Freshwater Aquatic Biomes - Online Tutor, Practice Problems & Exam Prep

Lakes are classified into oligotrophic and eutrophic types. Oligotrophic lakes are nutrient-poor but oxygen-rich, supporting fewer primary producers and clearer waters. Eutrophic lakes, in contrast, are nutrient-rich but oxygen-poor, leading to abundant plant and algae growth that can deplete oxygen during decomposition. Streams and rivers are flowing bodies of water, with streams being smaller than rivers. Wetlands, characterized by saturated land, include marshes, swamps, bogs, and fens, supporting diverse life. Estuaries, where freshwater meets saltwater, are highly productive ecosystems that support various species.

Lakes

This video, we're going to talk about the very first aquatic biome in our lesson, which are lakes. Now a lake can be defined as a stationary or motionless body of freshwater that is surrounded by land. Lakes can be divided into 2 major categories that are on opposite ends of a spectrum. So, they represent the extremes on the spectrum, but there are lakes that fall in between at different points between these two extreme categories. These two categories are oligotrophic lakes and eutrophic lakes.

Oligotrophic lakes have the Greek root "oligo", which means "few", and the Greek word "trophic", which means "nutrients". Therefore, oligotrophic lakes have few nutrients or, in other words, are nutrient-poor. By being nutrient-poor, they do not have a lot of nutrients to go around and support many primary producers like plants and algae, and therefore, oligotrophic lakes tend to have low primary productivity. Despite being nutrient-poor, oligotrophic lakes are actually oxygen-rich, and so that's going to support specific species of plants and animals that rely on higher oxygen concentrations. These oligotrophic lakes tend to have much clearer water since they don't have abundant algae growing on the surface of the water, and they also tend to have colder waters as well.

Oligotrophic lakes are often found in remote locations that are further away from human activity. Now moving on, eutrophic lakes, on the other hand, have the Greek root "eu", which means "good". And again, the word "trophic" means "nutrients". So, eutrophic lakes have a good amount of nutrients, or in other words, are nutrient-rich. However, eutrophic lakes are oxygen-poor, and so eutrophic lakes are really the opposite of these oligotrophic lakes.

Eutrophic lakes tend to have abundant plant and algae growth. It might be a little counterintuitive to think that having abundant amounts of primary producers that are photosynthetic producing oxygen leads to an oxygen-poor environment. However, it's important to keep in mind that abundant plant and algae growth is occurring mainly on the surface of these waters, but as you go deeper into the water, it is going to be an oxygen-poor environment. Once all of this abundant plant and algae growth on the surface dies, it will start to sink towards the bottom.

As it sinks towards the bottom, it's going to decay and decompose, and the decomposition process is going to consume a lot of oxygen, creating an oxygen-poor environment. Having lots of nutrients but poor oxygen is going to support different animal species. And it's important to note that, again, these represent opposite ends of a spectrum. So a lake is not going to be permanently categorized into any one of these categories. It's possible to take any oligotrophic lake and convert it into a eutrophic lake, and it's also possible to take any eutrophic lake and convert it into an oligotrophic lake.

And so this here concludes our brief lesson on lakes.

Streams & Rivers

This video, we're going to talk about streams and rivers. Streams and rivers are both bodies of water that are constantly flowing or moving in one particular direction, and that's going to be from areas of high elevation down to areas of low elevation because of gravity. Streams and rivers are actually quite similar to each other, except they are at different scales in terms of their size. Streams are going to be at a much smaller scale. On the other hand, rivers are going to be at a much larger scale, and so rivers tend to have larger volumes of water.

They're wider. They're deeper. They're longer in terms of their length, and they have higher or faster flow rates of water. Rivers also have more tributaries in comparison to streams. Tributaries are really just bodies of water that are flowing and contributing to other bodies of water.

And so if we take a look at this image in the top left here, what you'll notice is we're labeling the larger scaled river right here. Notice that we're also labeling these much smaller streams, which you can see here and over here as well. What you'll notice is that these streams are flowing into the river and contributing to the river, and therefore, these streams are also serving as tributaries to the river. Another thing to keep in mind is that the aquatic productivity of streams and rivers actually varies. So, this here concludes our brief lesson.

