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Looking at aerial photos of boreal forests, with dense woods clear-cut by quiet lakes, I wondered why exactly are the woods so clear-cut at the edge of water? Why won't trees develop adaptations that will let them grow from a shallow lake bottom, with the lower part of the trunk in the water and the crown above the water?
It seems to me that this would give them some significant advantages. Lake bottoms are rich in organic nutrition, and insolation will also be plentiful above water, at least at first when there's little competition. So why are lakes' surfaces so clear and open, instead of overgrown? Of course there are aquatic and semi-aquatic plants like water lilies, Scirpus or Typha, but they are a far cry from the nearby terrestrial forests, in terms of biomass. Why don't they develop into large amphibian trees, or why don't terrestrial trees try to re-colonize lakes?
- Deep roots to get more water and anchor their growth.
- Strong trunks to support themselves against gravity.
- A vascular system to move water and nutrients throughout the tree.
- Small leaves that can be supported high by the trunk to compete for sunlight.
Water plants need:
- Just enough root to anchor its location.
- No vascular system. Water is everywhere.
- Leaves that are more substantial than the stems to gather as much sunlight as possible through the cover of water.
So the kind of body that has to develop under water to thrive is in many ways the opposite of the kind of body needed to thrive on land.
Water plants would have to waste energy on
- Vast roots.
- A strong trunk.
- A vascular system.
… Things it wouldn't need till later while receiving little sunlight on small leaves. It would have to shed its thirsty skin like a snake on the above water parts. Too complex and little or no demand for it.
If water plants had evolved a way to turn oxygen into helium and keep much of it trapped within its leaves, then we'd have tall ocean forests. The plants could grow just like they do now but with slightly fluffy leaves. As soon as it broke water surface, the abundance of oxygen would ramp up helium production and really fluff them leaves. The slight stems would have to be scrappy instead of massive.
There would be Greek mythology that Gaia was married to Helios but left him for Poseidon the Gaia-Shaker. Poseidon and Gaia were cursed with children (the vast ocean forests) who rebel against them and adopt a lifestyle where they are always reaching out to Helios and later in life shedd their bodies to be closer to him in spirit. Some early humans tried to rob the Helium spirits of the ocean forests by inhailing them out of their plant bodies. They were cursed and turned into chipmunks with only their hands to remind them of their past humanity.
Edit to add reference: A piece by Mickey Walburg on eHow.com
Though I would call mangroves amphibian trees, I wouldn't call them large and I was trying to ascertain the spirit of what @kai teorn was asking rather than let the question sit unanswered when I believe I can answer it. You learn something new often if you're looking and today @MattDMo introduced mangroves into my awareness. If he thought it was the answer to the spirit of the question post, he might have elaborated on it as an answer instead of a comment. I could be wrong about that.
Mangroves are mostly coastal. They are usually at the edges of the water. The ones that are a few meters in the water are usually more like shrubs than majestic boreal forest trees. They end up shooting roots everywhere and kinda lounge around compared to the typical tree standing straight reaching for the sun. Also the incidences of Mangroves in the ocean away from the shoreline are of maybe a handful bunched up, hardly a species wide return to the the oceans. Seen from aerial photos, Mangrove concentrations look like boreal forests surrounding lakes, not swamp lands.
Why are there no tree-like plants that grow in lakes?
Looking at aerial photos of boreal forests, with dense woods clear-cut by quiet lakes, I wondered why exactly are the woods so clear-cut at the edge of water?
I think the spirit of the next question is about trees in general in lakes. Not the few instances peppered around the world. Also some lakes grow and shrink throughout time, sometimes long enough for trees to gain a little ground and survive lake growth. But I don't think those trees as a species have developed adaptations to grow from shallow lake bottoms.
Why won't trees develop adaptations that will let them grow from a shallow lake bottom, with the lower part of the trunk in the water and the crown above the water?
… and from the end of the post…
Of course there are aquatic and semi-aquatic plants like water lilies, Scirpus or Typha, but they are a far cry from the nearby terrestrial forests, in terms of biomass. Why don't they develop into large amphibian trees, or why don't terrestrial trees try to re-colonize lakes?
… I eliminated mangroves from qualification. Interesting but I still don't think it's what @kai teorn had in mind. I think @MattDMo introduced mangroves as a comment to enhance our knowledge.
The question of "why are there no/few aquatic trees?" can be approached in two ways.
Why are land trees tall?
Is it harder to be tall in a lake?
Land trees are tall to shade competitors and spread their seeds and fruits. To get tall, they need extensive root structures to anchor and provide enough water to the trunk. If there are no competitors to shade out and the water provides long-distance seed dispersal, why bother growing tall?
It's much harder to be tall in a lake. Nutrient uptake is a problem, as is proper anchoring. Large amounts of organic biomass may exist, but iron, phosphorus, and other micronutrients are more important. A large oak can be 15 tons, which is harder to support using only sediment on the lakebed. It's also understandably difficult to germinate and sprout if you're an aquatic tree. See mangrove propagules for an example of the problems and how to get around them(sort of). Most mangrove species need lenticels in the trunk to provide enough oxygen, and long roots require periodic pneumatophores to provide oxygen to the roots.
Looking at all the pressures on plant life in lakes, it's a lot of work to be a tree, and much easier to be a lilypad. More of the biomass can be concentrated on photosynthesis, and structural concerns are a lot less troublesome. Additionally, many lakes simply do not have the nitrogen or phosphorus content to support tree-sized growth. See trophic state index in lakes. If the lake can't support algae, there's no way it can support a tree.
Cypress swamps are an example of tree like plants in lakes. There is even a lake in Louisiana called Cypress Lake
Photosynthesis in Aquatic Plants
Both terrestrial plants and water plants photosynthesize with the help of light energy to make carbohydrates. Photosynthesis in aquatic plants takes place in the same way as the land plants undergo to produce foods. Read on to know more about how photosynthesis takes place in aquatic plants.
