Freshwater Life

Freshwater Life

The animals and plants that live in freshwater are called aquatic life. The water that they live in is fresh, which means that it is less salty than the ocean.The terrestrial (land) environment that surrounds the freshwater environment has a large impact on the animals and plants that live there. Some factors that influence the freshwater environment include climate, soil composition, and the terrestrial animals and plants in the area.

Just as on land, aquatic plants require carbon dioxide, nutrients (substances such as phosphate and nitrogen needed for growth) and light for photosynthesis, the process where plants make their food from sunlight, water, and carbon dioxide. Aquatic animals need to breathe in oxygen and consume food.

The physical conditions surrounding the body of water or wetland (lands that are covered in water often enough so that it controls the development of the soil) control the availability of these resources.

Groundwater Formation

Groundwater Formation

Groundwater is fresh water in the rock and soil layers beneath Earth’s land surface. Some of the precipitation (rain, snow, sleet, and hail) that falls on the land soaks into Earth’s surface and becomes groundwater. Water-bearing rock layers called aquifers are saturated (soaked) with groundwater that moves, often very slowly, through small openings and spaces.

This groundwater then returns to lakes, streams, and marshes (wet, low-lying land with grassy plants) on the land surface via springs and seeps (small springs or pools where groundwater slowly oozes to the surface).

Groundwater makes up more than one-fifth (22%) of Earth’s total fresh water supply, and it plays a number of critical hydrological (water-related), geological and biological roles on the continents. Soil and rock layers in groundwater recharge zones (an entry point where water enters an aquifer) reduce flooding by absorbing excess runoff after heavy rains and spring snowmelts.

Lakes

Lake

Lakes are large inland bodies of fresh or saline (salty) water. Lakes form in places where water collects in low areas or behind natural or man-made dams (barriers constructed to contain the flow of water).

Some lakes are fed by streams (natural bodies of flowing freshwater), and some form where groundwater (water flowing in rock layers beneath the land surface) discharges onto the land surface.

Water leaves lakes by flowing into outlet streams, infiltrating (soaking in) into groundwater reservoirs called aquifers, and by evaporating into the atmosphere (mass of air surrounding Earth). Lakes vary in size from large lakes such as the Great Lakes of North America, to small mountain lakes.

Ponds

Pond

A pond is a depression in the ground that is filled with water that remains year round. Ponds range in size from the artificial backyard projects about the size of a bathtub to bodies of water that are about the size of a football field. Ponds support a variety of animal and plant life, and are also used as recreational sites by people.

The difference between a pond and a lake involves size and water depth. A lake is big enough to have at least one beach (sand or rock that slopes down to the water) and contains enough water to generate waves from the wind that blows across the surface of the water.

In contrast, a pond is usually too small for waves of any size to form. At the center of a lake, the water can reach depths of many hundreds, even thousands of feet (meters). A pond, however, is a shallow and still body of water where sunlight can usually reach down to the bottom.

Rivers

Kawarau River in Queenstown

Rivers are bodies of flowing surface water driven by gravity. Hydrologists, scientists who study the flow of water, refer to all bodies of flowing water as streams. In common language, it is accepted to refer to rivers as larger than streams. Water flowing in rivers is only a very small portion of Earth’s fresh water.

The oceans contain about 96% of the water on Earth, and most fresh water is bound up in glacial ice near the North and South Poles. Rivers shape the landscape and are integral to the hydrologic cycle (circulation of water on and around Earth) on the continents.

Rivers shape the lands as they erode (wear away) and deposit sediment (particles of gravel, sand, and silt) along their courses. Running river water acts to level the continents. When geologic forces slowly raise (uplift) mountain ranges, rivers wear them away.

Stream Systems

Stream passing through the valley, Tash Rabat, Kyrgyzstan

Streams are any size body of moving surface fresh water driven towards sea level by gravity (force of attraction between two masses). Water scientists refer to all bodies of flowing surface water as streams regardless of size, yet in common language, streams are considered smaller than rivers.

Stream systems are networks that collect fresh water runoff from the land and carry it to the ocean. Together, tree-shaped systems of small branch streams drain vast areas of the continents into large rivers.

Stream systems of all sizes erode (wear down) sediment (particles of gravel, sand, and silt) along their courses and carve complex patterns into the landscape. They wear down slowrising mountains and fill valleys and lowlands (low and level lands) with layers of sediment. Stream systems change character along their courses.

