Freshwater Systems

Front

Salinity Noun

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[suh-lin-i-tee]

Back

Salinity

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A measure of the total amount of dissolved salts in a body of water, often expressed in parts per thousand.

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Example: This diagram shows that seawater's salinity comes from dissolved salts, with most of the salt being made of chloride and sodium, the components of table salt.

Front

Hydrosphere Noun

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[hy-droh-sfeer]

Back

Hydrosphere

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The collective mass of all water found on, under, and over the surface of a planet, especially Earth.

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Example: This diagram shows how all of Earth's water (the hydrosphere) moves in a cycle, including freshwater systems like rivers, rain, and groundwater.

Front

Plankton Noun

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[plangk-tuhn]

Back

Plankton

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A diverse group of mostly microscopic organisms that float or drift freely in the water column of aquatic environments.

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Example: Plankton are a diverse group of small organisms, including plant-like and animal-like forms, that drift in the water column below the surface.

Front

Nekton Noun

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[nek-ton]

Back

Nekton

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Aquatic animals that are able to swim and move independently of water currents, such as fish and whales.

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Example: This diagram shows that nekton, like the fish, are animals that actively swim in the water, unlike plankton that drift or benthos that live on the bottom.

Front

Benthos Noun

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[ben-thos]

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Benthos

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The community of organisms that live on, in, or near the bottom of a sea, lake, or river.

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Example: This diagram shows that benthos are organisms, like crabs and clams, that live on the bottom sediment of an aquatic system, below free-swimming nekton.

Front

Photic Zone Noun

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[foh-tik zohn]

Back

Photic Zone

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The uppermost layer of an aquatic ecosystem that receives sufficient sunlight to allow for photosynthesis to occur.

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Example: This diagram shows that the Photic Zone is the top layer of a body of water, where sunlight can reach, unlike the darker, deeper zones.

Front

Aphotic Zone Noun

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[ey-foh-tik zohn]

Back

Aphotic Zone

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The portion of a lake or ocean where there is little or no sunlight, preventing photosynthesis from occurring.

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Example: This diagram shows the aphotic zone is the deepest part of a water body, located below the photic and dysphotic zones where no sunlight penetrates.

Front

Benthic Zone Noun

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[ben-thik zohn]

Back

Benthic Zone

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The ecological region at the lowest level of a body of water, including the sediment surface and sub-surface layers.

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Example: This image shows the different vertical zones of the ocean based on depth, such as the Sunlit and Midnight zones, but does not identify the Benthic Zone.

Front

Dissolved Oxygen Noun

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[dih-zolvd ok-si-jen]

Back

Dissolved Oxygen

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The amount of gaseous oxygen dissolved in water, which is available for respiration by aquatic organisms.

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Example: This diagram shows how oxygen enters freshwater from the air through aeration and diffusion, and from underwater plants through photosynthesis.

Front

Littoral Zone Noun

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[lit-er-uhl zohn]

Back

Littoral Zone

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The shallow, nutrient-rich area near the shore of a lake where sunlight reaches the bottom, supporting rooted plants.

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Example: This diagram shows the littoral zone as the shallow area of a freshwater body near the shore, where sunlight reaches the bottom, allowing rooted plants to grow.