Both terrestrial plants and water plants photosynthesize with the help of light energy to make carbohydrates. Photosynthesis in aquatic plants takes place in the same way as the land plants undergo to produce foods. Read on to know more about how photosynthesis takes place in aquatic plants.
Ability to perform photosynthesis is the main distinguishing feature between green plants and other organisms on Earth. In this chemical process, carbon dioxide and water are combined in presence of light energy to produce carbohydrate and other byproducts. This process of converting carbon dioxide to glucose with the help of radiant energy is observed in cyanobacteria (blue-green algae), some types of algae and all green plants, irrespective of the growing environment.
Show/hide words to know
Anther: the part of a flower that creates and stores the male reproductive cells (pollen) of a plant.
Cultural generation: all of the individuals born at about the same time.
Inheritance: genetic information passed down from a parent.
Mated: putting together male and female reproductive cells to create offspring.
Ovary: creates and stores the female reproductive cells in plants and animals.
Phenotype: the appearance of an individual that results from the interaction between their genetic makeup and the environment. Phenotypic trait. more
Trait: a characteristic of an organism that can be the result of genes and/or influenced by the environment. Traits can be physical like hair color or the shape and size of a plant leaf. Traits can also be behaviors such as nest building behavior in birds.
Whether in rolling fields, a greenhouse, or small growing chambers, plants are steeped in biochemistry that is ripe for study.
Studies of plants in the University of Wisconsin–Madison Department of Biochemistry span everything from how they can be grown or consumed for agricultural or bioenergy purposes to a basic understanding of cell biology in plants and animals. Professors Richard Amasino, Sebastian Bednarek, John Ralph, Ivan Rayment, and Mike Sussman — and students in their labs — all take advantage of the unique properties of plants to investigate how plants work and can be better utilized, but also what that understanding can mean in other contexts.
“Plant cells, for the most part, are immobile,” Bednarek explains. “It’s one of the reasons plants are interesting to study. This makes the cells have unique properties we are able to exploit to draw conclusions about plants but also other types of organisms.”
Using Biochemistry and Genetics to Engineer Better Plants
Amasino is a plant biochemist in the department who uses biochemical techniques and genetics to unravel what regulates plant growth and development, with a particular focus on the act of flowering. He studies how the environmental conditions that plants experience affect them on the molecular and genetic level to bring about flowering.
His work in recent years has focused on vernalization, a process in which flowering in plants is blocked until it has gone through a sufficient cold spell. Examples of this include flowers like lilies and vegetables like beets, cabbage, or carrots. The plants he studies include the grass Brachypodium and the member of the cabbage family Arabidopsis.
“In the plants we study that require winter, there is a gene encoding a repressor protein that is expressed in the fall that prevents the plant from flowering,” Amasino explains. “Then, over the winter, changes in gene expression occur that mitigate this repression. In Arabidopsis, the repressor gene is epigenetically switched off during winter whereas in Brachypodium the repressor gene remains active in the spring but other flowering activator genes are turned on during winter that override the repression.”
Amasino and his team are working to reveal what genes are involved in this process and how they keep grasses from entering their flowering cycle until the season is right. For example, they recently uncovered a gene they called RVR1, for its role in repressing another gene called VRN1 that helps initiate vernalization.
Plant breeders are interested in genetic findings like this because it allows them to explore ways to develop crops that are more efficient and have higher yields of food or energy.
Kevin Mayer (back left) of the Amasino Lab observes plants in a growth chamber with undergraduate John Barth (right).
Photo by Robin Davies.
Also investigating ways to get more energy and value out of plants is Professor John Ralph. Plants are sturdy in part because of the polymer called lignin that binds plant fibers together and makes stems hard and durable. These characteristics are great for the plants — they’ve allowed them to endure for millions of years — but not ideal for releasing the energy stored in the plants for uses like bioenergy.
Biochemistry professor and energy researcher John
Ralph is an authority on the biochemistry of lignin, especially when it comes to synthesizing it and breaking it down. His group studies what’s responsible on the genetic level for synthesizing lignin and how those genes can be altered to create lignin that’s easier to break down or to provide additional value.
Over the years Ralph and his team at the Great Lakes Bioenergy Research Center, housed in the Wisconsin Energy Institute, have made lots of progress. They have been involved in the discovery of new genes involved in lignin production. Most recently, they’ve worked with collaborators in discovering new “monomers” from which the polymer is made, some of which can be used to make lignins that are more uniform rather than complex.
The group has also discovered that there might be a way to incorporate valuable commodities and substances like pharmaceutical compounds into lignin, making them available by the ton in what is currently waste material.
With the help of collaborators, he’s taken his idea of changing lignin to make it chemically break down easier through a sophisticated research pipeline. They demonstrated the workability of a model system, found the gene required, and eventually genetically engineering poplar trees to produce “zip lignin” that others in the bioenergy field are now utilizing to produce liquid fuels and paper more efficiently.
“The least appreciated thing about lignin is that, although it is structurally complex, it is a polymer that is produced in plants from its monomers by a purely chemical process,” Ralph says. “This means that there are unparalleled opportunities to alter the polymer in numerous ways, including many that plants themselves have ‘explored’ over their evolutionary history, to make it more valuable for humankind.”
Structural Biology and Biochemistry Aid in Combatting Crop Disease
The lab of biochemistry professor Ivan Rayment uses structural biology to discern how proteins function. While much of the lab’s work focuses on motor proteins in muscle — in fact he was the one to first solve the structure of myosin, muscle’s most important motor protein — one graduate student’s project is taking on Fusarium head blight, a fungal infection that can affect crops.
Graduate student Karl
Karl Wetterhorn has been continuing a line of work in the Rayment Lab investigating a way to inactivate a toxin the fungal head blight releases onto plants once it lands on them. Started by a graduate student over a decade ago and then passed to a second and finally Wetterhorn, the research has successfully enhanced a naturally occurring enzyme from rice to potentially prevent the fungus from spreading on cereal crops like wheat.