Stream Water Flow

Stream Water Flow

Water flows downhill due to Earth’s gravity (force of attraction between two masses) pulling it. Streams, like rivers, are gravity-driven bodies of moving surface water that drain water from the continents.

Water scientists, called hydrologists, refer to all bodies of running water as streams, no matter their size so, in one sense, rivers are large, well-established streams). In everyday communication, it is common to refer to streams as smaller than rivers.

Streams transfer water that falls on the land as precipitation (rain, snow, sleet, and hail) to the oceans. Streams, again like rivers, constantly shift their courses and change length. The stream is carried along a defined path, called a channel. Water flowing in stream channels is a powerful sculptor that carves landscapes and molds sediment (particles of rock, sand, and silt).

Estuaries

Kilchis Estuary, Oregon

Estuaries are the areas where rivers run into oceans. They often exist where the opening to the sea is somehow obstructed, for example by a sandbar or a lagoon (sandbars are ridges of sand built up by water; lagoons are shallow areas of water separated from the ocean by sandbars or coral). The water in estuaries is dominated by the flow of the tides.

When tides are high, the ocean water washes through the estuary bringing with it sediments (particles of sand, silt, and gravel), nutrients, and organisms from the ocean. When the tide is low, the freshwater of the river floods the area, releasing its load into the estuary.

Because estuaries exist where two different types of water come together and where the land meets the water, estuaries provide many different types of habitats for animals and plants. In addition, both the river and the ocean bring estuaries nutrients such as nitrate and phosphate, which plants need to grow.


This results in a complex range of plants and animals that thrive there. Estuaries are also important to human settlement and economics. As a result, estuaries are often subject to pollution and other environmental stresses.

Wetlands

African wetland

Wetlands are areas of land where water covers the surface for at least part of the year and controls the development of soil. Plants and animals that live in wetlands are adapted to living in conditions where the soil is waterlogged.

There are many different types of wetlands, but they fall into five general classifications: freshwater marshes, freshwater swamps, salt marshes, mangrove swamps, and bogs (also called fens).

In general, swamps have trees, while marshes have plants that have soft stems like grasses, reeds, and sedges (grass-like plants). Bogs are characterized by thick mats of peat, which is made of mosses growing on decayed plants and animals.

Arctic and Subarctic Regions

Arctic ocean

The region encircling the North Pole is called the Arctic Circle, an invisible circle of latitude (imaginary line around the Earth parallel to the equator) at 66°33’ North. The arctic region sits inside the Arctic Circle and the subarctic region lies just below it.

Earth’s arctic and subarctic regions are extremely cold, icy areas of land and sea that receive almost no sunlight during their long, dark winters. Temperatures rarely rise above freezing. This is true even during summer in the “land of the midnight sun.”

The Sun’s rays hit the poles at a very shallow angle and the summer sunlight—while long-lasting—is too weak to provide much heat. Arctic and subarctic regions, however, support diverse groups of land and marine (ocean) plants and animals, including humans that have learned how to survive in their harsh climates.

Ice, Sea-level, and Global Climate

Ice, Sea-level, and Global Climate

The amount of water frozen in Earth’s ice has changed throughout the planet’s history. Earth’s ice budget (total ice volume) grows when the planet’s average temperature falls and shrinks when it rises.

During colder periods called ice ages, ice caps (large dome-shaped glaciers) extend far from the North and South Poles, and mountain glaciers (large masses of moving ice) advance into lowlands. During warmer periods, ice retreats back toward the poles and up mountain valleys. Earth has even been completely ice-free several times during its long history.

Earth’s water budget, the total amount of water on the planet, does not change over time. When more water freezes into ice on land, there is less water in the oceans, so global sea level falls during ice ages.

Glaciers

Glaciers

Glaciers are large masses of moving ice. Glaciers form by the accumulation of snow over tens, hundreds, and even thousands of years. Glaciers grow in cold places where more ice forms than melts each year, namely, close to the north and south poles and at high elevations (near the summits of tall mountains.)

Today, ice covers about one tenth of Earth’s surface. Huge dome-shaped masses of glacial ice, called continental glaciers or ice sheets, cover the arctic island of Greenland and the most of the continent of Antarctica at the South Pole. Mountain (alpine) glaciers flow down valleys in the Himalayas, Andes, Alps and other major mountain ranges.

