organisms ingested cadmium-laden sediments, which might be stored in their tissues or discharged through excretion.  They may deposit their wastes in or out of the cove, depending on their habits and behavior, so animals’ feeding behavior affects cadmium distribution, too.

Possible pathways for cadmium:

  • Transported out of Foundry Cove
  • Buried by new sediments
  • Redistributed within the cove
  • Eaten by organisms, stored in tissues, and/or excreted



It has been said that, “there is no ‘away.’” Ask students what they think this means with respect to the cadmium pollution at Foundry Cove.



  • Part B of the worksheet can be used to assess student understanding of cadmium movements. Students can also make a sketch or diagram to show this.  Make sure that students are clear about how tides and sedimentation affected the change in cadmium levels over time. 
  •  “Cadmium and Marathon Battery Reading with Questions” can be assigned in class or as homework.  In addition to using it as an assessment, it provides students with background information about Foundry Cove food webs and the Marathon Battery Factory in preparation for the following lesson “The Marathon Battery Factory.”


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