The fungus is devastating — and can result in more than $1 billion of lost profits on a bad year — because after finding its way onto a wheat head, it produces a mycotoxin that prevents the plant from defending itself. Wherever the toxin gets, the plant can’t synthesize any enzymes to protect itself. A previous student had found an enzyme that reduced the damage from the toxins dramatically but the structure and the chemical mechanism were still unknown.
“The next step was to determine that structure and mechanism and then expand the specificity of the enzyme because it was only working on a portion of the toxins the fungus produces,” Wetterhorn explains. “We took the structural information that we gained from determining the structure of the enzyme and used that to expand the active site.”
Journal cover depicting Fusarium
head blight from the Rayment Lab.
The enzyme adds a glucose molecule — a type of sugar — to a specific part of the toxin. The big molecule probably prevents the toxin from binding to the plant’s protein-producing machinery, which would cause it to stop working. He says the next step is plant breeders engineering wheat to express this enzyme to test if it helps them combat the fungus.
The next challenge Wetterhorn is facing is that even though their new enzyme can likely stop the fungus from spreading, any presence of the fungus can still be toxic to animals and humans. They are looking to break a particular bond in the toxin to inactivate it for good. They are both looking for a naturally-occurring enzyme and trying to engineer one that can help with this problem.
“Overall, I am interested in how evolution has impacted enzymes and their specificity,” Rayment says. “We are taking a two-pronged approach to finding this enzyme that can totally inactivate the toxin. You really need both. We are excited to see where this work continues to go.”
What Can Plants Tell Us About Animals?
Studying plants doesn’t just shed light on how plants work. It can also shed light on how animal cells — including those in humans — work.
The laboratory of Professor Sebastian Bednarek uses Arabidopsis thaliana, a plant related to cabbage and mustard, to study cell biology broadly. His research explores how plant cells divide to create new cells and how cellular processes in plants are related to those in animal cells.
Both plants and animals get bigger by dividing their cells to make more cells, and the process involves the use of some common evolutionarily conserved proteins. However, unlike animal cells, construction of the new membrane and cell wall that separate the dividing daughter cells is an inside out process. Rather than the cell wall coming together from the outside and pinching off to form two cells, plant cells must build a new structure from the inside out to divide two cells that are fixed in place.
This cell structure — called the cell plate in plants — is a complex yet organized amalgam of proteins, lipids, and cell wall polysaccharides that is the gatekeeper of what gets in and what gets out of the cell. Because of this, creating a cell plate in dividing plant cells, which will become the membrane and cell wall between the new daughter cells, is no small feat.
The individual components of the cell plate are largely made inside and shuttled to the division region to assemble it. This is the process that Bednarek studies closely.
Top: Graduate student Jessica Cardenas of the Bednarek Lab shows
a high school intern how to work with seedlings.
Bottom: Graduate student Dana Dahhan of the Bednarek Lab
manipulates a plant in the lab.
“You have very complex trafficking going on as vesicles, or compartments, arrive at the division plane,” Bednarek explains. “The vesicles fuse and basically expand out like the iris of a camera. It gets bigger and bigger from the inside out until it fuses with the outer membrane. And at this point it looks like Swiss cheese. But we know the cell membrane is a more solid structure so the cell then must do more work to accomplish this. We study how all of this takes place.”
For Bednarek, using Arabidopsis as a model organism isn’t just to be able to provide insight about how other plants work, but also animals like humans. His lab is highly interested in protein trafficking — how the mind-boggling array of proteins in the cell are taken where they are needed after being created and finally taken to be broken down or recycled afterward.
For example, graduate students Jessica Cardenas (pictured at top) and Dana Dahhan investigate a protein called CDC48 that is essential for the formation of the cell plate, along with many other functions. They say the ring-shaped protein is analogous to a socket wrench handle. Different proteins, or different sized “sockets,” attach to it and help it bind to many other protein complexes. Inactivating or losing this protein causes plant growth to arrest at the embryo or seedling stage, the researchers say.
“I was attracted to UW–Madison because I knew there were so many strong labs that worked in plants in the department,” Dahhan says. “Plants are a model you can hold in your hand and because they are stationary there are disadvantages but also advantages that help us study them better. I also knew that membrane trafficking is very applicable to many areas of research.”
One of the “socket” proteins that CDC48 works with is called PUX1. When it binds to the wrench handle, it breaks it apart so it can no longer carry out its many functions. This means PUX1 is what’s called a disassembly factor.
The bizarre thing they’ve discovered is that inactivating PUX1 causes plants to grow faster and they are trying to find out why that is. Additionally,
a protein similar to CDC48 in humans has roles in diabetes and cancer and that is something the Bednarek Lab and others can explore as well.
“The reason we are using plants is that they are actually a fantastic tool to get at these problems,” he says. “There is a broad aspect to this work that allows us get at things that are both evolutionarily conserved between plants and other organisms and those that are plant specific. You can learn a lot by trying to see what’s conserved across all systems. You can see what is distinct where and when new cellular and molecular tools evolved.”
Read more about research areas and strategic priorities in the UW–Madison Department of Biochemistry:
Fertilizer From Air
In the early 1900s two German chemists, Fitz Haber and Carl Bosch, were studying gases. They figured out how to use nitrogen from the air to make ammonia, a plant fertilizer. Using nitrogen as well as phosphorus fertilizers allowed us to grow enough food to feed billions of people. However, using lots of fertilizer had an unexpected effect.
Over many generations, fertilization can cause plants to have small roots. Click for more detail.
With lots of nutrients available to plants, there was no advantage to larger roots. Plants with small roots, but big leaves or more seeds, reproduced more and passed on their genes. This led to more and more of our crops ending up with small root systems. We figured out a way to keep making plenty of nitrogen to use on these small rooted plants. But the situation is different for another nutrient, phosphorus.