Glacial ice affects Earth’s climate, drives ocean currents (a moving mass of water that may also differ from surrounding water in properties such as temperature or amount of salt (salinity), and determines global sea level. (When more water is bound up in ice on land, sea level falls. When glaciers melt, sea level rises.)

Polar Ice Caps

Polar Ice Caps

Ice covers Earth’s North and South Poles. Weak sunlight and long, dark winters at high latitudes (imaginary lines on Earth that tell how far north or south a place is from the equator) create frigid conditions that support the formation of year-round glaciers (large masses of moving ice) on land and seasonal ice in the oceans.

An ice cap is a permanent covering of ice over a large area. The arctic ice cap at the North Pole includes sea ice floating in the Arctic Ocean; glaciers in northern Asia, Europe, North America; and sheets of ice on the island of Greenland. The ice cap at the South Pole is made up of the massive Antarctic ice covering and ice in the Southern Ocean.

Polar ice caps play a vital role in regulating global climate, temperature, ocean currents, and sea level. They keep nutrientrich waters of the Arctic and Southern Oceans at a livable temperature for rich communities of biological life. A total of 99.997% of Earth’s fresh water is bound up in polar ice.

Clouds

Clouds

Clouds are made of very small drops of water of water, ice crystals, and other small particles in the atmosphere (mass of air surrounding Earth). The water comes from condensation, a process that allows small drops of water to form as the air cools. Cloud shapes and the way clouds form give scientists important clues about local weather and conditions in the atmosphere around the world.

Clouds are divided into several types or families of clouds. These families of clouds are named according to where or how they form, and include high-level clouds, middle-level clouds, and low-level clouds.

In addition to belonging to a family, clouds are also named for their shape. Puffy clouds are known as cumuliform clouds, and flat sheet-like clouds are known as stratoform clouds.

Climate

Climate

Global climate is the long-term pattern of temperature and precipitation on Earth’s surface. Heat and water are unevenly distributed around the globe, and Earth has many climate zones (areas with a characteristic climate) and subclimates (areas with unique climate features within a climate zone) with unique patterns of temperature, rainfall, winds, and ocean currents (the circulation of ocean waters that produce a steady flow of water in a prevailing direction).

Climate zones support communities of plants and animals (ecosystems) that have adapted to thrive there. The term climate refers to temperature and moisture patterns that characterize a large region over tens, hundreds, or even thousands of years. Local changes that last days, weeks, or seasons, like storms and droughts, are called weather.

Regulating sunlight: the ozone and greenhouse layers

Energy from the Sun drives Earth’s climate and biology. Sunlight heats the surface and nourishes plants that, in turn, feed animals. Heat drives ocean currents, winds, and the hydrologic cycle (the circulation of water between the land, oceans, and the layer of air surrounding Earth, called the atmosphere).

Monsoon

Monsoon

A monsoon is a regional wind that reverses directions seasonally. In southern Asia, wet, hot monsoon winds blow from the southwest during the summer months and bring heavy rains to a large area that includes India, Bangladesh, Sri Lanka, Pakistan, and Nepal. Northeasterly winds (winds are named by the direction from which they blow) that blow down from the Himalaya Mountains in the winter are cool and dry.

Monsoon winds occur in many regions around the world, in Africa, Australia, and in North America, where the Mexican monsoon brings over half of the year’s total rain to Northern Mexico, Arizona, and New Mexico each June through August. The Mexican monsoon is a smaller version of the classic and well-known southern Asian monsoon.

The word monsoon comes from the Arabic word mausim which means “season.” In southern Asia, the monsoon controls the seasons: hot and wet in the summer, cool and dry in the winter.

Storms

Storm

Storms are disturbances in the atmosphere (air surrounding Earth) that bring severe weather: heavy rain and snow, high winds, lightning and thunder, tornadoes, and hail.

There are storms that are mild, such as rainstorms, which are beneficial, bringing needed rainfall for plants, animals, and waterways. Yet storms also have the potential to cause great harm. Hurricanes batter coastlines and islands with high winds, drenching rain, and waves.

Thunderstorms and blizzards can cause floods and dangerous traveling conditions. During thunderstorms, lightning can ignite brush fires, and hail can destroy crops. Tornadoes can cut swaths of destruction across anything in its path.