Wetlands

This video, we're going to talk about wetlands. And so wetlands are pretty much what they sound like. It refers to land that is wet, or more specifically, it refers to land that is either permanently saturated with water all year round or periodically saturated with water during distinct periods of the year. And that water that it's saturated with can either be stationary or not flowing at all, or it could be very slow moving, very slow flowing water. And that water could either be freshwater or it could be saltwater.

And so really what this means is that there's a lot of diversity when it comes to these wetlands. And so wetlands include these four main types, which are marshes, swamps, bogs, and fens. All of them are going to be land saturated by water, but they're all also going to have their specific characteristics and specific species that they support. Now a characteristic feature of all wetlands is emergent vegetation, and emergent vegetation refers to plants that are growing or emerging above the water surface. Now it's also important to note that the aquatic productivity of these wetlands can actually vary, but often is quite high, and these wetlands support a lot of life.

So this here concludes our brief lesson on wetland.

Estuaries

This video, we're going to talk about estuaries. An estuary is defined as a coastal, transitional area between the end of a river and an ocean. The river is always going to be flowing into the ocean, and estuaries are prevalent as they're found along coastlines worldwide. An estuary is going to contain both freshwater and saltwater, making estuaries somewhat of a unique aquatic biome. It allows estuaries to support a wide variety of species, species that rely on saltwater, but also species that rely on freshwater. Additionally, it supports species that require very specific concentrations of both freshwater and saltwater. Often, in estuaries, the denser saltwater is going to occupy the bottom layer of the water, while the lower density river water, which is freshwater, will be found at the surface of the water.

Notice in this image in the top left, we've got this aerial view of an estuary where you can see that the river is flowing in this particular direction, indicated here, into the ocean. This entire region would be the estuary. During the high tide, the ocean water can kind of come upwards in the river, higher like this, and so there will be higher salt concentrations during the high tides. But then during the low tide, the ocean water kinda falls back down and the freshwater from the river kinda takes over these regions here. As a result, the saltwater in these regions can be quite dynamic.

Now, these estuaries often have a very high aquatic productivity that supports a wide variety of different species. This here concludes our brief lesson on estuaries.

Freshwater Aquatic Biomes Example 1

So here we have an example problem that asks, in which of the following aquatic biomes would you expect to find organisms that can tolerate both saltwater and freshwater? And we've got these four potential answer options down below. Now, of course, the aquatic biome that we might expect to have organisms that can tolerate both saltwater and freshwater would be the aquatic biome that has both freshwater and saltwater. And, of course, we know from our last lesson video that estuaries are somewhat of a unique aquatic biome because they contain both freshwater and saltwater, since an estuary is where a river meets an ocean, and the river has freshwater, whereas the ocean has saltwater. And so the mixture of the two gives it both, freshwater and saltwater, and so we would expect to find organisms there that can tolerate both.

And so we can indicate the answer option B, estuaries, is the correct answer to this example problem. Now option A says lakes, but recall from our previous lesson videos that lakes are defined as stationary bodies of freshwater surrounded by land. And so most of these lakes are going to have freshwater, so we can eliminate that option because we wouldn't expect to find organisms that can tolerate high salt concentrations in most lakes. Option D says streams, and again, we know that streams and rivers contain freshwater, so we can eliminate option D for a similar reason. And then option C says riverine wetlands, which we did not cover in our previous lesson videos.

We did talk about wetlands, but riverine wetlands are just wetlands that are found along rivers. And, again, we know that rivers contain freshwater, so we can eliminate option C. So, again, B here is the correct answer, and I'll see you all in our next video.

Which of the following is a characteristic of oligotrophic lakes?

• A. Murky water.
• B. Dense vegetation.
• C. Summer turnover.
• D. Relatively low biomass & primary productivity.

What is the most significant physiological barrier for an aquatic organism traveling through an estuary?

• A. Change in water temperature.
• B. Change in water salinity.
• C. Changes in light availability.
• D. Change in water O₂ concentration.