You may not have heard of phosphorus before, yet it is a very important element. It stiffens our bones. It’s in our DNA. It’s in adenosine triphosphate (ATP), which is the molecule that provides the energy for nearly every single thing your cells do. Plants also need it to get energy from the sun.
Plants gather phosphorus from the soil in the form of phosphate. Phosphate is simply a phosphorus atom bonded to four oxygen atoms. We use tons of phosphate fertilizer on our crops to produce the yields we depend on. Yet unlike nitrogen, phosphate can’t come from the air. The renewal of phosphate depends on the movement of the Earth. Lands and continents have to shift and push up new rocks that hold phosphate. These changes take thousands or millions of years.
Phosphate used to be mined from bat guano (poop) but now phosphate is mined from phosphate rock. Click to enlarge.
Why are there no tree-like plants that grow in lakes? - Biology
A lake is a body of water that is surrounded by land. There are millions of lakes in the world.
Biology, Ecology, Earth Science, Experiential Learning, Geography, Physical Geography
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A lake is a body of water that is surrounded by land. There are millions of lakes in the world. They are found on every continent and in every kind of environment&mdashin mountains and deserts, on plains, and near seashores.
Lakes vary greatly in size. Some measure only a few square meters and are small enough to fit in your backyard. Such small lakes are often referred to as ponds. Other lakes are so big that they are called seas. The Caspian Sea, in Europe and Asia, is the world&rsquos largest lake, with an area of more than 370,000 square kilometers (143,000 square miles).
Lakes also vary greatly in depth. The world&rsquos deepest lake is Lake Baikal, in Russia. Its bottom is nearly 2 kilometers (more than 1 mile) below the surface in places. Although Lake Baikal covers less than half the surface area of Lake Superior&mdashone of North America&rsquos Great Lakes&mdashit is about four times deeper and holds nearly as much water as all five of the Great Lakes combined. Other lakes are so shallow that a person could easily wade across them.
Lakes exist at many different elevations. One of the highest is Lake Titicaca, in the Andes Mountains between Bolivia and Peru. It is about 3,810 meters (12,500 feet) above sea level. The lowest lake is the Dead Sea, between Israel and Jordan. It is more than 395 meters (1,300 feet) below sea level.
The water in lakes comes from rain, snow, melting ice, streams, and groundwater seepage. Most lakes contain freshwater.
All lakes are either open or closed. If water leaves a lake by a river or other outlet, it is said to be open. All freshwater lakes are open. If water only leaves a lake by evaporation, the lake is closed. Closed lakes usually become saline, or salty. This is because as the water evaporates, it leaves behind solids&mdashmostly salts. The Great Salt Lake, in the U.S. state of Utah, is the largest saline lake in North America. Its water is saltier than the ocean. Surrounding the Great Salt Lake are salt flats, areas where the lake has evaporated, leaving only stretches of white salt.
How Lakes Are Formed
All lakes fill bowl-shaped depressions in the Earth&rsquos surface, called basins. Lake basins are formed in several ways.
Many lakes, especially those in the Northern Hemisphere, were formed by glaciers that covered large areas of land during the most recent ice age, about 18,000 years ago.
The huge masses of ice carved out great pits and scrubbed the land as they moved slowly along. When the glaciers melted, water filled those depressions, forming lakes. Glaciers also carved deep valleys and deposited large quantities of earth, pebbles, and boulders as they melted. These materials sometimes formed dams that trapped water and created more lakes.
Many areas of North America and Europe are dotted with glacial lakes. The U.S. state of Minnesota is nicknamed &ldquoThe Land of 10,000 Lakes&rdquo because of the number of glacial lakes. Many lakes in North America, including the Great Lakes, were created primarily by glaciers.
Some lake basins form where plate tectonics changed the Earth&rsquos crust, making it buckle and fold or break apart. When the crust breaks, deep cracks, called faults, may form. These faults make natural basins that may fill with water from rainfall or from streams flowing in the basin. When these movements occur near the ocean, part of the ocean may be trapped by a new block of land thrust up from below the Earth&rsquos surface. The Caspian Sea was formed this way. Lake Baikal was also formed by the movement of tectonic plates.
Many lakes form as a result of volcanoes. After a volcano becomes inactive, its crater may fill with rain or melted snow. Sometimes the top of a volcano is blown off or collapses during an eruption, leaving a depression called a caldera. It, too, may fill with rainwater and become a lake. Crater Lake, in the U.S. state of Oregon, one of the deepest lakes in the world, was created when ancient Mount Mazama&rsquos volcanic cone collapsed.
Not all lakes are created by basins filling with water. Some lakes are formed by rivers. Mature rivers often wind back and forth across a plain in wide loops called meanders. During periods of flooding, a swollen, rushing river may create a shortcut and bypass a meander, leaving a body of standing water. This type of small lake is called an oxbow lake, because its shape resembles the U-shaped frame that fits over an ox&rsquos neck when it is harnessed to pull a wagon or a plow.
Lakes may also be created by landslides or mudslides that send soil, rock, or mud sliding down hills and mountains. The debris piles up in natural dams that can block the flow of a stream, forming a lake.
Dams that beavers build out of tree branches can plug up rivers or streams and make large ponds or marshes.
People make lakes by digging basins or by damming rivers or springs. These artificial lakes can become reservoirs, storing water for irrigation, hygiene, and industrial use. Artificial lakes also provide recreational use for boating, swimming, or fishing.
Artificial lakes can provide electricity through hydroelectric power plants at the dam. Lake Mead, in the U.S. states of Arizona and Nevada, was formed when the Hoover Dam was built during the Great Depression. The dam was built to control the unpredictable Colorado River and provides electricity to the western United States.
Chemical and Physical Aspects of Lakes
Temperature, light, and wind are three of the main factors that affect the physical characteristics of a lake. Temperature and light vary from lake to lake. Depth, plant growth, dissolved materials, time of day, season, and latitude can all affect light&rsquos ability to pass through the lake&rsquos water.
