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Activity 9 Effect of Salinity on Aquatic life and Field trip #2

Salinity and Aquatic Life

Estimated Time of Activity: 1.5 hrs

Goals: Process Skills and Content Knowledge:


  • Salinity PPT
  • Hydrometers
  • Papertowels
  • Mystery solutions
    • A – 35 ppt      (35 g table salt + 1 L water)
    • B – 25 ppt      (25 g table salt + 1 L water)
    • C – 5 ppt        (5 g table salt + 1 L water)

Activity Instructions:

Background Information

  • Ask students “What is the earth sometimes called? What kind of planet?” – Earth is called the Water planet. (Slide 1)
  • Tell students the following fact: Approximately Three-fourths of the Earth’s surface is covered with water.
  • Ask them “Where can water be found on earth?”  Write student answers on the boards which should include: Oceans; Ice caps/glaciers/ Ground water; Surface water (which include Lakes, rivers, streams, ponds); Atmosphere. (Slide 2)
    • Give student sheet
  • Tell students to look at the water % column. Ask “Are the %s matched to their correct source?” Have the students work in teams to guess the % of water found in each of these locations. Have them match the % on the right with the sources on the left. Have teams choose one person to write their answers on the board (Slide 2).
  • Give the students the correct answers (Slide 3):
    • Oceans – 97.2%
    • Icecaps/glaciers – 2.38%
    • Groundwater – 0.397%
    • Surface water – 0.022?
    • Atmosphere – 0.001%
  • The Earth’s oceans are a vast storehouse of resources. As rivers and streams empty into the ocean, they carry mineral resources with them. Thus the oceans contain all the minerals that have drained off the land. (Slide 4)
    • The salts present are typically dominated by four cations: (click)
      • Calcium – Ca 2+
      • Magnesium – Mg 2+
      • Sodium – Na+
      • Potassium – K+
    • Three Anions (click)
      • Carbonate – HCO3-/ CO3 2-
      • Sulfate – SO4 2-
      • Chloride – Cl-​
  • In general Na and Cl are the most abundant ions present in saline aquatic ecosystems. (click)
  • The sources of these salts are: (Slide 5)
    • rainfall, which carries low concentrations of salts that have accumulated in our landscapes over thousands of years
    • weathering and erosion of surface rocks
    • groundwater that has soaked through sediments and sedimentary rocks that originally formed in salty marine environments. (click)
  • Seawater is about 3.5% salt, which is about 35 grams per liter. Salinity is the amount of salt in seawater, given in either percentages or parts per million (Friedl 439). Oceans contain not only mineral resources, but important nonmineral resources such as food (fish, etc.) and water as well. (Slide 6)
  • Three Categories

Freshwater    (0 – 0.5 ppt)
Brackish     (0.5 – 30 ppt)
Salt/Marine    (> 30 ppt)

  • Adding salt to water increases its density and makes it heavier. Density is the mass per unit volume of a substance (Friedl 434). So saltwater, which is denser than freshwater, is heavier than freshwater.
  • Ask a student to explain what a Salt Wedge is using the diagram.
    • An Estuary is a type of wetland where there are a number of salinity zones found because it is partially enclosed by land and fed by freshwater rivers.
  • A salt wedge estuary is the most highly stratified type in which there is a strong river flow compared to the mixing that is generated by tidal currents. A distinct freshwater layer flows out over a distinct saltwater layer (or "wedge") and the two are distinct over some length of the estuary. (Slide 7)
  • What affects Salinity? (Slide 8)
  • Weather (click)
    • During dry seasons, water evaporates, making salty water saltier (the concentration increases).
    • When it rains, salty water is diluted by the added fresh water.
  • Salinity has an effect Dissolved Oxygen. (Slide 9)
    • Ask students to describe the trend illustrated in the graph
      •  increase in Salinity à decrease in DO
    • Ask students why this trend occurs.
    • Salt molecules take up more space between water molecules
  • Salinity has an effect of the plant and wildlife found (Slide 10)
    • Plants
      • Develop barriers in their outer layer to block salt from entering
      • Some secrete excess salt through salt glands
  • Animals
    • Aquatic life must adjust its internal chemistry in response to its surroundings. They take in water, salt and minerals but block out toxic excess of the same. Is it healthy for us to drink salt water? No it causes our cells to shrink and die because of osmosis – diffusion of water from a place of high concentration to low concentration.
    • Some animals can only live in a certain range, i.e. freshwater fish like goldfish, can live in ponds and freshwater streams but will die in saltwater.
    • Some animals in salty environment can tolerate a wide range of salinity, i.e. salmon, migrate from salt to fresh water to spawn (reproduce)
  • Show students the table of Clam shrimp data and ask if they can determine what type of water this species can survive in. (Slide 11)
    • What is the range of salinity for Puddle 1 and Puddle 8?
    • Are there any abnormal numbers?
    • What are some reasons for the increase in salinity?
  • Many wetlands are becoming more saline because of: (slide 12)
    • rising salty groundwater entering the wetland; and
    • wetting and drying of the wetland without flushing.
    • Salt are building up in wetland sediments as water enters the wetland and evaporates, leaving the salt behind. If floods do not flush the salts from the wetland they accumulate over time.

