Seawater

Relationship Between Chemical Composition and Water Quality of Seawater

Understanding the Factors Influencing Seawater Quality

Chemical Composition of Seawater

H20 and Sodium Chloride: The basic parts of seawater. Water molecules
are polar, meaning they have a positive and negative charge.

pH: Out acidic/basic the water is. This is greatly influenced by the presence of dissolved gases like carbon dioxide (CO2)

Nutrient Levels: These included nitrogen, phosphorus, and silica, vital for the growth of marine plants (phytoplankton) and other organisms. Excessive amounts of levels can lead to eutrophication (excessive nutrients), causing algal blooms and depletion of oxygen.
​Salinity: Concentration of Dissolved Salts/solids in Seawater Average salinity is 35 parts per 1000

Composition of Seawater

What else makes up seawater?

1. Trace Elements

2. Pollutants

3. Dissolved Oxygen

4. Temperature

Multiple Choice

What type of molecule is water?

• elemental

• polar

• negative

• positive

Draw

Water molecules are formed by covalent bonds, these bonds are positive and negative. How would you depict two molecules bonded together?

The Most abundant Dissolved Gases In Seawater

1. Oxygen (02): Oxygen is essential for marine life

2. Carbon Dioxide (CO2): Plays are role in the carbon cycle. Marine plants (phytoplankton) use CO2 for photosynthesis.

3. Nitrogen (N2): It is essential for the growth of marine plants and plays a role in the nitrogen cycle.

Open Ended

What are the most abundant dissolved gases in the ocean?

Oxygen (O2)

Oxygen is crucial for marine life, supporting respiration in fish, mammals, and other organisms. It is also involved in various biochemical processes in the ocean, such as the oxidation of organic matter.

Carbon Dioxide (CO2)

CO2 is an essential component of seawater, playing a role in the carbon cycle and ocean acidification. Marine plants (phytoplankton) use CO2 for photosynthesis, and it can also be exchanged with the atmosphere, affecting global climate dynamics

Nitrogen(N2)

Nitrogen is relatively abundant in seawater, primarily in the form of dissolved molecular nitrogen (N2). It is essential for the growth of marine plants and plays a role in nitrogen cycling processes like nitrogen fixation and denitrification.

Open Ended

Oxygen, Carbon Dioxide, and Nitrogen are the main dissolved gases in the ocean, but what do you think is the most abundant element in ocean water?

Quality of a body of water: What does it depend on?

Open Ended

What do you think the quality of a body of water depends on and how do you think it would effect the water?

Quality of Water/Dissolved Gases

Henry's Law and Exchange at the Air-Sea Interface:

Henry's Law describes the principle of gas solubility, stating that the amount of gas dissolved in a liquid (such as seawater) is directly proportional to the partial pressure of that gas in the atmosphere above the liquid. Meaning the
Gases like oxygen (O2), carbon dioxide (CO2), and nitrogen (N2) continuously exchange between the atmosphere and seawater at the air-sea interface. This exchange is influenced by factors such as temperature, pressure, and gas solubility constants.

Open Ended

After listening to the explanation of quality of water, re-state the information in your own words.

Effects of Excess Gases

Oxygen

Excessive dissolved oxygen levels can occur due to increased photosynthesis (e.g., algal blooms) or reduced oxygen consumption (e.g., low microbial activity). This can lead to supersaturation, potentially causing harm to aquatic organisms adapted to lower oxygen levels and disrupting ecological balance in aquatic ecosystems.

Open Ended

So what is the relationship between Phytoplankton and Oxygen?

Effects of Excess Gases

Carbon Dioxide (CO2)

Elevated levels of dissolved CO2 can occur due to increased atmospheric CO2 concentrations (linked to climate change) or local sources such as coastal upwelling or industrial discharges. This can contribute to ocean acidification, lowering seawater pH and impacting marine calcifying organisms like corals, shellfish, and planktonic species.

Effects of Excess Gases

Nitrogen (N2)

While excess dissolved nitrogen (in the form of nitrate or ammonia) can lead to eutrophication and harmful algal blooms, nitrogen gas (N2) itself does not typically cause direct harm in its dissolved form. However, excessive nitrogen inputs can contribute to water quality issues and ecosystem imbalances.

Effects of Excess Nutrient Levels

Nutrient Levels

-Essential nutrients in seawater (nitrogen, phosphorus, and silica)
-Excess nutrients levels can cause Eutrophication and harmful algal blooms

Open Ended

What is eutrophication and why is it harmful to oceans?

Effects of pH

pH (Ocean Water pH: 8.1) (Freshwater: 6)

If more Carbon Dioxide is dissolved in seawater, it can affect marine life. The water becomes more acidic (acidification) and can cause "shells" (coral, mollusks, shellfish) to dissolve. The loss of ecosystems and food effects the overall biodiversity of ocean life.