Light and wind affect the temperature in lakes. Sunlight warms the water, and wind cools it down. Most lakes go through a process called thermal stratification. Thermal stratification refers to a lake&rsquos three main layers, each with a different temperature range. A lake&rsquos shallowest layer is the epilimnion. Its middle layer is the metalimnion, or thermocline. The deepest layer is the hypolimnion.
The most important chemicals in a lake are nitrogen and phosphorus. These chemicals allow nutrient-rich plants and algae to grow. Other organisms feed off these plants and algae, creating a complex, healthy ecosystem.
The chemistry of a lake is affected by biological, geological, and human processes. The balance of nutrients may be altered by biological phenomena such as &ldquoalgal blooms,&rdquo when algae reproduces so rapidly it prevents any nutrients from reaching below the lake&rsquos surface. Natural processes such as the eruption of a nearby volcano can alter the chemical aspect of a lake by introducing new gases or minerals. Pollution, such as the introduction of toxic chemicals from industry or agriculture, can also affect a lake&rsquos chemistry.
The amount of oxygen and the pH level can also affect a lake&rsquos chemistry. A lake must have a healthy amount of oxygen to sustain life. Lakes that do not have enough oxygen to sustain life are abiotic.
The pH level is a chemical property of all substances. A substance&rsquos pH level indicates whether it is an acid or a base. Substances with a pH of less than 7 are acidic substances with a pH greater than 7 are basic. Lakes have different pH levels, with life adapting to different chemical environments. Lake Tanganyika, one of the African Great Lakes, has an extremely high pH. It is full of dissolved minerals. Fish such as cichlids thrive in Lake Tanganyika. Tilapia, a variety of cichlid, can also thrive in lakes with very low pH.
The Life Cycle of Lakes
Once formed, lakes do not stay the same. Like people, they go through different life stages&mdashyouth, maturity, old age, and death. All lakes, even the largest, slowly disappear as their basins fill with sediment and plant material. The natural aging of a lake happens very slowly, over the course of hundreds and even thousands of years. But with human influence, it can take only decades.
A lake&rsquos plants and algae slowly die. The warm, shallow water of the upper layer of the lake causes plants and algae to decompose, and eventually they sink to the basin. Dust and mineral deposits on the bottom of the lake combine with the plants to form sediment. Rain washes soil and pebbles into the basin. The remains of fish and other animals pile up on the lake&rsquos bottom. The lake becomes smaller, starting at the edges and working toward the middle. Eventually, the lake becomes a marsh, bog, or swamp. At this point, the drying-up process slows down dramatically limnologists, people who study lakes and ponds, aren&rsquot sure why. Eventually, the lake becomes dry land.
Dry lake beds are a perfect place to find and study fossils. Archaeologists often excavate ancient lake beds, such as Fossil Butte in the U.S. state of Wyoming. The remains of organisms, from single-celled bacteria to dinosaurs, were preserved over time as sediment on the lake bed built up around and on top of them. In fact, some scientists believe the first living organisms on Earth developed in lakes.
There are three basic ways that limnologists classify lakes: how many nutrients lakes have, how their water mixes, and what kinds of fish live in them.
When lakes are classified by the amount of nutrients they have, limnologists are using the trophic system. Generally, the clearer the water in the lake, the fewer nutrients it has. Lakes that are very nutrient-rich are cloudy and hard to see through this includes lakes that are unhealthy because they have too many nutrients. Lakes need to have a balance of nutrients.
Lakes can also be classified by how the water mixes, or turns over from top (epilimnion) to bottom (hypolimnion). This is called lake turnover. Water in some lakes, mostly shallow ones, mixes all year long. These lakes have very little lake turnover.
Deep lakes experience lake turnover on a large scale. The middle layer, the thermocline, mixes and turns over throughout the year. It turns over due to climate, nutrient variations, and geologic activity such as earthquakes. However, major lake turnover happens during the fall and spring, when the lake&rsquos cold and warm waters mix and readjust. Most lakes that experience lake turnover are dimictic lakes, meaning their waters mix twice a year, usually in fall and spring.
Lake turnover changes with the seasons. During the summer, the epilimnion, or surface layer, is the warmest. It is heated by the sun. The deepest layer, the hypolimnion, is the coldest. The sun&rsquos radiation does not reach this cold, dark layer.
During the fall, the warm surface water begins to cool. As water cools, it becomes more dense, causing it to sink. This cold, dense water sinks to the bottom of the lake. It forces the water of the hypolimnion to rise.
During the winter, the epilimnion is coldest because it is exposed to wind, snow, and low air temperatures. The hypolimnion is the warmest. It is insulated by the earth. This is why there is ice on lakes during the winter, while fish swim in slightly warmer, liquid water beneath.
During the spring, the lake turns over again. The cold surface water sinks to the bottom, forcing the warmer, less dense water upward.
The final way to classify lakes is by the kinds of fish they have. This helps people in the fishing industry identify what kinds of fish they might be able to catch in that lake. For example, calling a lake a cold-water lake tells a fisherman that he can probably expect to find trout, a cold-water fish. A lake that has thick, muddy sediment is more likely to have catfish.
There are other ways of classifying a lake, such as by whether it is closed or fed by a river or stream. States also divide lakes into ones that are available for public use and ones that are not. Many people refer to lakes by size.
How Animals and Plants Use Lakes
Lakes are important in preserving wildlife. They serve as migration stops and breeding grounds for many birds and as refuges for a wide variety of other animals. They provide homes for a diversity of organisms, from microscopic plants and animals to fish that may weigh hundreds of kilograms. The largest fish found in lakes is the sturgeon, which can grow to 6 meters (20 feet) and weigh more than 680 kilograms (1,500 pounds).