Different organisms can tolerate different salinity levels. (Slide 13)

  • Have students: Describe the relationship between salinity and the number of species.  As salinity increases, there is a decrease number of species
  • Why do different organisms die at different salinity levels?
  • Could this be useful to someone investigating wetland health?



  • The graph above shows a series of three fill events (floods) in a wetland over time. Describe how water levels in the wetland changed over time. Slide 14

Water level increases and decreases over time

  • Analyse the graph above. What happens to the salinity level of the water in the wetland as it dries out? Slide 15

As water level decreases, there is an increase in salinity



  • This graph shows three fill events followed by drying each time. Explain why the salt level in the sediment increases each time. Slide 16

Some of the salt is left over from the last time it dried out

  • Describe what happens to the organisms in the wetland when the salt level gets high?

The animals would either die or leave the area if they can.

* Have them use the basic fish tank hydrometers to get an accurate reading on the salinities of the mystery solutions

  • A hydrometer is an instrument that measures specific gravity or density of liquids.
  • Salinity solutions: 0.5, 10, 20, 35 ppt
    • 1ppt = 1 g salt + 1 L water; 10 ppt = 10 g salt + 1 L water; etc.


            Do Now

  • How much percent of the Earth is covered by water?
  • Of this water, what % is saltwater?


  • Read Wetland Salinity Fact sheets on Aquatic Plants and Aquatic Invertebrates.
  • Have students answer the following questions for each:
  • What was the objective of the project (in your own words)?
  • What background information is given so that you can understand the project?
  • Visualize the Methods. Draw diagrams showing what was done in the experiment.
  • Write the results next to the appropriate diagrams drawn for the Methods.
  • What are the overall results of the project?
  • How can the results of this project help with the conservation of wetlands?


  • Answers to Wetland Salinity Fact Sheet analyses.
  • Lab report.

 Testing Salinity of pond water – Field Trip #2

Estimated Time of Activity: 1.5 – 2 hrs

Goals: Process Skills and Content Knowledge:

  • Students will learn different methods for finding out about a study site.
  • Students will conduct a visual survey of study site to discover information about local land cover, water quality and document their findings.
  • Students will test the salinity of the water found in a local park.


  • Hydrometer
  • Digital water quality meter
  • Digital cameras.
  • GPS
  • Water monitoring sheet

Activity Instructions:

  • Hand out Water Monitoring Sheet and give the students 10 – 15 minutes to complete.
  • Hand out materials for salinity testing (might be best to prepare ahead of time in plastic baggies for distribution to individual groups) – Hydrometer and Water quality meter.
  • Have students collect the salinity at 3 different locations, 3x at each location.
  • Have students’ record data in their appropriate data sheets.
  • Remind students to take pictures with their digital cameras of the field site and the act of performing the salinity test.


Start lab report for the days activities by asking students to hypothesize the salinity of the water body that you will be testing. (Students should have researched this for last lessons H.W.)


  • Have students email pictures taken on today’s field trip – at least three of the field site and two of sampling.
  • Have students complete a lab report. Students should hand in a copy of the Water Monitoring Form per pair/team.


 Lab report


Return to ARM introduction.