Bioaccumulation of Heavy Metals

Bioaccumulation

Some of the substances that make up Earth’s crust are elements, substances that cannot be naturally broken down into simpler substances. A few of these elements are poisonous even if present in a low concentration. These are known as heavy metals. Examples of heavy metals include mercury, cadmium, arsenic, chromium, thallium, and lead.

The heavy metal-water connection

There is a connection between heavy metals and water. Because heavy metals are part of Earth’s crust, they can be worn away by the action of weather. When they are worn off of rock, they can collect in surface or groundwater (fresh water in rock and soil layer beneath Earth’s surface).

Depending on the chemistry of the water, the metals might stay in the water, or come out of the water and gather on an available surface such as plants. Heavy metals can, therefore, enter peoples’ bodies via drinking water and food.

Weather

Weather

Weather is the state of the atmosphere (mass of air surrounding Earth) at a particular place and point in time. Rain showers, gusty winds, thunderstorms, cloudy skies, droughts (prolonged period of dry weather), snowstorms, and sunshine are all examples of weather conditions.

Weather scientists, called meteorologists, use measurable factors like atmospheric pressure (pressure caused by weight of the air), temperature, moisture, clouds, and wind speed to describe the weather. Meteorologists make predictions of future weather based on observations of present regional weather patterns and past trends.

Weather prediction, or forecasting, is an important part of meteorology (weather science). Advance warning of such weather phenomena as extreme hot and cold temperatures, heavy rainfall, drought, and severe storms can protect people’s property and save lives.

Beach Erosion

Beach Erosion

Erosion is the removal of soil and sand by the forces of wind and water and it has occurred for as long as land has met water. Erosion is a continual natural process; material is constantly being shifted around to change the shape of a stream, riverbank, or beach.

Today, when much available land bordering the ocean (coastlines) is developed for housing, the erosion of beaches is an important concern. Wave action can cause erosion that can remove the support for a house, causing it to tumble into the ocean.

Along the 80,000 miles (128,748 kilometers) of coastline in the United States, beach erosion has become a big problem. While erosion is a natural process, humans have caused the rate of erosion to increase. The main factor causing the increased erosion damage is development.

Eutrophication

Eutrophication

Eutrophication is a process in which a body of water changes with time as deposits of nutrients and sediments (particles of sand, silt, and clay) from the surrounding area accumulate.

The process of eutrophication

In euthrophication, the chemical characteristics of the water changes. The biology of the water, in terms of the types of organisms that can live in that water body, also changes. Eutrophication involves an increase in the level of plants’ food sources in the water.

Younger water bodies that have lower levels of nutrients do not support much life. As the nutrients increase, more life can develop in the water. Indeed, the word eutrophic comes from the Greek word eu meaning “well” and trophic, meaning “feeding.”

Desertification

Desertification

Desertification is a term used to describe the gradual changes that take place over a region or area of land that ultimately result in the formation of a desert.

Although many places in the world are called deserts, scientists usually define a desert as a region or area that receives less than 10 inches (25.4 centimeters) of water from precipitation (rain, slow, sleet, or hail) during a year.

Desertification harms many people. During the late 1960s and early 1970s, desertification brought on by a severe drought (an extended period with little or no rain) in the Sahel region of Africa devastated the local agriculture of six African countries located on the southern border of the Sahara Desert.

Floods and Flood Control

Flood

Floods occur when a normally drier land area is temporarily submerged in water overflowing from rivers, dams (barrier to contain the flow of water), runoff, or tides. Runoff is water that accumulates and flows after heavy rainstorms or snowmelts.

Floods occur in all fifty states and around the world. Floods can be caused by several factors: heavy rainfall over a short period, moderate rainfall over a long period, melting snow, hurricane storm surge (a dome of water that builds up as a hurricane moves over water), ice or debris jams on rivers, and dam failures.

Floods can cause great harm to people and property. Floods are the deadliest form of natural disasters, killing more Americans every year than tornados, lightning, earthquakes, and forest fires combined. Due to the potential harm, government agencies work to prevent and predict floods.

Global Climate Change

Global Climate Change

Global climate change, often simply referred to as “global warming,” is a complex and scientifically controversial issue that attributes an increase in the average annual surface temperature of Earth to increased concentrations of carbon dioxide and other gases in the atmosphere (air surrounding Earth). Many scientists disagree on how to best interpret data related to climate change.