Plants growing along the lakeshore may include mosses, ferns, reeds, rushes, and cattails. Small animals such as snails, shrimp, crayfish, worms, frogs, and dragonflies live among the plants and lay their eggs on them both above and below the waterline. Farther from the shore, floating plants such as water lilies and water hyacinths often thrive. They have air-filled bladders, or sacs, that help keep them afloat. These plants shelter small fish that dart in and out under their leaves. Waterbugs, beetles, and spiders glide and skitter across the surface or just below it. Small islands, floating plants, or fallen logs provide sunny spots for turtles to warm themselves.
Other animals live near the lake, such as bats and semi-aquatic animals, such as mink, salamanders, beavers, and turtles. Semi-aquatic animals need both water and land to survive, so both the lake and the shore are important to them.
Many kinds of water birds live on lakes or gather there to breed and raise their young. Ducks are the most common lake birds. Others include swans, geese, loons, kingfishers, herons, and bald eagles.
Many people think of fish when they think of lakes. Some of the most common fish found in lakes are tiny shiners, sunfish, perch, bass, crappie, muskie, walleye, perch, lake trout, pike, eels, catfish, salmon, and sturgeon. Many of these provide food for people.
How People Use Lakes
Lakes are an important part of the water cycle they are where all the water in an area collects. Water filters down through the watershed, which is all the streams and rivers that flow into a specific lake.
Lakes are valuable resources for people in a variety of ways. Through the centuries, lakes have provided routes for travel and trade. The Great Lakes of North America, for example, are major inland routes for ships carrying grain and raw materials such as iron ore and coal.
Farmers use lake water to irrigate crops. The effect of very large lakes on climate also helps farmers. Because water does not heat or cool as rapidly as land does, winds blowing from lakes help keep the climate more even. This is the &ldquolake effect.&rdquo The city of Chicago, in the U.S. state of Illinois, benefits from the lake effect. Chicago sits on the shore of Lake Michigan. When the western part of Illinois is snowing, Chicago often remains slightly warmer.
The lake effect can help farmers. In autumn, lakes blow warmer air over the land, helping the season last longer so farmers can continue to grow their crops. In spring, cool lake winds help plants not to grow too soon and avoid the danger of early-spring frosts, which can kill the young crops.
Lakes supply many communities with water. Artificial lakes are used to store water for times of drought. Lakes formed by dams also provide hydroelectric energy. The water is channeled from the lake to drive generators that produce electricity.
Because they are often very beautiful, lakes are popular recreation and vacation spots. People seek out their sparkling waters to enjoy boating, swimming, water-skiing, fishing, sailing, and, in winter, ice skating, ice boating, and ice fishing. Many public parks are built near lakes, allowing people to picnic, camp, hike, bike, and enjoy the wildlife and scenery the lake provides.
For some people, lakes are permanent homes. For example, indigenous people called the Uros have lived on Lake Titicaca in the Andes Mountains for centuries. The lake supplies almost everything the Uros need. They catch fish from the lake and hunt water birds.
The Uros also use the reeds that grow in Lake Titicaca to build floating &ldquoislands&rdquo to live on. The islands are about 2 meters (6.5 feet) thick. On them, the Uros build reed houses and make reed sleeping mats, baskets, fishing boats, and sails. They also eat the roots and the celery-like stalks of the reeds.
Lake Health: Blue-Green Algae
Although lakes naturally age and die, people have sped up the process by polluting the water. A major problem that threatens many lakes is blue-green algae. Blue-green algae is sometimes referred to as &ldquopond scum&rdquo and can be blue-green, blue, green, reddish-purple, or brown. It stays on the surface of the water and forms a sort of mat. When the conditions are just right, the algae multiplies quickly. This is called an algal bloom and is harmful to lakes, animals, plants, and people.
Blue-green algae is different from true algae because it is not eaten by other organisms. True algae is an important part of the food web because it supplies energy for tiny animals, which are then eaten by fish, which are then eaten by other fish, birds, animals, or people.
Blue-green algae, also called cyanobacteria, is not a part of the food web. It uses up important nutrients without contributing to the lake ecosystem. Instead, the algal bloom chokes up a lake and uses up the oxygen that fish and other living things depend on for survival. Plants die more quickly, sinking to the bottom and filling up the lake basin. Blue-green algae also can become so dense that it prevents light from penetrating the water, changing the chemistry and affecting species living below the surface.
When an algal bloom happens, water becomes contaminated. The toxic water can kill animals and make humans sick. Blue-green algae is not a new problem. Scientists have found evidence of it from hundreds of years ago. The problem has increased, though, as humans pollute lakes.
Eutrophication is when a lake gets too many nutrients, causing blue-green algae growth. How do the excess nutrients get into lakes? Sewage from towns and cities causes explosive growth of blue-green algae, and waste from factories can wash into the lakes and pollute them. Phosphorus-based fertilizers from farms, golf courses, parks, and even neighborhood lawns can wash into lakes and pollute them. The phosphorus seeps into the ground and eventually reaches the lake. Phosphorus is an important nutrient for a lake, but too much of it is not a good thing because it encourages blue-green algae.
How can blue-green algae be prevented or reduced? At home, people can help by using phosphorus-free fertilizer and by fertilizing only where it&rsquos needed. Preventing lawn clippings and leaves from washing into the gutter and maintaining a buffer of native plants help filter water and stop debris from washing away. Making sure septic systems don&rsquot have leaks, safely disposing of household chemicals (like paint), and minimizing activities that erode soil also help prevent the spread of blue-green algae.
Controlling phosphorous and chemicals from factories and farms is much more complicated. Citizens need to work with businesses and elected leaders to help reduce the amount of runoff and water pollution.
Lake Health: Invasive Species
When a plant or animal species is moved to a location where it&rsquos not originally from, the species is called an exotic species. When that species harms the natural balance in an ecosystem, the species is called invasive. Invasive species can harm life in a lake by competing for the same resources that native species do. When introduced to new food sources, invasive species multiply quickly, crowding out the helpful native species until there are more invasive than native species.
