LWE: Lesson - Aquatic Biomes (Topic 1.3) 📖

⏳ Estimated Reading Time: 10 - 12 minutes

Describe the global distribution and principal environmental aspects of aquatic biomes.

Water: Necessary for Life

a satellite image of the earth on a black background, showing the abundant water on the planet. — ***Water is very important and covers 75% of Earth. Most (97.5%) is salty. Only 2.5% is fresh. But most fresh water is frozen and not usable. Less than 1% of water is fresh and usable for us.***

Water has a very high specific heat capacity. This means that water absorbs and retains heat very well. This keeps the temperature of large bodies of water from changing too fast and keeps the environment relatively constant for the organisms living in bodies of water.

an image of an iceberg floating in clear blue water — ***Look at the picture above. Solid water floats in liquid water, and the air has gaseous water too. All three phases in one picture!***

Water is also most dense at 4^oC. This means that water at temperatures below and above 4^oC is less dense. Because of this, cold, unfrozen water, sinks to the bottom of large bodies of water and warmer waters (and frozen water) float to the surface. This sets up convection currents in our oceans (we will talk about these more later). Also, because solid water is less dense than liquid water, it keeps rivers, ponds, and oceans from freezing solid. The ice on top insulates the water below the ice from freezing temperatures. You can look at the picture to the left and can see solid water floating in liquid water.

Water is also transparent. This makes it easy for light to penetrate, allowing photosynthetic organisms to photosynthesize under the water.

Another important aspect of water is that it is found on Earth in all three phases. Very few substances are found in all three phases at “normal” temperatures.

Water can also turn into a gas without boiling. For example, if you leave a cup of water out, it will eventually be empty, even without drinking it. This is because the water evaporates.

Essential Knowledge

Freshwater biomes are a vital resource for drinking water.

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Freshwater Biomes

Diagram showing zonation in lakes & ponds. 5 zones: Littoral, Limnetic, Photic, Aphotic (Profundal), & Benthic. — A lake is a large, inland body of freshwater formed by various geological processes, such as glacial activity, tectonic movements, or volcanic action. Lakes are distinct from rivers and ponds due to their considerable size and depth.

If the water in an ecosystem flows from one place to another, it is known as a moving water ecosystem. If the water in the ecosystem does not flow and remains relatively stationary, it is known as a standing water ecosystem.

Both types of systems have benthic plants, which are plants that grow on the bottom. Submerged aquatic vegetation (SAV) are aquatic plants that live completely underwater and do not break the surface of the water. Emergent vegetation are plants that have some part of the plant that breaks the surface of the water into the air. Phytoplankton are photosynthetic algae and are usually not attached to anything, but they can grow and cover vegetation or rocks if the water is calm enough.

For example, moving bodies of water make it difficult for organisms to take hold in that ecosystem because they are often swept away by the moving water. Lakes, in contrast, do not move as much, so they are easier for vegetation to take hold.

Explore the different types of freshwater biomes below. Which would you most like to visit?

Wetland
Rivers
Ponds
Lake

A natural scene within a circular frame, featuring a calm body of water surrounded by marsh grass. — ***A wetland is an area where the land is saturated with water.***

Wetlands

Wetlands are transitional areas that are found between aquatic and terrestrial ecosystems. These are the freshwater equivalent of an estuary.

Marshes, swamps, and bogs are types of these coastal wetlands.

These biomes have the largest diversity of any biome and are important protectors because they reduce flooding in terrestrial biomes, filter pollutants coming off of the land into the water, which improves water quality, and they serve as a breeding ground for many animals, such as birds and fish.

Rivers

a tranquil scene of a stream within a circular frame. Water flows over rocky tiers, surrounded by lush greenery, with the motion artistically blurred to convey gentle movement. The cool color palette highlights the white water against dark rocks and green foliage, evoking a sense of calm. — ***A river is a natural flowing watercourse characterized by a significant and continuous movement of water.***

Rivers can be slow- or fast-moving. If a river moves too fast, algae cannot grow in the river, because it cannot start growing before the fast-moving water sweeps it away. This is why fast-moving river water tends to be clearer than slow-moving river water – the fast-moving river has less algae in it.

