Modeling the interaction of

salinity and diatom populations

in the Hudson Estuary

Day 1: Graphing Salinity Data from HRECOS

Objectives: Day 1

• Students will be able to construct a food web, showing relationships between organisms.
• Students will be able to name abiotic factors, and show their interactions with biotic factors.
• Students will be able to accurately plot data and calculate averages.
• Students will be able to identify and explain cyclical patterns from graphed data.

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Brainstorm!

What organisms live in the Hudson River?

List as many as you can!

Report Out

After sharing your answers, how many organisms were you able to list?

Which are producers?

Which are consumers?

Which are decomposers?

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Make a Food Web

Working with your classmates, draw arrows between your organisms to create a food web.

Abiotic Factors

How many abiotic factors can you think of in this ecosystem?

Place these abiotic factors on your diagram.

Think of one way that changing each abiotic factor could affect the ecosystem.

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Salinity

Salinity is a measure of the amount of salt in

a given amount of water.

Salinity can be measured in units of PSU (Practical Salinity Unit). This is equivalent to parts per thousand or to g/L.

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Graphing Salinity

Graph the data on salinity at your station over a two day period.

Use the data chart to calculate the average salinity at your station.

Does the salinity at your station change over time? If so, is there a pattern? What do you think might cause this pattern?

HRECOS Data

Sample graph: Pier 26 salinity by hour

August 12-13, 2017

Sample graph: Marist salinity by hour

August 12-13, 2017

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Salinity in the Lower Hudson River

Locate your station on the Hudson River map and place your graph at the station.

How do the salinity graphs change from the mouth of the river as you move north? What causes this change?

The Salt Front

• The salt front is the leading edge of salt water entering an estuary. It can be located by finding the border between brackish and freshwater.
• �Where is the salt front located on your map of the Hudson River?
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Freshwater and Saltwater

• Think about the ecosystems on either side of the salt front.
• How might these ecosystems differ?

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Day 2-3: Using HRECOS data to find and map Freshwater and Saltwater Diatoms

in the Hudson Estuary��

Objectives: Day 2

• Students will be able to follow directions to carry out diatom collection.
• Students will be able to demonstrate proper use of a microscope.
• Students will be able to produce accurate and detailed sketches of diatoms, including magnification and identification.
• Students will be able to correctly place diatom species on Hudson River map using salinity data.
• Students will be able to explain the relationship between salinity and the presence of certain species.
• Students will be able to ask three questions that they have about the relationship between diatoms, salinity, and the Hudson River.

The Hudson Estuary contains floating communities of phytoplankton, comprised of diverse algae and other tiny photosynthetic organisms.

Bacilliariophyta aka diatoms dominate, especially in the winter when other phytoplankton populations are low. Click on each algae to learn more.

Diatoms are “algae in glass houses”

Diatoms have transparent silica cell walls that are formed in two pieces which fit together like a pillbox. Silica is the main component of glass, so diatoms are often referred to as “algae in glass houses.”

Freshwater diatoms are generally pennate or centric

Pennate diatoms live in benthic zones but may be suspended in the water column. They can be somewhat motile. Centric diatoms are circular and are a part of the phytoplankton. They do not move on their own but can be moved by waves, etc.

Diatoms are highly sensitive to abiotic factors so are often used as environmental indicators.

• Before zebra mussels After zebra mussels

Invasive zebra mussels initially depleted Hudson Estuary phytoplankton levels by 85%

����Collecting diatoms in the Hudson Estuary

…in floating phytoplankton:

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…in benthic zones (in sediment or sublayers of water body):

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OR

String

OR

Microplankton net

2 Liter bottle

Toothbrush Method

Preparing diatom samples for light microscope viewing

1. Separate a small amount of the collected sample and use for viewing under the microscope alive

2. Add Lugol’s solution to remaining collected sample until it is a dark yellow/light brown (“weak tea”) color

3. Allow the organisms to settle to the bottom over 16-24 hours. (Taylor, 2007)

http://microalgal.com.au/lugols-iodine/

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Identifying and recording diatom populations

• Use a pipette to put a droplet of sample on the center of the slide and add a cover slip on top of the sample.  For living samples, use concave slides so pennate diatoms may be seen moving  For non-living samples, standard slides are fine.

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• View at low power magnification (10x eyepiece lens X 4x objective lens. Use coarse and then fine focus knob when you have found an object of interest

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• Center diatom(s) of interest and increase to medium or high power magnification

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• Refocus with the fine focus knob

Identifying and recording diatom populations (continued)

• Use the microscope drawing worksheet to draw what you see.  
• Use pencil to record a  detailed drawing for each type of diatom you observe
• Be sure to include the eyepiece, objective and total magnifications with the drawing.

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Identifying and recording diatom populations (continued)

• Create a data table in Excel or Google Sheets to record your data.

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Identifying and recording diatom populations (continued)

• Record the name of each diatom population and how many were counted to the data table.

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Mapping diatom populations (species, collection date and location) with salinity data and location��

• Add the collected data to the Hudson River Estuary Map/Model

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• Did your results match your hypothesis/es?

Questions (& answers) Diary: Write down 3 questions you have about the work we are doing (use your composition book)

Why do marine diatoms have a centric

shape and freshwater diatoms have a

pennate shape?

If fish eat diatoms how do they “eat” glass?

Why do diatoms have

glass walls…

Which algae prefer saltwater

And why?

What do diatoms tell us about

The environment they are in?