Invasive species can change the natural habitat of the lake and are known as biological pollutants when this happens. Once non-native species have been introduced into a lake, they are almost impossible to get rid of.
How do invasive species invade in the first place? Non-native plants and animals are almost always introduced by people. As people use waterways more frequently, they may inadvertently move organisms from one area to another.
Plants such as Eurasian watermilfoil, an invasive aquatic plant in the U.S., may cling to boats, clothing, pets, equipment, and vehicles. Small animals such as the spiny water flea can travel unnoticed by hopping onto a kayak or other recreational equipment.
Species are also carried by large ships bringing goods from one country to another. These ships take in ballast water, which helps stabilize the ship as it crosses the ocean. When the ship reaches its destination, it releases the ballast water. The water may be full of non-native species accidentally captured as the ship took on ballast.
The most famous invasive species in lakes is probably the zebra mussel, a small mollusk native to the Black Sea and the Caspian Sea in Europe and Asia. In the late 1980s, zebra mussels were found in several of North America&rsquos Great Lakes. Since then, zebra mussels have spread to lakes from the U.S. state of Louisiana to the Canadian province of Quebec. Zebra mussels devastate native plants and animals. Some scientists say they carry a type of disease that is deadly to birds that eat the mussels. Zebra mussels multiply so quickly that they clog pipes. This harms machinery at industrial plants that use water, including hydroelectric dams and water filtration plants. Ships, docks, anchors, and buoys have also been destroyed by the invasive zebra mussel.
Communities have worked to reduce the impact of invasive species. Many states have laws prohibiting the sale or transport of non-native species. People are encouraged to inspect their boats and other equipment for wildlife. Boaters should remove plants, animals, and mud before leaving the water-access area. They should also drain any water from their boat. Rinsing boats, equipment, and even people can help reduce the transfer of harmful species. People should also get rid of leftover bait and report any species they see that look like they might not be native. These steps can make a big difference in keeping the habitat of a lake healthy.
Lake Health: Acid Rain
Another major threat to lakes today is acid rain. Some acid is natural, even in pure rain. This slightly toxic chemical slowly weathers rocks and soil. Acid rain, however, is caused by human activities and is harmful. It is caused by toxic gases from factories, coal-fired power plants, vehicle exhaust, and home furnaces.
Nitrogen and sulfur, the main ingredients of acid rain, rise in the air and may be carried hundreds of kilometers by wind. When these gases mix with the moisture in clouds, they form strong acids, which kill fish, plants, and other organisms when the acids fall as rain or snow on lakes. Acid rain can also affect humans, causing asthma and bronchitis, and damaging lung tissue. Methylmercury, a toxic form of mercury, has been linked to acid rain. Eating fish containing high levels of this mercury is particularly harmful for pregnant women, the elderly, and children.
Lakes and soil can neutralize normal levels of acid, but acid rain is too strong for lakes to combat. Eventually, acid rain leaves lakes sterile and lifeless. There are many lakes today in the United States, Canada, and parts of Europe dead or drying up because of acid rain.
Some steps have been taken to curb acid rain. The Clean Air Act was passed by the United States Congress in 1990. It required all utility companies to reduce the amount of toxic emissions by 40 percent by the year 2000. At home, people can help the problem by replacing old furnaces, turning off electronics when they&rsquore not being used, and using fans or opening windows in the summer instead of air conditioning. Using compact fluorescent light bulbs (CFLs) and energy-efficient vehicles also help reduce the amount of pollution going into the air.
Lakes are among the most valuable and most beautiful of the Earth&rsquos resources. Most experts agree that lakes must be kept clean and free from pollution if they are to continue to provide the many benefits that we receive from them today.
Photograph by Diane Chatterton, MyShot
The Lake District is a famous wilderness area in northern England. Lake District National Park is one of the countrys most popular parks. Besides lakes, the Lake District is filled with mountains and hills, valleys and streams, bogs and plains. The Lake District was a favorite place of the so-called Lake Poets, a group of 19th-century English writers including William Wordsworth and Samuel Taylor Coleridge.
A Lake by Any Other Name
A mere is a large, shallow lake. Meres are common in the United Kingdom, while meers (the Dutch word for lake) are found in the Netherlands.
Lochs are lakes or bays mostly found in Scotland.
Lake Vostok, in Antarctica, is one of the largest subglacial lakes in the world. Lake Vostok is about the same size as Lake Ontario, and even has an island in the middle of it. On top of the lake is an icecap 4 kilometers (2.5 miles) thick. The ice actually insulates the water, preventing it from freezing.
Eutrophication and its Impacts
Eutrophication is the process of enrichment of lakes and streams with nutrients, and the associated biological and physical changes. Eutrophication is a natural process, but human activity has dramatically increased its rate in many waterbodies. * Lakes and ponds are particularly vulnerable to eutrophication because the nutrients carried into them continue to buildup in contrast, the nutrients can be carried away in moving water.
Some results of excessive eutrophication are visible: thick mats of algae in the water scum and foam odor and taste problems and death and disease of fish and other aquatic organisms. Other effects, such as the reduction in dissolved oxygen, cannot be seen directly, although the conditions often produce visible results such as dead fish.
An increase in the water's pH as a result of the increased growth of algae is another impact that is not directly visible. High pH can be toxic to fish and other organisms, and it can also make other substances, such as ammonia, even more toxic than they are otherwise.
Excess nutrients not only affect stream health but also may impact human health and livestock. Although phosphorus is not toxic to human adults in moderate concentrations, high levels of nitrate in drinking water (10 milligrams per liter or greater) can injure or kill livestock or human infants. Nuisance species of algae, such as some cyanobacteria (also called blue-green algae), produce toxins that affect the nervous system and liver, posing a threat to animals and humans who ingest them.