Rivers are home to a variety of invertebrates. Arthropods, like small crustaceans and insect larvae, often make rivers their homes. Rivers are often home to a variety of fish species, such as trout and salmon.

Downstream, where a river flows into a pond or a lake, the water is often murkier than the upstream portions of the river. This is because the water slows down and phytoplankton can now grow. These parts of the river are home to frogs, waterfowl, LOTS of insects, catfish, and other bottom-dwelling fish. These fish have barbels on the sides of their mouths, which allow the fish to find their food through scent, since the water is so murky.

Pond

A serene natural scene within a circular frame, featuring a reflective body of water surrounded by lush greenery and vibrant yellow wildflowers. A wooden dock extends from the grassy shore into the calm water, under a partly cloudy sky, conveying tranquility and the beauty of nature. — ***A pond is a small, still body of water that is usually shallow enough to allow sunlight to reach the bottom.***

A pond is a small, freshwater ecosystem characterized by its still or slow-moving water. Ponds are typically shallow, allowing sunlight to penetrate to the bottom, supporting the growth of various aquatic plants. These water bodies play a crucial role in local ecosystems by fostering biodiversity and serving as habitats for a diverse array of organisms.

Ponds are essential components of the hydrological cycle, contributing to water storage and regulating water availability in terrestrial ecosystems. They provide breeding grounds for amphibians, insects, and other aquatic organisms, contributing to the overall health of ecosystems. Additionally, ponds serve as valuable resources for both wildlife and human communities, offering water for drinking, irrigation, and recreational activities.

Human activities, such as urbanization and agricultural practices, can impact pond ecosystems. Pollution, habitat destruction, and alterations to water flow can threaten the delicate balance of pond ecosystems, emphasizing the importance of responsible environmental stewardship in preserving these vital water bodies.

Lake

These aquatic ecosystems play a crucial role in supporting biodiversity, providing habitats for a diverse array of flora and fauna.

Lakes are characterized by distinct zones, including the littoral zone near the shore, the limnetic zone in open water, and the profundal zone at greater depths. Each zone harbors different species adapted to specific environmental conditions. Flora in lakes might include submerged plants like Elodea or emergent species such as cattails, while fauna encompasses fish like bass or trout, amphibians, insects, and various waterfowl.

Human activities can significantly impact lakes, from nutrient pollution leading to harmful algal blooms to alterations in water levels and the introduction of non-native species.

Essential Knowledge

Freshwater biomes include streams, rivers, ponds, and lakes. These freshwater biomes are a vital resource for drinking water.

Salt Water

The oceans cover 71% of the Earth’s surface and represent an even larger volume because the ocean is a 3-dimensional living surface. Over 97% of the water on Earth is in the ocean and over 50% of the world’s population lives within 100 km of the ocean.

The depths to which the sun penetrates is known as the photic zone and the depths to which light does not penetrate is known as the aphotic zone.

Within the photic zone, the ocean is further divided into different zones. Each zone has characteristic organisms that live within that zone.

Explore the zones of the ocean below:

Essential Knowledge

The global distribution of nonmineral marine natural resources, such as different types of fish, varies because of some combination of salinity, depth, turbidity, nutrient availability, and temperature.

Marine Biomes

Marine ecosystems encompass a diverse range of environments, from the sunlit surface layers to the depths of the ocean floor. Please explore the presentation below to learn more about the most important marine biomes:

image of microscopic phytoplankton — ***Marine algae, particularly phytoplankton, plays a crucial role in generating oxygen and absorbing carbon dioxide.***

Importantly, some of the smallest organisms in the oceans are arguably the most important.

Through photosynthesis, these microscopic organisms convert carbon dioxide into organic compounds, releasing oxygen into the atmosphere. Marine algae contribute significantly, producing around half of the world's oxygen. Additionally, they help regulate the carbon cycle by absorbing substantial amounts of carbon dioxide, aiding in mitigating global climate change. Recognizing and preserving the health of marine algae ecosystems is essential for maintaining Earth's atmospheric balance.

Marine biomes include oceans, coral reefs, marshlands, and estuaries.

Algae in marine biomes supply a large portion of the Earth's oxygen and also take in carbon dioxide from the atmosphere.

AP Exam Tip

You will not need to know everything about each aquatic biome, but you will need to know major characteristics of each biome and how humans have had an effect on these biomes.

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