Scientists also argue about which data (for example, measurements of changes of thickness in arctic ice, measurements of sea temperatures at critical locations, or measurements of certain chemicals in the atmosphere, etc.) should be used to make informed decisions about the extent and rate of global climate change.

Climate describes the long-term conditions or average weather for a region. Throughout Earth’s history, there have been dramatic and cyclic changes (changes that repeat themselves in cycles that can last from thousands to millions of years) in climatic weather patterns corresponding to cycles where glaciers of ice advance and retreat over the landscape.

Groundwater

Groundwater

Many of Earth’s groundwater supplies are threatened, mainly by human population growth and contamination. Groundwater is freshwater that resides underground; it collects following the movement of water from the surface down through soil and rock.

As the water moves downward, a zone or line is formed underground, above which the spaces in the soil and rock are filled with air and water (called the zone of infiltration) and below which water occupies every available opening (called the zone of saturation). The water table is at the top of the zone of saturation, and groundwater lies beneath the water table.

In a desert, groundwater is a vital source of life to plants, which can produce roots that are dozens of feet (meters) long, to reach down from the dry surface to the water below. Groundwater is also important to humans for drinking water, growing crops (irrigation), and other uses.

Industrial and Commercial Waste

Industrial landscape

Many everyday activities create waste. Even cutting the lawn makes grass clippings that can stress water bodies such as streams and rivers if too much washes into the water.

This is because the grass is food for in the water. Microorganisms can grow quickly in great numbers, and rob the water of the oxygen that is needed by fish and other living creatures inhabiting the water.

One person alone might not produce enough waste material to contaminate a water source. However, a community of many people and large industries produce large amounts of waste.

Habitat Loss and Species Extinction

Wetlands Habitat

Habitat (natural environment) loss is the number one threat to the survival of many animal species (organisms that share a unique set of characteristics), and water is part of any habitat.

Coastal marshes and wetlands in the United States and elsewhere are shrinking every year. Wetlands are areas of land where water covers the surface for at least part of the year and controls the development of soil; marshes are wetlands dominated by grass-like plants.

Wetlands in particular support a great variety of bird, fish, and other animal life, and can be used by migrating (periodic traveling) birds as a stop-off point on their long journeys.

Landfills

Landfill

Landfills are areas where solid garbage is buried. The construction, use, and maintenance of landfills can impact aquifers and groundwater that lie underneath and around the landfill.

Groundwater is fresh water in the rock and soil layers beneath Earth’s land surface; aquifers are a type of groundwater source that yields water suitable for drinking. The material inside a landfill can contain harmful chemicals and microorganisms.

As some of the material in a landfill decomposes (breaks down), other harmful chemicals can be created and released. One wellknown example is methane gas; another is leachate, the acidic liquid that contains water and contaminants from the products of decomposition.

Non-point Sources of Pollution

pollutants enter water body from different locations

Non-point source pollution is pollution that enters water from many different sites, rather than from just one site. Examples of non-point source pollution are contaminated rain falling from the sky, polluted melting snow, runoff (water flow on land) of polluted water, and impure water draining down into the groundwater from many different sites on the surface. In contrast, an example of point source pollution is a polluted river flowing into a lake.

Because non-point source pollutants enter a water body such as a stream, river, or lake at different locations, the control and prevention of non-point pollution can be much more difficult than when the contaminants are entering at a single site.

As the water runs over the land or through the ground on its way to the body of water, it can pick up a variety of pollutants. These chemicals and undesirable microscopic organisms in the water pollute the water into which they flow.

Oil Spills

Oil spill

Oil is a critical resource for the world. Millions of barrels of oil are shipped from where the oil is taken from the Earth to where it is processed (refined) into substances varying from fuel to plastics.

Because the world’s demand for crude oil is great, oil must be shipped in large quantities by oceanic tankers, barges on inland waters, and pipelines that run over the land and under the sea. When there is a mistake or accident that causes oil to spill from any of these means of transport, damage to the water, beaches, and economy can be devastating.

Oil (also known as petroleum) is a naturally occurring thick liquid mixture of the elements hydrogen and carbon combined to form chemicals known as hydrocarbons. The oil taken from the ground (or seafloor) is called crude oil.