The worldwide increase in red tides and other blooms of toxic algae in coastal ocean waters has been linked to nutrient enrichment coming from coastal rivers. Nuisance species such as these, in fresh water as well as coastal oceans, can increase and force out less tolerant species, resulting in a loss of aquatic biodiversity .
Organ Pipe Cactus (Stenocereus thurberi)
The organ pipe cactus lives up to its name because of the long tubular succulent stems that look like a pipe organ. These common desert plants grow up to 16 ft. (5 m) and the thick-ribbed stems are covered in sharp spines. Desert dwellers prized these plants due to their large tasty fruits. Some say that the delicious fruits from this plant taste better than watermelon.
These drought-tolerant plants grow well in gardens that get full sun and little shade. As with most succulent and cacti, plant them in well-draining, sandy soil. In their native habitat, the cacti are found in Arizona and Mexico in the Sonoran Desert.
Why are there no tree-like plants that grow in lakes? - Biology
The word "native" means "originally coming from a certain area." If you were born in Greensboro, NC, you can say that you are native to Greensboro. A native species is any species that originally came from the area in which it now lives.
Non-native means not originally coming from a certain area. If you were born in Venezuela, you can say that you are non-native to the United States. A non-native species is a species that did not originally come from the area in which it now lives.
The danger of non-native species
Although there are many beautiful plants in Hawaii, it is not a good idea to bring them to North Carolina. A flower from Hawaii may have no natural predators, or things that eat it, in North Carolina. If you bring the seeds of a Hawaiian flower back to North Carolina and plant it in your backyard, that flower may grow and soon overtake your entire backyard since there are no predators to eat it. Soon, that flower may grow all over your neighborhood. Your neighbors may not appreciate having their entire yard taken over by that plant, no matter how beautiful you used to think it was!
One important component of any ecosystem is biodiversity. Biodiversity is a measurement of the number of different species living in an area. Rainforests and coral reefs are known for having many different species. We say that they have high biodiversity.
An ecosystem that has low biodiversity may contain lots of living things but they are almost all the same. For example, a cornfield may be full of corn plants, but it only contains one type of plant- corn.
The growth of a non-native species can pose a great threat to the biodiversity of an ecosystem. If a non-native species is brought to an ecosystem, it may overtake native plants and animals. Eventually, the only organism that lives in an area might be the non-native species. The overgrowth of non-native species usually lowers the biodiversity of an area.
Examples of invasive non-native species
Rabbits in New Zealand
When European sailors first came to New Zealand in the 1700s and 1800s, they had a hard time finding food. Some sailors thought it would be a good idea to bring over some rabbits from Europe and let them live in the wild of New Zealand. The sailors could let the rabbit population increase for a while, then hunt the rabbits for food. What the sailors didn't realize was that these rabbits had no natural predators on New Zealand and that the rabbits would thrive on the island. After a few years, the rabbit population was out of control. Rabbits reproduce very rapidly, and even though the sailors tried to limit their population by hunting the rabbits, rabbits continued to take over the island. The rabbits ate and destroyed crops and continue to be a nuisance on New Zealand today.
Kudzu in the Southeastern United States
Have you ever seen piles and piles of green, leafy vines covering land on the side of roads and highways? This rampantly growing invasive species is kudzu. Kudzu is a climbing vine plant in the pea family, native to Japan. Kudzu is a vine that climbs over trees and bushes and grows so rapidly that it kills plants by keeping them from getting any sunlight.
Kudzu was brought to the United States in 1876 for a fair celebrating America's 100th birthday in Philadelphia, Pennsylvania. Japanese gardeners created beautiful, lush displays using the kudzu plant, which has sweet-smelling purple blooms on its green vines. Soon after, gardeners in Florida introduced the kudzu plant in the 1920s as an easily grown food for animals.
During the 1930s, environmental agencies promoted the use of Kudzu to prevent soil from washing away after heavy rain. Farmers were paid to plant kudzu in empty fields to prevent erosion.
Unfortunately, the hot, moist climate of the Southeastern United States is too perfect for kudzu. Kudzu can grow over 1 foot a day during warm summer months. Kudzu grew all over empty land and began growing on and "choking out" trees and other native plants by blocking out sunlight. Attempts at killing kudzu with herbicides and other weedkillers proved futile as kudzu is resistant to most weedkillers.
Kudzu is currently spreading at the rate of 150,000 acres in the United States each year.
Zebra Mussels in North America
Zebra mussels are small, freshwater mussels native to Russia. Zebra mussels can grow out of control in waterways with few or no native predators. Zebra mussels were accidentally brought to North America on the underside of boats that traveled from Russian waters to the Great Lakes. Soon, these mussels began growing out of control. They out-competed native species and began to damage boats, docks, and water treatment machinery.
Killer Bees and Brazil
Africanized honey bees, also known as killer bees, were created by mating African bees with European honey bees. These Africanized bees are a great deal more aggressive than the European honey bee species.
Killer bees in North and South America descended from 26 bees that were accidentally released by a researcher in São Paulo in southeastern Brazil. As of 2002, these bees have spread from Brazil to Central America, Mexico, Texas, and Louisiana.
Although Africanized bees are called "killer bees," their sting is no more dangerous than a normal honey bee. What makes Africanized honey bees dangerous is that they are more easily provoked, or angered, than the honey bees native to North and South America.
Roots and Stems
Woody stems and mature roots are sheathed in layers of dead cork cells impregnated with suberin &mdash a waxy, waterproof (and airproof) substance. So cork is as impervious to oxygen and carbon dioxide as it is to water. However, the cork of both mature roots and woody stems is perforated by nonsuberized pores called lenticels. These enable oxygen to reach the intercellular spaces of the interior tissues and carbon dioxide to be released to the atmosphere.
Figure 188.8.131.52 Lenticels. The photo shows the lenticels in the bark of a young stem.
In many annual plants, the stems are green and almost as important for photosynthesis as the leaves. These stems use stomata rather than lenticels for gas exchange.